Document Modesto_doc_c5614e6475

City of Modesto 2008 Storm Drainage Master Plan DRAFT Prepared for: City of Modesto 1010 Tenth Street Modesto, CA 95353 Prepared by: Stantec Consulting Inc. 2590 Venture Oaks Way Sacramento, CA 95833 (916) 569-2500 tel (916) 921-9274 fax March 2008 ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan Table of Contents Page GLOSSARY OF TERMS/ACRONYMS 1.0 INTRODUCTION 1.1 1.2 BACKGROUND 1.3 AUTHORIZATION AND SCOPE 1.4 PREVIOUS 1.4.1 1958 Storm Drainage, A Community Wide 1.4.2 1976 Storm Water Management 1.4.3 1989, 9th Street Flood Alleviation 1.4.4 2000 Stormwater Master Plan, Volume 1, Conceptual Plan for Selected Comprehensive Planning 1.4.5 2002 Storm Drainage Mater Plan Update for the Village One Community Facilities 1.5 PHYSICAL CHARACTERISTICS OF THE STUDY AREA 1.5.1 1.5.2 Precipitation 1.5.3 1.5.4 1.5.5 Soils 1.5.6 Groundwater Table 2.0 PLANNING AREA DESCRIPTION 2.1 2.2 STUDY 2.3 GENERAL LAND USES 2.4 REDEVELOPMENT 2.4.1 Downtown 2.4.2 Large Areas of Undeveloped Parcels Outside of the Downtown Area 2.5 PROJECTED 3.0 EXISTING 3.1 3.2 POSITIVE SYSTEMS 3.2.1 McHenry Avenue Corridor 3.2.2 9th Street 3.2.3 Yosemite Boulevard Corridor system 3.3 DETENTION BASINS AND PUMP 3.3.1 Discharge into Irrigation District Owned 3.3.2 Recreational 3.4 RETENTION (PERCOLATION) v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc i ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Table of Contents 3.5 OVERFLOW DISCHARGE INTO THE SANITARY SEWER SYSTEM 3.5.1 Cross 3.5.2 Hot Zone 3.6 ROCKWELL 3.7 FLOOD HAZARDS 4.0 PLANNING AND DESIGN 4.1 4.2 DESIGN 4.3 FACILITY DESIGN STANDARDS 4.4 WATER 5.0 SYSTEM HYDROLOGY AND 5.1 5.2 WATERSHED 5.3 WATERSHED MODELING AND 5.3.1 Sub-basin 5.3.2 Watershed Soil 5.3.3 Rainfall Loss 5.3.4 Land 5.3.5 5.3.6 Unit 5.3.7 Lag 5.3.8 5.4 CONVEYANCE SYSTEM ANALYSIS 5.4.1 Pipe 5.4.2 Open 5.5 RESULTS 6.0 PROPOSED CAPITAL 6.1 6.2 TYPES OF PROPOSED 6.2.1 Positive Storm Drains 6.2.2 Detention 6.2.3 Pump 6.2.4 Open 6.2.5 6.3 PHASING AND 6.4 PROPOSED INFRASTRUCTURE IMPROVEMENTS 6.4.1 Watershed Group v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc ii ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Table of Contents 7.0 OPINION OF PROBABLE COSTS 7.1 7.2 COST ESTIMATING 7.2.1 Basis of Developing Opinion of Probable Costs 7.2.2 Opinion of Probable Cost 7.2.3 Unit Cost Estimates 7.2.4 Soft Cost 7.3 INFRASTRUCTURE OPINION OF PROBABLE COSTS 7.3.1 Watershed 8.0 FUNDING 8.1 8.2 DEVELOPMENT IMPACT FEES (CAPACITY 8.3 ASSESSMENT DISTRICTS (1913/15 8.4 SPECIAL TAX DISTRICTS - MELLO ROOS COMMUNITY FACILITIES DISTRICT (ACT OF 8.5 STORM DRAINAGE UTILITY RATE 8.6 STATE AND FEDERAL GRANTS 8.7 GENERAL FUND 9.0 RECOMMENDATIONS 10.0 ACKNOWLEDGEMENTS 11.0 REFERENCES v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc iii ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Table of Contents LIST OF TABLES Table 1-1 Average Table 2-1 Summary of Land Use Table 3-1 Summary of Pump Table 4-1 Design Storm Event Table 5-1 Hydrological Parameters used in Table 5-2 Impervious Cover Percentages Table 5-3 Design Table 6-1 Proposed Detention Table 7-1 Unit Cost Data for Table 7-2 Unit Cost Data for Pump Table 7-3 Cost Estimate Example Table 7-4 Summary of Facility Table 7-5 through Table 7-25 Proposed Infrastructure Cost LIST OF FIGURES (after page) Figure 1.1 Contour Map and Study Area Figure 2.1 Land Uses Figure 2.2 Redevelopment Project Area Figure 2.3 Proposed Downtown Figure 3.1 Areas Currently Served by Positive Storm Drain Systems Figure 3.2 Existing Detention and Retention Basins Figure 3.3 Discharges Into Irrigation District Owned Facilities Figure 3.4 Park Planning Figure 3.5 Cross Connections, Hot Zones, and Proposed Improvements Figure 3.6 Hot Zones and Proposed Storm Drainage Figure 3.7 Location of Existing Catch Basins Connected to Figure 3.8 100-Year Floodplain v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc iv ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Table of Contents Figure 5.1a Watershed Groupings Figure 5.1b Offsite Figure 5.2a Hydrologic Soil Figure 5.2b Offsite Watershed Hydrologic Soil Figure 6.1 Typical Cross Section, 60 ft Right-of-Way Open Figure 6.2 Proposed Storm Drain Infrastructure (enlarged version in pocket at end of report) Figure 6.3 Proposed Storm Drain Infrastructure on an Aerial (enlarged version in pocket at end of report) Figure 6.4 Airport Drainage System Figure 6.5 Offsite Watershed Proposed Infrastructure APPENDIX Appendix A City / MID Discharge Agreement Example v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc v ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan Glossary of Terms/Acronyms BMP An acronym for Best Management Practice as applied to any program, technology, or process used to improve or maintain water quality under the NPDES program CFD An acronym for Community Facilities District CPD An acronym for Comprehensive Planning District Detention Basin A depressed or bermed area that collects and stores surface runoff for regulated release Discharge A rate of stormwater runoff experienced at a given location and at a given point in time during or after a storm event, usually expressed in cubic feet per second (cfs) Dual-function Facility Storm drainage detention basin for use with industrial/commercial land use Dual-use Facility Storm drainage detention basin that includes recreation elements as dual-use within residential land uses First Flush The initial part of a storm event or the initial storm of the wet season General Plan City of Modesto Urban Area General Plan MEP An acronym for Maximum Extent Practicable, a standard for water quality that applies to all MS4 operators regulated under the NPDES program. MID An acronym for Modesto Irrigation District NRCS An acronym for National Resource Conservation Service NPDES An acronym for National Pollution Discharge Elimination System, a program that regulates stormwater quality from nonpoint sources Offsite Referring to a location other than the subject site Percolation The gravity flow of groundwater through the pore spaces in rock or soil v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc vi ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Glossary of Terms/Acronyms March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc vii Permeability The ability of a porous rock, sediment, or soil to transmit fluid through pores and cracks Positive SD System A Positive Storm Drainage System collects runoff in catch basins or other inlets, conveys it through pipelines, and discharges it using either pumping or gravity into open channels or recharge/detention basins PR&N An acronym for the City of Modesto Parks, Recreation, and Neighborhood Department RDA An acronym for the City of Modesto Redevelopment Agency Retention Basin A depressed or bermed area that collects and stores surface runoff and that does not have an outlet other that infiltration or evaporation Return Period The reciprocal of the percent probability of a flood event of a certain magnitude occurring in a given year, often expressed in terms of 10- year flood, 100-year flood, etc. ROW An acronym for Right-of-Way SDMP An acronym for Storm Drainage Master Plan SOI An acronym for Sphere of Influence per the City’s General Plan Specific Plan Area An area defined and affected by a city’s specific plan, which is a tool for the systematic implementation of the General Plan Study Area Sphere of Influence plus “offsite” watershed Surcharging An overload of a storm drain system occurring when volumes beyond the system’s capacity are introduced and the water level in a storm drain pipe rises above the crown of the pipe SWMP An acronym for Storm Water Management Plan, a plan developed to implement measures to improve stormwater quality TID An acronym for Turlock Irrigation District TMDL An acronym for Total Maximum Daily Load, the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards/beneficial uses ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 1.0 Introduction 1.1 GENERAL The purpose of any community’s storm drainage system is to provide a reasonable and assured level of protection to its citizens and their property from the consequences of flooding, while at the same time meeting all of the water quality regulatory requirements governing stormwater runoff discharges. Having a current and comprehensive Storm Drainage Master Plan (SDMP) is a critical first step in solving many of the problems associated with conveying, attenuating, and discharging stormwater runoff that meets regulatory water quality standards. This is done by performing the necessary hydrological and hydraulic analyses that result in identifying the improvements needed to provide for the construction of new conveyance and storage facilities and upgrading of deficient existing facilities. It is important that the SDMP be flexible enough to adapt to general and specific revisions, and be feasible from both a technical and fiscal perspective. This SDMP identifies the major (backbone) storm drainage infrastructure improvements needed to effectively accommodate stormwater runoff under both existing and future developed conditions within the City of Modesto’s (City) Sphere of Influence (SOI) plus an “offsite” watershed (this resulting area defines the Study Area). The recommended improvements have been formulated in consideration of existing planning and engineering documents, studies, and regulations. Cost estimates and phasing priorities are also presented. This document will also provide a basis for the preparation of an Engineer’s Report that will determine the cost allocations of new infrastructure improvements between existing rate payers and future users. As related to the City’s 2001 Strategic Plan, this SDMP specifically supports the goal of having a properly planned, designed, and operating storm drainage conveyance, storage, and treatment system that operates as an integral component of the City’s economic development plan. This SDMP in conjunction with the City’s revised Storm Drainage Standards (2006), supersede prior storm drainage planning documents where applicable. 1.2 BACKGROUND Much of the City does not have a positive storm drainage conveyance system because of past reliance on the use of rockwells that attempt to percolate stormwater runoff directly into the ground. The use of a rockwell storm drainage system is expensive because it is highly dependent on preventative maintenance in order to function properly. Though there are stormwater quality benefits associated with the rockwells’ capturing of “first flush” stormwater from a surface water perspective, there are also groundwater quality concerns regarding percolated stormwater runoff via rockwells. Also, standing water that is prevalent on the surface v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.2 after storms resulting from the use of a marginally effective rockwell system has a significant detrimental effect on roadway pavement. While a number of repairs and improvements have been made over the years, the overall system is still deficient in its ability to drain stormwater runoff and minimize localized flooding in many areas of the City. There are also areas of the City that contain positive storm drainage conveyance systems, with discharges to the Tuolumne River, Dry Creek, detention basins, terminal retention basins, and irrigation facilities owned and operated by the Modesto Irrigation District (MID) or the Turlock Irrigation District (TID). Some of these systems function well, and others require upgrades and retrofits in order to achieve the desired level of service. The primary objectives of this SDMP are to: ‰ Provide a reference document and decision making tool for both short and long range planning; ‰ Evaluate the carrying and holding capacity of existing facilities; ‰ Identify the infrastructure needed to manage stormwater runoff in existing developed areas more effectively, specifically in those areas that experience recurring flooding; ‰ Identify the capital improvement projects necessary to accommodate new development; ‰ Identify issues regarding possible storm drainage constraints associated with the future build-out of the Study Area; ‰ Develop cost estimates associated with the capital improvement projects proposed to serve existing and future developments; and ‰ Form a basis for establishing updated utility rates and a justifiable capacity charge to finance the identified improvements. 1.3 AUTHORIZATION AND SCOPE The City Council approved a professional services agreement with Stantec Consulting Inc. (Stantec) to prepare this SDMP, which, in general, includes the following tasks: ‰ Review and evaluate existing data, studies, policies, planning documents, ordinances, regulations, and other background information ‰ Perform general field reconnaissance, as necessary ‰ Evaluate the conveyance capacities of the existing facilities ‰ Develop and perform hydrologic modeling of watersheds and facilities and hydraulic modeling of selected facilities ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.3 ‰ Generate system wide estimates of peak runoff rates produced during applicable storms based on adopted and proposed land usages ‰ Propose specific upgrades and solutions to improve deficient portions of the existing storm drainage system and to alleviate existing flooding problems ‰ Identify new infrastructure needed to serve future development areas ‰ Meet with City and MID Staff in an effort to understand issues and assist the City in facilitating a workable agreement between the agencies regarding continued stormwater discharges into MID facilities ‰ Identify system wide major infrastructure improvements ‰ Develop a master plan overview of priority phased capital improvements ‰ Provide an opinion of probable costs for the recommended capital improvements ‰ Participate in various workshops and public meetings ‰ Identify possible funding alternatives The land use assumptions used in the development of this SDMP were based on amendments to the City’s Urban Area General Plan1 (General Plan) and projected future development within the SOI accelerated growth, more intense developments, etc.). Significant future changes to these adopted land uses may require subsequent revisions and adjustments to the findings contained in this SDMP. It is also intended that the pertinent elements of this SDMP will be adopted as the storm drainage element of the General Plan. This SDMP does not analyze portions of the Study Area where there are existing positive storm drainage systems, such as Community Facility Districts (CFD’s), and it does not analyze internal storm drainage infrastructure needs for small, future land development projects (onsite facilities). The infrastructure identified in the SDMP does include County islands located within the City’s sphere of influence. Regional flood control proposals dealing with major waterways passing through the City, such as the Tuolumne River and Dry Creek, are outside the scope of evaluation covered in this SDMP, except as they relate to local storm drainage system recommendations provided herein. Similarly, analyzing the capacity of the various irrigation district owned facilities is not included. 1 Urban Area General Plan Adopted by Modesto City Council Resolution No. 95-409 (August 15, 1995) as amended by Resolution No 2003-122 (March 4, 2003). ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.4 1.4 PREVIOUS STUDIES The following storm drainage master planning reports were previously prepared to address storm drainage issues within the City: ‰ 1958 Storm Drainage, A Community Wide Problem (City of Modesto Department of Public Works) ‰ 1976 Storm Water Management Study (George Nolte and Associates) ‰ 1989, 9th Street Flood Alleviation Scheme (H.I.L. Technology Inc.) ‰ 2000 Stormwater Master Plan, Volume 1, Conceptual Plan for Selected Comprehensive Planning Districts (City of Modesto) ‰ 2002 Storm Drainage Master Plan Update for the Village One Community Facilities District (Camp Dresser & McKee Inc.) Other storm drainage studies have also been prepared to address flooding issues and facility requirements, including several Specific Plan studies that have been completed for new and planned developments. These, along with other applicable studies listed in the references section of this report, have been reviewed and considered in the preparation of this SDMP. 1.4.1 1958 Storm Drainage, A Community Wide Problem This early document was a relatively comprehensive and detailed study of the City’s storm drainage issues. It divided the City into several districts and delineated contributing watershed areas for each and recommended solutions to the storm drainage problems that existed at the time. The report presented long-range plans for providing drainage facilities to serve projected future growth, and a number of key ideas were presented, including an emphasis on the utilization of “the holding basin concept” to reduce peak stormwater flows. It appears that existing positive storm drain systems along Yosemite Boulevard and McHenry Avenue were constructed per the recommendations contained in this report. 1.4.2 1976 Storm Water Management Study This study was undertaken to investigate various methods of stormwater disposal, including detention ponds, rockwells, percolation ponds, and connections to sanitary sewer systems. Emphasis of this study was on establishing a logical method of selecting which stormwater disposal system would work best for a given location or development. 1.4.3 1989, 9th Street Flood Alleviation Scheme This study evaluated the City’s downtown area centered along 9th Street. The recommendation of this study was to use an inlet control system to control stormwater flows upstream of the ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.5 critical areas. This would be accomplished by attenuating excess storm flows using underground storage facilities. 1.4.4 2000 Stormwater Master Plan, Volume 1, Conceptual Plan for Selected Comprehensive Planning Districts The purpose of this study was to provide conceptual level master planning for storm drainage systems serving several Comprehensive Planning Districts (CPDs). The CPDs generally correspond with the original Villages 2 through 8 Specific Plan areas, however, general references to “Village Specific Plans” have since been dropped (except for Village One) in favor of named specific plan areas. The study evaluated storm drainage conveyance system needs for both 5-year and 10-year frequency design storms using updated rainfall intensity data, and recommended the use of a 10-year design standard based on the relatively small infrastructure cost differential between the two standards The study also provides recommendations for storm drainage improvements (including associated costs) to serve the investigated CPDs. 1.4.5 2002 Storm Drainage Mater Plan Update for the Village One Community Facilities District This study was prepared to update the Village One storm drainage system presented in Village One Facility Master Plan of June 1996. This analysis indicated that storm drainage infrastructure requirements recommended in the 1996 study were understated due to low impervious surface assumptions and the effect of backwater from detention basins. The prior study was also based on the use of a 5-year frequency storm design standard and prior rainfall intensity data. This study presented updated infrastructure requirements and costs to meet the new 10-year design standard. 1.5 PHYSICAL CHARACTERISTICS OF THE STUDY AREA In evaluating runoff quantities and drainage facilities for an area, several aspects of the physical environment must be considered, including climate, precipitation, topography, hydrology, soil, and groundwater characteristics. These are briefly discussed below. 1.5.1 Climate The Modesto area is typical to that of San Joaquin County and the broader Central Valley, with two distinct weather seasons; wet and cool winters along with dry and hot summers. Average high temperatures in the winter are in the 50s, and summer temperatures average in the low 90s. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.6 1.5.2 Precipitation Precipitation records obtained from rain gage data monitored by MID and located in downtown Modesto (from 1888 to 2004) indicate the amount of normal annual rainfall in the Modesto area averages about 12 inches per year. Approximately 95 percent of this rainfall typically occurs from early fall through mid-spring (generally October through May), although infrequent summer showers do occur. Storm events during the rainy season consist of either individual storms or clusters of storms. An evaluation of daily rainfall data for the Modesto area from January 1983 to August 1991 indicates that approximately 88 percent of the precipitation during this period resulted from storm events with a 2-year or less return period. 2 Major storms of greater magnitude and duration generally occur during the rainy season; however, high intensity thunderstorms (though relatively infrequent) can occur in any season. Average precipitation records from the downtown MID rain gage are shown in Table 1- 1. Table 1-1. Average Precipitation Month Rainfall January 2.37 February 2.05 March 1.94 April 0.94 May 0.50 June 0.10 July 0.02 August 0.03 September 0.22 October 0.61 November 1.36 December 2.06 2 City of Modesto Village One Facilities Master Plan (August 1992). ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.7 Major storm events were experienced in the Modesto area in 1997 and 1998 and are briefly described below: January 1997 – A significant storm event with extensive coverage occurred over much of Northern California (smaller Modesto watersheds were less affected). This wide area of coverage, combined with the relatively “warm” rain that fell in the Sierra’s, ended up melting a significant amount of snow-pack causing many major rivers and streams to swell and exceed their banks. Significant flooding occurred adjacent to these major rivers and streams based on high flow rates and levee failures. The City’s Primary Wastewater Treatment Plant, located adjacent to the Tuolumne River, flooded and was shut down for a number of days, and the floodwaters remained in many areas of the City for weeks. February 1998 – A series of local storms occurred in the Modesto area, including a high intensity storm that produced 3 inches of precipitation in a 36-hour period (a 50-year return period storm event) followed by a number of smaller events over the next week and one-half. The storm caused extensive local flooding; however, the nearby major rivers and streams were substantially unaffected. The northeast area of the City experienced flooding that lasted for several days and was exacerbated by additional runoff from offsite areas below the MID Main Canal east of the City. 1.5.3 Topography The Study Area is located within a portion of the broad valley floor of the San Joaquin Valley, and generally slopes from northeast to southwest at an average topographic gradient of approximately 0.1 percent. The ground surface elevations above mean sea level range from about 120 feet in the northeast area to about 75 feet in the southwestern area of the City, excluding the Tuolumne River, which is somewhat lower in elevation (Figure 1.1). Over the years, several datums have been used within the City that differ from each other by a few feet, and this SDMP has not been based on any one datum in particular. Prior to the City’s urban development, the Study Area was prone to flooding during the winter and early spring, where stormwater undoubtedly moved across the Study Area predominantly as sheet flow. As the City developed, railroads, roadways, irrigation laterals, and other facilities were constructed that obstructed the natural flow of stormwater runoff. In general, and as a result of the relatively flat topography, storm drainage improvements required within the Study Area, particularly those that are needed to retrofit facilities and relieve flooding in existing developed areas, are relatively costly to construct. 1.5.4 Hydrology The segments of the two principal waterways passing through the study area, the Tuolumne River and Dry Creek have been historically used as outfalls for stormwater generated from various areas within the study area, and are characterized by well-defined channels and densely vegetated overbank areas. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.8 The Tuolumne River and Dry Creek have significant flow carrying capacity for storm water, particularly given that the storm term discharge of urban runoff would generally occur non- concurrently with the passage of peak flows in these waterways given the significant size of their respective watersheds and their long times of concentration. In a major flood event along these streams, additional study area runoff would create an almost negligible incremental increase in flow discharges. The Tuolumne River flows from east to west and extends along the southern corporate limit of the City east of Highway 99 and through southern portions of the City west of Highway 99. Its headwaters originate at the Mount Lyell glacier in Yosemite National Park, draining a watershed (upstream from the City) of approximately 1,885 square miles between the watersheds of the Stanislaus and Merced Rivers. Several dams and reservoirs regulate the upper Tuolumne River with the main flood control structures being the Hetch Hetchy Reservoir, the new Don Pedro Reservoir, and the La Grange Reservoir. Flow in the portion of the lower Tuolumne River passing through the study area is supplied primarily by releases from La Grange Dam, stormwater runoff, groundwater inflow (in general, but not under all conditions), and agricultural tail water discharges entering the lower reaches. Dry Creek passes through the east central portions of the study area, also flowing from east to west. Dry Creek drains a watershed of approximately 190 square miles and discharges into the Tuolumne River just east of the City’s downtown area. The headwaters of Dry Creek originate west of the new Don Pedro Reservoir at an elevation of approximately 1,000 feet, just east of the Tuolumne County line. Land uses within the Dry Creek watershed consist mostly of orchards, vineyards, dairies and livestock grazing, plus the City’s urban land uses in the lower areas of the watershed. Flow in Dry Creek occurs throughout the year and is not regulated by any upstream storage facilities. In the absence of stormwater runoff, water in Dry Creek is mainly composed of return flows from agricultural uses and groundwater inflow. There is also an extensive system of irrigation facilities that traverse through the Study Area. These facilities are owned and operated by either MID or TID, who also jointly own and operate the La Grange Reservoir that diverts water into canals and laterals that were designed and built to supply irrigation water for agricultural purposes. Additionally, various above and below grade drains are used for the conveyance of excess irrigation water or tail water away from agricultural land. The movement of irrigation water generally occurs during the dry season. As a second function, many of the irrigation laterals currently serve as discharge points for some of the City’s urban runoff as they traverse through the Study Area. These discharges of City stormwater runoff usually occur during the rainy season when the irrigation facilities are not transporting water for irrigation purposes, and are typically covered by individual agreements between the City and the irrigation districts. The flow carrying capacity of these irrigation facilities decreases in the direction, which limits their ability to accept significant amounts of stormwater runoff. