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09_Preliminary Stormwater Drainage Report
Preliminary Stormwater Drainage Report Steve Street Park Prepared for: Greenworks Prepared by: Sofi Lam and Cami Lamont Project Engineer: Jessica Zink, PE September 2025 | KPFF Project # 2400268 KPFF’S COMMITMENT TO SUSTAINABILITY As a member of the US Green Building Council, KPFF is committed to the practice of sustainable design and the use of sustainable materials in our work. When hardcopy reports are provided by KPFF, they are prepared using recycled and recyclable materials, reflecting KPFF’s commitment to using sustainable practices and methods in all of our products. City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Designer’s Certification and Statement “I hereby certify that this Stormwater Drainage Report for the City of Tigard – Steve Street Park has been prepared by me or under my supervision and meets the minimum standards of the City of Beaverton and normal standards of engineering practice. I hereby acknowledge and agree that the jurisdiction does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities designed by me.” Jessica Zink, PE 91718PE EXPIRATION DATE: OREGON 6/30/2024 2025.09.12 15:14:45 -07'00' 06/30/26 DIGITALLY SIGNED EXPIRATION DATE: City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT This page left blank to facilitate double-sided printing City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Table of Contents Project Overview and Description ..................................................................................................................... 1 Existing Conditions ......................................................................................................................................... 2 Proposed Conditions ...................................................................................................................................... 2 Methodology ...................................................................................................................................................... 2 Water Quality Treatment ............................................................................................................................... 3 Hydromodification Assessment ..................................................................................................................... 4 Conveyance ........................................................................................................................................................ 4 Operations and Maintenance ............................................................................................................................ 4 Tables and Figures FIGURE 1: Vicinity Map ...................................................................................................................................... 1 TABLE 1: On-Site Existing and Post-Development Areas ................................................................................... 2 TABLE 2: Required Treatment Area (Basin A & E).............................................................................................. 3 TABLE 3: Basin Areas and Treatment Type ........................................................................................................ 3 TABLE 3: Existing and Post-Development Flows ................................................................................................ 4 Appendices Appendix A Basin Map Appendix B Hydraflow Modeling Appendix C Water Quality Calculations Appendix D Conveyance Calculations Appendix E Operations and Maintenance Plan 1 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Project Overview and Description This report describes the stormwater management design strategies for the proposed development. The basis for this report is the Clean Water Services requirements. The purpose of the proposed stormwater management facilities is to protect existing public stormwater infrastructure and to improve the overall health of the watershed. The 1.5-acre Steve Street Park property is located near the intersection of Highway 217 and Pacific Hwy W in Tigard, Oregon, at the north end of SW 84th Avenue. The site lies within the Fanno Creek Watershed. The proposed park improvements include a paved loop trail, three play areas, and a paved turnaround area at the end of SW 84th Ave. The improvements will be accessible to all and will provide ADA compliant trails, play areas, and parking. The runoff from the disturbed impervious area and new impervious area will be collected and treated by a stormwater facility. FIGURE 1: Vicinity Map 2 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Existing Conditions The topography of the site has a high point on the south edge of the property and slopes down towards the north edge of the site. The existing