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City of Fernley Department of Public Works DESIGN STANDARDS 10.0 - STORMWATER DRAINAGE 10.1 GENERAL 10.1.1 DRAINAGE REPORT All developments of land shall submit for approval, unless waived by Public Works, a drainage report signed and stamped by a Nevada Registered Civil Engineer in accordance with Public Works standards. Permits: Where the permit relates to coverage of 10,000 or more square feet of impervious surface within the property. Where development is in a critical drainage area as defined by the City Engineer. Grading permit which entails 20,000 sq. ft. or greater. Improvement plans. Where required by Public Works. The drainage report shall be based on current zoning, the proposed development, or Master Plan whichever process produces the greater runoff. 10.1.2 RETENTION/DETENTION Whenever a drainage report indicates that the 5-year storm runoff from a development cannot be handled by the existing onsite retention system, the developer is to upgrade the existing system to accommodate the runoff; or provide on-site detention and controls for acceptable disbursement into the system; or provide an on-site infiltration or retention system verified by the Engineer-of- Record to be adequate to accommodate the increase in runoff. Infiltration systems shall require a minimum percolation test rate of sixty (60) minutes per inch as basis of design. The operation and maintenance of such a system is the responsibility of the property owner or homeowner's association. Prior to Improvement Plan approval, an operations and maintenance agreement must be signed by property owner or homeowner’s association. Multi-use ponds such as detention ponds that also serve as parks or soccer fields are encouraged. The slopes and depths must be consistent with public health and safety concerns. Such basins will be reviewed on a case-by-case basis. 10.1.3 MAXIMUM CAPACITY Discharge of storm drain waters into a major drainage facility or natural water course when added to the 100-year peak flow of storm drainage runoff must not exceed the existing capacity of said drainage facility or natural water course. For consideration by Public Works, the Engineer-of- Record must provide conclusive proof in the drainage report that any increase in peak flow will not adversely affect or cause damage to any property along said drainage facility or water course now or in the future, based on existing zoning, the proposed development, or the master plan and elements thereof, whichever is more restrictive. 10.1.4 IMPACTS ON EXISTING DRAINAGE Development of property shall not adversely affect any natural major drainage facility or natural water course. Natural facilities shall remain in as near to the natural state as is practicable, with any modification proposed, including any erosion mitigating measures, addressed in the drainage report and drainage plan. SD-1 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.1.5 SAFETY Fencing shall be provided to prevent public access to drainage facilities when the flows, velocity, or side slope indicate a potential safety issue, as determined by the Drainage Report. 10.1.6 DRAINAGE FACILITY DELINEATION All storm drainage relating to a subdivision or development shall be collected on-site by facilities to accommodate the storm drain waters for the 5-year return frequency storm flow, both entering the site and generated on-site and piped in accordance with Public Works standards to an existing adequate public storm drain system, major drainage facility or natural watercourse. Where by reason of terrain or other circumstances, Public Works determines that piping storm drain waters is inappropriate or unnecessary, alternative methods of transporting such waters may be approved in lieu of piping. Storm drain waters generated within the boundaries of a subdivision or development which discharge from a public drain system onto and across private property require that a permanent easement for access and maintenance be dedicated to the City from the subdivision or development boundary to the point of discharge into an existing public storm drain system, major drainage facility or natural water course. The easement shall be adequately fenced on both sides at the time of construction of the drainage feature. The drainage feature shall be constructed of an impermeable, permanent surface in which private fencing cannot interrupt the feature and the feature cannot be removed or filled in by Homeowners. The drainage feature, if terminating onto a public street, shall be gated such that unauthorized personnel, including off-road vehicles cannot enter. Locks for the gates must be provided to Public Works at final acceptance of the work. 10.2 DRAINAGE REPORT The following criteria shall be considered for a Drainage Report. A drainage report will be required with the submittal, or prior to the submittal of, improvement plans. Standards for Drainage Report - The report is required to identify problems and present solutions with engineering documentation. Tabulated data on maps is preferred to written descriptions except for unusual items such as detention, complex hydrologic analysis, etc. 10.2.1 TITLE PAGE a) Project name. b) Preparer's name, firm, date. c) Professional engineer's seal of preparer and signature. 