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Introduction March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 1.9 1.5.5 Soils The Study Area contains many separate soil types, and published information was used to define and estimate the general permeability and potential percolation rates of those soils. In general, approximately 60 percent of the Study Area is suited for the construction of detention and retention basins with soils characterized as having deep, well-drained sands or gravels, moderately well to well-drained sandy-loam with moderately coarse textures, all having high to moderate infiltration rates. The remaining 40 percent of the Study Area has silty-loam soils that somewhat impede the downward movement of water, soils with moderately fine to fine texture, or clayey soils with low to very low infiltration rates when underlying a basin. As part of the development process, site-specific subsurface soil investigations should always be completed to confirm a given site’s ability to allow percolation from a proposed detention basin. 1.5.6 Groundwater Table The groundwater table (as opposed to deeper confined groundwater aquifers) in the Study Area is generally replenished by a combination of rainfall, unused irrigation waters, and, under certain conditions, surface waterways such as the Tuolumne River. Groundwater levels within the Study Area were examined from data provided by the City. Generally, the depth to groundwater ranges from 25 feet to 100 feet below ground elevation, depending on location and time of year. These groundwater levels indicate that detention basins can generally be located throughout the Study Area, but site-specific subsurface borings should be completed to confirm the depth to groundwater so that an appropriate amount of separation can be included between the deepest part of the basin and the highest seasonal elevation of the groundwater table. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 2.0 Planning Area Description 2.1 GENERAL This chapter presents a discussion of the Study Area’s land use designations and characteristics. Also, as related to the anticipated future timing of development within the SOI, information from a recent report on population projections is provided. 2.2 STUDY AREA Modesto is the largest City in Stanislaus County. It is also the County Seat and is located in the heart of a large and very productive agricultural area that has a strong influence on the local economy. The Study Area of this SDMP is the SOI boundary (plus a local “offsite” watershed that extends beyond the SOI due to local topography) and consists of approximately 37,700 acres (59 sq. mi.) (minus the offsite watershed) (Figure 1.1). Approximately 23,200 of these acres are within the current City limits, but the Study Area also includes the unincorporated community of Empire, a portion of north Ceres, the Beard Industrial Park, some unincorporated County “islands”, and other adjacent unincorporated areas. Approximately two-dozen CPDs and eight Community Facility Districts (CFDs) exist within the Study Area. The General Plan contains various policies and guidelines intended to govern their development in certain ways and with particular characteristics. Conceptual storm drainage plans for a number of the CPD areas have been summarized in the report entitled “2000 Stormwater Master Plan, Volume 1, Conceptual Plan for Selected Comprehensive Planning Districts” and in the report entitled “Storm Drainage Master Plan Update for the Village One Community Facilities District.” Specific elements related to the proposed storm drainage systems of the CFDs can be found in the public report for each CFD and are not further analyzed in this SDMP. Aside from these CPDs, most of the Study Area (minus the offsite watershed) is already developed. 2.3 GENERAL LAND USES In order to predict the amount of stormwater runoff from areas to be developed in the future (and to facilitate the locating and sizing of the needed infrastructure), land use information from the General Plan has been used. However, if a new development is within a designated Specific Plan area, the proposed storm drainage facilities need to be in general accordance with that Specific Plan’s Facility Master Plan and infrastructure financing plan documents, but may still need to be evaluated on a case-by-case basis as development occurs. The City is primarily a residential community, but there exists an active promotion of new, and the rebuilding of existing commercial and industrial areas. The northerly portions of the Study Area are slated to be a mixture of various residential and commercial uses. The City’s proximity v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 2.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning Area Description March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 2.2 to highway and rail access is a factor in the attraction of new industrial development in certain areas, and it is envisioned that these types of developments will continue. It is not expected that the various development projects currently being reviewed by City staff will significantly affect, or require altering, the stormwater runoff calculations made in the preparation of this SDMP. However, if significant changes do occur from the original land use designations, the realignment and resizing of certain drainage facilities may be required. The City’s 2003 Urban Growth Policy Review Report3 conducted an inventory of “vacant” and “underdeveloped” properties within the SOI as being slated for residential, commercial, and industrial type development. The capital improvement projects proposed in this SDMP as flood control and water quality discharge solutions assume a built-out scenario, in that, the residential, commercial, and industrial properties designated as vacant and underdeveloped would be fully developed. General land use designations within the Study Area, as taken from the General Plan, are briefly described below and are shown on Figure 2.1. Residential: This consists of primarily single-family detached housing, but also includes mobile homes, schools, parks, churches, and some multi-family housing. Village Residential: These are mixed-use, pedestrian, and transit oriented types of developments. They are predominantly single-family residential, but also include multi-family and senior housing, commercial uses, schools, and parks. Redevelopment Planning District: Housing will be an integral part, but light industrial and various commercial uses are also included. Commercial: This encompasses the entire range of service and retail uses, including but not limited to, offices, neighborhood retail centers, downtown commercial districts, and regional retail centers serving the needs of the entire region. Regional Commercial: To provide for large-scale commercial areas for the sale of goods and services that meets the needs of the region as well as the community. Industrial: This provides for many different types of industrial uses, including manufacturing, food processing, trucking, packing, recycling, etc. Mixed Use: This designation is intended to characterize those areas of the City that are already developed (as of January 1, 1995) and contain large areas of multi-family housing; and a mixture of multi-family residential, commercial, office, and institutional uses in close proximity to each other. The targeted land use mix is 60 percent residential and 40 percent institutional, office, and commercial uses. 3 The purpose of the Urban Growth Policy Review Report is to assist the City in determining the timing and direction of growth so that the needed infrastructure can be identified. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning Area Description March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 2.3 Business Park: Areas intended for light industrial and employment intensive uses that produce an environment conducive to industries and employers seeking an aesthetically attractive “campus-like” setting. Open Space: This is intended to provide for regional recreation (active and passive) along the Tuolumne River and Dry Creek, community and neighborhood parks, smaller greenbelt type areas, and agriculture. The approximate acreage totals for the various land use designations within the Study Area (minus watershed OS) are summarized in Table 2-1.4 Table 2-1. Summary of Land Use Designations Land Use Acres* Residential 13,400 Village Residential 7,560 Redevelopment Planning District 1,970 Commercial 1,470 Regional Commercial 360 Industrial 3,280 Mixed Use 3,430 Business Park 2,180 Open Space 2,150 TOTAL 35,800 * Acreages are approximate 2.4 REDEVELOPMENT AREAS As a separate project and contract from the development of this SDMP, Stantec has been retained by the City’s Redevelopment Agency to review the storm drainage needs of its newly proposed Redevelopment Area (RDA) Master Plan (Redevelopment Agency Project Storm Drain Capacity Study - Preliminary Draft, June 2005). This includes making recommendations for additional infrastructure, based on the proposed intensification of land use and associated increase of runoff potential, provided by the community and economic development department as taken from the City’s geographic information system, and preparing cost estimates for those improvements. This study will also provide a basis for the preparation of a proportional cost 4 City of Modesto Housing Element (2003-2008), Adopted by City Council Resolution Number 2004-233, April 27, 2004. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning Area Description March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 2.4 share analysis and the development of potential impact fees to fund the needed storm drainage improvements to serve parcels within the RDA project area (Figure 2.2). The infrastructure proposed within the RDA area is not included in the SDMP. The proposed RDA project consists of almost 2,000 acres located in downtown Modesto and other areas that generally extend in a northwesterly direction along State Route 99. With respect to storm drainage infrastructure, the RDA project can be divided into two general regions with opportunities for development and redevelopment. 2.4.1 Downtown Area The downtown area (being largely infill with approximately 200 available parcels totaling about 58 acres) would be made up of neighborhood mixed use, light industrial mixed use, commercial, low and high-density residential. The downtown area has an existing positive storm drainage system with a main trunk along 9th Street that serves much of the downtown RDA project area. This pipeline discharges directly to the Tuolumne River, and is undergoing a redesign to upgrade its various segments. Since the RDA project will contribute a substantial amount of stormwater runoff to this system, a hydraulic capacity analysis was performed under an RDA built-out scenario. This included an analysis to determine if the existing infrastructure serving the RDA parcels has sufficient capacity and what upgrades might be needed to ensure the stormwater runoff can reach and be conveyed by the 9th Street line for ultimate discharge. As a result, a number of needed improvements have been identified for the downtown area (Figure 2.3). 2.4.2 Large Areas of Undeveloped Parcels Outside of the Downtown Area Generally, the RDA areas outside of the downtown area do not have positive storm drain systems and are currently served by rockwells. The rockwells do not typically provide sufficient drainage to serve these areas and nuisance flooding occurs. Peak flows at key locations have been identified, detailed hydraulic grade line calculations have been prepared, and a storm drainage system consisting of trunk lines and detention basins has been proposed via the RDA Storm Drainage Capacity Study. 2.5 PROJECTED GROWTH The study area has a current population of approximately 218,000, and it is estimated that this population will grow at an average annual rate of approximately 1.6 percent from 2007 to 2011 and 1.75 percent from 2012 to 2030.5 At this rate, build-out of the study area will include 5 Information from a May 2006, report and a July 2006, report on population projections by the City’s Community and Economic Development Department and Public Works Department, respectively. ---PAGE BREAK--- ---PAGE BREAK--- McClatchy Rose Garden Tuolumne River Regional Park T.B. Scott Park Enslen Park Graceada Park Brookway Park 17th & G St. Park Cesar E. Chavez Park Beard Brook Park Moose Park Kewin Park Mellis Park Stoddard Ave. Scenic Dr. Downey Ave. Elm Ave. Laurel Ave. K St. La Loma 9th St. I St. Washington St. Paradise Ave. Martin Luther King Dr. HWY 99 Kansas Ave. J St. McHenry Ave. 7th St. E St. 30 24 30 24 24 F St. H St. 8th St. 66 66 66 72 84 96 96 96 42 96 10th St. 11th St. 54 14th St. 17th St. 13th St. 18 12 Jefferson St. Madison St. Needham St. 8 8 24 24 G St. 12th St. 15th St. MID Lat No. 4 MID Lat No. 5 36 36 36 36 36 36 30 36 24 24 24 24 24 24 36 36 36 24 24 24 24 20 16 8 42 6 66 10 ? 18 12 12 15 10 12 12 12 36 30 12 15 33 18 42 18 12 8 42 12 24 10 6 12 30 36 18 60 12 12 24 8 12 36 12 30 21 8 12 8 18 12 18 12 16 12 18 8 18 12 18 36 12 30 24 24 12 12 12 18 24 8 12 18 18 12 12 12 18 12 24 12 42 12 36 12 16 8 18 12 16 12 12 12 84 18 8 16 12 8 12 8 8 8 24 18 Scenic Dr. McClatchy Rose Garden Tuolumne River Regional Park T.B. Scott Park Enslen Park Graceada Park Brookway Park 17th & G St. Park Cesar E. Chavez Park Beard Brook Park Moose Park Kewin Park Mellis Park Stoddard Ave. Scenic Dr. Downey Ave. Elm Ave. Laurel Ave. K St. La Loma 9th St. I St. Washington St. Paradise Ave. Martin Luther King Dr. HWY 99 Kansas Ave. J St. McHenry Ave. 7th St. E St. 30 24 30 24 24 F St. H St. 8th St. 66 66 66 72 84 96 96 96 42 96 10th St. 11th St. 54 14th St. 17th St. 13th St. 18 12 Jefferson St. Madison St. Needham St. 8 8 24 24 G St. 12th St. 15th St. MID Lat No. 4 MID Lat No. 5 36 36 36 36 36 36 30 36 24 24 24 24 24 24 36 36 36 24 24 24 24 20 16 8 42 6 66 10 ? 18 12 12 15 10 12 12 12 36 30 12 15 33 18 42 18 12 8 42 12 24 10 6 12 30 36 18 60 12 12 24 8 12 36 12 30 21 8 12 8 18 12 18 12 16 12 18 8 18 12 18 36 12 30 24 24 12 12 12 18 24 8 12 18 18 12 12 12 18 12 24 12 42 12 36 12 16 8 18 12 16 12 12 12 84 18 8 16 12 8 12 8 8 8 24 18 Scenic Dr. V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_2.3_downtown.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project PROPOSED DOWNTOWN IMPROVEMENTS FIGURE 2.3 Title 84010174 JANUARY 2008 SCALE 1" = 1000' Legend Existing Storm Drains Parks and Open Space MID Canals Available Parcels Proposed Parallel Infrastructure Proposed Replacement Infrastructure 9th St. Replacement Project (Boyle Engineering) ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning Area Description March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 2.5 approximately 343,000 people around the year 2030. While population numbers themselves are not particularly useful from a SDMP perspective (like they are for Water and Wastewater master planning), this information is useful in that it helps set the time frame for when the various pieces of the proposed storm drainage capital improvement projects identified in this SDMP may need to be operational. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 3.0 Existing Facilities 3.1 GENERAL The Study Area contains three basic types of areas from a storm drainage perspective: those with a positive system, those with a rockwell system, and those without improvements. About 70 percent of the Study Area is served by a positive storm drainage system or is currently undeveloped and is proposed to be served by a positive storm drainage system. A positive system collects stormwater runoff in catch basins, conveys it through underground pipelines, and discharges it into either detention/retention basins (approximately 40 percent of the Study Area), irrigation district owned laterals/drains (approximately 10 percent), or natural waterways (approximately 20 percent). In the case of detention basins (where the stormwater is only temporarily held), another step is involved with the pumping from the detention basin into an irrigation lateral/drain, or natural waterway. A rockwell system also collects stormwater runoff via catch basins, but differs in that the stormwater is held underground in what is basically a deep vertical hole filled with gravel where the stormwater is allowed to gradually percolate. The balance of the remaining Study Area, about 30 percent, consists of existing development that is served by rockwells. The City’s Public Works Department operates and maintains approximately 77 miles of storm drain lines (ranging from 8 to 96”) inches in diameter), 21 pump stations, 24 drainage basins, and approximately 10,500 rockwells. This Chapter discusses the following publicly-owned existing facilities: ‰ Positive systems ‰ Detention basins and pump stations ‰ Retention (percolation) basins ‰ Overflow discharge into the sanitary sewer system ‰ Rockwell systems 3.2 POSITIVE SYSTEMS The 1997 edition (and previous versions) of the City’s Standard Specifications for Storm Drainage Design (Section recommended that conveyance facilities (storm drain pipes) be designed to convey a 5-year storm event. In 2002 that criteria was updated to be in line with the more common industry practice of utilizing a 10-year storm event as the design standard for storm drains. As a result, infrastructure built before 2002 generally has the capacity to convey a 5-year storm event to its terminal outfall point. The areas of the City served by positive storm drain systems are shown in Figure 3.1 and these areas were not analyzed further in this SDMP. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.1 ---PAGE BREAK--- Village 1 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 78 79 81 82 83 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 102 103 Village 1 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 78 79 81 82 83 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 102 103 V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_3.1_positive_sd.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project AREAS CURRENTLY FIGURE 3.1 84010174 JANUARY 2008 SERVED BY POSITIVE STORM DRAIN SYSTEMS Title WITHIN THE SOI ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.2 The three largest positive storm drainage systems within the City that intercept stormwater runoff and convey it to either the Tuolumne River or Dry Creek are briefly described as follows: 3.2.1 McHenry Avenue Corridor system This system centers about McHenry Avenue and originates south of Sylvan Avenue and extends south along McHenry Avenue for several miles, eventually discharging into Dry Creek. The storm drainage pipe sizes range from 24” to 84” in diameter, and the watershed of this system mainly consists of residential areas with some commercial land uses along and near McHenry Avenue. 3.2.2 9th Street system The area served by this system is bounded by MID Lateral No. 4 on the north and west and by State Route 99 on the south. The system originates south of Morris Avenue and east of Tully Road and drains much of the downtown area. The pipe sizes vary from 24” to 96” in diameter and discharges through other structures into the Tuolumne River at the Union Pacific Railroad Bridge. Presently, there is a separate storm drainage project under design by the City for this area, which will supplement the capacity of the existing line in 9th Street by adding a larger parallel line down segments of 7th and 8th Streets to improve the flow carrying capacity of this system. 3.2.3 Yosemite Boulevard Corridor system This system commences near Riverside Drive and drains urban commercial and limited residential areas adjacent to Yosemite Boulevard. The pipe sizes range from 42” to 60” in diameter and discharge into Dry Creek, upstream of the confluence with the Tuolumne River. Though not described in detail, there are other positive storm drainage systems serving smaller areas of development that also drain into the Tuolumne River, Dry Creek, or an irrigation district-owned lateral. 3.3 DETENTION BASINS AND PUMP STATIONS In implementing flood control measures, the use of storm drainage detention basins is a common component of an overall flood control program, especially in the flat areas of the central San Joaquin Valley. Not only do these detention basins attenuate and regulate stormwater runoff peak flows by collecting, storing, and controlling their release, but they are also a very effective means of improving the quality of stormwater prior to its discharge. These detention basins have predominantly been constructed in conjunction with new residential and commercial development, and are often adjacent to an irrigation district owned lateral or natural waterway. Currently, there are 13 city-owned detention basins located throughout the study area (Figure 3.2), ranging in size from approximately 0.3 acre to 13 acres. Stormwater runoff originating from these areas is directed to and stored temporarily in the detention basins before it is pumped into an irrigation lateral or natural waterway at a controlled and reduced rate. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.3 In general, it is estimated that each of the City’s detention basins built before 2002 has the capacity to hold runoff generated by anywhere from a 10- to 50-year storm event. This is based on the fact that the majority of the detention basins were designed per the City’s 1997 (and earlier editions) Standard Specifications that required using a volume of two inches of water from the contributing commercial areas and one inch of water from the contributing residential areas as a design criteria in calculating the associated basin volume, and their subsequent enlargement by City crews over the years. This standard was updated in 2002 to require detention basins to hold a 100-year, 24-hour storm runoff volume resulting from 2.88 inches of rainfall occurring over the entire contributing area. Pump stations are used to drain the City’s detention basins and selected pipelines, and Table 3- 1 describes the City’s existing 21 pump stations (13 serving detention basins and 8 directly serving pipelines). Typically, the pump stations contain either a single primary pump with a backup pump or two pumps with a combined capacity equal to the design flow without any redundancy. Table 3-1. Pump Station Table ID Location/ Discharges to Number & Discharge Capacity of Pumps (Including Standby if Applicable) Standby Pumps Drainage Area/ Date Pump Stations Located at Detention Basins 1 Orchard Lift Station MID Lateral #3 2 pumps @ 2,500 gpm or 5.6 cfs each 1 466 acres 12/11/1978 2 Costco Lift Station MID Lateral #6 2 pumps @ 1,200 gpm or 2.7 cfs each 1 75 acres 5/23/2000 3 Johansen Lift Station MID Lateral #2 2 pumps @ 800 gpm or 1.8 cfs each 1 4 Stonebridge Lift Station MID Lateral #7 2 pumps @ 900 gpm or 2 cfs each 1 9/16/1986 5 Veneman Lift Station MID Lateral #7 1 pump @ 720 gpm or 1.6 cfs 0 6 Coffee Briggsmore Lift Station MID Lateral #3 2 pumps @ 540 gpm or 1.2 cfs each 1 27 acres 9/2/1997 7 Carpenter Lift Station MID Lateral #3 2 pumps @ 400 gpm or 0.9 cfs each 1 20 acres 3/31/1998 8 Central Basin MID Lateral #3 3 pumps @ 3,400 gpm or 7.6 cfs each 1 1,450 acres 5/6/2003 9 Twin Basins MID Lateral #6 4 pumps @ 2,300 gpm or 5.1 cfs each 2* 640 acres 12/8/1998 10 Cheyenne/Terneuzen MID Lateral #7 1 pump @ 300 gpm or 0.7 cfs 0 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.4 Table 3-1. Pump Station Table ID Location/ Discharges to Number & Discharge Capacity of Pumps (Including Standby if Applicable) Standby Pumps Drainage Area/ Date 11 Coffee/Claratina Grecian Basin 12 Fairview Village Tuolumne River 2 pumps @ 5,370 gpm or 12.0 cfs each 1 13 West Basin Central Basin 1 pump @ 1,200 gpm or 2.7 cfs 0 42 acres 6/24/2003 Pump Stations Located at Pipe Discharges 14 Briggsmore South Lift Station MID Lateral #3 2 pumps @ 500 gpm or 1.1 cfs each 1 15 Briggsmore North Lift Station MID Lateral #3 2 pumps @ 500 gpm or 1.1 cfs each 1 16 Tully Briggsmore Lift Station MID Lateral #3 1 pump @ 1,150 gpm or 2.6 cfs 0 5/23/1993 17 Hatch-Dallas TID Lateral #1 1 pump @ 263 gpm or 0.6 cfs 0 18 College & Ashford Cavil Drain 1 pump @ 449 gpm or 1 cfs 0 5.5 Acres N/A 19 Naraghi Lakes Cavil Drain 1 pump @ 3,500 gpm or 7.78 cfs 0 168 acres 20 Tokay & Sunrise Cavil Drain 1 pump @ 900 gpm or 2 cfs 0 1.58 acres 3/19/1996 21 Prescott/Standiford MID Lateral #7 2 pumps @ 325 gpm or 0.7 cfs each 1 See Figure 3.2 for locations * The only permanent backup generator at any of the pump stations sites is at the West Basin. 