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La r r y M . A l l e n , P LS Ja mi e W . V a n A g t m a e l G r e g J . Z a r t ma n , P . E S A L E M – C o r p o r a t e O f f i c e 2 5 6 4 1 9 t h S t r e e t S E S a l e m , O r e g o n 9 7 3 0 2 P 5 0 3 . 3 9 9 . 3 8 2 8 F 8 6 6 . 2 3 2 . 6 7 9 0 www.leiengineering.com MEMORANDUM To: West Coast Home Solutions, LLC From: Greg J. Zartman, P.E. Date: October 15, 2025 Pages: 16 Job Number: 60-32 – Hermanson Preserve Subject: Preliminary Stream Crossing Analysis for Deer Run Lane Connection Dear West Coast Home Solutions, This memorandum presents a preliminary stream crossing analysis for the conveyance system for the completion of Deer Run Lane as part of the Hermanson Preserve Planned Unit Development (PUD) in Woodburn, Oregon following the City of Woodburn Stormwater Drainage Master Plan (Stormwater Standards), USACE wetlands and waterbodies permit, ODFW fish passage requirements, and guidance provided for FEMA No-Rise Certification. This planned PUD is located west of Highway 99E and North of Bell Passi Road NE, Tas Lot 00100 of Marion County Assessor’s Map 06 1W 18D. The Stormwater Standards state the all conveyance systems within a primary drainageway must provide conveyance for flow from the 100-year design storm. ODFW, as provided in ODOT Hydraulics Design Manual, requires all stream crossings shall pass a 100-yr design storm and provide acceptable fish passage during High Passage design flow and Low Passage design flow, if applicable. FEMA requires that any development that takes place within a regulated floodway, with exception to very minor improvements and replacements, must be evaluated to ensure that there is no increase in base flood elevations. The base flood elevation is defined by FEMA as the water surface elevation which corresponds to the 100-yr design storm. See the attached FIRM panel for details. USACE requirements for wetland mitigation strategies and erosion control will be addressed later in the design of this stream crossing. HEC-RAS version 6.6 was used to perform the preliminary analysis of the planned Deer Run Lane connection. Design flow rates, cross sections, and water surface elevations from the Flood Insurance Study (FIS) were used in this analysis to properly compare this stormwater analysis to the FEMA effective model (eff. Jan. 19, 2000). See attached excerpts from FIS study. During the 100-yr design storm, 140 cfs of floodwater is expected to pass through the proposed Deer Run Lane connection. To provide conveyance per the Regulatory Standards, a 75” x 112” corrugated metal pipe arch will be placed in Mill Creek underneath the proposed Deer Run Lane connection. This pipe arch can pass the full 140 cfs of floodwater. However, due to the flow characteristics of the 100- yr design storm, this also causes an increase of a couple inches in water surface level upstream of the ---PAGE BREAK--- Page 2 of 2 proposed Deer Run Lane connection. This is unacceptable under the FEMA No-Rise Certification requirements. To comply with FEMA requirements, a portion of the proposed Deer Run Lane was lowered, allowing floodwater to overtop the road during the 100-yr design storm event. This lowered section of road will be armored to prevent erosion during the 100-yr design storm event. Two 24” relief culverts have also been added to maintain natural stream course during the 100-yr design storm event. The combination of pipe arch, lowered section of road, and relief culverts allow the proposed Deer Run Lane connection to convey the 100-yr design storm event with no meaningful increase in the water surface elevation upstream of the development. See attached HEC-RAS outputs and site plan sheet SP-3. The planned Deer Run Lane connection meets all regulatory requirements of the aforementioned government agencies, as preliminarily designed. Please don’t hesitate to call