10.2.2 INTRODUCTION a) Site location: i. Street location, assessor's parcel number(s), and section reference. ii. Adjacent developments. b) Site description: i. Topography, ground cover, etc. ii. Existing drainage facilities, major drainage facilities, flood hazard areas, TCID drainages or irrigation ditches, and other site conditions that must be considered. c) Proposed project description. d) Other previous studies relevant to site. SD-2 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.2.3 HISTORIC DRAINAGE SYSTEM (DISCUSS THE FOLLOWING) a) Major basins: i. Relationship to major drainage facilities. ii. Major basin drainage characteristics (topography, runoff, cover, use, erosion, etc.). b) Sub-basin and site drainage (i and ii may be tabulated on map): i. Minor (5-year) and major (25-year) storm flows for each sub-basin affecting the site. ii. Existing drainage patterns: channelized or overland flow, point of discharge, etc. iii. Effect of historic flows on adjacent properties. 10.2.4 PROPOSED (DEVELOPED CONDITION) DRAINAGE SYSTEM (DISCUSS EACH OF THE FOLLOWING) a) Criteria: i. Size of major basins and tributary sub-basins. ii. Hydrologic method to be used for analysis (Rational, SCS, HEC, etc.). iii. Design storm intensities for minor (5-year, 6-hour duration) and major (25- year, 6-hour duration) events or as required by the City Engineer. b) Runoff: i. Historic storm flow rates and paths. ii. Developed condition storm flow rates and paths for minor and major storms. c) Piping: i. Design the storm drain system to pass the 5-year, 6-hour storm including all improvements. ii. Verify storm flows from inlets to ultimate outlets of the drainage system. d) Detention of 25-year, 6-hour storm(s) is required based on unconstrained conditions For example, if the piped system cannot convey the 5-year flow, the peak outflow shall be controlled to match the system capacity. In addition, if the overland flow or drainage channels cannot convey flows in excess of the 5- year storm, additional detention or controls may be required as determined by the City Engineer. Provide discussion on each of the following: i. Volume required and provided for zero increase in peak flows. ii. Release rates and method of release. iii. Passage of storms exceeding the 5-year up to and including the 25-year. iv. Provide for an emergency overflow which will not cause a direct impact to neighboring sites. v. Engineer-of-Record to provide detailed description of constraints (or none) and design calculations on how to mitigate the problem. vi. Need for detention shall be clearly identified in the preliminary or schematic report and the necessary detention area shall be identified on preliminary plans. e) Streets (This information may be shown on the plans.): i. Depth and velocity of flow for major and minor storms. SD-3 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS ii. Drainage system. f) Open channel flow (This information may be shown on the plans.): i. Type. ii. Depth and velocity. iii. Freeboard. g) Storm drains and culverts (Show all data on plans.) 10.2.5 AREAS WITHIN FLOOD HAZARD ZONE WHEN APPLICABLE a) Impacts. b) Protection. c) Compliance with Federal Emergency Management Administration (FEMA) requirements and RMC 12.24, "Flood Hazard Areas". 10.2.6 CONCLUSIONS - DISCUSS IMPACT OF IMPROVEMENTS a) Benefits. b) Adverse effects with solution to mitigate adverse impacts. 10.2.7 APPENDICIES a) Hydrologic and hydraulic computations: 1) List and explain basic assumptions and input factors used: a) Tabularized and/or discussed as necessary. b) Indicate any sensitivity analysis performed. c) Include source tables and references for parameters, such as soils groups, SCS curve numbers, C values, n values, etc. 2) Historic runoff: a) Off-site. b) On-site. 3) Developed runoff: a) Off-site. b) On-site. 4) Detention for up to and including the 25-year, 6-hour storm. 