site is almost completely vegetated with grass areas and outer tree coverage. See Appendix A for the Existing Conditions Basin Map. The existing stormwater onsite is primarily untreated as most of the project site is undeveloped. The majority of the existing runoff sheet flows along the vegetated surface into the existing wetland located on the north edge of the site. There is an existing water quality facility located on the southern portion of the site. This facility treats runoff collected by the catch basins along SW 84th Ave. Overflow from the facility is piped through a storm drain located in a 20 ft wide storm and sanitary sewer easement that runs on the eastern edge of the project site. See Appendix A for the Existing Conditions Basin Map. Proposed Conditions The proposed improvements include the construction of a new turnaround area with an adjacent curb, gutter, and sidewalk. Additionally, there will be a series of concrete and wood chip trails connecting 3 playground structures throughout the park. The project will minimize the amount of new impervious areas by using pervious surfaces as much as possible. However, to ensure ADA compliance for the looped trail, turnaround, and play areas, these surfaces will be impervious, ultimately adding approximately 17,101 sf of imperious area. See Table 1 below for the total existing and proposed impervious areas for the site. TABLE 1: On-Site Existing and Post-Development Areas Description Impervious Area (sf) Pervious Area (sf) Total Area (sf) (acres) Existing 865 66,154 67,019 1.54 Post-Development 17,996 49,053 67,019 1.54 The proposed storm design will collect and treat runoff from the offsite turnaround area and the onsite park. The offsite area includes the turnaround area and the sidewalk adjacent to the turnaround area. The concrete sidewalk and pavement drainage in the turnaround area is collected by a catch basin. The catch basin is piped to the onsite storm system. The onsite storm system includes a network of pipes collecting runoff from the turfed playground areas and the offsite improvements to the stormwater facility onsite. The stormwater facility will be a flow-through lined stormwater plater and contain a flow control structure to meet hydromodification requirements before it is piped into the 12” City owned storm line located in the storm and sanitary sewer easement. The proposed loop trail will have both concrete and mulch chip surfacing. These areas will sheet flow into the onsite stormwater facility. Methodology The proposed stormwater management systems are designed in accordance with Clean Water Services. The proposed storm design will collect and treat runoff from the paved turnaround, vegetative landscaping, trail loop and playground areas. The stormwater facility design was calculated utilizing the Autodesk Hydraflow Hydrograph 2024 modeling software. See Appendix B for hydrographs. 3 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Water Quality Treatment A storm system retrofit is required to provide water quality treatment that meets the City of Tigard and CWS Design and Construction Standards. The required treatment area is calculated as outlined in CWS 4.08.1.d: Required Treatment Area = New Impervious + 3 (Modified Impervious-Permanently Removed Impervious) The stormwater facility is sized using the Autodesk Hydraflow Hydrograph 2024 modeling software to meet both hydromodification and water quality requirements described in the Clean Water Services Standard 4.08.6.c. Table 2 below provides a summary of the total new and modified impervious areas, as well as the calculated required treatment area. See Appendix A for Basin Map. TABLE 2: Required Treatment Area (Basin A & E) Modifier New Impervious Area Modified Impervious Area Permanently Removed Area Required Treatment Area Hydraflow Storm Facility Size 1x 3x Proposed 15,381 sf 31 sf 0 sf 15,474 sf 1,945 sf TABLE 3: Basin Areas and Treatment Type Basin Description Impervious Area (sf) Modified Impervious Area (sf) Pervious Area (sf) Total Area (sf) Treated by A AC turnaround, concrete trail, park landscaped areas 15,295 0 21,816 37,111 Stormwater Facility B Onsite undisturbed areas draining offsite 745 0 23,454 24,199 None C Onsite concrete trail draining offsite 897 0 1,408 2,305 None D Offsite untreated disturbed areas 822 90 430 1,342 None E Offsite treated disturbed areas 86 31 0 117 Stormwater Facility SD Facility SD Facility 0 0 1,945 1,945 N/A Total 67,019 The project proposes to treat the new impervious areas as much as possible, but a portion of the trail is not possible due to existing topography and its location within the 50-foot wetland buffer. To minimize disturbance to the wetland buffer and since this area is only 2% of the total project area, the impervious trail will not be treated but will utilize existing adjacent landscaping to slow flows into the wetland. This