3.3.1 Discharge into Irrigation District Owned Facilities MID operates a network of man-made irrigation laterals, drains, and a main canal that flow through the Study Area (Figure 3.3). TID has one lateral crossing the southernmost portion of the City and it receives a minor amount of stormwater runoff from one pump station at Hatch Road and Dallas Street. The primary function of the Main Canal and laterals, which are open, concrete lined facilities with some underground reaches, is to deliver irrigation water for agricultural purposes to customers within and beyond the Study Area. The irrigation season typically begins in mid-March and extends through October, and this is when these facilities convey the majority of their irrigation water. Depending upon their location, the drains are used to convey and ---PAGE BREAK--- Village 1 1 2 3 4 12 13 14 15 16 21 23 34 35 36 53 55 57 81 82 83 85 86 89 91 93 80 100 101 54 76 52 22 TERNEUZEN AVE VENE MAN AVE TULLY RD TULLY RD W. BRI GGSMORE AVE W. BRI GGSMORE AVE OAKDA LE RD MC HENRY AVE LAGUNA DR CLARATINA AVE Auto Center Ct. Cheyenne/ Terneuzen Prescott Standiford Veneman LS Stonebridge Apts Briggsmore Drain Carpenter Tully Briggsmore Coffee Briggsmore Naraghi Lakes Orchard LS Tidewater Sump Big Valley Church College Ashford Costco LS DAL E RD CHAPMA N RD Fleur DeVille KANSAS AVE NEEDHAM AVE Kansas/Needham Modesto Plaza Cavil Drain MID Lat No3 MID Lat No4 TID Lat No1 MID Lat No3 MID Lat No6 Twin Basins 25 56 90 92 87 88 98 FLOYD AVE ROSE AVE Central Basin Johansen Dry Creek Tuolumne River Tokay/Sunrise TOKAY AVE SUNRI SE AVE Johansen CPD Abandoned MID Lat No2 102 103 HWY 99 HWY 99 9TH ST TULLY RD TULLY RD TRASK LN CLAUS RD COFFEE RD MABLE AVE RUMBLE RD LAGUNA DR COFFEE RD RUMBLE RD COFFEE RD SCENIC DR SNYDER AVE OA KDAL E RD SYLVAN AVE OA KDAL E RD SNYDER AVE MARTIN AVE KIERNAN AVE HAZELNUT DR PRESCOTT RD PRESCOTT RD KIERNAN AVE CLARIBEL RD ROSELL E AVE SUNRISE AVE PHOENIX AVE CARPENTER RD SHERWOOD AVE KATHRINE AVE MC HENRY AVE MC HENRY AVE WOODLAND AVE PELANDALE AVE PRINCETON AVE ORANGEBURG AVE STANDIFORD AVE ORANGEBURG AVE YELLOWSTONE AVE TID Lat No1 MID Lat No3 MID Lat No6 MID Lat No4 MID Lat No1 MID Lat No5 MID Lat No7 Encina Storm Drain (City-Owned) Main Canal Village 1 1 2 3 4 12 13 14 15 16 21 23 34 35 36 53 55 57 81 82 83 85 86 89 91 93 80 100 101 54 76 52 22 TERNEUZEN AVE VENE MAN AVE TULLY RD TULLY RD W. BRI GGSMORE AVE W. BRI GGSMORE AVE OAKDA LE RD MC HENRY AVE LAGUNA DR CLARATINA AVE Auto Center Ct. Cheyenne/ Terneuzen Prescott Standiford Veneman LS Stonebridge Apts Briggsmore Drain Carpenter Tully Briggsmore Coffee Briggsmore Naraghi Lakes Orchard LS Tidewater Sump Big Valley Church College Ashford Costco LS DAL E RD CHAPMA N RD Fleur DeVille KANSAS AVE NEEDHAM AVE Kansas/Needham Modesto Plaza Cavil Drain MID Lat No3 MID Lat No4 TID Lat No1 MID Lat No3 MID Lat No6 Twin Basins 25 56 90 92 87 88 98 FLOYD AVE ROSE AVE Central Basin Johansen Dry Creek Tuolumne River Tokay/Sunrise TOKAY AVE SUNRI SE AVE Johansen CPD Abandoned MID Lat No2 102 103 HWY 99 HWY 99 9TH ST TULLY RD TULLY RD TRASK LN CLAUS RD COFFEE RD MABLE AVE RUMBLE RD LAGUNA DR COFFEE RD RUMBLE RD COFFEE RD SCENIC DR SNYDER AVE OA KDAL E RD SYLVAN AVE OA KDAL E RD SNYDER AVE MARTIN AVE KIERNAN AVE HAZELNUT DR PRESCOTT RD PRESCOTT RD KIERNAN AVE CLARIBEL RD ROSELL E AVE SUNRISE AVE PHOENIX AVE CARPENTER RD SHERWOOD AVE KATHRINE AVE MC HENRY AVE MC HENRY AVE WOODLAND AVE PELANDALE AVE PRINCETON AVE ORANGEBURG AVE STANDIFORD AVE ORANGEBURG AVE YELLOWSTONE AVE TID Lat No1 MID Lat No3 MID Lat No6 MID Lat No4 MID Lat No1 MID Lat No5 MID Lat No7 Encina Storm Drain (City-Owned) Main Canal V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_3.3_mid.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project EXISTING AND PROPOSED FIGURE 3.3 Title 84010174 JANUARY 2008 DISCHARGES TO IRRIGATION Legend Existing City Discharges to MID Facilities Existing Non-City Discharges to MID Facilities Existing Discharges to TID Facilities Storm Drainage Master Plan Sub-basins 1 Colors Denotes Existing and Proposed Areas That Discharge to MID Facilities MID and TID Canals Cavil Drain Proposed Discharges FACILITIES ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.5 discharge agriculture tail water and storm water runoff to the San Joaquin, Tuolumne, or Stanislaus Rivers. However, in the rainy season when irrigation waters are not required to water crops, some of the laterals and drains are also used to convey drainage from fields outside of the City and urban stormwater runoff from several areas within the City (this is also when the irrigation districts perform maintenance activities on their facilities), and Figure 3.3 shows the location of these discharge points. The ability to discharge stormwater into the irrigation laterals depends on a number of factors. Some of these laterals occasionally reach their carrying capacity during certain times of the year. The laterals were built as an irrigation distribution system, and as such, they were designed with size and capacity reductions in the direction. These laterals do not have an unlimited capacity to convey stormwater runoff, and MID works a delicate balance among irrigation supply needs, the City’s need to pump stormwater into MID’s facilities, and the need to maintain safe water levels within the laterals. Almost all of the urban stormwater discharged into MID-owned laterals is attenuated by detention basins, with the outfall pumping occurring at a significantly reduced rate as capacity becomes available. The City also needs to address the very real possibility that there will be future water quality restrictions on the City’s stormwater discharges to MID irrigation canals resulting from the Regional Water Quality Control Board’s adoption of an Agricultural Discharge Waiver. Dependence upon the MID canal system to drain stormwater runoff from City detention basins and deliver it to the San Joaquin River (an impaired water body) is a risky disposal solution with unknown future costs and discharge prohibitions. Since the irrigation laterals and drains are owned and operated by MID, the authorization to discharge City runoff into these facilities requires formal agreements between the City and MID. To date, a number of agreements have been executed that authorize and establish the requirements (primarily related to water quantity and quality) for these discharges. Some of the more note-worthy provisions of the standard drainage agreements executed between the City and MID include: ‰ The City is liable and responsible for the quantity and quality of the water that is discharged ‰ There are provisions for MID to direct the City to discontinue discharging at any time for any reason (see Item No. 4 in Chapter 9 for additional discussion) ‰ Discharges are typically limited per location to five cubic feet per second ‰ A 48-hour holding settling-out period is required for water quality control purposes prior to pumping An example of a discharge agreement between the City and MID is provided in Appendix A. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.6 3.3.2 Recreational Dual-Use In December 2000, the Modesto City Council amended the General Plan to include new dual- use storm drainage design policies (“Design Standards for Dual Use Flood Control/Recreation Facilities,” Stantec) that require certain new parks and storm drainage detention basins to be integrated into a single facility to maximize the recreational value and aesthetic appearance in residential areas. The City’s Parks, Recreation, and Neighborhood Department has divided the SOI into ‘Park Planning Areas’ (Figure 3.4) that depicts areas that may ultimately have a neighborhood ‘dual-use’ park built in them. Many detention basins are essentially dry, minus intermittent nuisance water, for much of the year. This condition creates opportunities for the inclusion of active or passive recreational elements as dual-use functions within detention basins (as opposed to retention basins with their frequency and duration of standing water). Several factors contribute to the suitability of incorporating dual-use amenities in the design of detention basins. These factors include the frequency of storm events that produce inundation of the basin, duration of the inundation, size and configuration of the overall detention site, amount of incoming sediments, and safety concerns. If an evaluation of the above factors creates a favorable opportunity for the inclusion of active or passive recreation elements as a dual-use within a given detention basin, the following are a few of the fundamental design approaches that should be utilized: ‰ Low flow must be accommodated in a manner that confines the frequent inundations to areas that will characteristically require only limited maintenance ‰ Contouring within a detention basin is recommended to create internal elevation variations (tiers) that have differing frequencies and depths of inundation and flood risk. The following hierarchy may be utilized as a starting point in evaluating design opportunities ‰ Lowest lying areas = semi-natural riparian areas and ponds ‰ Lower elevated tiers = picnic areas, passive turf, and vegetation zones ‰ Intermediate elevated tiers = ball fields ‰ Upper elevated tiers = court games and parking areas ‰ Areas above the 100-year flood level = restrooms and habitable structures ‰ Internal drainage within the detention basin should provide for positive flow across elevated tiers and to the basin’s lowest areas to prevent standing water within the recreation areas Another key factor to be evaluated is the use of landscaping to improve the aesthetics of such facilities. The policies adopted for residential dual-use basins that anticipate active recreational ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.7 areas designed into the detention basin are not directly applicable to commercial and industrial detention basins; however, commercial and industrial detention basin standards would most likely require that landscaping be incorporated into the basin’s design. The commercial and industrial detention basins would be considered dual-function rather than dual-use. The intended goal for incorporating dual-function facilities into certain business and industrial park developments is to eliminate the need for aesthetically unappealing detention basins and fences by replacing them with landscaped areas and passive recreation elements that enhance the quality of the development. As a result, City staff is working to identify how certain elements of the dual-function concept could be incorporated into a new set of commercial and industrial park development guidelines. Industrial park development has not occurred on the scale that residential development has; therefore, the design of non-residential detention basins has been done on a case-by-case basis. The following are the existing dual-use detention basins within the Study Area: ‰ West Basin at Hillglen and Bear Cub Lane, this basin discharges to the Central Basin and accepts stormwater runoff from the surrounding neighborhoods. ‰ Coffee Claratina Park at Grecian and Drakeshire, this basin discharges to the Grecian Basin located near Grecian and McHenry and also accepts water from the surrounding neighborhoods. Other sites with proposed dual-use detention basins anticipated to be built in the near future include: ‰ Fairview Park along Salazar Circle will be a dual-use basin in which the stormwater will ultimately be pumped into the Tuolumne River. ‰ Freedom Park (Maid Mariane and Sharon) and Sanders Park (Litt Road and Kodiak Drive) both collect on-site water and store it on-site and then have an overflow for worst-case scenario; they do not discharge except in extreme circumstances. They are both presently under construction. ‰ Mary E. Grogan Community Park has a dual use basin designed into the master plan also to collect on-site water and will have a discharge to the West Basin. Details are not completed yet and the park will not be constructed for a few years. 3.4 RETENTION (PERCOLATION) BASINS In many areas of the City where discharge points do not currently exist, the local drainage infrastructure directs stormwater runoff into retention (percolation) basins as terminal facilities. A retention basin is a terminal stormwater drainage facility specifically sized to impound runoff from a given drainage area with a predetermined calculated design storm event and is emptied from the basin by a combination of percolation and evaporation. By definition retention basins ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.8 are not associated with pump stations, and there are 11 such city-owned retention basins serving different areas of the City, with sizes ranging from approximately 0.1 acre to 10 acres (Figure 3.2). It is important that retention basins be located in areas with a relatively deep groundwater table to allow percolation of stormwater. At least ten feet separates the bottom of the lowest part of the proposed basin and the highest ground water elevation measured at the site (during the time of year having the historically highest groundwater levels). Within the study area, the difference between groundwater levels at the same location can vary greatly at different times of the year. It is estimated that many of the retention basins constructed before 2002 have the capacity to contain runoff from their respective tributary area for storms approaching a 50-year return period due to their enlargement by City crews over the years. However, many of them do not function in the way they were originally intended because some are located in areas that have underlying soils with very low percolation rates, thus inhibiting their receiving capacity as a result of the presence of residual water from prior storms that did not fully infiltrate into the ground. Others are located in areas with a high local groundwater table. While some amount of percolation usually does occur, the slow accumulation of fine sediments or silts conveyed with stormwater runoff slowly accumulates and often results in marsh-like conditions by allowing weed growth, stagnant water, and insect breeding. These facilities are thus costly to maintain, can become (with excessive weed growth and security fencing), and require higher levels of maintenance. As is the case with most of the detention basins, the majority of the City’s retention basins were designed according to an outdated set of standards only requiring the entrapment of a volume of two inches of water from contributing commercial areas and one inch of water from contributing residential areas. The City’s current Standard Specifications require that retention basins hold a 100-year, 6-day storm runoff volume resulting from 5.6 inches of rainfall occurring over the entire contributing area. As development continues to occur in areas where positive storm drainage systems do not exist and retention basins are used, issues with the appearance and maintenance requirements of these types of basins are becoming more of a concern. While they may operate adequately in the early years of usage, their appearance and ultimately their function has made this type of storm drainage facility less favorable. 3.5 OVERFLOW DISCHARGE INTO THE SANITARY SEWER SYSTEM In some areas where positive storm drainage systems are not available, portions of the sanitary sewer system are presently used as a means of draining stormwater collected in streets. The City currently employs two methods of discharging stormwater runoff into the sanitary sewer system. The first is through a physical connection with a pipe joining the two systems, known as a cross connection. The second is more indirect and relates to areas that have ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.9 historically experienced localized flooding due to the lack of adequate storm drainage facilities (hot zones), wherein the ponded water is collected into vacuum trucks and transported to the nearest location able to take the water, which is usually the sanitary sewer system. Adding stormwater runoff to the sanitary sewer system is generally undesirable for a number of reasons. Primarily, it is expensive to treat stormwater to the same level as wastewater and valuable conveyance capacity is lost within the sanitary sewer system. As a separate study and contract from the development of this SDMP, Stantec has been retained by the City to determine the infrastructure needed to eliminate selected storm drainage cross connections and stormwater discharged from hot zone areas to the sanitary sewer system (see the “Storm Drain Cross Connections to Sanitary Sewer System” – Technical Memorandum; June 2007). Since storm drainage discharges into the sanitary sewer system will be significantly reduced or eliminated (depending on the number of cross connections and changes to the hot zones discharge practices), this study has identified the new storm drainage infrastructure needed to accommodate the stormwater no longer able to enter the sanitary sewer system. This study also includes recommendations for the required storm drainage infrastructure and the preparation of cost estimates for those facilities. General findings from this study are discussed below. 3.5.1 Cross Connections The direct disposal of stormwater into the sanitary sewer system is performed through special cross connection piping, and this method of disposal is used in an emergency to remove limited quantities of water from small locally flooded areas. There are between 45 and 50 locations within the City where a cross connection from the storm drainage system to the sanitary sewer system exists, and most are located either within the northwest portion of the City or the downtown area (Figure 3.5). Twenty-five to 30 cross connections are located in the northwest portion of the City where stormwater is primarily drained via rockwells and a minimal amount of storm drain pipes exist. By constructing new storm drainage trunk lines (and smaller laterals as needed) the existing storm drainage cross connections can be disconnected from the sanitary sewer system. Most of the proposed storm drainage pipes will ultimately be used to convey stormwater runoff to future detention basins. However, since it is not economically feasible to construct the proposed detention basins at this time, the new storm drainage trunk lines may be used to provide temporary underground storage that will utilize existing or new rockwells for drainage of stormwater stored in the pipes. Approximately 20 of the cross connections are located in the downtown area of the City, and because there is an existing positive storm drain system in the downtown area, some of these cross connections can be eliminated by the addition of lateral storm drain lines to establish a new connection with an existing storm drain pipe. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.10 While removing the cross connections to the sanitary sewer system and installing the proposed interim storm drainage infrastructure will eliminate the need to discharge stormwater directly into the sanitary sewer system, it is likely that some of the affected areas will still experience some degree of periodic flooding until the proposed improvements are constructed. The cross connections were evaluated within each applicable area. The goals for the proposed infrastructure are three fold: ‰ Eliminate as many of the storm drainage cross connections to the sanitary sewer as possible ‰ Reduce street flooding ‰ Reduce or eliminate the burden and cost of treating stormwater runoff at the City’s wastewater treatment plant The City has approved an initial phase of the proposed improvements to eliminate the storm drain cross connections to the sanitary sewer system. A portion of the proposed infrastructure in this SDMP will be constructed (in the immediate vicinity of cross connection locations) utilizing the wastewater fund as its funding source and the remaining portion of the storm drainage system will be constructed at a later date when funds become available. A temporary rockwell manhole (a rockwell with manhole access) is proposed at the terminus of each of the proposed storm drain pipes. The purpose of the rockwell manhole is to allow drainage/infiltration of the stormwater that is stored in the storm drainage pipe. Any existing rockwells along the proposed pipe alignment will typically remain in place. 3.5.2 Hot Zone Areas City staff has previously identified developed areas that do not have an existing positive storm drainage system and have historically experienced flooding. These areas are defined as hot zones and drainage from the hot zone areas is provided via rockwells. The hot zones identified in this evaluation are seen as “indirect” cross connections because standing surface stormwater is pumped into the sanitary sewer system periodically by City operations and maintenance crews to alleviate local flooding problems after storms. Possible methods for eliminating “indirect” cross connections associated with City pumping of surface drainage into the sanitary sewer system within the storm drainage hot zones have been discussed with City staff. These “indirect” cross connections include specific intersections and other areas that are known to flood even during small rain events. Figure 3.6 shows the hot zone areas with the new storm drainage infrastructure needed to provide flood relief to these areas. While the installation of the proposed drainage infrastructure will allow a reduction of the practice of discharging stormwater accumulated in drainage hot zones to the sanitary sewer system, it is likely that the affected areas will still experience some ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.11 degree of periodic flooding until the down gradient SDMP proposed infrastructure is constructed. 3.6 ROCKWELL SYSTEMS The City’s storm drainage system is unique in that a large portion of the stormwater runoff does not directly discharge to an irrigation lateral or natural waterway, but is percolated into the ground via catch basins to rockwells (Figure 3.7). This is due to the fact that many developed areas of the City are not in close proximity to irrigation laterals or natural waterways. A rockwell is a 30-inch diameter vertical hole drilled in the ground to a depth of typically 50 feet and filled with graded rocks with a 20 foot-long perforated pipe down its center, usually located in depressed areas where stormwaters are likely to collect. Rockwells function by receiving and holding stormwater runoff from catch basins, which capture the runoff from at-grade street gutter pans and low-lying areas, and allowing the stormwater to gradually percolate. Rockwells have been permitted as a storm drainage solution for new development in the City for many years and are still allowed under certain circumstances by the General Plan and current Standard Specifications with prior approval by the City Engineer (only in infill areas without a positive drainage system). Their intended function is to allow stormwater runoff to percolate through the rock and sand layers and into the ground. A single rockwell can drain approximately 10,000 square feet of impervious area and most locations have multiple rockwells. Most rockwells perform well for a few years, but without continuous maintenance they eventually lose their ability to function as intended because of sedimentation buildup, which results in reduced stormwater infiltration. At many locations, rockwells do not have adequate capacity to handle all of the runoff produced during annual storm events, resulting in the periodic flooding of certain streets. One of the goals of this SDMP is to reduce the level of dependency on rockwells as a storm drainage solution. Because they are highly dependent on continuous, preventative maintenance to function properly, they are expensive to operate. The City’s use of a rockwell system is highly dependent on preventative maintenance in order to function properly. While a number of improvements have been made over the last few years, and some areas served by rockwells have performed adequately, the overall system is still deficient in its ability to convey stormwater runoff and minimize localized flooding in many areas of the City. As with other jurisdictions built on relatively flat terrain, part of the City’s storm drainage system strategy is the temporary holding of some stormwater within the curb and gutter area of its streets. This type of ponding is basically in-transit storage, and unless this ponding exceeds the right-of-way limits or presents a significant traffic hazard, it amounts to a relatively short-period nuisance. Many cities anticipate this temporary detention storage as part of the overall storm drainage system provided that the temporary ponding of water is short-term and minimal. ---PAGE BREAK--- ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 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! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 78 79 81 82 83 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_3.7_rockwells.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project FIGURE 3.7 Title 84010174 JANUARY 2008 LOCATION OF EXISTING CATCH BASINS CONNECTED TO ROCKWELLS ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Existing Facilities March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 3.12 Since property damage has historically been slight to non-existent, totally eliminating the use of all rockwells within the City is not an intended outcome of this SDMP, and it would also be cost- prohibitive. However, to the extent practical, a key goal is to create positive storm drainage solutions within areas that are currently served exclusively by rockwells. As needed, many rockwells will remain in service as a part of the implementation of this SDMP, in that they will continue to serve as water quality treatment devices (especially for first flush events) and supplemental storage structures. 3.7 FLOOD HAZARDS Regional flood control issues dealing with the Tuolumne River and Dry Creek as they pass through the Study Area are outside the evaluation scope of this SDMP except as they relate to local storm drainage system recommendations provided herein. In general, some of the low- lying areas of the lower reaches of the Tuolumne River, including areas near the confluence with Dry Creek, are subject to periodic flooding. The 100-year floodplain is delineated on the Federal Emergency Management Agency Flood Insurance Rate Maps (FIRMs). The current FIRMs are effective as of May 7, 2001 and include the following maps: ‰ 060387 0005D ‰ 060387 0015D ‰ 060387 0020D ‰ 060384 0510B Some of the areas proposed for development are within the 100-year floodplain (Figure 3.8), and development in these areas will be restricted by the City’s floodplain zoning ordinance. Typically, these areas are removed from the 100-year floodplain designation by elevating the properties using fill or by construction or rehabilitation of existing flood control levees in order to minimize potential flood damage. The Tuolumne River and Dry Creek are two natural waterways that have been historically used as outfalls for stormwater derived from several sections of the City. The Tuolumne River and Dry Creek have significant flow carrying capacity for stormwater, particularly given that the short term discharge of urban runoff would generally occur non-concurrently with the passage of peak flows in these streams given the significant size of their watersheds and their long times of concentration. In a major flood event along these streams, additional City runoff would create a small incremental increase in flow discharges and most likely a negligible increase in flood stage. Currently, the existing positive storm drain systems serving portions of the City drain into the Tuolumne River and Dry Creek. The locations of existing storm drainage outfalls into the Tuolumne River and Dry Creek are depicted on Figure 6.2. ---PAGE BREAK--- Dry Creek Tuolumne River V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_3.8_fema.