or email me with any questions. Thank you. Sincerely, LEI ENGINEERING & SUREYING OF OREGON, LLC Greg J. Zartman, P.E. Principal Engineer ---PAGE BREAK--- AREA OF INTEREST ---PAGE BREAK--- Flooding Source and Location Glenn Creek (Square Miles) 10-Year 50-Year 100-Year 500-Year Just of Wallace Road 3.7 265 365 410 535 Just of Glenn Creek Road 2.72 210 290 325 425 Just upstream of confluence of Unnamed Tributary footbridge 2.15 175 245 275 355 Just of Fernwood Court 1.79 155 215 240 260 Lake Labish Ditch At Burlington Northern Railroad 63.83 I 611 At confluence with East Fork Pringle Creek and Pringle Creek 5.7 8202 1,2403 1,4503 2,1003 At confluence with West Fork Pringle Creek 2.4 270 510 800 1,280 Mill Creek A (Near Woodburn) At Cross Section A 11.8 700 1,020 1,170 1,510 At Cross Section D 10.8 640 940 1,080 1,400 At Cross Section J 9.2 550 810 920 1,200 AtCrossSection0 7.6 460 670 770 1,010 At Cross Section R 7.1 430 620 720 940 At Cross Section U 6.3 390 570 650 840 At Cross Section W 5.3 320 480 550 710 At Cross Section AB 4.5 230 340 390 510 At Cross Section AD 3.8 210 310 350 450 At Cross Section AH 3.7 200 300 340 440 At Cross Section AK 3.3 180 270 300 390 At Cross Section AO 2.2 140 210 240 310 At Cross Section AZ 1.9 125 180 210 270 At Cross Section BB 1.2 80 120 140 170 Table 4. Summary of Discharges (Cont'd) Drainage Area Peak Discharges (Cubic Feet per Second) Middle Fork Pringle Creek 1Data not applicable 2Urbanized runoff from Pringle Creek basin 3Overflow from Mill Creek ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- BD BE CENTERLINE OF PROPOSED CROSSING ---PAGE BREAK--- 0 100 200 300 400 500 600 700 165 170 175 180 185 190 Stormwater Conveyance_Existing Plan: Plan 01 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Crit 100-yr Ground Bank Sta .05 . 0 3 5 .05 CROSS SECTION BD ---PAGE BREAK--- 0 100 200 300 400 168 170 172 174 176 178 180 Stormwater Conveyance_Existing Plan: Plan 01 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Ground Bank Sta .05 . 0 3 5 .05 CROSS SECTION AT CENTERLINE OF PROPOSED CROSSING ---PAGE BREAK--- 0 100 200 300 400 500 600 170 172 174 176 178 180 182 184 186 Stormwater Conveyance_Existing Plan: Plan 01 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Ground Bank Sta .06 . 0 3 5 .05 CROSS SECTION BE ---PAGE BREAK--- HEC-RAS Plan: FEMA1 River: Mill Creek Reach: Mill Creek Profile: 100-yr Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Mill Creek 2200 100-yr 140.00 169.66 174.200 174.20 0.000064 0.74 401.32 264.13 0.07 Mill Creek 2100 100-yr 140.00 169.81 174.191 174.20 0.000094 0.87 333.69 222.06 0.08 Mill Creek 2000 100-yr 140.00 169.84 174.185 174.19 0.000063 0.71 383.14 222.20 0.07 Mill Creek 1900 100-yr 140.00 169.84 174.178 174.18 0.000067 0.75 401.49 246.17 0.07 Mill Creek 1821 100-yr 140.00 170.14 174.174 174.18 0.000049 0.69 427.22 227.11 0.06 Mill Creek 1700 100-yr 140.00 169.31 174.168 174.17 0.000039 0.65 450.25 247.85 0.06 Mill Creek 1600 100-yr 140.00 169.36 174.164 174.17 0.000040 0.68 460.92 246.92 0.06 Mill Creek 1500 100-yr 140.00 169.00 174.162 174.16 0.000030 0.46 533.99 259.49 0.04 Mill Creek 1400 100-yr 140.00 169.22 174.159 174.16 0.000026 0.38 555.48 275.76 0.03 Mill Creek 1299 100-yr 140.00 170.01 174.158 174.16 0.000008 0.28 1073.51 563.64 0.02 Mill Creek 1200 100-yr 140.00 169.75 174.158 174.16 0.000008 0.30 891.63 362.83 0.03 Mill Creek 1100 100-yr 140.00 169.47 174.156 174.16 0.000013 0.38 700.71 280.62 0.03 Mill Creek 1000 100-yr 140.00 169.20 174.155 174.16 0.000013 0.40 679.10 270.65 0.03 Mill Creek 899 100-yr 140.00 169.16 174.154 174.15 0.000009 0.35 719.30 240.69 0.03 Mill Creek 863 100-yr 140.00 168.93 174.153 174.15 0.000011 0.38 685.13 244.02 0.03 Mill Creek 819 100-yr 140.00 168.63 174.153 174.15 0.000008 0.32 785.74 264.34 0.03 Mill Creek 800 100-yr 140.00 168.46 174.153 174.15 0.000008 0.33 770.88 260.96 0.03 Mill Creek 700 100-yr 