portion of the impervious trail will only be accessible by foot except for the occasional maintenance vehicle that happens a few times a year. 4 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Hydromodification Assessment The total addition of new and modified impervious areas will be greater than 1,000 square feet which requires a hydromodification assessment, per CWS 4.03.1. The risk level was determined to be moderate, the development class is a developed area, and the project size category is medium. Based on this assessment, the project falls under Category 2. Category 2 requires either an infiltration facility, peak-flow matching detention, or a combination of infiltration facility and peak-flow matching. Due to low infiltration rates onsite, a 1945-sf flow-through facility is designed to meet the peak-flow matching detention criteria for the 2-, 5- and 10-year storm event. To meet the hydromodification requirement, the post-development flow rate must meet the pre-development flow rates of the 5- and 10-year storm event and 50% of the pre- development flow rate for the 2-year storm event. See Appendix B for the Hydraflow Hydrographs and Table 3 for the pre-development and post-development. The captured runoff will be conveyed to the facility and routed to a flow control manhole before discharging offsite through the existing 12” storm line. TABLE 3: Existing and Post-Development Flows Post-Developed Flow Control Pre-Development Flow Rate Target Flow Rate Post-Development Flow Rate (cfs) (cfs) (cfs) 2-year 50% Pre-Developed 0.151 0.075 0.075 5-year 100% Pre-Developed 0.247 0.247 0.134 10-year 100% Pre-Developed 0.308 0.308 0.159 Conveyance The proposed stormwater conveyance pipes are sized to meet the 25-year storm event, using the Rational Method and Manning’s Equation. These calculations are provided in Appendix D. Operations and Maintenance The water quality and conveyance systems shall be operated and maintained in accordance with the CWS standards. Refer to the Operation and Maintenance Plan in Appendix E. City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Appendix A Basin Map SW S T E V E S T R E E T SW 84TH AVE 15' SANITARY SEWER EASEMENT EXISTING ONSITE WATER QUALITY FACILITY 20' STORM AND SANITARY SEWER EASEMENT PROPERTY LINE SHEET LEGEND 50 FT WETLAND BUFFER LINE IMPERVIOUS - EXISTING AREA = 865 SF PERVIOUS - EXISTING AREA = 66,154 SF SITE BOUNDARY TOTAL AREA = 67,019 SF SCALE 20 1 INCH = 20 FEET 20 400 \\ C I V I L P D X 1 \ C I V I L - P R O J E C T S \ C \ P \ 2 0 2 4 \ 2 4 0 0 2 6 8 - S T E V E - S T - P A R K \ P R O J - I N F O \ P L A N N I N G - D E S I G N \ S T O R M \ B A S I N M A P \ 2 4 0 0 2 6 8 - I M P E R V I O U S CA L C S . D W G 110 SE Main St., Suite 100 Portland, OR 97214 Ph: 503 222 5612 Fax: 503 222 2283 Email: info@greenworkspc.com LANDSCAPE ARCHITECTURE ENVIRONMENTAL DESIGN THESE DRAWINGS ARE THE PROPERTY OF GREENWORKS, P.C., AND ARE NOT TO BE USED OR REPRODUCED IN ANY MANNER, EXCEPT WITH THE PRIOR WRITTEN PERMISSION OF GREENWORKS, P.C. GREENWORKS, P.C. 2022, ALL RIGHTS RESERVED© Pr o j e c t : VERIFY SCALE: DRAWINGS ARE TO SCALE IF BAR MEASURES 1" 0"1/2"1" Checked By: Job No. Approved: Drawn By: Sheet No.of Date: Revisions: Sh e e t T i t l e : Su b m i t t a l : St e v e S t r e e t P a r k Ci t y o f T i g a r d 13 1 2 5 S W H a l l B l v d . Ti g a r d , O R 9 7 2 2 3 50 3 - 7 1 8 - 2 7 8 8 Ca r l a @ T i g a r d - O R . g o v 09/02/2025 200249.5 39 JZ JZ CL/SL 111 SW Fifth Ave., Suite 2600 Portland, OR 97204 O: 503.542.3860 F: 503.274.4681 www.kpff.com LA N D U S E A P P L I C A T I O N EXH 1 EX I S T I N G IM P E R V I O U S M A P SW S T E V E S T R E E T SW 84TH AVE 15' SANITARY SEWER EASEMENT EXISTING ONSITE WATER QUALITY FACILITY 20' STORM AND SANITARY SEWER EASEMENT PROPERTY LINE SHEET LEGEND 50 FT WETLAND BUFFER LINE PERVIOUS - PROPOSED AREA = 49,053 SF IMPERVIOUS - PROPOSED AREA = 17,845 SF MODIFIED - PROPOSED AREA = 121 SF SITE BOUNDARY TOTAL AREA = 67,019 SF \\ C I V I L P D X 1 \ C I V I L - P R O J E C T S \ C \ P \ 2 0 2 4 \ 2 4 0 0 2 6 8 - S T E V E - S T - P A R K \ P R O J - I N F O \ P L A N N I N G - D E S I G N \ S T O R M \ B A S I N M A P \ 2 4 0 0 2 6 8 - I M P E R V I O U S CA L C S . D W G 110 SE Main St., Suite 100 Portland, OR 97214 Ph: 503 222 5612 Fax: 503 222 2283 Email: info@greenworkspc.com LANDSCAPE ARCHITECTURE ENVIRONMENTAL DESIGN THESE DRAWINGS ARE THE PROPERTY OF GREENWORKS, P.C., AND ARE NOT TO BE USED OR REPRODUCED IN ANY MANNER, EXCEPT WITH THE PRIOR WRITTEN PERMISSION OF GREENWORKS, P.C. GREENWORKS, P.C. 2022, ALL RIGHTS RESERVED© Pr o j e c t : VERIFY SCALE: DRAWINGS ARE TO SCALE IF BAR MEASURES 1" 0"1/2"1" Checked By: Job No. Approved: Drawn By: Sheet No.of Date: Revisions: Sh e e t T i t l e : Su b m i t t a l : St e v e S t r e e t P a r k Ci t y o f T i g a r d 13 1 2 5 S W H a l l B l v d . Ti g a r d , O R 9 7 2 2 3 50 3 - 7 1 8 - 2 7 8 8 Ca r l a @ T i g a r d - O R . g o v 09/02/2025 200249.5 39 JZ JZ CL/SL 111 SW Fifth Ave., Suite 2600 Portland, OR 97204 O: 503.542.3860 F: 503.274.4681 www.kpff.com LA N D U S E A P P L I C A T I O N EXH 2 SCALE 20 1 INCH = 20 FEET 20 400 PR O P O S E D IM P E R V I O U S M A P SW S T E V E S T R E E T BF WAT SW 84TH AVE 15' SANITARY SEWER EASEMENT EXISTING ONSITE WATER QUALITY FACILITY 20' STORM AND SANITARY SEWER EASEMENT PROPERTY LINE SHEET LEGEND 50 FT WETLAND BUFFER LINE SUB-BASIN A - ONSITE - FACILITY TREATED SUB-BASIN B - ONSITE - UNDISTURBED AND UNTREATED SUB-BASIN C - ONSITE - DISTURBED AND UNTREATED SUB-BASIN D - OFFSITE - DISTURBED AND UNTREATED SUB-BASIN E - OFFSITE - DISTURBED AND TREATED \\ C I V I L P D X 1 \ C I V I L - P R O J E C T S \ C \ P \ 2 0 2 4 \ 2 4 0 0 2 6 8 - S T E V E - S T - P A R K \ P R O J - I N F O \ P L A N N I N G - D E S I G N \ S T O R M \ B A S I N M A P \ 2 4 0 0 2 6 8 - B A S I N M A P . D W G 110 SE Main St., Suite 100 Portland, OR 97214 Ph: 503 222 5612 Fax: 503 222 2283 Email: info@greenworkspc.com LANDSCAPE ARCHITECTURE ENVIRONMENTAL DESIGN THESE DRAWINGS ARE THE PROPERTY OF GREENWORKS, P.C., AND ARE NOT TO BE USED OR REPRODUCED IN ANY MANNER, EXCEPT WITH THE PRIOR WRITTEN PERMISSION OF GREENWORKS, P.C. GREENWORKS, P.C. 2022, ALL RIGHTS RESERVED© Pr o j e c t : VERIFY SCALE: DRAWINGS ARE TO SCALE IF BAR MEASURES 1" 0"1/2"1" Checked By: Job No. Approved: Drawn By: Sheet No.of Date: Revisions: Sh e e t T i t l e : Su b m i t t a l : St e v e S t r e e t P a r k Ci t y o f T i g a r d 13 1 2 5 S W H a l l B l v d . Ti g a r d , O R 9 7 2 2 3 50 3 - 7 1 8 - 2 7 8 8 Ca r l a @ T i g a r d - O R . g o v 09/02/2025 200249.5 39 JZ JZ CL/SL 111 SW Fifth Ave., Suite 2600 Portland, OR 97204 O: 503.542.3860 F: 503.274.4681 www.kpff.com LA N D U S E A P P L I C A T I O N EXH 3 SCALE 20 1 INCH = 20 FEET 20 400 PR O P O S E D B A S I N MA P Project SiteA1A2A3A4A5A6 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Appendix B Hydraflow Modeling Hydrograph Summary Report 1 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SBUH Runoff 0.151 2 480 2,743 ------ ------ ------ Pre-Development 2 SBUH Runoff 0.264 2 478 4,045 ------ ------ ------ Post-Development 4 Reservoir 0.075 2 608 3,546 2 188.74 989 Flow Control Structure Steve-Street-Park-20250605.gpw Return Period: 2 Year Monday, 06 / 16 / 2025 Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 1 Pre-Development Hydrograph type = SBUH Runoff Peak discharge = 0.151 cfs Storm frequency = 2 yrs Time to peak = 480 min Time interval = 2 min Hyd. volume = 2,743 cuft Drainage area = 0.850 ac Curve number = 80* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 2.50 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.850 x 80)] / 0.850 2 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Pre-Development Hyd. No. 1 -- 2 Year Hyd No. 1 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 2 Post-Development Hydrograph type = SBUH Runoff Peak discharge = 0.264 cfs Storm frequency = 2 yrs Time to peak = 478 min Time interval = 2 min Hyd. volume = 4,045 cuft Drainage area = 0.850 ac Curve number = 87* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 2.50 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.500 x 80) + (0.350 x 98)] / 0.850 3 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Post-Development Hyd. No. 2 -- 2 Year Hyd No. 2 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 4 Flow Control Structure Hydrograph type = Reservoir Peak discharge = 0.075 cfs Storm frequency = 2 yrs Time to peak = 608 min Time interval = 2 min Hyd. volume = 3,546 cuft Inflow hyd. No. = 2 - Post-Development Max. Elevation = 188.74 ft Reservoir name = Storm Facility Max. Storage = 989 cuft Storage Indication method used. 4 0 240 480 720 960 1200 1440 1680 1920 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Flow Control Structure Hyd. No. 4 -- 2 Year Hyd No. 4 Hyd No. 2 Total storage used = 989 cuft Pond Report 5 Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Pond No. 1 - Storm Facility Pond Data Trapezoid -Bottom L x W = 101.0 x 14.0 ft, Side slope = 3.00:1, Bottom elev. = 187.43 ft, Depth = 2.83 ft, Voids = 40.00% Stage / Storage Table Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft) 0.00 187.43 1,414 0 0 0.28 187.71 1,612 171 171 0.57 188.00 1,816 194 365 0.85 188.28 2,026 217 583 1.13 188.56 2,241 241 824 1.41 188.85 2,462 266 1,090 1.70 189.13 2,689 292 1,382 1.98 189.41 2,922 318 1,699 2.26 189.69 3,161 344 2,044 2.55 189.98 3,405 372 2,415 2.83 190.26 3,655 400 2,815 Culvert / Orifice Structures Weir Structures [A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in)= 8.00 2.00 1.75 0.00 Span (in)= 8.00 2.00 1.75 0.00 No. Barrels = 1 1 1 0 Invert El. (ft)= 187.43 188.15 188.75 0.00 Length (ft)= 1.00 0.00 0.00 0.00 Slope (%)= 1.00 0.00 0.00 n/a N-Value = .013 .013 .013 n/a Orifice Coeff.