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project FEMA FLOODPLAIN FIGURE 3.8 Title 84010174 JANUARY 2008 Legend FEMA 100-yr Floodplain Source: FEMA Flood Insurance Rate Maps 060387 0005D, 0015D, 060387 0020D, and 060384 0510B effective May 7, 2001 BOUNDARY ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 4.0 Planning and Design Criteria 4.1 GENERAL The design of a citywide storm drainage system is based upon many factors, and the purpose of this Chapter is to define some of the more important elements so that a uniform set of criteria can be followed. Specifically, the City’s proposed storm drainage system needs identified in this SDMP have been evaluated primarily using the design criteria defined herein. It is important to note that the criteria used on the master planning level (as in the development of this SDMP) are different than those used on a site design level using City Standards). For instance, the HEC-HMS computer program described in Section 5.3 of this SDMP vs. the rational formula and the unit hydrograph methods described in the City Standards used to determine design flow rates. The criteria presented below include excerpts from the City’s current Standard Specifications for Storm Drainage Design (Standards), Chapter 4. 4.2 DESIGN CAPACITIES The design flow rate is the amount of peak stormwater runoff that would be expected to occur from a selected design storm event over a defined area. The design capacity for a storage facility (detention or retention basin) is related to the runoff volume produced by the contributing watershed or sub-basin during a specified design storm event. A key step in the design process is determining the design capacity that a given storm drainage facility would be expected to carry or store without surcharging. The design storm event criteria for frequency and duration used for master planned facilities in this SDMP is shown in Table 4-1. Table 4-1. Design Storm Event Criteria* Storm drains and open channel 10-year, 24-hour P = 1.92 inches Detention basins 100-year, 24-hour, considering outflow rate P = 2.88 inches Retention basins 100-year, 6-day P = 5.6 inches Pump stations N/A Discharge rate of less than 10 cfs * Pertains to both on-site and off-site facilities The use of a design capacity of less than 10 cfs for pump stations that will serve the larger, master planned detention basins in this SDMP is based on inherent limitations of the MID’s laterals’ ability to receive significant additional discharges and stormwater quality issues associated with direct discharges to Dry Creek and the Tuolumne River. For the terminal detention basins, this limitation on pumping rates will produce greater requirements for storage volumes (as presented herein) and drain times that are longer than prescribed per City v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 4.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning and Design Criteria March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 4.2 Standards for local facilities and for dual-use facilities after the occurrence of a 100-year storm event. Drain times for the larger detention basins will be a function of a combination of pumping outflow rates, percolation rates, and evaporation rates and may be determined as a part of actual facility design. If residual water will remain in a detention basin for a prolonged period of time after a major storm event, there may be a need for temporary mosquito abatement procedures to be implemented. Further, the detention basin sizing represented herein accounts for the storage volumes needed for flood control only, and additional land will be required to incorporate provision for dual-use recreation facilities, if such facilities are proposed. 4.3 FACILITY DESIGN STANDARDS The reader is directed to the relevant sections of the Standards for specific guidelines governing the design of underground pipelines, detention and retention basins, pump stations, rockwells, and other storm drainage facilities. Additionally, the following adopted City documents should also be consulted: ‰ Design Standards for Dual Use Flood Control / Recreational Facilities (Dual Use Standards), December 2000 ‰ Guidance Manual for New Development Stormwater Quality Control Measures Guidance Manual, January 2001 Many areas within the City either presently or will ultimately drain to a detention or retention basins. The basins are "flood control" facilities that should meet a reasonable standard, and the 100-year, 24-hour design storm event is the standard utilized by the City and many other communities for these types of facilities. The contributing storm drains have a 10-year, 24-hour design storm event standard, which means that the streets will offer temporary storage during the infrequent occurrence of storms that are greater in magnitude than a 10-year, 24-hour event. The storm drains will be surcharged in storm events greater than the 10-year, 24-hour design event and they will be delivering flows to the detention basin at their conveyance "capacity" level for a prolonged period of time until the pipeline capacity begins to exceed the inflow rate from the streets. Concurrently, the detention basin will be filling up toward the 100- year, 24-hour design storage level. Hence, during a 100-year, 24-hour design storm event, the sustained 10-year, 24-hour storm drain flows will eventually discharge into a detention basin that has a water surface level in it that is greater than the 10-year, 24-hour stormwater level. This is especially relevant to Modesto as detention basins will generally be limited to very low outflow rates. In consideration of these conditions, the design of storm drain pipelines shall utilize the 100-year, 24-hour design storm event water surface elevation in detention basins as the “tail water” elevation in determining the 10-year, 24-hour design storm event hydraulic grade line elevations within the storm drain pipelines. The same approach shall be utilized for storm drain pipelines discharging into retention basins. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning and Design Criteria March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 4.3 4.4 WATER QUALITY The City is required by State and Federal regulations to develop a comprehensive inventory, monitoring, and management program to reduce the amount of pollutants in stormwater runoff discharged to receiving waters of the United States to the maximum extent practicable. The City is a National Pollutant Discharge Elimination System (NPDES) Phase I community and has complied with these regulations and received a NPDES Permit from the Regional Water Quality Control Board in 1994, and an updated Permit in 2002 (city staff is currently working with the California Regional Water Quality Control Board on the City’s updated 12007 permit). The NPDES Permit stipulates numerous requirements and practices that are needed to improve the quality of the City’s stormwater discharges and all new projects meeting certain minimum threshold requirements are subject to these regulatory provisions. As a result, the City is developing a Stormwater Management Plan (SWMP) that prescribes specific Best Management Practices (BMPs) and performance standards to be implemented. BMPs represent control mechanisms to reduce the discharge of pollutants from new or existing developments to the maximum extent practicable. We will probably see some form of LID design requirements in the New Development/ Redevelopment section of our 2007 NPDES permit. A key BMP is capturing the “first flush” runoff (the initial part of a storm event or the initial storm of the wet season) and detaining that runoff to allow pollutants to settle out. Typically, the “first flush” of stormwater runoff from urban areas contains the highest concentrations of heavy metals, petroleum hydrocarbons, animal waste, pesticides, sediments, and products associated with motor vehicles. These concentrations generally reduce with subsequent storms. The Tuolumne River receives stormwater discharges from some areas of the City and has been classified as an “impaired water body”, per the 2002 Federal Clean Water Act, and is included on the Section 303(d) List of Water Quality Limited Segments developed by the State Water Resources Control Board. Under this classification, stricter requirements pertaining to stormwater discharge quality, as measured by Total Maximum Daily Loads are likely to be enacted in the future. Storm drainage facilities for all commercial, industrial, and residential projects, regardless of size, shall include stormwater quality control measures in their design. The City’s “Stormwater Quality Control Measures” document contains guidelines for the design, construction, and maintenance of storm drainage treatment facilities. This manual establishes the requirements for stormwater quality control measures and provides guidance for their use to developers, contractors, and engineers. The proposed solutions presented in this SDMP to relieve flooding and improve stormwater conveyance have been developed in consideration of these concerns and requirements (existing and future) and will also provide opportunities for improving the quality of stormwater runoff prior to discharge. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning and Design Criteria March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 4.4 One of the most cost effective methods to improve the quality of stormwater runoff is to utilize detention basins which provide attenuation storage and opportunities for pollutants to settle and be retained within the basin prior to the stormwater being discharged into receiving waters. Detention basins have been used as an acceptable BMP to help the City meet the requirements of their NPDES permit. Allowing urban runoff to flow through grassy swales and turf areas also provides a filtering mechanism that serves to improve the quality of urban runoff. This SDMP includes recommendations for the future construction of several detention basins that will provide flood control attenuation as well as water quality treatment opportunities to satisfy NPDES requirements. The use of rockwells also has inherent treatment capabilities for storm runoff that may ultimately reach surface waters by capturing and storing “first flush” surface runoff. To date, staff of the Parks, Recreation and Neighborhoods Department (PR&N) has discouraged the incorporation of new storm drainage connections into existing parks that will provide for attenuation storage and water quality treatment. However, PR&N staff has suggested that it may be possible to incorporate some types of wetland features near the gateway area with the Tuolumne River Regional Park (as per the Parks Master Plan) for water quality treatment purposes grassy swales, etc.) into the future development. In general, a properly designed and maintained detention basin (that holds stormwater for a prescribed period of time) will reduce the concentration of constituents discharged into receiving waters by providing for volatization, settlement, and subsequent absorption by vegetative matter and the soil. Suspended solids, heavy metals, hydrocarbons, and possibly some organic compounds are the most predominant constituents that would be expected to have reduced levels of concentrations after detention storage. As related to the City’s NPDES permit and the various discharge agreements with MID, a certain amount of detention basin monitoring water quality testing) has taken place over the years. It has been demonstrated, in general, that a properly designed detention basin improves the stormwater quality due to the settlement and volatization that occurs in the basin. In addition to the stormwater quality benefit associated with the detention basins that are proposed in this SDMP, the City may encourage developers to utilize Low Impact Design (LID) methods on individual sites. LID is an approach to managing stormwater runoff that models the natural pre-development hydrology of the site by using design techniques that infiltrate, filter, store, treat, evaporate, and detain stormwater runoff close to the source. Almost all areas of site design can incorporate LID such as residential landscaping, open space, streetscapes, parking lots, sidewalks, and medians. LID can be used in combination with traditional storm drain systems to infiltrate the smaller, more frequent storms, while allowing the larger storms to flow to pipes and basins for flood control (possibly with lower off-site costs than traditional non-LID system). LID techniques offer great benefits to stormwater quality for the smaller return interval storm events. LID will help reduce the amount of runoff entering the City’s system and will aid in recharging ground water. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Planning and Design Criteria March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 4.5 If stormwater quality discharge regulations become extremely restrictive in the future, there will most likely be significant costs to retrofit existing storm drainage facilities with more advanced treatment methods. It is difficult and somewhat impractical to plan for these potential events by identifying infrastructure to implement full treatment measures at this time; thus, this set of possible future circumstances has not been incorporated into the infrastructure and capital costs identified in this SDMP. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 5.0 System Hydrology and Modeling 5.1 GENERAL This Chapter briefly discusses the various watersheds located within the Study Area and the basic attributes of the different hydrologic and hydraulic models used in the development of this SDMP. In general, this SDMP emphasizes the formulation of drainage solutions for areas without positive storm drainage systems. 5.2 WATERSHED DESCRIPTIONS The Study Area for this SDMP basically covers the City’s SOI (with a few noted exceptions) that is generally bounded by Claribel Road on the north; Vivian Road, Morse Road, and Highway 99 on the west; Whitmore Avenue and the Tuolumne River on the south; and the AT&SF Railroad on the east. The Study Area is approximately 56 square miles in area and includes a combination of residential, commercial, industrial, institutional, and recreational development, as well as currently undeveloped agricultural land and open space. The Study Area has been subdivided into 24 major watershed groups, Watersheds A through V plus an offsite Watershed OS, which are composed of one or more sub-basins. The establishment of major watershed groups has been based on interpretations of man-made and natural topographic features, land use designations, property boundaries, and common drainage solution opportunities. Figures 5.1a and 5.1b depict the watershed groups and sub- basin boundaries. In the hydrologic analysis, there are a total of 103 sub-basins ranging in size from 12 acres to 2,140 acres. The following is a brief description of each watershed group under existing conditions: Watershed A is located both east and west of Coffee Road, south of Mabel Avenue and north of Dry Creek, and consists of sub-basins 12, 19, 20 and 71. This watershed is approximately 5.1 square miles in area and mainly consists of residential properties, with some commercial developments along Coffee Road. No major storm drain system exists in this watershed except for minor storm drains extending along short segments of Coffee Road both north and south of Briggsmore Avenue. The storm drain along Coffee Road north of Briggsmore Avenue is a 42” diameter concrete pipe and originates at the intersection of Coffee Road and Floyd Avenue, then drains into a detention basin north of Briggsmore Avenue before being pumped into MID Lateral No. 3. The storm drain south of Briggsmore Avenue commences at the intersection of Coffee Road and Coolidge Avenue and drains into Dry Creek south of Scenic Drive. These storm drainage systems are designed to intercept runoff generated by commercial properties along Coffee Road and do not drain much of the large residential areas within Watershed A. Under existing conditions, there are no positive storm drainage systems within the residential areas. The primary storm drainage solution currently consists of hundreds of rockwells scattered throughout this watershed to provide limited stormwater drainage disposal for the residential areas. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.1 ---PAGE BREAK--- Village 1 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 78 79 81 82 83 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 WATERSHED OS AS SHOWN IN FIGURE 5.1b 102 103 Village 1 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 78 79 81 82 83 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 WATERSHED OS AS SHOWN IN FIGURE 5.1b 102 103 V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_5.1a_watersheds.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project MAJOR PROPOSED FIGURE 5.1a Title 84010174 JANUARY 2008 WATERSHED GROUPINGS NOTE: White areas denote Non-CPD Areas with Existing Positive Storm Drain Facilities Watershed Group O P R S T U Village 1 A B C D E F G H I J K L M N Q V ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.2 Watershed B is approximately 4.2 square miles and is located to the west of Watershed A. This watershed is bounded by the Hetch Hetchy Aqueduct on the north; McHenry Avenue, Sherwood Avenue, and the Virginia Corridor on the east; Briggsmore Avenue and MID Lateral No. 3 on the south; and Highway 99 on the west. Watershed B includes sub-basins 1, 82 and 89. Sub-basins 82 and 89 consist primarily of residential land use, but with some commercial developments. Sub-basin 1 is currently under agricultural use. There is no positive storm drainage system serving this watershed. Almost all of the residential areas are drained using rockwells. Watershed C is a relatively small watershed and consists of sub-basins 85, 86 and 91. It is bounded by MID Lateral No. 6 on the north; MID Lateral No. 7 and Prescott Road on the west; the Hetch Hetchy Aqueduct on the south; and Tully Road on the east. The total area of this watershed is approximately 0.42 square miles. The watershed is substantially developed and consists primarily of residential land uses. There are no positive storm drain systems serving the existing residential areas. The area is drained by rockwells. Watershed D includes the areas of sub-basins 2, 80, and 83 is located in the northwest portion of the City. This watershed is approximately 1.43 square miles in area and currently consists of a mix of residential, commercial and agricultural land uses. Watershed D is primarily residential with some commercial land uses. There is no positive storm drain system serving this watershed. Stormwater runoff from sub-basins 2 and 80 is drained by rockwells. Watershed E is approximately 4.2 square miles and is located northwest of the City’s downtown area. Watershed E consists of sub-basins 22, 23, 52 and 53. Sub-basins 22, 52 and 53 are primarily developed with residential, commercial and industrial land uses and sub-basin 23 is primarily agricultural. Stormwater runoff within the developed portions of this watershed is directed to rockwells. There are no major positive storm drain systems serving Watershed E except along a short segment of Carpenter Road. This storm drain line originates south of Elm Avenue and continues north along Carpenter Road, discharging into a small detention basin south of Brink Avenue. Water from the detention basin is pumped along Brink Avenue and discharged into MID Lateral No. 3. The size of this storm drain system is 18” diameter concrete pipe in the upstream portion, graduating to a 30” diameter concrete pipe near the outlet. Watershed F is located southwest of the City’s downtown area just east of Carpenter Road and north of the Tuolumne River. This watershed is about 3.6 square miles in area and includes sub-basins 24, 26 and 41. The eastern and southern portions of sub-basin 41 that are located adjacent to the Tuolumne River are planned by the City to be retained as open space. The remainder of Watershed F is primarily residential with some commercial land uses, plus existing agricultural land uses in sub-basin 26. There is no positive storm drain system serving Watershed F. Stormwater disposal is accomplished by directing runoff to rockwells that are scattered throughout this area. Watershed G is located in the extreme southwest corner of the Study Area and includes sub- basin 27. This watershed is approximately 1.1 square miles and is bounded by the Tuolumne ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.3 River on the north, Vivian Road on the west, Carpenter Road on the east and Whitmore Avenue on the south. Current land use within Watershed G is mainly agricultural, with small residential development in the northern portion adjacent to the Tuolumne River. There are no stormwater conveyance or disposal facilities currently serving this watershed. Watershed H includes sub-basins 9, 10, 11 and 43 and is located in the southern portion of the Study Area, south and east of the Tuolumne River. This watershed consists primarily of residential properties with some industrial and agricultural land uses. The total area of this watershed is approximately 2.2 square miles and there are some rockwells within the watershed. Watershed I is approximately 1.8 square miles and includes sub-basins 6, 17, 62, 67 and 69. This watershed is generally bordered by Dry Creek and on the north, Claus Road on the east, Yosemite Boulevard on the south and La Loma and Las Flores Avenues on the west. This watershed is fully developed with residential units. There are no positive storm drain systems serving the majority of this watershed; however, the City recently acquired ownership of the right-of-way for MID Lateral No. 2 west of McClure Road (Encina Drain) which traverses through the area and serves as a storm drainage outfall to Dry Creek. Also, rockwells provide for limited runoff disposal in sub-basin 69 and the western portions of sub-basins 6 and 67. Watershed J is located in the southeast portion of the Study Area just south of the Yosemite Boulevard. The watershed area is approximately 2.5 square miles in area and consists of sub- basins 13, 14, 15, 16 and 59. Current land uses consists mainly of industrial, with residential uses occurring only in sub-basin 59. There are limited stormwater conveyance facilities currently serving this watershed. Watershed K includes sub-basin 18 and is located south of Briggsmore Avenue, west of Claus Road, north of Dry Creek and east of Lakewood Avenue. This watershed is about 0.48 square miles and currently consists of primarily residential land uses. This area is drained by rockwells. Watershed L is located along the east edge of the Study Area and includes a portion of Empire with sub-basins 7, 94 and 95. The watershed is approximately 0.86 square miles in area. Sub- basin 7 is fully developed with residential land uses, and sub-basins 94 and 95 are currently under agricultural use. There are no stormwater conveyance or disposal facilities currently serving this watershed. Watershed M represents the area of the Modesto City/County Airport, which lies contiguous to the north of the Tuolumne River and south of Yosemite Boulevard between Tioga Drive and Mitchell Road and includes sub-basin 8. This watershed is approximately 0.9 square miles and consists of runways, taxiways and other airport facilities. There are several small storm drain systems serving this watershed that discharge into the Tuolumne River floodplain and channel at various locations to the south. According to City storm drainage maps, portions of the County industrial developments within the contiguous areas of sub-basins 48 and 58 to the north are also discharging runoff into the airport storm drainage facilities. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.4 Watershed N includes sub-basins 46, 74 and 75 and is located along the north bank of Tuolumne River both east and west of the Modesto Airport. It is about 2.2 square miles in area. Sub-basins 74 and 75 currently consist of mainly residential land uses with some open space (floodplain areas) along the Tuolumne River and near the confluence of the Tuolumne River and Dry Creek. Sub-basin 46 is substantially undeveloped and consists of agricultural land use with some industrial land use in the northwest corner. Rockwells serve a portion of this watershed, along with the Tuolumne River and Dry Creek waterways. Watershed O, Johansen CPD, includes sub-basins 30, 96, and 97 and is located west of the Santa Fe Railroad and south of Dry Creek. It is about 1.0 square miles in area. There are currently no storm drainage facilities within this watershed. Watershed P, Roselle/Claribel CPD, includes sub-basins 88 and 98 and is located in northeast Modesto. The watershed is bound to the east by the Santa Fe Railroad to the north by Claribel Ave, and to the west by Oakdale. It is about 2.6 square miles in area. There are currently no storm drainage facilities within this watershed. Watershed Q, Paradise/Carpenter CPD, includes sub-basin 25 and is located west of Carpenter Rd, south of MID Lateral No. 4, and north of MID Lateral No. 5. It is about 1.3 square miles in area. There are no existing storm drainage facilities in this watershed. Watershed R, Kiernan/Carver CPD, includes Sub-basins 54, 55, and 56 and is located in northwest Modesto bound to the north by Kiernan Ave, to the west by Dale Rd, and to the east by Tully Rd. It is about 1.3 square miles in area. There are no existing storm drainage facilities within this watershed. Sub-basins 54 and 55 will have their own separate storm drain system that are self contained on site. Watershed S, Kiernan/McHenry CPD, includes sub-basin 90 and is bound to the north by Kiernan Ave, to the east by McHenry Ave, to the west by Tully Rd, and to the south by MID Lateral No. 6. It is about 0.71 square miles in area. There are no existing storm drainage facilities within this watershed. Watershed T, Coffee/Claratina and Hetch Hetchy CPDs, includes sub-basins 87, 92, 93, and 99 and is located south of Kiernan Ave, west of Oakdale Rd, and east of McHenry Ave. The Hetch Hetchy Aqueduct and MID Lateral No. 6 both pass through this watershed. It is about 2.1 square miles in area. Sub-basins 87 and 99 have existing storm drain pipe draining to small detention basins. Watershed U, Fairview CPD, includes sub-basins 50 and 51 and is bound to the north by the Tuolumne River, to the west by Carpenter Rd, and to the south by Whitmore Ave. It is approximately 0.6 square miles in area. There are currently stormwater conveyance facilities in the northeast portion of the watershed that discharge to the Tuolumne River. Watershed V is a relatively small watershed, consisting of only sub-basin 102. Located in the northwest corner of the SOI at the intersection of Dale Rd and Bangs Rd, Watershed V includes ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.5 Kaiser Modesto facilities. This watershed has its own separate, self contained storm drain system on site. Watershed OS is a watershed located outside the SOI and was delineated in the “Northeast Area Offsite Watershed Storm Drainage Evaluation,” Draft March 2005 prepared by Stantec. The study identified this watershed as having the potential to contribute stormwater runoff to the northeast area of the City. The watershed was defined based on input provided by MID staff and a hydrologic analysis. The limits for the watershed extending upstream to the east of the AT & SF railroad to the MID Main Canal were obtained by field investigation and available topographic information. Village 1 includes sub-basin 35, but was not included in the analysis because it was recently master planned separately and is in the process of being built-out. 5.3 WATERSHED MODELING AND ANALYSIS The U.S. Army Corps of Engineers’ HEC-HMS computer program was used to develop a rainfall/runoff computer simulation for the watersheds and sub-basins in the Study Area. The Soil Conservation Service, SCS dimensionless unit hydrograph method, frequently used in practice, was used for the analysis. The HEC-HMS computer model develops a runoff hydrograph for individual sub-basins through the input of numerical representations of their physical and hydrological characteristics. The computed hydrographs are then routed and/or combined with hydrographs from other sub-basins to yield a dynamic numerical analysis of peak discharges (design flows) that may be expected to occur at key locations within the Study Area during the 10-year, 24-hour and 100-year, 24-hour storm events. These design flows are subsequently used for pipeline and detention basin sizing. The input parameters utilized for sub-basins in the HEC-HMS analysis are presented in Table 5- 1 (located at the end of this chapter) and are described in the following paragraphs. 5.3.1 Sub-basin Delineation The boundaries for each sub-basin were determined based on field investigations, U.S. Geological Survey 7.5 minute quadrangle maps, prior studies and reports, aerial photographs, a digital terrain model developed from the City’s Geographic Information System, and available maps. The location of various physical features such as roadways, irrigation laterals, storm drainage facilities, the Hetch Hetchy improvements, and railroad tracks were also factors in establishing the sub-basins boundaries. 5.3.2 Watershed Soil Groups Watershed soil groups were determined using soil maps contained in a report entitled “Soil Survey, Eastern Stanislaus Area, California,” issued September 1964, prepared by the Natural Resources Conservation Service (NRCS) - formerly the US Department of Agriculture Soil Conservation Service. Soil groups are classified as A, B, C, or D with Group A having the ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.6 highest rate of infiltration (lowest runoff production) and Group D having the lowest rate of infiltration (highest runoff production). The central part of the City was excluded in the NRCS soil survey and was assumed to consist entirely of Soil Group C, based on the characteristics of surrounding soils. Soil groups with sub-basin boundaries superimposed upon them are depicted in Figures 5.2a and 5.2b. 5.3.3 Rainfall Loss Rainfall loss is that portion of the precipitation depth that is lost due to evaporation, interception by vegetation, infiltration into soil, and surface depression storage. Rainfall excess is that portion of the precipitation depth that appears as surface or collected stormwater runoff during and after a storm event. Rainfall loss consists of both initial and constant losses and were determined using the NRCS Curve Number (CN) Method that uses a soil cover complex for estimating watershed losses. The CN is related to the underlying hydrologic soil group B, C, or land use, cover density, and soil moisture conditions. The four hydrologic soil groups are described in greater detail as follows: ‰ Group A: Low runoff potential soils having high infiltration rates even when thoroughly wetted and consisting chiefly of deep, well-drained sands or gravels. These soils have a high rate of water transmission. A CN of 39 was used for Group A in the SDMP. ‰ Group B: Soils having moderate infiltration rates when thoroughly wetted and consisting chiefly of moderately deep to deep, moderately well to well-drained sandy-loam with moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. A CN of 61 was used for Group B in the SDMP. ‰ Group C: Soils having a low infiltration rate when thoroughly wetted and consisting chiefly of silt-loam soils with a layer that impedes downward movement of water, or soils with moderately fine to fine texture. These soils have a slow rate of water transmission. A CN of 74 was used for Group C in the SDMP. ‰ Group D: High runoff potential soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have slow rate of water transmission. A CN of 80 was used for Group D in the SDMP. 5.3.4 Land Use Land uses used in this SDMP were taken from the City’s General Plan. The percent of impervious area for each sub-basin was based on a weighted average of the amount and type of the different land uses within the sub-basins, as estimated by direct measurements of the various land uses shown in the General Plan. This is an important input parameter in the HEC- HMS program because the model relates the amount of impervious area to the total area of a given sub-basin to estimate the amount of runoff losses attributed to pervious areas. For the ---PAGE BREAK--- 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 79 81 82 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 Snyder A v. Pela ndale Rd . Mer le Av. Floyd Av. Oakdal e Rd. Dal e R d. Mor r ow Rd. Car ver R d. Bangs Rd. Blue Bi r d D r. Chenyen ne Wy. Mar sal a Wy. Venem an Av. Sta ndif or d A v. Pr escot R d. Conant Av. Beckwi th R d. Sta ndif or d A v W. Br ig gsmor e Av. Mi tchel l Rd. Gr anger A v. Kear ney Av. Or angebur g Av. Col lege Av Rosebur g Av. Cof fee Rd . Fair m ont Av. Rose Av. Oakdal e Rd. Col dwel l Av. Mor r is Av Sto ddar d A v. Dow ney A v. Laur el Av. K S t. J St . 15th St . La Lo ma Robl e A v. N. Conej o A v. Maze Bl vd. I str eet Haddon Av. I St . Lapham D r. Wa shingt on St . Par adise Av. Mar t in Luth er Ki ng Am ador Av. Rio G ran de A v. Ham mo nd S t. Rouse Av. Gl enn A v. Hat ch R d. Rober t son R d. Par adise Rd . E.B ri ggsm or e A v. Lil lia n D r. Rive rsi de R d. W. Rosebur g Av. Car ver R d. HWY 99 Wo odland Av. Kansas Av. Kansas Av. Rosem or e A v. Elm Av. Cal if orni a Av. Car pent er Rd . Mer cy Av. Ohi o A v. Sylvan Av. Rosel le Av. Cla us R d. Kier nan Av. CLAR IB EL AV. McH enr y Av. Tul y R d. Cla rat ina Av. Cor alw ood Dr . Uni on A v. Sylvan Av. Shel don D r . Wo odro w Av. Kel er S t. Tul y R d. Rum ble Rd . Yukon Dr . Cof fee Rd . Rum ble Rd . Moun t Ver non Dr . Edwa rd Av. Floyd Av Rose Av. Fre mont Av. McH enr y Av. Cel este Dr . Sunr ise Av. Vi r gin ia R a il ro ad Vi rg ini a R ail r oad WATERSHED OS AS SHOWN ON FIGURE 5.2b 102 103 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 18 19 20 21 23 24 25 26 27 28 29 30 33 34 35 36 37 38 39 41 42 43 44 49 50 51 53 55 56 57 59 60 61 62 63 64 65 66 67 68 69 70 71 72 77 79 81 82 84 85 86 89 90 91 92 93 94 95 96 97 98 88 87 99 80 100 101 54 58 48 46 74 8 32 40 75 73 76 52 22 45 17 31 Snyder A v. Pela ndale Rd . Mer le Av. Floyd Av. Oakdal e Rd. Dal e R d. Mor r ow Rd. Car ver R d. Bangs Rd. Blue Bi r d D r. Chenyen ne Wy. Mar sal a Wy. Venem an Av. Sta ndif or d A v. Pr escot R d. Conant Av. Beckwi th R d. Sta ndif or d A v W. Br ig gsmor e Av. Mi tchel l Rd. Gr anger A v. Kear ney Av. Or angebur g Av. Col lege Av Rosebur g Av. Cof fee Rd . Fair m ont Av. Rose Av. Oakdal e Rd. Col dwel l Av. Mor r is Av Sto ddar d A v. Dow ney A v. Laur el Av. K S t. J St . 15th St . La Lo ma Robl e A v. N. Conej o A v. Maze Bl vd. I str eet Haddon Av. I St . Lapham D r. Wa shingt on St . Par adise Av. Mar t in Luth er Ki ng Am ador Av. Rio G ran de A v. Ham mo nd S t. Rouse Av. Gl enn A v. Hat ch R d. Rober t son R d. Par adise Rd . E.B ri ggsm or e A v. Lil lia n D r. Rive rsi de R d. W. Rosebur g Av. Car ver R d. HWY 99 Wo odland Av. Kansas Av. Kansas Av. Rosem or e A v. Elm Av. Cal if orni a Av. Car pent er Rd . Mer cy Av. Ohi o A v. Sylvan Av. Rosel le Av. Cla us R d. Kier nan Av. CLAR IB EL AV. McH enr y Av. Tul y R d. Cla rat ina Av. Cor alw ood Dr . Uni on A v. Sylvan Av. Shel don D r . Wo odro w Av. Kel er S t. Tul y R d. Rum ble Rd . Yukon Dr . Cof fee Rd . Rum ble Rd . Moun t Ver non Dr . Edwa rd Av. Floyd Av Rose Av. Fre mont Av. McH enr y Av. Cel este Dr . Sunr ise Av. Vi r gin ia R a il ro ad Vi rg ini a R ail r oad WATERSHED OS AS SHOWN ON FIGURE 5.2b 102 103 Group A Low runoff potential soils having high infiltration rates even when thoroughly wetted and consisting chiefly of deep, well-drained sands or gravels. These soils have a high rate of water transmission. Group B Soils having moderate infiltration rates when thoroughly wetted and consisting chiefly of moderately deep to deep, moderately well to well-drained saindy0loam with moderately fine to moderately coarse textrues. These soils have a moderate rate of water transmission. Group C Soils having a low infiltration rate when thoroughly wetted and consisting chiefly of silt-loam soils layer that impedes downward movement of water, or soils with moderately fine to fine texture. The soils have a slow rate of water transmission. Group D High runoff potential soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with moderately fine to fine texture. The soils have a slow rate of water transmission. Group R Rivers and streams. Sub-basins Soils A B C D R Legend * Hydrologic Soil Groups Derived from "Soil Survey of Eastern Stanislaus Area, California". Non-mapped area in Central City assumed to be Soil Group C. HYDROLOGIC SOIL GROUPS & SUBBASIN BOUNDARIES V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_5.2a_soils.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project FIGURE 5.2a Title 84010174 JANUARY 2008 ---PAGE BREAK--- Group A Low run off potential soils having high infiltration rates even when th oroughly wetted and consisting chiefly of deep, wel- drained sands or gr avels. These soils have a high rate of water tr ansmission. Group B Soils ha ving modera te infiltration rates when thoroughly wetted a nd consisting chiefly of moderately deep t o deep, moderately well to well-dr ained saindy0loam with moderately fine to moderately coarse t extrues. These soils have a moderate rate of water transmission. Group C Soils ha ving a low in filtration rate when thoro ughly wetted and consisting chiefly of silt-loam soils layer that impedes downward movemen t of water, or soils with moderately fin e to fine texture. The soils have a slow rate of water tr ansmission. Group D High runoff potential soils having very slow infiltrat ion rates when thoroughly wett ed and consisting chiefly of clay soils with a high swelling potential, soils with moderately fine to f ine texture. The soils have a slow rate of water tr ansmission. Group R Rivers Sub-basins Soils A B C D R Legend ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.7 purposes of hydrologic modeling, design flow determination, and the planning of storm drainage facilities in this SDMP, future build-out of the SOI was assumed. Table 5-2 shows the impervious cover percentages of the different land uses utilized in the model. Table 5-2. Impervious Cover Percentages Land Use Designation Description Percent Impervious Cover R Residential 60% VR Village Residential 60% RPD Redevelopment Planning District 78% C Commercial 90% RC Regional Commercial 90% I Industrial 80% MU Mixed Use 72% BP Business Park 90% OS Open Space 25% 5.3.5 Rainfall The City’s Standards for rainfall depths of 1.92 inches for a 10-year, 24-hour storm event and 2.88 inches for a 100-year, 24-hour event were utilized in the hydrologic model. 5.3.6 Unit Hydrograph For runoff computations from each sub-basin, the NRCS Dimensionless Unit Hydrograph option was utilized in the HEC-HMS computer model. 5.3.7 Lag Time Input data for NRCS dimensionless Unit Hydrograph includes the parameter, TLAG, which is equal to the lag time (in hours) between the center of mass of rainfall excess and the peak of ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.8 the unit hydrograph. The lag time was estimated utilizing the NRCS method of computing the watershed lag value from the time of concentration. The equation is as follows: TLAG = 0.6 tc where: tc = Time of concentration The time required for stormwater to flow in the form of runoff from the most hydraulically remote point in the drainage sub-basin or watershed to a collection point is the time of concentration. Time of concentration is the sum of the minimum overland travel time (initial time of concentration) and the concentrated flow time. The concentrated flow time was calculated by dividing the maximum length of travel by the velocity of the gutter/pipe flow. For gutter/pipe flow, an average velocity of two feet per second was assumed based on the relatively flat street gradients that exist throughout most of the City. 5.3.8 Routing The Modified Puls Reservoir Routing method was used to route flow through detention basins. 5.4 CONVEYANCE SYSTEM ANALYSIS 5.4.1 Pipe Network The pipe network for the SDMP level of analysis utilizes a minimum sub-basin area of 40 acres. The pipe network system was sized using Manning’s Equation with the following parameters: ‰ Pipe slope 0.1% ‰ Roughness coefficient 0.013 5.4.2 Open Channel In the locations where an open channel was used to convey runoff due to large flows, Manning’s Equation was used to size a typical open channel. The following input parameters were assumed: ‰ Channel slope 0.5% minimum ‰ Roughness coefficient 0.035 ‰ Bottom width 20 feet ‰ Side slopes 2(H):1(V) ‰ Channel depth 6 feet ‰ Freeboard 1 foot ‰ Top width 44 feet ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN System Hydrology and Modeling March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 5.9 5.5 RESULTS The results of the HEC-HMS analysis are summarized on Table 5-3 (located at the end of this chapter), which lists the computed 10-year, 24-hour and 100-year, 24-hour design flows generated by each sub-basin within the Study Area. The 10-year, 24-hour discharges were used to size new positive storm drainage systems and the 100-year, 24-hour routing analyses were used to size proposed new detention basins, for master planning lever analysis. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 6.0 Proposed Capital Improvements 6.1 GENERAL The proposed improvements presented in this SDMP have been formulated to serve the Watershed Groups that make up the Study Area (with the exception of Watershed OS) and that are not presently served by positive storm drainage facilities. Specifically, the areas of emphasis include the large portions of the City where stormwater runoff solutions are currently relegated to retention basins, rockwells, or the City’s sanitary sewer system as terminal facilities, as well as undeveloped areas that will eventually require storm drainage facilities. The location and size of the major facilities pipelines, open channels, detention basins, pump stations, and outfalls) necessary to provide conveyance, attenuation, and discharge to receiving waters are identified, and their associated costs are presented in Chapter 7. The costs for minor improvements that will be tributary to the major infrastructure system are accounted for separately and in a lump sum fashion. All storm drains and open channels presented herein have been sized to accommodate a 10- year, 24-hour storm event, and the proposed detention basins are sized for the 100-year, 24- hour storm storage volume. Proposed detention basins that are located adjacent to irrigation laterals are anticipated to discharge into them at attenuated and metered rates. 6.2 TYPES OF PROPOSED FACILITIES The following is a brief description of the general types of drainage infrastructure components proposed to resolve problems associated with areas that frequently flood and to accommodate the stormwater runoff anticipated to occur under future build-out conditions within the Study Area. 6.2.1 Positive Storm Drains Storm drainage pipelines are proposed within the majority of the undeveloped portions of the Study Area that currently lack positive systems and are intended to provide a master plan level of guidance for future pipeline designs. As previously discussed, there are several drainage “hot zone” areas in the City where pipelines are proposed to exclusively eliminate frequent nuisance flooding. Other pipelines are needed for both existing conditions and future build-out scenarios. So that these pipelines will have sufficient capacity, the proposed sizes represent the ultimate diameter in cases where further upsizing for build-out conditions would have been required. In areas where future cover problems may exist, multi-sized smaller diameter pipes or equivalent capacity alternatives can be used in place of the pipe sizes represented in this SDMP. All of the pipelines were sized to convey the 10-year, 24-hour storm discharges operating under uniform flow conditions. Sizing of pipelines will need to be verified and possibly adjusted as a part of their future detailed design. Within the existing developed areas, all of the proposed pipelines are anticipated to be constructed within the public right-of-way (ROW). v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.2 It should be noted that the continuous, open space nature of the Virginia Corridor might at first appear to provide an opportunity for some of the City’s future storm drainage conveyance facilities. However, based on a more detailed topographic review of the surrounding area, much of the corridor sits as a north-south linear high point. Therefore, it is not expected that the Virginia Corridor will contain a major component of the City’s future positive storm drainage infrastructure. At most, it may serve the trail system planned within the corridor itself and possibly some adjacent local roadways. 6.2.2 Detention Basins The proposed detention basins will temporally attenuate the stormwater runoff, which will significantly reduce the peak flows that would have otherwise overburdened the available outfall systems, and they will provide opportunities for water quality treatment prior to discharge. Due to the capacity limitations associated with the outfall systems and stormwater quality issues, the 22 detention basins proposed in this SDMP will have limited and regulated outflows as listed in Table 6-1. (Outflow rates are estimates only and final design rates will be determined on a case-by-case basis with MID staff.) Additionally, four detention basins are proposed for Watershed OS (not included in Table 6-1). All detention basins have been sized to accommodate a 100-year, 24-hour storm volume, under build-out conditions, and will be drained by pump stations. The surface areas of the proposed detention basins range from five to 42 acres and their depths range from four to 16 feet, including one foot of freeboard above the 100-year water surface elevation. During actual design of the detention basins, their depths and surface areas may need to be adjusted per land sizes and locations, local topography, and groundwater depths. If berms are integrated into the basin’s design, spillways should be provided above the 100-year water surface elevation in order to control any overflow and provide for emergency releases should the design storm be exceeded. All detention basins should have vehicular access around them and to the lower areas to facilitate maintenance. As part of the future detailed design of the detention basins recommended in this SDMP, the City may require the integration of aesthetic treatments with or without active or passive dual- use recreational components. Dual-use facilities in predominantly residential watersheds should be designed in conformance with the “City of Modesto Design Standards for Dual Use Flood Control/Recreation Facilities,” dated December 2000, which includes recommendations for design layouts, grading, integration of recreation elements, and water quality treatment processes. The requirement for dual-use facilities used in conjunction with detention basins will be based on the size and type of development and the watershed being served. No attempt has been made in this SDMP to identify any park-related dual-use facilities that might be incorporated into any of the proposed detention basins, because that effort would come at a much later date and be undertaken by others. Also, the detention basin land areas and costs only reflect the relevant “flood control” component for each facility. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.3 Table 6-1. Proposed Detention Basins Detention Basin Sub-basins Location Surface Area (ac) 100-yr Inflow (cfs) 100-yr Inflow Volume (ac-ft) Outflow (cfs) 100-yr Storage Volume (ac-ft) Depth of Water (ft) Freeboard (ft) Assumed Depth of Basin (ft) 1 6 Encina Ave. & Rosina Ave. 9 207 74 4.3 70 9 1 10.0 2 9,10,11,43 Kendee St. 20 863 255 9.3 245 14 1 15.0 3 27 W. Hatch Rd. 12 350 105 9.0 96 9 1 10.0 4 24,41 West, 26 Grimes Ave. & Paradise Rd. 23 724 301 9.0 292 14 1 15.0 5* 41 East Tuolumne River/Dryden 8 70 31 3.6 27 4 1 5.0 6 22,23,52,53 MID Lat No. 4 & Morse Rd. 42 1483 543 8.9 534 14 1 15.0 7 13,14 MID Lat No. 1 & Garner Rd. 27 783 225 8.8 216 9 1 10.0 8 1,82,89 MID Lat No. 3 & Morse Rd. 35 1146 477 8.8 468 15 1 16.0 9 2, 80, 83 West of Dale Rd. & Bangs Rd. 14 573 181 9.5 171 14 1 15.0 10 15,16 MID Lat No. 1 & Beard Ave. 11 351 93 4.5 88 9 1 10.0 11 97 Encina Storm Drain 7 152 27 4.0 23 3.5 1.5 5.0 12 88 North of Claratina Ave. 20 541 221 5.0 220 12 1 13.0 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER Proposed Capital Improvements PLAN March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.4 Detention Basin Sub-basins Location Surface Area (ac) 100-yr Inflow (cfs) 100-yr Inflow Volume (ac-ft) Outflow (cfs) 100-yr Storage Volume (ac-ft) Depth of Water (ft) Freeboard (ft) Table 6-1. Proposed Detention Basins Assumed Depth of Basin (ft) 13 98 South of Claratina Ave. 10 344 82 5.0 78 8.5 1.5 10.0 14 93 North of MID Lat No. 6 10 186 54 5.0 48 5 1 6.0 15 92 South of MID Lat No. 6 10 162 54 5.0 49 5 1 6.0 16 87 Hetch Hetchy & Claratina Ave. 11 287 93 5.0 88 8.5 1.5 10.0 17 90 MID Lat No. 6 & Pelandale Rd. 12 412 98 5.0 92 8.5 1.5 10.0 18 56 MID Lat No. 6 & Bangs Rd. 11 271 90 5.0 85 8.5 1.5 10.0 19 25 MID Lat No. 5 30 500 166 5.0 161 5.5 1.5 7.0 20 50 Tuolumne River and Carpenter Rd. 10 189 44 6.0 37 4 1 5.0 21 51 TID Lat No. 1 & Carpenter Rd. 5 59 14 3.0 10 2 2 4.0 22 96 Encina Storm Drain 12 230 62 5.0 57 5 1 6.0 * Detention Basin No. 5 will be constructed as a wetland facility ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.5 6.2.3 Pump Stations A pump station will be needed to drain each of the 22 proposed detention basins in Watersheds A through V, and they have been conceptually sized to limit pumping to less than a 10 cfs discharge rate. An additional pump station will be used in sub-basin 99 to drain the existing Rose Lane Detention Basin. Watershed OS will require a single pumping station for its four proposed detention basins. For the larger detention basins, the limitation on pumping rates will produce inundation times that are longer than those prescribed in the City Standards after a 100-year storm. This is due to the combined hydraulic limitations of a discharge rate of 10 cfs, an initial holding period of 48 hours, and a subsequent emptying period of 48 hours. Drain times for the larger detention basins will be a function of a combination of pumping outflow rates, percolation rates, and evaporation rates and may be determined as a part of actual facility design. If residual water remains in a detention basin for a prolonged period of time after a major storm event, there may be a need for temporary mosquito abatement procedures to be implemented. Detention basin pumping facilities are assumed to consist of a low flow pump, a high flow pump, and a backup (redundant) pump. 6.2.4 Open Channels Excluding the CPDs, the majority of the Study Area is substantially urbanized, and the available ROW and space for open channels as a stormwater control option is limited. Therefore, open channels are only proposed for lower reaches of Watershed B and Watershed E, where vacant (agricultural) land is still available and where the rate of the 10-year, 24-hour storm event discharges in these reaches exceeds the capacity of 2-84” storm drainage pipes. The proposed open channel serving Watershed B is located in sub-basin 1 and starts west of Highway 99, across from Plaza Parkway, and drains into proposed detention basin number 8 to be located south of Shoemaker Avenue and north of MID Lateral No. 3. The proposed channel serving Watershed E is located in sub-basin 23 and starts south of Kansas Avenue, runs along the west side of Rosemore Avenue, and north of MID Lateral No. 4 before discharging into proposed detention basin number 6. Open channels are proposed to have a 60-foot ROW, a 20-foot bottom width and side slopes of 2:1 (two horizontal to one vertical). The ROW also includes room for an all-weather maintenance access road on one side of the channel. Native grasses should be utilized to stabilize these open channels and they will aid in water quality treatment. A minimum of one foot of freeboard shall be maintained above the design 10-year, 24-hour storm event water surface elevation. Figure 6.1 depicts a typical cross-section of a proposed open channel. 