5) Hydraulic computations: a) Hydraulic grade line (HGL) minor storm. b) Hydraulic grade line (HGL) major storm. c) Inlet/outlet calculations. b) Drainage plan: 1) Site location map - On a USGS map or larger, as appropriate, show relation of site to major drainage basin and sub-basin. Show flood hazard areas if applicable and off-site flows through project. Show SCS soils map and applicable soil descriptions where appropriate. 2) Site drainage plan: a) Show the existing and proposed contours at least 100 feet beyond property line. SD-4 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS b) The site drainage plan should be at the same scale as the grading plan. Show all sub-drainage areas per catch basin or channel and tabulate existing and proposed drainage showing length, assumed velocity and time of concentration on various runs of grass, gutters, etc., cumulative time of concentration, average rainfall intensity, area, runoff coefficient (adjusted if necessary), and peak flows for 5- and 25-year, 6-hour storms. c) All inlets and manholes shall be labeled to correspond to tabular numbering system. Pipe sizes, grades, velocities, peak flows and hydraulic grade lines shall be shown for all parts of the system in a tabular form on the plans. d) Both location plan (overall drainage) and sub-drainage plan shall be signed and sealed by a Nevada Registered Civil Engineer and shall be included in the construction plans for the subdivision/development. Tables detailing design data of rational formula and inlet and pipe and channel design to be shown on plan. e) On grading plans show peak flows for 5- and 25-year storms at inlets, in pipes and other sub-basin points of concentration and at discharge points and in channels. Show peak flows entering and leaving the site; trace path leaving site to nearest major drainage facility without adverse impact to owners. f) On plan and profile sheets, show peak flows for 5- and 25-year storms at all inlets and in pipes as per above, and in pipes show slope, velocity, and capacity, and hydraulic grade line if above top of pipe. 3) Bench marks - To be shown on plans with description and elevation. 4) Existing and proposed property lines. 5) Existing and proposed drainage easements. 6) Street names, grades, widths and rights-of-way or easements. 7) Routing and cumulative flows at the upstream and ends of the site and at various critical points on-site for both minor and major runoff. Inflow and outflow for both storms for all sub-basins. 8) Street cross sections showing 100-year flood elevations. 9) Existing and proposed major drainage facilities. 10) Open channel flow in major channels shall be provided with the following information on plans: a) Channel and hydraulic grade line (HGL) profiles. b) Cross sections and required rights-of-way at 100 foot intervals. c) Location and size of all existing and proposed structures. d) Channel section and lining details. e) Freeboard for 100-year flows. f) Channel capacity and storm flows, 5- and 25-year flows and velocities. 11) Storm sewers (show on plans): a) Hydraulic grade line (HGL) profiles. b) Location and size of all existing and proposed structures. c) Proposed materials. d) Pertinent elevations and slopes. e) Pipe capacity and 5- and 25-year flows and velocities. SD-5 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.3 DESIGN REQUIREMENTS (PUBLIC AND PRIVATE) 10.3.1 MANNING’S ROUGHNESS COEFFICIENT Manning’s Formula is to be used in computing capacities of all open channels and closed conduits with the following minimum values for roughness coefficient PVC or ABS 0.012 Concrete 0.014 Corrugated Metal Pipe 0.015 Corrugated Metal Pipe (paved 0.019 Corrugated Metal (plain) 0.024 Open channels with gunite lining 0.019 Open channels with paved 0.025 Earth channels (no rock or 0.030 Rock or gravel per approved Engineers Manual based on size and placement of materials. 10.3.2 METHODS The Rational Method may be used in computations for the rate of runoff for urban and small watersheds 100 acres or less. The SCS method, SCS TR-55 "Urban Hydrology for Small Watersheds" and HEC may be used for small or larger watersheds. Watersheds in excess of 500 acres shall utilize HEC-1 method only. In addition to the criteria described herein, all development shall provide emergency flow paths for a storm event with a 100- year return period, 6-hour duration. 