140.00 168.08 174.152 174.15 0.000008 0.31 787.44 256.97 0.02 Mill Creek 599 100-yr 140.00 167.66 174.151 174.15 0.000007 0.31 834.47 270.85 0.02 Mill Creek 500 100-yr 140.00 167.78 174.151 174.15 0.000006 0.33 846.58 262.23 0.02 Mill Creek 400 100-yr 140.00 168.41 174.151 174.15 0.000001 0.13 1175.82 255.06 0.01 Mill Creek 300 100-yr 140.00 168.62 174.151 174.15 0.000001 0.13 1106.58 250.54 0.01 Mill Creek 200 100-yr 140.00 168.69 174.151 174.15 0.000001 0.13 1147.70 264.52 0.01 Mill Creek 124 100-yr 140.00 168.55 174.150 174.15 0.000001 0.15 1111.88 261.53 0.01 Mill Creek 34 100-yr 140.00 168.81 174.150 174.15 0.000004 0.24 961.66 269.13 0.02 Mill Creek 20 100-yr 140.00 167.85 174.150 169.75 174.15 0.000004 0.28 926.80 255.06 0.02 BE BD CENTERLINE OF PROPOSED CROSSING ---PAGE BREAK--- BD BE CENTERLINE OF PROPOSED CROSSING ---PAGE BREAK--- 0 100 200 300 400 500 600 700 165 170 175 180 185 190 Stormwater Conveyance_Proposed Plan: Plan 04 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Crit 100-yr Ground Bank Sta .05 . 0 3 5 .05 CROSS SECTION BD ---PAGE BREAK--- 0 100 200 300 400 166 168 170 172 174 176 178 180 182 Stormwater Conveyance_Proposed Plan: Plan 04 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Crit 100-yr Ground Ineff Bank Sta .05 . 0 3 5 .05 CROSS SECTION AT CENTERLINE OF PROPOSED CROSSING ---PAGE BREAK--- 0 100 200 300 400 500 600 170 172 174 176 178 180 182 184 186 Stormwater Conveyance_Proposed Plan: Plan 04 10/2/2025 Station (ft) Elevation (ft) Legend EG 100-yr WS 100-yr Ground Bank Sta .06 . 0 3 5 .05 CROSS SECTION BE ---PAGE BREAK--- HEC-RAS Plan: Test2 River: Mill Creek Reach: Mill Creek Profile: 100-yr Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Mill Creek 2200 100-yr 140.00 169.66 174.204 174.21 0.000063 0.74 402.54 264.15 0.07 Mill Creek 2100 100-yr 140.00 169.81 174.195 174.20 0.000093 0.86 334.55 222.27 0.08 Mill Creek 2000 100-yr 140.00 169.84 174.189 174.19 0.000063 0.71 384.01 222.38 0.07 Mill Creek 1900 100-yr 140.00 169.84 174.182 174.18 0.000067 0.75 402.47 246.35 0.07 Mill Creek 1821 100-yr 140.00 170.14 174.178 174.18 0.000048 0.69 428.12 227.22 0.06 Mill Creek 1700 100-yr 140.00 169.31 174.172 174.18 0.000038 0.65 451.25 247.96 0.06 Mill Creek 1600 100-yr 140.00 169.36 174.168 174.17 0.000040 0.67 461.92 247.13 0.06 Mill Creek 1500 100-yr 140.00 169.00 174.166 174.17 0.000030 0.46 535.05 259.58 0.04 Mill Creek 1400 100-yr 140.00 169.22 174.163 174.16 0.000022 0.48 555.95 275.78 0.04 Mill Creek 1299 100-yr 140.00 170.01 174.163 174.16 0.000008 0.27 1075.95 565.91 0.02 Mill Creek 1200 100-yr 140.00 169.75 174.162 174.16 0.000008 0.30 893.48 362.92 0.03 Mill Creek 1099 100-yr 140.00 169.48 174.161 174.16 0.000013 0.39 700.35 280.71 0.03 Mill Creek 999 100-yr 140.00 169.18 174.159 174.16 0.000013 0.40 680.55 270.67 0.03 Mill Creek 899 100-yr 140.00 169.16 174.158 170.89 174.16 0.000009 0.35 709.15 240.76 0.03 Mill Creek 863 Culvert Mill Creek 819 100-yr 140.00 168.63 174.153 170.85 174.15 0.000008 0.33 741.29 264.24 0.03 Mill Creek 799 100-yr 140.00 168.46 174.153 174.15 0.000008 0.33 770.88 260.96 0.03 Mill Creek 699 100-yr 140.00 168.08 174.152 174.15 0.000008 0.31 787.44 256.97 0.02 Mill Creek 599 100-yr 140.00 167.66 174.151 174.15 0.000007 0.31 834.35 270.90 0.02 Mill Creek 500 100-yr 140.00 167.78 174.151 174.15 0.000006 0.33 846.58 262.23 0.02 Mill Creek 400 100-yr 140.00 168.41 174.151 174.15 0.000001 0.13 1176.04 255.04 0.01 Mill Creek 300 100-yr 140.00 168.62 174.151 174.15 0.000001 0.13 1106.82 250.63 0.01 Mill Creek 200 100-yr 140.00 168.69 174.151 174.15 0.000001 0.13 1147.79 264.45 0.01 Mill Creek 123 100-yr 140.00 168.55 174.150 174.15 0.000001 0.15 1111.88 261.53 0.01 Mill Creek 34 100-yr 140.00 168.81 174.150 174.15 0.000004 0.24 961.66 269.13 0.02 Mill Creek 20 100-yr 140.00 167.85 174.150 169.75 174.15 0.000004 0.28 926.80 255.06 0.02 BE CENTERLINE OF PROPOSED CROSSING BD