6.2.5 Outfalls Twenty new outfalls (also known as points of discharge) are proposed with this SDMP: 14 to irrigation laterals, five to the Tuolumne River, and one to Dry Creek. The outfalls will discharge stormwater from a detention basin into the receiving water via a storm drain pump station. ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.6 Based on the capacity of the pump stations, the new outfalls would be approximately 12-inches in diameter. The outfalls will be designed to minimize impact on the receiving water by incorporating the following permanent control measures: 1) pumps would be equipped with a high-water shutoff feature; 2) the discharge pipe will angle 3) the outfall pipe will be recessed into the bank and will not be protruding; 4) riprap and possibly a geotextile fabric will be installed at the outlet; 5) permanent restabilization of the site. In addition, there are five locations where the SDMP proposes to discharge into an existing pipe with an existing outfall; four outfalls to Dry Creek and one to the Tuloumne River, the existing capacity of the outfalls would be evaluated in consideration of future planned increases in stormwater discharges, and these outfalls would be upgraded with larger diameter pipes and appropriate discharge controls, if necessary. 6.3 PHASING AND PRIORITIES The magnitude of the capital improvement costs associated with implementation of this SDMP is quite significant (over $600 million). Even the capital improvement costs associated with the infrastructure needed for individual Watershed Groups are very large. Thus, it is evident that implementation of this SDMP will need to be performed in phases, as funding sources become available. It is anticiapted that buildout of the SOI portion of the study area would occur over the next 20 or more years. The precise order of project phasing will, by and large, depend on the sequencing of specific parcel development and the general patterns of the City’s future growth (except where development is occurring along the upstream portion of a proposed system prior to the construction of improvements). Other than the development applications currently being processed by the City, the majority of the capital improvement projects identified in this SDMP cannot be prioritized with any degree of certainty at this time. The City has completed a cross connection study to analyze the storm drain connections to the sanitary sewer system. As a result of the study, the City has approved an initial phase of proposed improvements to eliminate the storm drain cross connections to the sanitary sewer system. A portion of the proposed infrastructure in this SDMP will be constructed (in the immediate vicinity of cross connection locations) with sanitary sewer funds and the remaining portion of the storm drainage system will be constructed at a later date when funds become available. The following is a sequence of implementation that may occur. First priority should be given to constructing pipelines and detention basins in developed areas that currently do not have positive storm drainage systems and that have historically experienced flooding. These areas within the City have been previously designated as storm drainage “hot zones” (see Chapter In some cases, the infrastructure may be downsized to account for lower rates of runoff associated with undeveloped areas, as a first phase, with additional capacity being provided at such time as new development warrants parallel pipes or larger replacement pipes). Also a first priority is the proposed flood control solution to provide flood protection to existing and new development areas in the northeast quadrant of the City (as described for Watershed OS in the following section). ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.7 The second recommended priority is to provide positive storm drainage systems within the areas of the City that are currently served by retention basins or rockwells, but outside of the storm drainage “hot zones” areas and to complete the upgrade storm drainage facilities for the airport. The third priority should be to upgrade storm drainage lines in areas currently served by positive systems that only have the capacity to accommodate the discharge from a 5-year, 24-hour storm event (or less). The upgrading would be performed to achieve the conveyance capacity of a 10-year, 24-hour storm event, conforming to the City’s current Standard Specifications. The fourth recommended priority pertains to areas that have not yet been developed. The applicable storm drainage facilities, unless they are a part of the outfall for a higher priority area, may have their construction delayed until the need arises. 6.4 PROPOSED INFRASTRUCTURE IMPROVEMENTS The recommended major improvements within each Watershed Group and CPD that are needed to accommodate build-out of the Study Area are shown on Figure 6.2 and 6.3 and are also described in the following subsections. These recommendations do not constitute a design of such facilities, only a master plan level of identification. Subsequent detailed design is required to determine the exact sizes and locations of the proposed improvements. 6.4.1 Watershed Group Improvements Watershed A Watershed A encompasses sub-basins 12, 19, 20, and 71. This watershed is predominantly developed (primarily residential, with commercial uses along major streets). Under existing conditions, there is only a minor storm drain system serving Coffee Road and there are no positive storm drainage systems serving the remainder of the watershed. The primary drainage solution currently consists of hundreds of rockwells scattered throughout the watershed that provide limited stormwater drainage disposal. Infrastructure recommendations for this watershed are considered to be a first priority and include installing trunk lines to route stormwater to Dry Creek, at the southern border of the watershed. Proposed infrastructure for each sub-basin is as follows: Sub-basin 12 ‰ 1,070 LF of 48” trunk line extending along Dragoo Park Dr from Sylvan Meadows Dr to Sylvan Ave ‰ 1,441 LF of 60” trunk line extending along Dragoo Park Dr from Sylvan Ave to Claremont Ave ‰ 1,505 LF of 60” trunk line extending along Claremont Ave from Dragoo Park Dr to E. Rumble Rd ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.8 ‰ 1,342 LF of 72” trunk line extending along E. Rumble Rd from Claremont Ave to Edward Ave ‰ 1,302 LF of 78” trunk line extending along Edward Ave from E. Rumble Rd to Floyd Ave ‰ 686 LF of 78” trunk line extending along Floyd Ave from Edward Ave to Sunrise Ave ‰ 1,982 LF of 78” trunk line extending along Sunrise Ave from Floyd Ave to Tokay Ave ‰ 1,471 lf of 2-66” trunk lines extending along Sunrise Ave from Tokay Ave to E. Briggsmore Ave ‰ 1,614 LF of 42” trunk line extending along Sylvan Ave from Palmwood Dr to Keller St ‰ 1,833 LF of 60” trunk line extending along Keller St from Sylvan Ave to South of Colin Ln ‰ 826 LF of 2-54” trunk line extending along Keller St from south of Colin Ln to E. Rumble Rd ‰ 1,320 LF of 2-54” trunk lines extending along Keller St from E. Rumble Rd to Floyd Ave ‰ 934 LF of 2-60” trunk line extending along Floyd Ave from Keller St to Rose Ave ‰ 2,122 LF of 2-60” trunk lines extending along Rose Ave from Floyd Ave to Celeste Dr ‰ 1,580 LF of 36” trunk line extending along Celeste Dr from Vera Cruz Dr to Rose Ave ‰ 34 LF of 36” trunk line extending across Ellison Dr ‰ 272 LF of 36” trunk line extending along Ellison Dr from Wolcott Way to Celeste Dr ‰ 1,012 LF of 36” trunk line extending along Celeste Dr from Ellison Dr to Rose Ave ‰ 1,737 LF of 2-66” trunk lines extending along Rose Ave from Celeste Dr to E. Briggsmore Ave Sub-basin 19 ‰ 631 LF of 2-84” trunk lines extending along Sunrise Ave from Palm Ave to E. Fairmont Ave ‰ 1,337 LF of 2-84” trunk lines extending along E. Fairmont Ave from Sunrise Ave to El Vecino Ave ‰ 835 LF of 36” trunk line extending along El Vecino Ave from Multnomah Dr to E. Fairmont Ave ‰ 487 LF of 2-84” trunk lines extending along E. Fairmont Ave from El Vecino Ave to El Terino Ave ‰ 1,654 LF of 2-84” trunk lines extending along El Terino Ave from E. Fairmont to Lucern Ave ‰ 805 LF of 2-84” trunk lines extending along Lucern Ave from El Terino Ave to Coffee Rd ‰ 1,327 LF of 2-84” trunk lines extending along Coffee Rd from Lucern to Scenic Dr ‰ 1,384 LF of 2-72” trunk lines extending along Rose Ave from E. Briggsmore Ave to E. Orangeburg Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.9 ‰ 1,207 LF of 2-72” trunk lines extending along Rose Ave from E. Orangeburg to Crestview Dr ‰ 1,287 LF of 2-84” trunk lines extending along Crestview Dr from Rose Ave to the west end of Crestview ‰ 1,134 LF of 36” trunk line near the east boundary of Downey Park from Orangeburg Ave to Crestview Dr ‰ 2,293 LF of 2-84” trunk lines extending along Brighton Ave from Crestview Dr to Locke Rd ‰ 1322 LF of 2-84” trunk lines extending along Brighton Ave from Locke Rd to Scenic Dr Sub-basin 20 ‰ 1,823 LF of 2-72” trunk lines extending along Sunrise Ave from E. Briggsmore Ave to E. Orangeburg Ave ‰ 1,644 LF of 2-78” trunk lines extending along Sunrise Ave from E. Orangeburg Ave to Palm Ave ‰ 984 LF of 42” trunk line extending along Palm Ave from Nelson Ave to Sunrise Ave Sub-basin 71 ‰ 329 Lf of 2-84” trunk lines extending south of the intersection of Coffee Rd and Scenic Dr to Dry Creek ‰ 1,324 LF of 2-84” trunk lines extending along Scenic Drive from Brighton Ave to Coffee Rd ‰ 325 Lf of 2-84” trunk lines extending south of the intersection of Coffee Rd and Scenic Dr to Dry Creek Watershed B Infrastructure was proposed to route stormwater runoff from sub-basins 1, 82, and 89 to the proposed Detention Basin No. 8, west of Highway 99. Sub-basins 82 and 89 consist primarily of existing residential development drained by rockwells and infrastructure proposed to serve them would be considered as a first priority. Sub-basin 1 is primarily agricultural land use; however it contains the proposed outfall facilities for the watershed that would also be considered as a first priority. Proposed infrastructure for each sub-basin is as follows: Sub-basin 1 ‰ 1,738 LF of open channel extending from the concrete box culvert under Highway 99 to Detention Basin No. 8 ‰ 107 LF of 24" storm drain from Detention Basin No. 8 to MID No. 3. Stormwater will discharge to MID No. 3 via an 8.8 cfs pump station ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.10 Sub-basin 82 ‰ 1,165 LF of 48" trunk line extending along Conant Ave from W. Rumble Ave to north of Nancy Ln ‰ 723 LF of 24" storm drain extending west from Park to Conant Ave ‰ 1,347 LF of 48" trunk line extending along Conant Ave from Eicher Ave to north of Nancy Ln ‰ 890 LF of 60" trunk line extending along Conant Ave from Eicher Ave to Sisk Rd ‰ 949 LF of 78" trunk line extending along Sisk Rd from Conant Ave to Plaza Pkwy ‰ 2,085 LF of 2-84" trunk line extending along Plaza Pkwy from Conant Ave to Prescott Rd ‰ 573 LF of a 10'x8' Concrete Box Culvert at Sisk Rd and under Hwy 99. A jack and bore will be required at Highway 99 for the box culvert. Sub-basin 89 ‰ 1,325 LF of 30" trunk line extending along Sheldon Ave from Shawnee Dr to Prescott Rd ‰ 955 LF of 42" trunk line extending along Prescott Rd from Sheldon Ave to W. Rumble Rd ‰ 1,836 LF of 48" trunk line extending along Prescott Rd from W. Rumble Rd to Peach Dr ‰ 1,901 LF of 60" trunk line extending along Prescott Rd from Peach Dr to Plaza Pkwy ‰ 2,565 of 2-78" trunk line extending along W. Briggsmore from Carver Rd to Prescott Rd ‰ 2,898 LF of 2-72" trunk line extending along W. Briggsmore from Tully Rd to Carver Rd ‰ 1,314 LF of 30" trunk line extending along W. Briggsmore from College Ave to Tully Rd ‰ 1,454 LF of 30" trunk line extending along Carver Rd from Sheldon Ave to Standiford Ave ‰ 1,351 LF of 48" trunk line extending along Carver Rd from Sheldon to W. Rumble Rd ‰ 1,817 LF of 54" trunk line extending along Carver Rd from W. Rumble Rd to Mount Vernon Dr ‰ 1,910 LF of 2-48" trunk lines extending along Carver Rd from Mt Vernon Dr to W. Briggsmore Ave ‰ 1,298 LF of 36" trunk line extending along Tully Rd from Standiford Ave to Woodrow Ave ‰ 1,323 of 48" trunk line extending along Tully Rd from Woodrow Ave to W. Rumble Rd ‰ 2,638 LF of 54" trunk line extending along Tully Rd from W. Rumble Rd to Bowen Ave ‰ 1,617 LF of 2-66" trunk line extending along Tully Rd from Bowen Ave to W. Briggsmore Ave ‰ 1,314 LF of 72" trunk line extending along Bowen Ave from Tully Rd to College Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.11 ‰ 1,329 LF of 30" trunk line extending along W. Union Ave from Marigold Ln to west of Poinsettia Ln ‰ 1,341 LF of 54" trunk line extending along the UPRR from W. Union Ave to Standiford Ave ‰ 1,341 LF of 54" trunk line extending along the UPRR from Standiford Ave to Woodrow Ave ‰ 1,315 LF of 60" trunk line extending along the UPRR from Woodrow Ave to W. Rumble Rd ‰ 1,305 LF of 30" trunk line extending along W. Rumble Rd from Waterbury Ct to west of Yukon Dr ‰ 1,330 LF of 72" trunk line extending along W Rumble Rd from West of Yukon Dr to East of Wales St ‰ 1,491 of 72" extending south from W. Rumble Rd to north of Durant St ‰ 1,491 of 72" trunk line extending along College Ave from north of Durant St to Bowen Ave Watershed C Watershed C includes existing developed residential areas within sub-basins 85 and 86 and a combination of developed and undeveloped properties in sub-basin 91. Storm drainage solutions are not represented in this SDMP and will be site and development specific. Storm drainage improvements that will serve new development within this watershed will be a fourth priority. Sub-basin 85 – No infrastructure proposed Sub-basin 86 – No infrastructure proposed Sub-basin 91 – No infrastructure proposed Watershed D Watershed D encompasses sub-basins 2, 80, and 83. Watershed D is primarily residential with some commercial land uses. There is no positive storm drain system serving this watershed. Stormwater runoff is drained by rockwells. Infrastructure recommendations include installing trunk lines to route stormwater to proposed Detention Basin No. 9 located north of Bangs Rd. and west of Dale Rd. that would be considered to be a first priority. Proposed infrastructure for each sub-basin is as follows: Sub-basin 2 ‰ 1,124 LF of 36” trunk line extending along Marsala Way from Veneman Ave to Konynenburg Ln ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.12 ‰ 1,640 LF of 42” trunk line extending along Cheyenne Way from St. Nicholas Dr to Konynenburg Ln ‰ 984 LF of 60” trunk line extending along Konynenburg Ln from Marsala Way to Viader Dr ‰ 1,596 LF of 66” trunk lines extending along Viader Dr from Konynenburg Ln to Snyder Ave ‰ 6,752 LF of 66” trunk lines extending along Snyder Ave from Carver Rd to Viader Dr ‰ 1,225 LF of 2-72” trunk lines extending along Snyder Ave from Viader Dr to Dale Rd Sub-basin 80 ‰ 1,211 LF of 30” trunk lines extending along Blue Bird Dr from Nightingale Dr to Snyder Ave ‰ 316 LF of 54” trunk lines extending along Blue Bird Dr from Snyder Ave to Silo Way ‰ 736 LF of 42” trunk lines extending along Akeby Dr from Timahoe Dr to Gagos Dr ‰ 1,429 LF of 48” Akeby Dr, Hennings, and Silo Way from Gagos Dr to Blue Bird Dr ‰ 997 LF of 66” trunk lines extending along Blue Bird Dr from Silo Way to Pelandale Ave ‰ 2,476 LF of 66” trunk lines extending along Pelandale Ave from Blue Bird Dr to Dale Rd ‰ 749 Lf of 48” trunk lines extending along Snyder Ave east of Blue Bird Dr to Blue Bird Dr ‰ 1,291 LF of 2-72” trunk lines extending along Dale Rd from Snyder Ave to Pelandale Ave ‰ 703 LF of 2-84” trunk lines extending along Dale Rd from Pelandale Ave to Fleur de Lis Dr ‰ 3,300 LF of 2-84” trunk lines extending along Dale Rd and Bangs Rd and west to Detention Basin No. 9. Stormwater will be discharged to MID Lateral No. 6 via a 9.5 cfs pump station Sub-basin 83 ‰ 654 LF of 30” trunk lines extending along Shawnee Dr from Patton Dr to Cheyenne Way ‰ 716 LF of 48” trunk lines extending along Cheyenne Way from Shawnee Dr to Seminole Ln ‰ 890 LF of 54” trunk lines extending along Carver Rd from Seminole Ln to Brixton Ln ‰ 1,001 LF of 66” trunk lines extending along Brixton Ln from Longbridge Dr to Carver Rd Watershed E Watershed E encompasses sub-basins 22, 23, 52, and 53. Sub-basins 22, 52, and 53 are primarily developed with residential, commercial and industrial land uses and sub-basin 23 is primarily agricultural. Stormwater runoff within the developed portions of this watershed is directed to rockwells. There is a minor positive storm drain along a short segment of Carpenter Road. Infrastructure recommendations are considered to be first priority recommendations and ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.13 include installing trunk lines to route stormwater to proposed Detention Basin No. 6, located north of MID Lateral No. 4 near the Paradise/Carpenter CFD. Proposed infrastructure for each sub-basin is as follows: Sub-basin 22 ‰ 1,991 LF of 42” trunk line extending along W. Orangeburg from Bronson Ave to Tully Rd ‰ 1,307 LF of 54” trunk line extending along Tully Rd from W. Orangeburg to W. Roseburg Ave ‰ 2,635 LF of 60” trunk line extending along Tully Rd from W. Roseburg Ave to Coldwell Ave ‰ 1,370 LF of 2-54” trunk lines extending along Coldwell Ave from Tully Rd to Kearney Ave ‰ 1,351 LF of 42” trunk line extending along Kearney Ave from Princeton Ave to Coldwell Ave ‰ 336 LF of 2-60” trunk lines extending along Coldwell Ave from Kearney Ave to N. 9 St th ‰ 2,099 LF of 66” trunk line extending along Carver Rd from Pearl St to W. Roseburg Ave ‰ 1,418 LF of 72” trunk line extending along Carver Rd from W. Roseburg Ave to N. 9 St th ‰ 1,726 LF of 2-60” trunk lines extending along N. 9 St from Carver Rd to Coldwell Ave th ‰ 1,591 LF of 2-78” trunk lines extending along Woodland Ave from N. 9 St to Lone Palm Ave th ‰ 2,150 LF of 36” trunk line extending along Graphics Dr/Hwy 99 from N/w of Kansas Ave to Woodland Ave Sub-basin 23 ‰ 2,831 LF of 66” trunk line extending along Elm Ave from N. Carpenter to Rosemore Ave ‰ 2,185 LF of open channel extending along Rosemore Ave and MID Lateral No. 4 from Kansas Ave to Detention Basin No. 6. Stormwater will be pumped into MID Lateral No. 4 via a 10 cfs pump station ‰ 691 LF of 66” trunk line extending in a north-south orientation from Kansas Ave to Detention Basin No. 6; pump station and discharge to MID Lateral No. 4 Sub-basin 52 ‰ 1,299 LF of 42” trunk line extending along McWilliams Way from Granite Ln to Woodland Ave ‰ 1,352 LF of 2-78” trunk lines extending along Woodland Ave from Reno Ave to Lone Palm Ave ‰ 2,653 LF of 2-84” trunk lines extending along Reno Ave from Woodland Ave to Kansas Ave ‰ 602 LF of 2-84” trunk lines extending along Kansas Ave from Reno Ave to N. Carpenter Ave ‰ 1,021 LF of 36” trunk line extending along N. Emerald Ave from Kansas Ave to Elm Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.14 ‰ 2,633 LF of 60” trunk line extending along Elm Ave from N. Emerald Ave to N. Carpenter Ave Sub-basin 53 ‰ 1,343 LF of 36” trunk line extending along Poust Rd from Blue Gum Ave to Chaparral Pl ‰ 1,373 LF of 48” trunk line extending along Poust Rd from Chaparral Pl to Woodland Ave ‰ 1,320 LF of 54” trunk line extending along Mercy Ave from Woodland Ave to Torrid Ave ‰ 1,274 LF of 60” trunk line extending along Mercy Ave from Torrid Ave to Kansas Ave ‰ 1,458 LF of 54” trunk line extending along Rosemore Ave from Blue Gum Ave to Chaparral Ave ‰ 1,202 LF of 54” trunk line extending along Rosemore Ave from Chaparral Pl to Woodland Ave ‰ 1,332 LF of 60” trunk line extending along Rosemore Ave from Woodland Ave to Torrid Ave ‰ 1,254 LF of 66” trunk line extending along Rosemore Ave from Torrid Ave to Kansas Ave ‰ 2,843 LF of 2-84” trunk lines extending along Kansas Ave from N Carpenter to Rosemore Ave Watershed F Watershed F encompasses sub-basins 24, 26, and 41. With the exception of City planned open space along the Tuolumne River, this watershed primarily includes existing residential land uses with some commercial land uses, plus existing agricultural land uses in sub-basin 26. There is no positive storm drain system serving the watershed and drainage disposal is accomplished using rockwells. The outfall and terminal detention basin are proposed to be located in sub- basin 26. Infrastructure recommendations within this watershed are considered to be first priority and include installing trunk lines to route stormwater to proposed Detention Basin No. 4. Proposed infrastructure for each sub-basin is as follows: Sub-basin 24 ‰ 2,610 LF of 42” trunk line extending along S Emerald Ave from Maze Blvd to California Ave ‰ 1,549 LF of 48” trunk line extending along California Ave from Emerald Ave to W. of Emerald Ave ‰ 1,192 LF of 60” trunk line extending along California Ave from East of S. Carpenter Rd to S. Carpenter Rd ‰ 1,343 LF of 66” trunk line extending along S. Carpenter Rd from California Ave to Houser Ln ‰ 1,278 LF of 72” trunk line extending along S. Carpenter Rd from Houser Ln to Chicago Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.15 Sub-basin 26 ‰ 1,150 LF of 30” trunk line extending along Grimes Ave from North of Cook Ave to Cook Ave ‰ 1,100 LF of 36” trunk line extending along Ohio Ave from S. of Beverly Dr to N. of Michel Ave ‰ 1,300 LF of 42” trunk line extending along a possible future extension of Cook Ave from Ohio Ave to Vineyard Haven ‰ 1,300 LF of 48” trunk line extending along Cook Ave from Vineyard Haven to Grimes Ave ‰ 4,092 LF of 2-78” trunk lines extending along Paradise Rd from S. Carpenter Rd to Detention Basin No. 4 ‰ 353 LF of a 24” outfall pipe will be constructed to discharge to Dry Creek via a 9 cfs pump station Sub-basin 41 ‰ 1,473 LF of 36” trunk line extending along Colorado Ave from Pelton Ave to Rouse Ave ‰ 1,322 LF of 48” trunk line extending along Rouse Ave from Colorado Ave to Sunset Ave ‰ 932 LF of 54” trunk line extending along Sunset Ave from Rouse Ave to Neece Dr ‰ 98 LF of 54” trunk line extending along Neece Dr from Sunset Ave to Detention Basin No. 5, which will be constructed as a wetland facility. Stormwater will discharge to Dry Creek via a 5 cfs pump station and a 24” outfall pipe ‰ 168 LF of 24” trunk line from Detention Basin No.5 to Tuolumne River ‰ 1,364 LF of 36” trunk line extending along Hammond St from Rouse Ave to Red Pine Dr ‰ 1,278 LF of 48” trunk line extending along Hammond St from Red Pine Dr to Robertson Rd ‰ 3,380 LF of 60” trunk line extending along Robertson Rd from Hammond St to S. Carpenter Rd ‰ 1,192 LF of 72” trunk line extending along S. Carpenter Rd from Robertson Rd to Paradise Rd ‰ 792 LF of 36” trunk line extending along California Ave from Spencer Ave to Seybold Ave ‰ 1,018 LF of 36” trunk line extending along Seybold Ave from California Ave to Briggs Ave ‰ 589 LF of 36” trunk line extending along Seybold Ave from Briggs Ave to Houser Lane ‰ 823 LF of 36” trunk line extending along Houser Ln from End of Houser to Alcamo Ave ‰ 639 LF of 36” trunk line extending along Alcamo Ave from Houser Ln to Chicago Ave ‰ 184 LF of 36” trunk line extending along Chicago Ave from Alcamo Ave to Harris Ave ‰ 1,571 LF of 54” trunk line extending along Harris Ave from Chicago Ave to Paradise Rd ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.16 ‰ 2,752 LF of 54” trunk line extending along Beverly Dr from Paradise Rd to S. Carpenter Rd ‰ 932 LF of 2-60” trunk lines extending along S. Carpenter Rd from Chicago Ave to Beverly Dr ‰ 1,852 LF of 2-72” truck lines extending along S. Carpenter Rd from Beverly Dr to Paradise Rd Watershed G Watershed G encompasses sub-basin 27 and is currently predominantly agricultural. Infrastructure recommendations will serve future development, are considered to be a fourth priority and will include installing trunk lines to route stormwater to proposed Detention Basin No. 3. Proposed infrastructure for sub-basin 27 is as follows: ‰ 1,430 LF of 42” trunk line extending north from W. Whitmore ‰ 1,284 LF of 54” trunk line extending west towards Vivian Rd ‰ 1,315 LF of 60” trunk line extending west towards Vivian Rd ‰ 1,388 LF of 42” trunk line extending north from W. Whitmore ‰ 1,270 LF of 72” trunk line extending north towards Detention Basin No. 3 ‰ 1,323 LF of 36” trunk line extending west towards Detention Basin No. 3 ‰ 385 LF of 72” trunk line to Detention Basin No. 3 ‰ 1,458 LF of 30" trunk line extending along W. Hatch from Rosemore Ave to Detention Basin No. 3 ‰ 436 LF of 24” force main extending from Detention Basin No. 3 to Tuolumne River. Stormwater will discharge to the Tuolumne River via a 9 cfs pump station Watershed H Watershed H encompasses sub-basins 9, 10, 11, and 43. This watershed consists primarily of residential properties with some industrial and agricultural land uses. Infrastructure solutions to serve existing development areas is considered to be a second priority and infrastructure to serve future development areas is considered to be a fourth priority. Infrastructure recommendations include installing trunk lines to route stormwater to proposed Detention Basin No. 2. Proposed infrastructure for each sub-basin is as follows: Sub-basin 9 ‰ 2,373 LF of 36" trunk line extending along Inyo Ave from Tuscon Ave to Frazier St ‰ 1,826 LF of 48” trunk line extending along Frazier St from Inyo Ave to Las Vegas St ‰ 1,610 LF of 54” trunk line extending along Glenn Ave from Las Vegas St to Spokane St ‰ 1,289 LF of 60” trunk line extending along Spokane St from Glenn Ave to Butte Ave ‰ 716 LF of 66” trunk line extending along Spokane St from Butte Ave to Amador Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.17 ‰ 843 LF of 66” trunk line extending along Amador Ave from Spokane St to Crows Landing Rd ‰ 666 LF of 66” trunk line extending along Crows Landing Rd from Amador Ave to W. Hatch Rd Sub-basin 10 ‰ 1,268 LF of 54” trunk line extending along Pearson Ave from South of Glenn Ave to Glenn Ave ‰ 1,098 LF of 72” trunk line extending along Pearson Ave from Glenn Ave to Parklawn Ave 2 of 1,633 LF of 66” trunk line extending along Pearson Ave from Parklawn Ave to Rio Grande Ave Sub-basin 11 – no infrastructure proposed Sub-basin 43 ‰ 929 LF of 72" trunk line extending along W. Hatch from Crows Landing Rd to Cascade Ave ‰ 782 LF of 72” trunk line extending along Cascade Ave from W. Hatch to