= 0.60 0.60 0.60 0.60 Multi-Stage = n/a No No No Crest Len (ft)= 1.50 Inactive Inactive 0.00 Crest El. (ft)= 190.26 0.00 0.00 0.00 Weir Coeff.= 3.33 3.33 3.33 3.33 Weir Type = Rect --- --- --- Multi-Stage = Yes No No No Exfil.(in/hr)= 0.000 (by Contour) TW Elev. (ft)= 0.00 Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s). 0.00 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30 Stage (ft) 0.00 187.43 1.00 188.43 2.00 189.43 3.00 190.43 Elev (ft) Discharge (cfs) Stage / Discharge Total Q Hydrograph Summary Report 6 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SBUH Runoff 0.247 2 480 4,090 ------ ------ ------ Pre-Development 2 SBUH Runoff 0.382 2 478 5,636 ------ ------ ------ Post-Development 4 Reservoir 0.134 2 542 5,136 2 189.05 1,305 Flow Control Structure Steve-Street-Park-20250605.gpw Return Period: 5 Year Monday, 06 / 16 / 2025 Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 1 Pre-Development Hydrograph type = SBUH Runoff Peak discharge = 0.247 cfs Storm frequency = 5 yrs Time to peak = 480 min Time interval = 2 min Hyd. volume = 4,090 cuft Drainage area = 0.850 ac Curve number = 80* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 3.10 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.850 x 80)] / 0.850 7 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Pre-Development Hyd. No. 1 -- 5 Year Hyd No. 1 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 2 Post-Development Hydrograph type = SBUH Runoff Peak discharge = 0.382 cfs Storm frequency = 5 yrs Time to peak = 478 min Time interval = 2 min Hyd. volume = 5,636 cuft Drainage area = 0.850 ac Curve number = 87* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 3.10 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.500 x 80) + (0.350 x 98)] / 0.850 8 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Post-Development Hyd. No. 2 -- 5 Year Hyd No. 2 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 4 Flow Control Structure Hydrograph type = Reservoir Peak discharge = 0.134 cfs Storm frequency = 5 yrs Time to peak = 542 min Time interval = 2 min Hyd. volume = 5,136 cuft Inflow hyd. No. = 2 - Post-Development Max. Elevation = 189.05 ft Reservoir name = Storm Facility Max. Storage = 1,305 cuft Storage Indication method used. 9 0 240 480 720 960 1200 1440 1680 1920 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Flow Control Structure Hyd. No. 4 -- 5 Year Hyd No. 4 Hyd No. 2 Total storage used = 1,305 cuft Hydrograph Summary Report 10 Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SBUH Runoff 0.308 2 480 4,927 ------ ------ ------ Pre-Development 2 SBUH Runoff 0.453 2 476 6,595 ------ ------ ------ Post-Development 4 Reservoir 0.159 2 540 6,096 2 189.25 1,522 Flow Control Structure Steve-Street-Park-20250605.gpw Return Period: 10 Year Monday, 06 / 16 / 2025 Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 1 Pre-Development Hydrograph type = SBUH Runoff Peak discharge = 0.308 cfs Storm frequency = 10 yrs Time to peak = 480 min Time interval = 2 min Hyd. volume = 4,927 cuft Drainage area = 0.850 ac Curve number = 80* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 3.45 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.850 x 80)] / 0.850 11 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Pre-Development Hyd. No. 1 -- 10 Year Hyd No. 1 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 2 Post-Development Hydrograph type = SBUH Runoff Peak discharge = 0.453 cfs Storm frequency = 10 yrs Time to peak = 476 min Time interval = 2 min Hyd. volume = 6,595 cuft Drainage area = 0.850 ac Curve number = 87* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = User Time of conc. (Tc) = 5.00 min Total precip. = 3.45 in Distribution = Type IA Storm duration = 24 hrs Shape factor = n/a * Composite (Area/CN) = [(0.500 x 80) + (0.350 x 98)] / 0.850 12 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Post-Development Hyd. No. 2 -- 10 Year Hyd No. 2 Hydrograph Report Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 06 / 16 / 2025 Hyd. No. 4 Flow Control Structure Hydrograph type = Reservoir Peak discharge = 0.159 cfs Storm frequency = 10 yrs Time to peak = 540 min Time interval = 2 min Hyd. volume = 6,096 cuft Inflow hyd. No. = 2 - Post-Development Max. Elevation = 189.25 ft Reservoir name = Storm Facility Max. Storage = 1,522 cuft Storage Indication method used. 13 0 240 480 720 960 1200 1440 1680 1920 Q (cfs) 0.00 0.00 0.05 0.05 0.10 0.10 0.15 0.15 0.20 0.20 0.25 0.25 0.30 0.30 0.35 0.35 0.40 0.40 0.45 0.45 0.50 0.50 Q (cfs) Time (min) Flow Control Structure Hyd. No. 4 -- 10 Year Hyd No. 4 Hyd No. 2 Total storage used = 1,522 cuft City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Appendix C Water Quality Calculations Appendix C Water Quality Calculations Job Name: Steve Street Park KPFF Job 2400268 Design Engineer: CL Stormwater Facility Quality = (New Impervious