10.3.2.1 THE RATIONAL METHOD a) The design flow for the Rational Method is expressed as: Q = CiA, where: Q = peak rate of runoff, cubic feet per second C = runoff coefficient i = average rainfall intensity, inches per hour A = watershed area, acres b) The following listed runoff coefficients, depending on future use, shall be used: NOTE: An adjusted C value may be required in special conditions such as very small lots with large houses or duplexes. SD-6 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS RUNOFF COEFFICIENTS Land Use Type Runoff Coefficient Rural 0.25-0.35 Single Family Residential 0.45-0.60 Multi-Residential 0.60-0.70 Neighborhood Commercial 0.85 Community Commercial 0.85 Tourist Commercial 0.85 Office 0.85 Manufacturing 0.85-0.90 Distribution and Warehousing 0.85-0.90 Public Facility 0.50-0.85 Pavement and Concrete Surfaces 0.90-0.95 Park 0.25 Open Space (0-5% grade - vegetated) 0.20-0.30 Open Space (0-5% grade - no vegetation) 0.30-0.40 Open Space (5-15% grade - vegetated or unvegetated) 0.40-0.50 Open Space (Over 15% grade - sparsely vegetated, rock or clay soils) 0.40-0.60 c) The rainfall intensity curve included in this Guideline on page SD-14 shall be used for determining the average intensity. The time of concentration, with a minimum build up time of 10 minutes is expressed as: tci = 10 or 60 × V L , whichever is greater where: tci = time of concentration at initial inlet, minutes L = length from uppermost point of watershed inlet, feet V = channel or overland velocity, feet per second Given the time of concentration at a design point, the time of concentration at the next design point is determined by adding travel time, expressed as: 60 × = V L t where: t = travel time, minutes L= length of channel or conduit between design points, feet V = channel or conduit velocity, feet per second SD-7 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.3.3 VELOCITY Minimum design velocity shall be 3 feet per second for storm drains. 10.3.4 OVERLAND FLOW Overland flow is to be provided for and channelized within dedicated easements or public right-of-way to protect structures from flood during periods of rainfall-intensity storms that exceed the 5-year storm, up to and including the 25-year return frequency storm. 10.3.5 MAINTENANCE ACCESS Easements with improved vehicular access in accordance with City standards shall be provided to publicly owned storm drain manholes, storm drain inlets and outlets, channels, storm drain ponds and to associated structures not located within an improved street section. Access shall include fencing on both sides of the easement, access gate and lock, and permanent, impervious surface. Easements for access to and maintenance of the 25-year storm floodway associated with a major drainage facility or natural water course are to be provided to the City. Improved vehicular access in accordance with Public Works standards shall be provided when determined necessary by Public Works. Access shall include fencing on both sides of the easement, access gate and lock, and permanent, impervious surface. 10.3.6 LOCATION Surface drainage from any developed area shall not cross any property line except by way of a natural watercourse, major drainage facility, an approved drainage system within a public storm drain easement, or a permanent surface drainage easement. Existing surface drainage from adjoining property shall be perpetuated through the development, or other means of disposal provided, acceptable to Public Works. 10.3.7 FUTURE DEVELOPMENT Storm drain facilities shall be extended with in a subdivision or development to adjacent undeveloped properties for future extensions in accordance with approved drainage plans, unless otherwise approved by Public Works. Drainage shall not be diverted from one major drainage facility to another. 10.3.8 SEPARATE CONVEYANCE Irrigation waters and public storm drain waters shall be conveyed by separate systems, unless specifically approved by TCID. All plans adjacent to or containing an irrigation ditch shall require the signature of TCID on the plans. 10.3.9 CHANNEL LINING Lining for drainage channels shall conform to the following requirements: a. Major drainage channels within easements or to detention facilities shall either be piped or concrete. b. Minor channels may be earthen or of a material suitable to Public Works. c. Access road to be constructed when required. SD-8 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS Storm drain waters piped to a major drainage facility shall extend, at a minimum, to the 25- year flood line and be rip-rapped from the outlet to the bottom of the channel in the direction of flow. Channel modifications for erosion control shall be designed so that the receiving channel or entering channel will contain the flows without erosion. 