Detention Basin No.2 ‰ 2 of 1,328 LF of 66” trunk line extending along Rio Grande Ave from Pearson Ave to Santa Fe Ave ‰ 2 of 1,364 LF of 72” trunk line extending along Rio Grande Ave from Santa Fe Ave to Crows Landing Rd ‰ 2 of 868 LF of 72” trunk line extending along Crows Landing Rd from Rio Grande Ave to Kendee Rd ‰ 2 of 347 LF of 72” trunk line extending along Kendee Rd from Crows Landing Rd Detention Basin No. 2 ‰ 1498 LF of 36” trunk line extending along Crows Landing Rd from Blankenburg Ave to Pecos Ave ‰ 931 LF of 48” trunk line extending along Crows Landing Rd from Pecos Ave to El Pason Ave ‰ 1295 LF of 30” trunk line extending along El Paso Ave from Santa Fe Ave to Crows Landing Rd ‰ 571 LF of 54” trunk line extending along Crows Landing Rd from El Paso Ave to Kendee Rd ‰ 141 LF of 24” trunk line from Detention Basin No.2 to Tuolumne River. Stormwater will discharge to Dry Creek via a 9.3 cfs pump station Watershed I Watershed I encompasses sub-basins 6, 17, 67, and 69. This watershed is fully developed with residential land uses. There are no positive storm drain systems serving the majority of this ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.18 watershed; however, the City recently acquired ownership of the ROW for the Encina Drain that traverses through the area and serves as a storm drainage outfall to Dry Creek. Also, rockwells provide for limited runoff disposal in much of the watershed. Infrastructure recommendations to serve this watershed are considered to be a first priority and include installing trunk lines to route stormwater to proposed Detention Basin No. 1 and to Dry Creek. Proposed infrastructure for each sub-basin is as follows: Sub-basin 6 ‰ 1,316 LF of 36” trunk line extending along Haddon Ave from Trask Ln to El Vista Ave ‰ 1,462 LF of 48” trunk line extending along Haddon Ave from El Vista to Phoenix Ave ‰ 592 LF of 54” trunk line extending along Phoenix from Haddon to Miller Ave ‰ 1,199 LF of 60” trunk line extending along Miller Ave from Phoenix to N. Conejo Ave ‰ 446 LF of 60” trunk line extending along N. Conejo from Miller to Haddon Ave ‰ 1,670 LF of 30” trunk line extending along Haddon Ave from N. Santa Cruz to Rosina Ave ‰ 615 LF of 30” trunk line extending along Haddon Ave from Rosina Ave to N. Conejo Ave ‰ 1,458 LF of 66” trunk line extending along N. Conejo from Haddon to Encina Ave ‰ 657 LF of 72” trunk line extending along Encina Ave from N. Conejo Ave to Rosina Ave ‰ 6,948 LF of 66” trunk line extending along Encina Ave from N. Riverside Dr to Covena Ave Sub-basin 17 ‰ 723 LF of 30” trunk line extending along Lincoln Ave from Japonica Way to Poppypatch Dr ‰ 704 LF of 48” trunk line extending along Poppypatch Dr from Whitehorn Dr to Lincoln Ave ‰ 1,000 LF of 54” trunk line extending along Lincoln Ave from Poppypatch Dr to Penny Ln ‰ 1,050 LF of 66” trunk line extending along Penny Ln from Lincoln Ave to Capistrano Dr ‰ 83 LF of 66” trunk line extending along Capistrano from Penny Ln to El Pasado Dr ‰ 1,613 LF of 66” trunk line extending along El Pasado Dr from Capistrano Dr to N. Riverside Dr ‰ 344 LF of 66” trunk line extending along N. Riverside Dr. from El Pasado Dr to Encina Ave ‰ 2,174 LF of 66” trunk line extending along Encina Ave from Covena Ave to Edgebrook Dr and discharging to Dry Creek Sub-basin 67 – no infrastructure proposed ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.19 Sub-basin 69 ‰ 126 LF of 72” trunk line from Encina Ave to Detention Basin No. 1 ‰ 80 LF of 24” trunk line from Detention Basin No. 1 to Encina Drain via a 5 cfs pump station Watershed J Watershed J encompasses sub-basins 13, 14, 15, 16, and 59. Current land uses consist mainly of industrial, with residential land uses occurring in sub-basin 59. There are no stormwater conveyance or disposal facilities serving this watershed. Infrastructure recommendations to serve this watershed are considered to be a first priority and include installing trunk lines to route stormwater to proposed Detention Basin Nos. 7 and 10 and a storm drain outfall to Dry Creek that would only serve sub-basin 59. Proposed infrastructure for each sub-basin is as follows: Sub-basin 13 – no infrastructure proposed Sub-basin 14 ‰ 3,235 LF of 48” trunk line extending along Finch Rd from Codoni Ave to Garner Rd ‰ 1,467 LF of 66” trunk line extending along Garner Rd from Finch Rd to Leckron Rd ‰ 1,478 LF of 48” trunk line extending along Leckron Rd west from Codoni Ave ‰ 1,787 LF of 54” trunk line extending along Leckron Rd west to Garner Rd ‰ 1,291 LF of 48” trunk line extending west of Leckron and north of Finch Rd ‰ 828 LF of 2-72” trunk lines extending along Garner Rd from Leckron Rd to Detention Basin No.7. Stormwater will be discharged to MID Lateral No. 1 via a 10 cfs pump station Sub-basin 15 – no infrastructure proposed Sub-basin 16 ‰ 1,843 LF of 36” trunk line extending along a possible future extension of Nathan Ave from Mariposa Rd to El Roya Ave ‰ 1,350 LF of 36” trunk line extending along El Roya Ave from Farrar Ave to Nathan Ave ‰ 777 LF of 60” trunk line extending along Nathan Ave from El Roya Ave to Beard Ave ‰ 767 LF of 42” trunk line extending along Nathan Ave from East of Beard Ave to Beard Ave ‰ 1,194 LF of 78” trunk line extending along Beard Ave from Nathan Ave to Detention Basin No. 10. Stormwater will be discharged to MID Lateral No. 1 via a 5 cfs pump station Sub-basin 59 ‰ 477 LF of 42” trunk line extending along Kerr Ave from Tenaya Dr to Mono Dr ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.20 ‰ 1,536 LF of 48” trunk line extending along Mono Dr from Kerr Ave to S. Santa Ana Ave ‰ 945 LF of 54” trunk line extending along Mono Dr from Santa Ana Ave to S. Santa Rosa Ave ‰ 512 LF of 54” trunk line extending along S. Santa Rosa Ave from Mono Dr to Hyde St ‰ 1,138 LF of 54” trunk line extending from Hyde St west and discharging to Dry Creek Watershed K Watershed K encompasses sub-basin 18. It is currently developed as residential land use, and there are no stormwater conveyance or disposal facilities serving the watershed. Infrastructure recommendations are considered to be a first priority and include installing trunk lines to route stormwater to Dry Creek. Proposed infrastructure for sub-basin 18 is as follows: ‰ 508 LF of 30” trunk line extending along E. Orangeburg from Pepper Tree Ln to Lillian Dr ‰ 1,443 LF of 36” trunk line extending along E. Orangeburg from Satariano Ln to Lillian Dr ‰ 1,107 LF of 54” trunk line extending along Lillian Dr from E. Orangeburg to Laramie Dr ‰ 165 LF of 60” trunk line extending along Lillian Dr from Laramie Dr to S. of Saginaw Ct ‰ 1,425 LF of 66” trunk line extending along Lillian Dr from S. of Saginaw Ct to Scenic Dr ‰ 722 LF of 66” trunk line extending along Sc enic Dr from Lillian Dr to Dry Creek Watershed L Watershed L encompasses sub-basins 7, 94 and 95. Sub-basin 7 is fully developed with residential land uses, and sub-basins 94 and 95 are currently undeveloped under agricultural use. There are no stormwater conveyance or disposal facilities serving the watershed. Infrastructure recommendations pertain only to sub-basin 7 and would be first priority facilities that include installing trunk lines to route stormwater to Tuolumne River. Future facilities that will serve the future development of sub-basins 94 and 95 will be fourth priority improvements. Proposed infrastructure for sub-basin 7 is as follows: ‰ 1,823 LF of 36” trunk line extending along Church St from McNavy Ct to 3rd St ‰ 1,432 LF of 48” trunk line extending along Church St from 3rd St to Yosemite Blvd ‰ 287 LF of 54” trunk line extending along Yosemite Blvd from F St to Santa Fe Ave ‰ 2,661 LF of 54” trunk line extending along Santa Fe Ave from Yosemite Blvd to South Ave ‰ 1,021 LF of 60” trunk line extending along Santa Fe Ave from South Ave to S. of South Ave ‰ 1,351 LF of 66” trunk line extending along Santa Fe Ave from S. of South Ave to Dry Creek ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.21 Watershed M Watershed M is primarily the airport property and is drained by a system of several storm drainage pipes that generally tend to align from north to south (Figure 6.4). The majority of these pipes discharge onto the north “bench” of the floodplain area of the Tuolumne River (within the Tuolumne River Regional Park), but two do not and extend through the floodplain area and discharge directly into the Tuolumne River. For the storm drainage pipes that discharge onto the north “bench” area, excellent water quality benefits result because this floodplain area contains low-lying spots that sustain dense vegetative growth and generally retain water. The dense vegetation offers excellent water quality treatment, and the physical evidence suggests that stormwater runoff seldom actually makes it as far as the river before evaporating or percolating into the ground. Even in the event of a flood along the Tuolumne River that causes inundation of the north “bench” area, any residual pollutants brought into suspension should be sufficiently diluted to negate the occurrence of any significant water quality issues. The two storm drainage lines that discharge directly into the Tuolumne River have a much greater potential for conveying runoff that may have an undesirable impact on the water quality of the river. This would include typical constituents associated with the “first flush” of urban runoff and possibly fuels and by-products associated with the operation of the airport. With direct discharge into the Tuolumne River and no upstream detention or treatment potential, there is limited opportunity to prevent or correct an unintended spill of pollutants that may enter the airport’s storm drainage system. This situation could be improved by installing oil water separators or other proprietary treatment devices (designed to treat the first flush flows) in the upstream portions of the watershed where targeted pollutants are anticipated. These would be considered to be second priority measures, unless storm water quality concerns make it a greater priority. Additionally, there is a large County area that includes the Beard Industrial Park and an MID pump station, lying north of the airport (within sub-basins 48 and 58), that discharges stormwater runoff into the airport storm drainage system. This is a concern because the City has little control over the nature of the discharges that may originate from this County industrial area or the MID pump station. In order for the County and MID to continue utilizing the City’s storm drainage facilities in this area, it is recommended that the City, County, and MID work out an agreement that addresses appropriate solutions related to the needed capital improvements and ongoing maintenance. This is an important issue for the City because it would be an opportunity to mitigate erosion, monitor potential water quality concerns, and limit the potential liability associated with an improper discharge directly into the Tuolumne River. Provisions in the agreement may include a program for testing and monitoring. In the absence of such an agreement, the City may wish to seek a method by which the City’s storm drainage system may be retrofitted to function independently from the County’s and MID’s discharges. ---PAGE BREAK--- 68 42 12 54 6 30 15 60 10 8 36 24 18 66 16 48 21 27 12 12 15 12 10 21 15 8 18 16 8 42 15 12 24 30 12 12 24 12 24 30 18 15 12 18 16 36 12 8 12 12 8 24 18 18 12 12 12 12 21 12 12 30 12 12 15 36 12 21 15 12 15 12 12 15 18 12 18 12 12 18 54 12 12 15 24 12 24 24 18 12 12 15 42 12 12 18 12 12 15 18 8 18 12 15 30 18 12 30 12 30 12 12 12 18 15 8 12 15 21 18 42 30 21 12 8 18 12 15 42 18 12 12 18 18 12 60 12 12 36 42 18 12 12 12 30 12 12 12 24 18 V:\52840\active\84010174\arcview\exhibits\final_mxd\fig_6.4_airport.mxd CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Client/Project AIRPORT DRAINAGE FIGURE 6.4 Title 84010174 JANUARY 2008 SYSTEM AND SURROUNDING AREA LEGEND Existing Storm Drain Lines and MID laterals Dry Creek COUNTY INDUSTRIAL AREA MODESTO CITY / COUNTY AIRPORT Encina Storm Drain MID Lateral No. 1 TID Lateral No. 1 Tuolumne River ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.22 Watershed N Watershed N encompasses sub-basins 46, 74 and 75. Sub-basins 74 and 75 currently consist of mainly residential land uses and some industrial land uses. Sub-basin 46 is substantially undeveloped and consists of primarily agricultural land use. Sub-basin 75 currently discharges to Dry Creek. Infrastructure recommendations provided in this SDMP are to relieve flooding in the residential portions of sub-basin 74 where no positive storm drain systems exist and would be a first priority. Recommendations include installing trunk lines to route stormwater to Tuolumne River Regional Park. Future development within sub-basin 46 will warrant new storm drainage facilities that will be a fourth priority. Proposed infrastructure for sub-basin 74 is as follows: ‰ 440 LF of 60” trunk line extending along S. Santa Cruz Ave from Hillside Dr to Monterey Ave ‰ 1,369 LF of 48” trunk line extending along S. Santa Cruz Ave from Monterey Ave to Oregon Dr Village 1 Village 1 encompasses sub-basin 35 and was master planned in a separate study. Watershed O, Johansen CPD Johansen CPD encompasses sub-basins 30, 96, and 97. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin No. 22. Proposed infrastructure for Johansen CPD would be a fourth priority and is as follows: Sub-basin 30 – low flow discharge from Sutton Park to drainage system serving sub-basin 31 Sub-basin 96 ‰ 1,480 LF of 30” trunk line extending in an east-west orientation from W. of Frazine Rd to Frazine Rd ‰ 1,500 LF of 48” trunk line extending along Frazine Rd from N. of Yosemite Blvd ‰ 1,400 LF of 54” trunk line extending along Frazine Rd from N. of Yosemite Blvd ‰ 440 LF of 66” trunk line extending along Frazine Rd from N. of Yosemite Blvd to Detention Basin No. 22 ‰ 1,500 LF of 48” trunk line extending along Norseman Dr from S. of Creekwood Dr to Creekwood Dr ‰ 850 LF of 48” trunk line extending along Norseman Dr from Creekwood Dr to S. of Encina SD ‰ 500 LF of 54” trunk line extending along the south side of the Encina Storm Drain to Detention Basin No. 22; pump station to Encina Storm Drain ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.23 Sub-basin 97 ‰ 1,400 LF of 36” trunk line extending along Lacoste Ln from Norseman Ln to Frazine Rd ‰ 1,000 LF of 48” trunk line extending along Frazine Rd from Lacoste Ln to Detention Basin No. 11; pump station and discharge to Dry Creek Watershed P, Roselle/Claribel CPD Roselle/Claribel CPD encompasses sub-basins 88 and 98. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basins Nos. 12 and 13 and ultimately to MID Lateral No. 6. Proposed infrastructure for Roselle/Claribel CPD would be a fourth priority and is as follows: Sub-basin 88 ‰ 1,800 LF of 30” trunk line extending in a north-south orientation east of Oakdale Ave ‰ 800 LF of 48” trunk line extending in an east-west orientation east of Oakdale Ave to Detention Basin No. 12 ‰ 1,450 LF of 30” trunk line extending along Plainview Rd west from Litt Rd ‰ 1,500 LF of 30” trunk line extending in a north-south orientation north of Plainview Rd ‰ 1,400 LF of 42” trunk line extending along Plainview Rd west of Litt Rd to Roselle Ave ‰ 1,500 LF of 30” trunk line extending along Roselle Ave north of Plainview Rd ‰ 1,400 LF of 54” trunk line extending along a possible extension of Plainview Rd west of Roselle Ave ‰ 1,500 LF of 36” trunk line extending in a north-south orientation west of Roselle Ave ‰ 1,250 LF of 60” trunk line extending along a possible future extension of Plainview Rd west of Roselle Ave to Detention Basin No. 12 ‰ 850 LF of 30” trunk line extending in an east-west orientation east of Oakdale Ave to the south end of Detention Basin 12 ‰ 2,859 LF of 24” force main extending in a north-south orientation from Detention Basin No. 12 north to MID Lateral No. 6; pump station and discharge to MID Lateral No. 6 ‰ 1,200 LF of 36” trunk line extending in an east-west orientation east of Litt Rd ‰ 1,400 LF of 42” trunk line extending along Litt Rd north of Sylvan Ave ‰ 1,450 LF of 54” trunk line extending in an east-west orientation from Litt Rd west towards Roselle Ave ‰ 1,350 LF of 60” trunk line extending in an east-west orientation east of Litt Rd to Roselle Ave ‰ 1,200 LF of 66” trunk line extending along Roselle Ave north of Sylvan Ave ‰ 2,650 LF of 72” trunk line extending in an east-west orientation from Roselle Ave to Detention Basin No. 12 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.24 ‰ 1,450 LF of 30” trunk line extending west from Litt Rd toward Roselle Ave ‰ 1,350 LF of 36” trunk line extending toward Roselle Ave Sub-basin 98 ‰ 1,500 LF of 42” trunk line extending in an east-west orientation north of Sylvan Ave east of Oakdale ‰ 1,350 LF of 48” trunk line extending in an east-west orientation north of Sylvan Ave west of McReynolds Ave ‰ 1,350 LF of 66” trunk line extending in a north-south orientation south of Mable Ave ‰ 1,500 LF of 30” trunk line extending in an east-west orientation south of Mable Ave east of Oakdale Ave ‰ 1,250 LF of 36” trunk line extending in an east-west orientation east of Mable Ave ‰ 950 LF of 78” trunk line extending in a north-south orientation north of Mable Ave to Detention Basin No. 13; pump station and discharge to MID Lateral No. 6 Watershed Q, Paradise/Carpenter CPD Paradise/Carpenter CPD encompasses sub-basin 25. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin No. 19 and MID Lateral No. 5. Proposed infrastructure for sub-basin 25 would be a fourth priority and is as follows: ‰ 1,300 LF of 42” trunk line extending along Grimes Ave from Maze Blvd to South of Maze ‰ 1,250 LF of 54” trunk line extending along Grimes Ave from South of Maze to California Ave ‰ 1,300 LF of 60” trunk line extending along Grimes Ave from California Ave to S of California Ave ‰ 1,400 LF of 66” trunk line extending along Grimes Ave from North of California Ave to California Ave ‰ 1,300 LF of 42” trunk line extending in a north-south orientation from Maze Blvd to South of Maze ‰ 1,250 LF of 54” trunk line extending in a north-south orientation from South of Maze Blvd to California Ave ‰ 1,300 LF of 60” trunk line extending along Ohio Ave from California Ave to S of California ‰ 1,700 LF of 66” trunk line extending along Ohio Ave from Houser Ln to Chicago Ave ‰ 1,300 LF of 72” trunk line extending along the north side of MID Lateral No. 5 W. of Chicago Ave ‰ 1,500 LF of 78” trunk line extending along the north side of MID Lateral No. 5 from W. of Chicago Ave to Detention Basin No. 19; pump station and discharge to MID Lateral No. 5 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.25 Watershed R, Kiernan/Carver CPD Kiernan/Carver CPD encompasses sub-basins 54, 55, and 56. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin No. 18 and MID Lateral No. 6. Proposed infrastructure for Kiernan/Carver CPD would be a fourth priority and is as follows: Sub-basin 54 – no infrastructure proposed Sub-basin 55 – no infrastructure proposed Sub-basin 56 ‰ 1,400 LF of 30” trunk lines extending from north of Bangs Ave to Bangs Ave ‰ 1,450 LF of 54” trunk line extending along Bangs Ave from Carver Rd to east of Carver Rd ‰ 1,400 LF of 30” trunk line extending along Carver Rd from north of Bangs Ave to Bangs Ave ‰ 1,900 LF of 60” trunk line extending along Bangs Ave from Carver Rd to Valley Dr ‰ 1,400 LF of 36” trunk line extending from north of Bangs Ave, west of Carver Rd to Bangs Ave ‰ 1,950 LF of 66” trunk line extending along Bangs Ave from Valley DR to Morrow Rd ‰ 1,400 LF of 42” trunk line extending along from Morrow Rd from north of Bangs Ave to Bangs Rd ‰ 500 LF of 78” trunk line extending along Bangs Rd from Morrow Rd to Detention Basin No. 18; pump station to MID Lateral No. 6 Watershed S, Kiernan/McHenry CPD Kiernan/McHenry CPD encompasses sub-basin 90. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin No. 17 and MID Lateral No. 6. Proposed infrastructure for sub-basin 90 would be a fourth priority and is as follows: ‰ 650 LF of 42” trunk line extending along Galaxy Way from Stratos Way to North Star Way ‰ 1,400 LF of 48” trunk line extending along North Star Way from Galaxy Way to Bangs Ave ‰ 350 LF of 60” trunk line extending along Bangs Ave to the railroad track ‰ 713 LF of 60” trunk line extending south from Bangs Ave to Detention Basin No. 17 ‰ 1,500 LF of 48” trunk line extending from north of Bangs Ave to Bangs Ave ‰ 1,250 LF of 66” trunk line extending from Bangs Ave to Pelandale Ave ‰ 850 LF of 72” trunk line extending along Pelandale Ave from east of Tully Rd to Detention Basin No. 17; pump station to MID Lateral No. 6 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.26 Watershed T, Coffee/Claratina CPD and Hetch Hetchy CPD Coffee/Claratina CPD and Hetch Hetchy CPD encompasses sub-basins 87, 92, 93, and 99. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin Nos. 14, 15, and 16 and ultimately to MID Lateral No. 6. Proposed infrastructure for Coffee/Claratina CPD and Hetch Hetchy CPD would be a fourth priority and is as follows: Sub-basin 87 ‰ 650 LF of 30” trunk line extending along Claratina Ave towards east end of Claratina Ave ‰ 2,000 LF of 36” trunk line extending in a north-south orientation north of Claratina Ave ‰ 1,750 LF of 54” trunk line extending along Claratina Ave from the east end of Claratina, and including an inlet from an overflow pump station from the Rose Lane basin on Claratina Ave ‰ 1,900 LF of 60” trunk line extending along Claratina Ave east of Coffee Rd ‰ 1,950 LF of 66” trunk line extending along Claratina Ave from Coffee Rd to Detention Basin No. 16 ‰ 249 LF of 66” trunk line extending from Detention Basin No. 16 to Detention Basin No. 15 Sub-basin 92 ‰ 2,600 LF of 42” trunk line extending along Vella Way east of Coffee Rd ‰ 800 LF of 48” trunk line extending along Coffee Rd south from Vella Way ‰ 1,700 LF of 54” trunk line extending in an east-west orientation west from Coffee Rd and north of Claratina Ave ‰ 650 LF of 60” trunk line extending in a north-south orientation west from Coffee Rd ‰ 1,450 LF of 66” trunk line extending in an east-west orientation west of Coffee Rd to Detention Basin No. 15; pump station and discharge to MID Lateral No. 6 Sub-basin 93 ‰ 1,900 LF of 30” trunk line extending in an east-west orientation west of Coffee Rd ‰ 700 LF of 42” trunk line extending in a north-south orientation to Detention Basin No. 14 ‰ 1,300 LF of 42” trunk line extending in a north-south orientation east of McHenry Ave ‰ 1,000 LF of 54” trunk line extending along east of McHenry to Detention Basin No. 14; pump station and discharge to MID Lateral No. 6 Sub-basin 99 ‰ 1 cfs overflow pump station to dewater the Rose Lane detention basin into the 54” trunk line on Claratina Ave ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.27 Watershed U, Fairview CPD Fairview CPD encompasses sub-basin 50 and 51. Infrastructure recommendations include installing trunk lines to route stormwater to Detention Basin Nos. 20 and 21 for discharge to the Tuolumne River and TID Lateral No. 1, respectively. Proposed infrastructure for Fairview CPD would be a fourth priority and is as follows: Sub-basin 50 ‰ 1,250 LF of 42” trunk line extending north towards W. Hatch ‰ 1,400 LF of 42” trunk line south of W. Hatch extending west towards S. Carpenter Ave ‰ 400 LF of 54” trunk line south of W. Hatch extending west towards S. Carpenter Ave ‰ 900 LF of 66” trunk line extending north towards W. Hatch ‰ 400 LF of 78” trunk line extending west to Detention Basin No. 20; pump station and discharge to existing 30” storm drain pipe discharging to the Tuolumne River Sub-basin 51 ‰ 1,300 LF of 30” trunk line north of W. Whitmore ‰ 1,150 LF of 42” trunk line north of W. Whitmore extending west to Detention Basin No. 21; pump station and discharge to TID Lateral No. 1 Watershed V Watershed V includes the Kaiser Modesto facilities within sub-basin 102. Storm drainage solutions are not represented in this SDMP and will be site and development specific. Storm drainage improvements that will serve new development within this watershed will be a fourth priority. Sub-basin 102 – No infrastructure proposed Watershed OS Watershed OS is located in the northeast portion of the Study Area (but lies outside the SOI) between the MID Main Canal and the AT & SF railroad. Watershed OS has the potential to cause flooding in the northeast portion of the City during large storms of sustained durations due to the significant rates and volumes of runoff that overwhelm the infrastructure. This condition has previously caused flooding within northeast portions of the City, as the drains become surcharged and are unable to handle the rates and volumes of inflow. The result is that the runoff enters a large, broad area between Briggsmore Avenue and Claribel Avenue as shallow sheet flow that may be impounded for long periods of time while drainage systems eventually derive capacity to allow floodwaters to drain slowly to the west and southwest. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Proposed Capital Improvements March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 6.28 As a separate project and contract from the development of this SDMP, Stantec has been retained by the City to determine the facilities needed to mitigate the flooding potential in the northeast portion of the City (see the Northeast Area Offsite Watershed Storm Drainage Evaluation - Draft, March 2005). This separate analysis included making recommendations for the required remedial storm drainage improvements and the estimation of their associated costs. The Draft Northeast Area Offsite Watershed Storm Drainage Evaluation report identifies a solution that includes the installation of a series of four detention basins on the east side of the AT & SF railroad to mitigate the potential flooding (Figure 6.5). The detention basins are proposed to have restricted discharges and to be connected with storm drainage pipes. The detention basins all drain in a southerly direction along the east side of the AT & SF railroad to the existing Ralston Drain. A single pump station at the Ralston Drain is proposed to provide for discharge into an MID pipeline that drains south to Dry Creek along the alignment of the AT & SF railroad. Results of the analysis show that a significant risk of flooding of the northeast area of the City will exist until proper storm drainage infrastructure is constructed to eliminate the flooding potential. A phased approach for constructing the offsite infrastructure required to mitigate potential flooding is feasible. As currently identified, the proposed detention basins would have the capacity to hold a 100- year, 24-hour storm event. The detention basins would also provide water quality treatment. Also, given that the Dry Creek watershed is significantly larger than the tributary area that would contribute the additional runoff, it is expected that the introduction of additional flow via the detention basins and outfall line would be relatively negligible. Additional benefits of the project include: reduction in extent and duration of flooding, preservation of capacity within drain systems to accept other locally generated runoff, and the possible elimination of several rockwells. The storm drainage infrastructure improvements associated with Watershed OS are considered to be a first priority and include: ‰ 52-acre detention basin A ‰ 52-acre detention basin B ‰ 52-acre detention basin C ‰ 72-acre detention basin D ‰ 1,900-linear feet of 18” trunk line from detention basin A to detention basin B ‰ 2,000-linear feet of 24” trunk line from detention basin B to detention basin C ‰ 2,500-linear feet of 24” trunk line from detention basin C to detention basin D ---PAGE BREAK--- ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 7.0 Opinion of Probable Costs 7.1 GENERAL This Chapter presents the opinion of probable costs and the methodology used to generate them for the proposed projects in this SDMP. Major facilities are described and costs are given for each Watershed Group. 