Area) + 3(Modified Impervious Area) Treatment Area: Assumptions: sf ac sf ac Storm Event 24-hr Rainfall Depth (inches) Vehicle Turnaround area 2533 0.06 31 0.001 2-year 2.50 AC Trail / Playgrounds 12848 0.29 5-year 3.10 Total 15381 0.35 31 0.001 10-year 3.45 25-year 3.90 100-year 4.50 15474 sf Curve Numbers Impervious 98 464 cu. ft Water Quality Flow: 0.0322 cfs Pervious 80Water Quality Volume = (0.36 [in] * Required Treatment Area [sq ft]) / 12 [in/ft]: Impervious Area Modified Impervious Area Source Required Treatment Area = (New Impervious Area) + 3(Modified Impervious Area): Updated 8/20/2025 Page 1 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Appendix D Conveyance Calculations Appendix D Preliminary Pipe Conveyance Calculations Job Name: Steve Street Park KPFF Job 2400268 Design Engineer: CL DESIGN SECTION Cumulative Intensity Area Runoff Flow Runoff Capacity Velocity Runoff Velocity PIPE CONTRIBUTING C I A Q Q Slope Diameter Qf Vf Ratio at Capacity BASIN/PIPE (in/hr) (sf) (cfs) (cfs) (%) (in) (cfs) ft/s Q/Qf Q/Qf Q vs. Qf 1 A1 0.90 3.40 2,564 0.18 0.18 2.0 4.0 0.27 3.08 0.67 3.28 OK* 2 A3 0.90 3.40 843 0.06 0.06 2.0 4.0 0.27 3.08 0.22 2.48 OK* 3 PIPE 1 + PIPE 2 0.90 3.40 3,407 0.24 0.24 2.0 6.0 0.79 4.04 0.30 3.54 OK* 4 1/2 of A2 0.90 3.40 893 0.06 0.06 1.0 4.0 0.19 2.18 0.33 1.95 OK* 5 1/2 of A2 0.90 3.40 893 0.06 0.06 1.0 4.0 0.19 2.18 0.33 1.95 OK* 6 PIPE 3 + 4 + 5 0.90 3.40 5,193 0.36 0.36 2.0 6.0 0.79 4.04 0.46 3.93 OK* 7 1/2 of A4 0.90 3.40 1,376 0.10 0.10 1.0 4.0 0.19 2.18 0.51 2.18 OK* 8 PIPE 6 + PIPE 7 0.90 3.40 6,569 0.46 0.46 2.0 6.0 0.79 4.04 0.58 4.20 OK* 9 A5 0.50 3.40 380 0.01 0.01 2.0 4.0 0.27 3.08 0.06 1.85 OK* 10 PIPE 8 + PIPE 9 0.90 3.40 6,949 0.49 0.49 2.0 6.0 0.79 4.04 0.62 4.24 OK* 11 1/2 of A4 0.90 3.40 1,376 0.10 0.10 1.0 4.0 0.19 2.18 0.51 2.18 OK* 12 PIPE 10 + PIPE 11 0.90 3.40 8,325 0.58 0.58 2.0 6.0 0.79 4.04 0.74 4.41 OK* 13 A6 0.50 3.40 592 0.02 0.02 1.0 4.0 0.19 2.18 0.12 1.48 OK* 14 BASIN A 0.12 0.12 2.0 10.0 3.10 5.68 0.04 3.41 OK*From Hydraflow 25-Year Storm DESIGN Rational Method Calculations Manning's Calculations Updated 7/2/2025 Page 1 185 19 0 19 5 20 0 184 18 6 18 7 18 8 18 9 19 1 192 193 19 4 19 6 19 7 19 8 199 (1 8 5 ) (1 9 0 ) (1 9 5 ) (2 0 0 ) (2 0 0 ) (2 0 0 ) (1 8 3 ) (1 8 4 ) (1 8 6 ) (1 8 7 ) (1 8 8 ) (1 8 9 ) (1 9 1 ) (1 9 2 ) (1 9 3 ) (1 9 4 ) (1 9 6 ) (1 9 7 ) (1 9 8 ) (1 9 8 ) (1 9 8 ) (1 9 9 ) (1 9 9 ) (1 9 9 ) (2 0 1 ) (2 0 1 ) (2 0 1 ) (2 0 2 ) (2 0 3 ) BF WAT SW S T E V E S T R E E T SW 84TH AVE 12' PUE 15' SANITARY SEWER EASEMENT 15' 1 20' STORM AND SANITARY SEWER EASEMENT SEE SEPARATE PFI SET FOR WORK IN THE RIGHT-OF-WAY 2 SD CO-02 RIM=199.82 IE 4" OUT=195.15 (SE) CONNECT TO EXISTING 12" STORM MAIN SD MH-01 RIM=192.12 IE 8" IN=185.50 (W) IE IN=185.42 (S) IE OUT=185.42 (N) FIELD VERIFY POINT OF CONNECTION SD CO-01 RIM=200.39 IE 4" OUT=195.50 (NE) SD CO-14 RIM=199.14 IE 4" IN=194.60 (SW) IE 6" IN=194.60 (S) IE 6" OUT=194.60 (N) SD FCS-01 RIM=191.47 IE 8" IN=186.58 (NW) IE 8" OUT=186.38 (E) SD OF-02 IE 4" IN=190.50 (W) SD CO-07 RIM=199.92 IE 4" OUT=198.42 (NW) SD CO-08 RIM=197.55 IE 4" OUT=196.05 (W) SD CO-05 RIM=191.70 IE 4" OUT=190.66 (E) SD CO-03 RIM=197.18 IE 6" IN=193.49 (S) SD OF-01 IE 6" IN=191.69 (S) SD CO-04 RIM=190.82 IE 4" OUT=187.43 (E) SD BH-01 RIM=190.26 IE 4" IN=187.09 (NE) IE 4" IN=187.09 (W) IE 8" OUT=187.09 (SE) SD CO-06 RIM=189.82 IE 4" OUT=187.43 (SW) 69 L F - 4 " S D S= 0 . 5 0 % SD CO-11 RIM=198.62 IE 4" OUT=197.12 (SE) SD CO-10 RIM=199.02 IE 4" OUT=196.40 (E) 45 LF - 4"SD S= 0 . 5 0 % 33LF - 4"SD S= 0 . 5 0 % SD CO-12 RIM=198.43 IE 4" IN=196.93 (NW) 38LF-4"SD S=0 . 5 0 % 31 LF - 4"SD S= 0 . 0 0 % SD CO-13 RIM=198.71 IE 4" OUT=197.21 (SE) SD INLET-02 RIM=199.26 IE=196.26 5 LF - 4"SD S=2.00% MIN 38 L F - 4 " S D S= 2 . 0 0 % 16 LF - 4"SD S=2.00% MIN 32 LF - 6"SD S=2.00% 18 LF - 4"SD S=2.00% MIN 15 LF - 6"SD S=2.00% 26 L F - 8 " S D S=2 . 0 0 % 90 LF - 6"SD S=2.00% 12 LF - 4"SD S=2.00% 14 LF - 8"SD S=6.45% 13 LF - 4"SD S=0.50% 36 L F - 4 " S D S=0 . 9 4 % 6 LF - 4"SD S=2.00% 6 LF - 4"SD S=2.00% 5 LF - 4"SD S=2.00% 5 LF - 4"SD S=2.00% 4 LF - 4"SD S=2.00% 18LF- 4"SD S= 0 . 5 0 % 35 L F - 4 " S D S=0 . 5 0 % 8 LF - 4"SD S=2.00% MIN 60 L F - 4 " S D S= 4 . 0 0 % 29 L F - 4 " S D S=2 . 0 0 % 48 L F - 4 " S D S=0 . 5 0 % 13 LF - 4"SD S=2.00% 7 LF - 4"SD S=2.00%16 LF - 4"SD S=2.00% MIN. 24 LF - 6"SD S=2.00% EX. 12" EX. 12" 19 5 193 194 19619 7 190 19 0 190189 19 1 8 LF - 6"SD S=2.00% NOTE DESCRIPTION 1 INSTALL CG-2 INLET PER ODOT STANDARD DRAWING RD366. 2 CONTRACTOR SHALL FIELD VERIFY POINT OF CONNECTION PRIOR TO ORDERING MATERIALS. NOTIFY ENGINEER OF ANY DISCREPANCIES. 1.ON-SITE PIPE BEDDING AND BACKFILL FOR ALL UTILITIES PER CWS DRAWING NO. 590. 2.STRUCTURES LOCATIONS ARE BASED ON CENTER OF STRUCTURE. 