10.3.10 PIPING REQUIREMENTS Constructed public drainage facilities with design flows of 60 cubic feet per second or less shall be piped in accordance with Public Works standards. Constructed drainage facilities with flows exceeding 60 cubic feet per second may be open channel construction in accordance with Public Works standards, when approved by Public Works. 10.3.11 PIPE CLASS All storm drain piping 36" and larger in diameter located within the City right-of-way shall be a minimum of RCP Class III or the appropriate class when design requires higher pipe support strength. Storm drain piping smaller than 36" shall be RCP Class III or solid wall plastic pipe with a minimum stiffness of 46 psi as specified in the Orange Book. Individual catch basin leads may be constructed of un-reinforced concrete pipe, Class III or solid wall plastic pipe with minimum stiffness of 46 psi as specified in the Orange Book. Corrugated metal pipe (CMP) for public improvements may be used only at specific locations approved by Public Works. Headwalls or culvert extensions with rip-rap shall be required on CMP culverts. (See Section 10.3.13) 10.3.12 PIPE DIAMETER Minimum pipe diameter for any public storm drain shall be 12-inch except for individual catch basin leads not exceeding 80 feet in length which may be 10-inch minimum diameter. Driveway culverts shall be 12-inch minimum CMP or RCP per specific review and approval by Public Works. Headwalls will be required on all driveway culverts. 10.3.13 HEADWALLS Standard headwalls shall be placed on the inlet and outlet of all public pipe culverts; flared end sections may be used only with approval of Public Works. For pipes up to and including 72 inches in diameter: the design, size, and material used shall comply in all cases with Public Works standards. Headwalls for pipes exceeding 72 inches require special design approved by Public Works. A minimum three steel "C"-shaped tie-backs per joint shall connect the last two pipe segments and the flared end section. Holes are to be grouted and tie-backs encased in concrete. 10.3.14 TRASH RACKS Trash racks shall be provided at the upstream and end of all closed public conduits as approved by Public Works. 10.3.15 SWALES Reinforced concrete interceptor swales are to be provided along the top of retaining walls and cut slopes to intercept drainage. Discharge shall be into an approved drainage facility. All backlot drainage shall utilize reinforced concrete swales to intercept drainage from adjacent property and shall include easements, fencing, and gates. SD-9 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.3.16 MANHOLES Manholes for public improvements shall be located at junction points, changes in horizontal or vertical alignment exceeding the maximum allowable pipe deflection, changes in conduit size and at the end of public lines unless approved otherwise by Public Works. When permitted by Public Works, pipe may be placed on curves (horizontal and vertical) and shall meet manufacturer's recommendations for curved alignment. All curves, radii, length of pipe joints, and types of pipe shall be shown on the plans. Manholes shall be spaced at intervals not greater than 350 feet for pipe sizes of 21 inches and smaller and at 600 feet maximum spacing for pipe sizing of 24 inches and larger, unless otherwise approved by Public Works. All manholes with a barrel diameter greater than 48 inches shall require installation of a 36 inch diameter lid. Concrete collars shall be placed around all manholes, valves or other appurtenances within any right-of-way or easement. Such collars shall encircle all casting with a minimum width of one foot. Manhole collars shall conform to standard details; all others shall extend to a minimum depth of one foot. 10.3.17 CATCH BASINS Catch basins shall be installed at low points of roadways and/or vertical curves, at all major street intersections, and at sufficient intervals to intake the peak flow for the 5-year storm runoff such that flows will not interfere with traffic or flood adjoining property. In no instance shall the flow of water from the 5-year storm extend more than halfway onto the lane adjacent from the curb. Streets without parking lanes will require more frequent inlet locations. Laterals from catch basins are to tie into manholes or into the main storm drain line in the direction of flow. Catch basins shall not tie into each other unless otherwise approved by Public Works. Flow along gutters and into inlets shall be computed by the Rational Method using coefficients based on zoning and ultimate future development. “Sur- trap” grease traps or an approved equal shall be installed within all catch basins. Alternate means of sediment and petroleum control, such as sand oil separators, "Storm-ceptor", etc., may be approved in lieu of a “sur-trap” grease traps. 