7.2 COST ESTIMATING METHODOLOGY 7.2.1 Basis of Developing Opinion of Probable Costs The basis for the opinion of probable costs comes from a number of sources, including bid results from similar projects, previous studies, and industry standardized cost data. They are tied to the June 2006 Engineering News Record Construction Cost Index (ENR CCI) of 8441 for the San Francisco Average, and should be adjusted accordingly for future construction time frames. 7.2.2 Opinion of Probable Cost Accuracy The project costs prepared for this SDMP are considered “order of magnitude” estimates and are relevant for initial budgeting and related master planning purposes. Final project cost will be dependent on a number of factors at the time of bidding, including actual scope of work, labor and material costs, number of competing projects, allotted construction schedule, and time of year, among other things. Order of magnitude estimates are appropriate for master planning level work, but it is important to note that they have been made without the benefit of detailed project specifications and design drawings; thus, they typically have an expected accuracy range of plus or minus 40 percent. 7.2.3 Unit Cost Estimates The unit costs presented in this Chapter represent installation costs under what would be considered “typical” site conditions and project schedules. Cost estimates for the various projects do not include right-of-way (ROW) or easement purchases for construction of the collection system improvements because it was assumed that public ROW would be utilized. However, land acquisition costs (based on information provided by City staff) are included for the purchase of property to be used for detention basins. Table 7-1 and Table 7-2 show generic cost data for large diameter pipe and pump stations (based on pumping capacity) that have been used in the various cost estimates. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Opinion of Probable Costs March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.2 Table 7-1. Unit Cost Data for Pipes* Pipe Size (inches) Cost per Linear Foot 24 $180 30 $225 36 $265 42 $305 48 $345 54 $390 60 $470 66 $550 72 $640 78 $720 84 $810 *Costs based on 2007 ENR CCI Table 7-2 Unit Cost Data for Pump Stations* Input Data Costs Max Flow Rate (cfs) # of Pumps Flow Rate per Pump Pump Size (hp) Discharge Pipe Size (in) Pump Equipment Mechanical Equipment Electrical Equipment Structural/ Building Site Preparation Total 5 3 2.5 9.5 12 60,000 80,000 130,000 200,000 200,000 670,000 10 3 5 18.9 16 70,000 130,000 170,000 280,000 290,000 940,000 * Costs based on 2006 ENR CCI ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Opinion of Probable Costs March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.3 7.2.4 Soft Cost Mark-Ups The types and amounts of soft cost mark-ups used in this SDMP are generally consistent with the estimated costs of capital improvements identified in other documents for the City’s water and wastewater systems. The actual costs for each item in the following four main categories of soft cost mark-ups will vary according to many individual project factors complexity of the project, existing site conditions, etc.), but, in general, they are supported historically as appropriate mark-up estimates for master planning purposes (standardized as a percentage relative to the estimated construction cost) and are included in each Watershed Group’s total estimated cost. Construction Contingency – Due to the fact that there are many unknowns related to a given project at the master planning level site conditions, unforeseen constraints, details of design alternatives, construction schedule uncertainty, etc.), a 20 percent construction contingency is added to the construction cost estimate. Planning and Design – These services typically include management of consultant agreements, preliminary site investigations, feasibility studies, plans and specifications, surveying and staking, geotechnical reports, and right-of-way acquisitions. The cost of this work is estimated to be 10 percent of the estimated construction cost. Construction Management – This primarily covers management of the construction contract, sampling and testing of materials, and site inspections during construction. This work is estimated to be 10 percent of the estimated construction cost. Program Implementation – Among other things, this category includes management and administrative costs, environmental review, permits, regulatory compliance, financing expenses, and legal review. This work is also estimated to be 10 percent of the estimated construction cost. Table 7-3 shows an example of the mark-ups used in generating the cost estimates provided in this SDMP. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Opinion of Probable Costs March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.4 Table 7-3. Cost Estimate Example Construction $100,000 Construction Contingency (20%) $20,000 Planning and Design (10%) $10,000 Construction Management (10%) $10,000 Program Implementation (10%) $10,000 Total Estimated Cost $150,000 7.3 INFRASTRUCTURE OPINION OF PROBABLE COSTS The total opinion of probable cost (construction and soft cost mark-ups) of the storm drainage facilities identified as being needed to serve build-out of the Study Area within each of the 24 Watershed Groups are summarized in Table 7-4. The costs shown in Table 7-4 include all of the SDMP proposed infrastructure and do not account for the $3,920,670 initial phase of the storm drain sanitary sewer cross connection study. It should be noted that these storm drainage facilities correspond only to major or backbone infrastructure projects large trunk pipelines, open channel facilities, pump stations, and detention basins) and do not include minor upstream storm drains and laterals serving small local areas that will also need to be installed. It is also assumed that for a given development project, all on-site facilities will be paid for and installed by the developer. However, as shown in Table 7-4, a “bulk cost” estimate for minor facilities has been incorporated into the overall total estimated cost. The infrastructure proposed in the SDMP has generally been established to serve roughly a minimum sub-basin size of 40 acres. The “bulk cost” is an allowance for infrastructure that is outside the limits of onsite development, but within the 40 acre sub-basin. These facilities would include smaller storm drain pipes, or laterals, that connect into the trunk storm drain system identified in this SDMP, and site specific developments would then be able to connect to the laterals. For a hypothetical section of land, the unrepresented smaller storm drain pipes and laterals would be serving the interior 160 acres of land within the center of the 640 acre section. This land area is 25% of the total area for the hypothetical section of land. Hence, the “bulk cost” estimate has been approximated by multiplying the sum of the estimated storm drainage infrastructure costs for all of the watersheds by 25%. Obviously, this is an approximation, and actual costs will be impacted by the size, orientation and configuration of individual development projects. However, this is considered to be a reasonable approach to utilize for the purpose of estimating the composite cost of minor storm drainage infrastructure at a master plan level. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Opinion of Probable Costs March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.5 Table 7-4. Summary of Facility Costs Watershed Group Total Storm Drainage Facilities Opinion of Probable Cost Watershed A $ 70,804,988 Watershed B $ 65,416,630 Watershed C $ - Watershed D $ 27,711,993 Watershed E $ 73,394,535 Watershed F $ 50,502,943 Watershed G $ 12,741,938 Watershed H $ 34,141,608 Watershed I $ 22,006,290 Watershed J $ 33,216,108 Watershed K $ 3,280,238 Watershed L $ 5,024,663 Watershed M $ 600,000 Watershed N $ 990,458 Village 1 $ - Watershed O $ 14,105,375 Watershed P $ 32,284,305 Watershed Q $ 21,415,500 Watershed R $ 11,333,500 Watershed S $ 9,685,350 Watershed T $ 26,845,550 Watershed U $ 18,910,750 Watershed V $ - Watershed OS $ 25,035,100 Subtotal $ 534,412,718 "Bulk Cost" Estimate for Minor Facilities $ 133,603,179 Total Opinion of Probable Cost $ 668,015,897 Initial phase of cross connections included in wastewater fund $ 13,900,000 Resulting Opinion of Probable Cost $ 654,115,897 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Opinion of Probable Costs March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 7.6 7.3.1 Watershed Groups The individual Watershed Group infrastructure cost estimates are provided in Tables 7-5 through 7-25 (located at the end of this chapter). Certain improvements and their associated cost estimates identified in this Section have been refined and updated as a result of other recently performed or completed project specific storm drainage analysis or capacity studies Cross Connection Elimination, Tivoli Specific Plan, RDA Master Plan, Kansas/Woodland Business Park Specific Plan, and the Pelandale/McHenry Specific Plan), but as stand alone documents, they represent an approximate duplication of the cost estimates presented here. The proposed improvements and the estimated costs associated with each of these project specific storm drainage analysis or capacity studies is available through the City. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 8.0 Funding Alternatives 8.1 GENERAL Unfortunately, the needed funding to maintain and operate the existing system functioning properly, plus make significant improvements to the storm drainage system is generally not available under the City’s current financing structure. Since it is likely that construction of the recommended facilities will be spread out over a number of years as funding does become available, and since the cost estimates in this SDMP have been developed without the benefit of design details, it is expected that the cost of implementing the recommendations will significantly increase over the years. Therefore, it is important that the funding mechanisms established to implement the various elements of this SDMP include provisions for the increased costs of deferred construction. In order to generate the revenue necessary to construct the improvements identified in this SDMP, several alternatives are discussed and funding may consist of one or more of the alternatives. They are presented in no particular order and will have varying applicability depending on the circumstances of the particular improvements being proposed. ‰ Development Impact Fees (capacity charges) ‰ Assessment District (1913/15 Act) ‰ Special Tax Districts (Mello Roos Community Facilities District Act of 1982) ‰ Storm Drainage Utility Rate Increase (subject to Proposition 218) ‰ State and Federal Grants ‰ General Fund Subsidy ‰ Subject to the Mitigation Fee Act known as AB 1600 In general, the timeframe to establish the financing structure to collect the necessary revenue to begin paying for the proposed improvements will be based on the pace of new development and the desire by the City to upgrade in existing developed areas. 8.2 DEVELOPMENT IMPACT FEES (CAPACITY CHARGES) To the extent that new development creates a need for new and upgraded storm drainage facilities to accommodate the resultant increase in stormwater runoff caused by their urbanization, new development that utilizes these facilities should be required to pay their fair share towards funding the required upgrades via development impact fees (capacity charges). v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 8.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Funding Alternatives March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 8.2 8.3 ASSESSMENT DISTRICTS (1913/15 ACT) The potential exists for the establishment of one or more assessment districts to fund the required storm drainage facilities and their maintenance, where a common interest is shared by a large, but clearly defined group of constituents. Assessment district financing provides a vehicle to apportion the cost of improvements to those who will benefit by typically issuing bonds (although they can be esta blished without bonding), which are then repaid with revenue generated by assessing those benefiting directly from the improvements. The establishment of an assessment district requires a finding of direct and special benefit to the parcels being assessed, which shall be set forth in an Engineer’s Report. Two public hearings and a mailed ballot are also required to establish an assessment district. If an assessment district is selected as a preferred financing mechanism, the SDMP may be utilized as a resource to assist in making the benefit findings required pursuant to Proposition 218 and preparing an Engineer’s Report as part of formation of the district. 8.4 SPECIAL TAX DISTRICTS - MELLO ROOS COMMUNITY FACILITIES DISTRICT (ACT OF 1982) If the City determines that more flexibility is needed in the allocation of costs and funding burdens, a Mello-Roos Community Facilities District (CFD) may be used instead of an assessment district. The Mello-Roos law does not require a finding of benefit for allocating costs among properties within the CFD, and the special tax can be spread in any “reasonable manner” according to the law. If a CFD is determined to be a more feasible funding tool, it will be necessary to prepare a Rate and Method of Apportionment of Special Tax for the CFD as a part of CFD formation and bond issuance. It does require a 2/3 approval of registered voters. However, if less than 12 registered voters reside in the area, which is typical of undeveloped land, the special tax can be implemented with a property owner vote. 8.5 STORM DRAINAGE UTILITY RATE INCREASE The City may initiate the steps that are required to increase the existing City-wide storm drainage utility rates (the existing rates have remained unchanged since 1995 when they were reduced by five percent) for the purpose of funding items such as rockwell related work, street sweeping, leaf collection, system maintenance, stormwater quality monitoring, storm drainage repairs, and capital improvements to improve existing storm drainage deficiencies. Many of these services are needed to meet the requirements of the Federal Clean Water Act, and the proposed rates may include both an operating component and a capital improvement component. The process of increasing the existing utility rates would be subject to the Proposition 218 (the “Right to Vote on Taxes Act” of 1996) governed ballot measure process. Under Proposition 218, there are two options for increasing storm drain fees, they are: ‰ A positive majority vote of the affected property owners (50%+1 of the returned ballots) ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Funding Alternatives March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 8.3 ‰ A positive two-thirds majority vote of the entire electorate residing in the affected area of the proposed increase (2/3 of the returned ballots) 8.6 STATE AND FEDERAL GRANTS The federal government, through the Economic Development Administration, has in the past provided grants to assist communities with the funding of public works projects that contribute to the creation or retention of private sector jobs and to the alleviation of unemployment and underemployment. Depending on circumstances, the construction of drainage improvements identified in this SDMP may be eligible. 8.7 GENERAL FUND SUBSIDY At various times in the past, the City’s General Fund has subsidized (sometimes via loans) certain storm drainage projects and studies because of the lack of available Storm Drain Enterprise funds. However, challenged with multiple revenue shortfalls due to state funding cuts and the like, it appears that continued general fund support is unlikely. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 9.0 Recommendations The following recommended action items resulted from the preparation of the SDMP: 1. Adopt this SDMP as a guide for the development of future storm drainage facilities. 2. Develop an Engineer’s Report that will provide the justifications for the various capital improvement projects identified in this SDMP and the rationale for determining the cost allocation of the new infrastructure between the existing rate payers and future users. 3. Consider developing pump station design criteria and standards standby pumps, backup power, etc.). 4. Develop a financing structure to fund construction of the proposed improvements identified in this SDMP. 5. The formation of an assessment district should be considered to identify the fair share portions of the costs associated with constructing the improvements in watershed OS for those benefiting 6. It is recommended that as a follow-up to the adoption of this SDMP, an analysis be made to determine the fair-share proportional cost split of the proposed storm drainage facilities presented in this document between existing and future customers. 7. Actively work towards eliminating storm drainage connections to the City’s sanitary sewer system. 8. In addition to the need to construct system improvements to meet the Study Area demands, the City should also plan to repair/replace aging storm drainage infrastructure. The decision to repair or replace existing facilities should be based primarily on facility condition. 9. Conduct representative condition assessment of the existing collection system pump stations, basins, and other related facilities. This would be to determine structural condition, characterize defects, identify deficiencies, and prioritize rehabilitation and reliability improvements. This condition assessment would include: ‰ Complete closed circuit television (CCTV) and digital photo inspection on the larger diameter pipes and key portions of the system to both assess pipe conditions and identify debris or siltation obstructions. Pipes should be cleaned as necessary. ‰ Research the age and material of various segments (report on the age of the system as a percentage of pipe on the ground, etc.). ‰ Develop cost estimates associated with renewal and replacement. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 9.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN Recommendations March 2008 v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 9.2 10. Proactively address current and expected future regulatory issues and requirements regarding the management, operation, and maintenance of the system. 11. Evaluate current maintenance procedures and recommend improvements, if necessary. 12. Coordinate with MID to possibly increase the carrying capacity of their facilities to which the City discharges. 13. Coordinate with MID to monitor and report the stormwater runoff water quality being discharged into their facilities and address their concerns regarding acceptance of additional City storm drainage into their facilities. 14. It has been well documented that the MID canal system has a limited capacity. As Modesto and the surrounding areas continue to grow, that capacity will be reached well before development in the area stops. Additional outfall to area waterways will be necessary to accommodate the long-term storm water drainage needs of Modesto and the surrounding communities. 15. Continue discussions with MID regarding the possibility of the City acquiring ownership of a portion of the Cavil Drain. 16. Develop an agreement with the County and MID regarding their utilization of the City’s storm drainage facilities in the airport area (Watershed The agreement should address issues associated with operation and maintenance, water quality, erosion/sedimentation, monitoring and liability. 17. Actively develop a mechanism to construct flood control improvements to eliminate the flood hazard that impacts the City’s northeast area from offsite watershed areas. 18. Promote and facilitate incorporating dual-use elements into the design and construction of future detention basins. 19. Consider incorporating selected Low Impact Development practices and policies into the City standards. 20. Implement a flow monitoring program. ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 10.0 Acknowledgements The following individuals have actively participated in the formulation and refinement of this SDMP and their contributions are appreciated. City of Modesto Jack Bond Garner Reynolds Will Wong Violet Jakab Rich Ulm Nick Pinhey Vickey Dion Adam Denlinger John Brusca Ken Merkle Robert Howard Alan Cozby Jim Niskanen Doug Critchfield Blair Bradley Dhyan Gilton Tony Souza Patrick Kelley Amy Gedney Dan Wilkowsky Modesto Irrigation District Bill Ketscher Dave Colby Consultant/Author Stantec Consulting Inc. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 10.1 ---PAGE BREAK--- City of Modesto 2008 Storm Drainage Master Plan 11.0 REFERENCES City of Modesto Department of Public Works, “Storm Drainage, A Community Wide Problem”, October 1958. City of Modesto, 2000 Stormwater Master Plan, Volume 1, Conceptual Plan for Selected Comprehensive Planning Districts”. City Modesto, “Area Wide Map of Storm Drainage System”. City of Modesto, “Village One Specific Plan”, February 1998. City of Modesto, “Standard Specifications”, 1997 Edition. City of Modesto, “Standard Specifications, Section 4, Storm Drainage Design”, Revised October 2002. City of Modesto Stormwater Management Program, “Guidance Manual for New Development Stormwater Quality Control Measures”, January 2001. City of Modesto, “Proposed Capital Improvement Program, Fiscal Year 2002-2003 through 2011-2012”. City of Modesto Village One Facilities Master Plan (August 1992). City of Modesto, “Pelandale-Snyder Specific Plan”, August 8, 2000. City of Modesto, “Coffee/Claratina Specific Plan”, November 16, 1999. City of Modesto, “Fairview Village Specific Plan”, November 4, 1997. City of Modesto, “Roselle/Claribel Specific Plan and General Plan Amendment”, February 2001. City of Modesto, “Carver-Bangs Specific Plan”, September 7, 1999. CDM, “City of Modesto Storm Drainage Master Plan Update for the Village One Community Facilities District”, April 26, 2002. CDM, “Review of the City of Modesto’s Stormwater Design Standards in Connection with Village One CFD”, February 19, 2002. CDM, “City of Modesto, Results of the Analysis of the Village One Storm Drainage System”, February 19, 2002. Corps of Engineers, Hydrological Engineering Center, “HEC-HMS Hydrological Modeling System Version 2.1”, January 2001. v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 11.1 ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN References March 2008 dg v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 11.2 Federal Emergency Management Agency, “Flood Insurance Study, City of Modesto, California”, Revised August 17, 1982. H.I.L. Technology Inc., “City of Modesto 9th Street Flood Alleviation Scheme, Executive Overview for a Stormwater Management Control Program”, March 1989. H.I.L. Technology Inc., “City of Modesto 9th Street Flood Alleviation Scheme, Report on the Implementation of a Stormwater Management Control Program, Phases 1A & 1B”, July 1989. Jones & Stokes Associates, Inc., “City of Modesto, Empire North Unit 1 Specific Plan”, November 21, 1996. Mid-Valley Engineering Inc., “City of Modesto North Beyer Park Specific Plan”, November 26, 1996. Mid-Valley Engineering Inc., “Northgate Village Shopping Center and West Kiernan Business Park, Master Storm Drainage Plan”, May 1999. Mid-Valley Engineering, Inc., “Pelandale/Snyder, Carver/Bangs Specific Plan Areas, Preliminary Storm Drainage Design”, April 16, 1998. Mid-Valley Engineering, Inc., “Expansion of Rose Lane Storm Drainage Basin, Preliminary Hydraulic Analysis and Cost Analysis”, March 16, 1999. George S. Nolte and Associates, “City of Modesto Storm Water Management Study”, April 1976. George S. Nolte and Associates, “County of Stanislaus Department of Public Works, Storm Drainage Study and Master Plan”, November 1976. Stanislaus County Department of Public Works, “Stanislaus County Standards and Specifications, Chapter 4: Storm Drainage”, June 12, 2001. Stantec, “City of Modesto, Design Standards for Dual Use Flood Control/Recreation Facilities”, December 2000. Stantec, “Tivoli Specific Plan Storm Drainage Assessment”, January 2006. Stantec, “Evaluation of Storm Drain Cross Connections to Sanitary Sewer System”, Draft, August 4, 2006. Stantec, “Redevelopment Agency Project Storm Drain Capacity Study”, Preliminary Draft, June 2005. Stantec, “Northeast Area Updated Offsite Watershed Storm Drainage Evaluation”, Draft, March 2005. ---PAGE BREAK--- CITY OF MODESTO 2008 STORM DRAINAGE MASTER PLAN References March 2008 dg v:\52840\active\84010174\sdmp report\pdf_april2008\rpt_modesto_sdmp_finance_cmte_dft_5_april2008.doc 11.3 Stantec, “Kansas-Woodland Business Park Storm Drainage Capacity Evaluation”, June 1, 2006. Stantec, “Pelandale/McHenry Specific Plan Area Storm Drain Capacity Study”, August 21, 2006. United States Department of Agriculture, Natural Conservation Service (NRCS), “Soil Survey Eastern Stanislaus Area, California”, Issued September 1964.