3.REFER TO SHEET L6.0 FOR ON SITE GRADING PLAN. 5.PROPOSED FRONTAGE IMRPOVEMENTS IN RIGHT-OF-WAY SHOWN FOR REFERENCE ONLY. TO BE PERMITTED UNDER SEPARATE PUBLIC FACILITY IMPROVEMENTS PERMIT. X UTILITY KEY NOTES SHEET NOTES PIPE LABEL XXLF - XX" XX UTILITY SIZE UTILITY LENGTH UTILITY TYPE S=X.XX% XX XX-XX RIM= IE IN = XX.X IE OUT = XX.X STRUCTURE TYPE CALLOUT UTILITY TYPE (SD=STORM DRAINAGE, S=SANITARY SEWER, W=WATER, FP=FIRE PROTECTION) ID NUMBER (WHERE APPLICABLE) STRUCTURE INFO (WHERE APPLICABLE) STRUCTURE LABEL SLOPE (WHERE APPLICABLE) UTILITY LABEL LEGEND STRUCTURE TYPE CALLOUT DESCRIPTION DETAIL CO CLEANOUT TO GRADE 500 & 510/C4.0 FCS FLOW CONTROL STRUCTURE 270/C4.0 OF OUTFALL 4/C4.2 & 5/C4.2 BH BEEHIVE INLET 405/C4.0 PROPERTY LINE UTILITY LEGEND STORMWATER FACILITY EX. CONTOUR MAJOR EX. CONTOUR MINOR 50 FT WETLAND BUFFER LINE 49 50 (49) (50) EASEMENT PROPOSED CONTOUR MAJOR PROPOSED CONTOUR MINOR 735C4.0 STORM PIPE PERFORATED STORM PIPE SD STRUCTURE TABLE STRUCTURE ID BH-01 CO-01 CO-02 CO-03 CO-04 CO-05 CO-06 CO-07 CO-08 CO-10 CO-11 CO-12 CO-13 CO-14 FCS-01 INLET-02 MH-01 OF-01 OF-02 NORTHING 142219.72 142014.36 142022.99 142106.32 142217.41 142202.23 142245.13 141989.94 142083.82 142071.69 142074.42 142044.39 142062.13 142050.44 142201.64 142016.07 142201.63 142196.51 142211.19 EASTING 324696.58 324643.91 324664.64 324664.64 324629.82 324588.03 324721.99 324703.65 324718.22 324589.43 324632.72 324721.16 324621.18 324664.64 324714.63 324607.52 324728.28 324664.61 324630.25 N: \ C \ P \ 2 0 2 4 \ 2 4 0 0 2 6 8 - S T E V E - S T - P A R K \ C A D \ P L O T \ 2 4 0 0 2 6 8 - U T I L . D W G 110 SE Main St., Suite 100 Portland, OR 97214 Ph: 503 222 5612 Fax: 503 222 2283 Email: info@greenworkspc.com LANDSCAPE ARCHITECTURE ENVIRONMENTAL DESIGN THESE DRAWINGS ARE THE PROPERTY OF GREENWORKS, P.C., AND ARE NOT TO BE USED OR REPRODUCED IN ANY MANNER, EXCEPT WITH THE PRIOR WRITTEN PERMISSION OF GREENWORKS, P.C. GREENWORKS, P.C. 2022, ALL RIGHTS RESERVED© Pr o j e c t : VERIFY SCALE: DRAWINGS ARE TO SCALE IF BAR MEASURES 1" 0"1/2"1" Checked By: Job No. Approved: Drawn By: Sheet No.of Date: Revisions: Sh e e t T i t l e : Su b m i t t a l : St e v e S t r e e t P a r k Ci t y o f T i g a r d 13 1 2 5 S W H a l l B l v d . Ti g a r d , O R 9 7 2 2 3 50 3 - 7 1 8 - 2 7 8 8 Ca r l a @ T i g a r d - O R . g o v 09/02/2025 200249.5 39 JZ JZ CL/SL 111 SW Fifth Ave., Suite 2600 Portland, OR 97204 O: 503.542.3860 F: 503.274.4681 www.kpff.com LA N D U S E A P P L I C A T I O N 26 SCALE 20 1 INCH = 20 FEET 20 400 ST O R M P L A N C3.0 Pipe 1Pipe 3Pipe 7Pipe 4Pipe 5Pipe 6Pipe 2Pipe 8Pipe 9Pipe 10Pipe 11Pipe 12Pipe 13Pipe 14 City of Tigard – Steve Street Park | KPFF Consulting Engineers STORMWATER DRAINAGE REPORT Appendix E Operations and Maintenance Plan Stormwater Operation &Maintenance Manual Steve Street Park Prepared for: Greenworks Prepared by: Sofi Lam and Cami Lamont Project Engineer: Jessica Zink, PE September 2025 | KPFF Project # 2400268 KPFF’S COMMITMENT TO SUSTAINABILITY As a member of the US Green Building Council, KPFF is committed to the practice of sustainable design and the use of sustainable materials in our work. When hardcopy reports are provided by KPFF, they are prepared using recycled and recyclable materials, reflecting KPFF’s commitment to using sustainable practices and methods in all of our products. 111 SW 5th Avenue, Suite 2600, Portland, OR 97204 503-542-3860 | www.kpff.com 1 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Table of Contents Responsibility ..................................................................................................................................................... 2 Description ......................................................................................................................................................... 2 Site Description .................................................................................................................................................. 2 Stormwater System Description..................................................................................................................... 2 Component Definitions .................................................................................................................................. 3 Inspection/Maintenance Schedule .................................................................................................................... 4 Inspection/Maintenance Procedure .................................................................................................................. 4 Individual Components .................................................................................................................................. 4 Inspection and Maintenance Logs ..................................................................................................................... 5 Infiltration/Flow Control ................................................................................................................................ 