10.3.18 STRUCTURES Drainage structures under and/or through all streets shall be designed to carry the runoff generated by the 25-year storm from fully developed conditions within the watershed, based on maximum density and in accordance with current zoning. 10.3.19 EASEMENTS Storm drain easements for public improvements shall be a minimum width of 10 feet. The final easement width shall be determined by pipe width, required trench clearance, and excavated trench side slopes not less than 1:1 horizontal to vertical, unless approved Public Works. 10.3.20 VALLEY GUTTERS Reinforced concrete valley gutters for public improvements may be placed at street intersections only when approved by Public Works. 10.3.21 CURB AND GUTTER All impermeable on-site private drainage shall be contained by Portland Cement concrete curb and gutter or longitudinal valley gutter to Public Works standards. SD-10 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.3.22 EMBANKMENTS Embankments shall not be placed within the 100-year flood plain of a major drainage facility without prior approval by Public Works. Where such approval is given, the embankment shall be faced with riprap to a minimum of 1 foot above the 100-year flood line. 10.3.23 NDEP APPROVAL Any work which requires fill intended to be placed within the "waters of the State of Nevada" shall receive permission from the State Department of Environmental Protection prior to beginning construction. Public Works shall receive a copy of this permission prior to issuance of any permit. The U.S. Army Corps of Engineers may require permitting for projects involving “waters of the State of Nevada and/or the United States”. Contractors will be required to prepare Storm Water Pollution Prevention Plans for all disturbances in excess of one acre. 10.3.24 NDOT PERMIT Prior to issuance of any permit for any facility encroaching on state right-of-way, and for disposal of any drainage onto state right-of-way, the approved NDOT encroachment permit shall be furnished to Public Works. 10.3.25 SAND-OIL SEPARATORS At the direction of Public Works, sand-oil separators will be required for storm drainage installations that drain parking lots or other areas that have the potential to contribute sediment or oil to the storm water runoff. The separators shall be constructed in accordance with Public Works Standard Details. 10.4 LOT DRAINAGE SWALES (PRIVATE) 10.4.1 REQUIREMENTS Surface drainage swales collecting runoff from the area of 2 or more lots are to be concrete in accordance with Public Works standards and are to be fenced and gated at the time of construction of the swale. The swale shall be maintained and perpetuated by the property owners. Paving is not required for common side lot swales serving only 2 adjacent lots. 10.4.2 EASEMENTS Easements for rear lot drainage swales shall be established by a note on the official plat substantially as follows: The rear 5.0 feet of Lots etc., shall be subject to a permanent private and reciprocal drainage swale easement. When Appropriate Add Which easement shall be further reciprocal with all lots the rear lot lines of which abut such easement. SD-11 May 2008 ---PAGE BREAK--- City of Fernley Department of Public Works DESIGN STANDARDS 10.4.3 DESIGN Standard lot line drainage swales are to be designed to carry the waters generated by a 25- year 6 hour frequency storm, with a maximum of 6 lots contributing run-off to the swale. Discharge from swales shall be conveyed to a central drainage facility. Should it be necessary to provide for drainage from more than 6 lots and/or to exceed the maximum horizontal or vertical alignment, a modified design capable of conveying the run-off from the 25-year 6 hour storm may be submitted for consideration by Public Works. 10.5 WATER SUPPLY/DRAINAGE DITCHES 10.5.1 NON-PERMITTED DISCHARGE No storm drainage runoff shall be allowed to flow or discharge into any TCID/BOR water supply ditch. Authorization for discharge into drainage facilities from urban or agricultural sources shall only be granted to established governmental entities like cities and counties and quasi-governmental entities upon approval by TCID/BOR. 10.5.2 LOCATION Where water supply ditches are located within or adjacent to a subdivision/development, improvements and access as required for the operation and maintenance of the ditch shall be provided to TCID. Any improvements within TCID easements are subject to TCID approval. 10.5.3 FENCING Property abutting or adjoining any water supply ditch shall have 54-inch fencing approved by Public Works. SD-12 May 2008