5 Pollution Prevention ....................................................................................................................................... 5 Vectors (mosquitoes and rodents) ................................................................................................................. 6 Maintenance .................................................................................................................................................. 6 Tables and Figures TABLE #1: Facility Summary Table ..................................................................................................................... 2 Appendices Appendix D: Exhibits Exhibit A: Basin Map Exhibit B: O&M Inspection Log Exhibit C: CWS O&M Manual 2 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Responsibility The stormwater facilities on this site are to be maintained by City of Tigard. City of Tigard employees in charge of conducting maintenance will conduct regular inspections of the stormwater facilities and perform any tasks required to keep them in working order, such as removing weeds and debris from catch basins. Any maintenance tasks that require special equipment should be conducted by a professional such as a contractor or landscape contractor hired by the City of Tigard. Stormwater facilities must be accessible for monitoring and maintenance. Adequately maintaining paths, gates, and ground cover is necessary to safely and efficiently locate and ensure access to facilities. A copy of the Operations & Maintenance Plan shall be provided to all property owners and tenants. Description Site Description The 1.5-acre Steve Street Park property is located near the intersection of Highway 217 and Pacific Hwy W in Tigard, Oregon, at the north end of SW 84th Avenue. The site lies within the Fanno Creek Watershed. The existing property is currently a neighborhood park made up of grassy areas and outer tree coverage. There are no existing structures on site. Stormwater System Description The Stormwater System collects, treats, and infiltrates runoff from pollution-generating surfaces within the site as required by Clean Water Services. The proposed storm design will collect and treat runoff from the offsite turnaround area and the onsite park. The offsite area includes the turnaround area and the sidewalk adjacent to the turnaround area. The concrete sidewalk and pavement drainage in the turnaround area is collected by a catch basin. The catch basin is piped to the onsite storm system. The onsite storm system includes a network of pipes collecting runoff from the turfed playground areas and the offsite improvements to the stormwater facility onsite. The stormwater facility will be a flow-through lined stormwater plater and contain a flow control structure to meet hydromodification requirements before it is piped into the 12” City owned storm line located in the storm and sanitary sewer easement. The proposed loop trail will have both concrete and mulch chip surfacing. These areas will be treated by adjacent landscaping or will sheet flow into the onsite stormwater facility. TABLE #1: Facility Summary Table Basin Contributing Source Impervious Area (sf) Modified Impervious Area (sf) Pervious Area (sf) Total Area (sf) Treatment Facility Discharge Point A AC turnaround, concrete trail, park landscaped areas 15,295 0 21,816 37,111 SD Facility OF-01 / Sheet Flow E Offsite AC turnaround area 86 31 0 117 SD Facility OF-01 3 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Component Definitions Beehive Grates: a raised grate placed on vertical overflow inlets and equalizers to prevent trash and debris from entering the piped system. The shape of the grate helps prevents debris from clogging the grate during rain events. Catch Basins (CB): a large box-shaped inlet structure that collects stormwater and conveys it to the storm system. It has square grates set flush with the ground that allows stormwater to enter the structure. Inside each catch basin there is a sump; a depression located below the pipe inlets and outlets that collects sediment and debris. The outlet pipe has a hood called a trap that prevents debris and grease from leaving the sump and entering the storm system. Cleanout (CO): a maintenance structure (at grade or buried) that connects to storm and sanitary lines and allows for surface access to inspect the pipe network. It is constructed of a vertical pipe with a lid that can be opened for inspection or to allow maintenance personnel to access the system to remove blockages. Flow Control Manhole/Structure (FCS): (found downstream of detention galleries) storm manholes with a flow-control device located on the outlet pipe. The flow-control device is comprised of a vertical pipe with a horizontal plate with a specific size hole on the bottom of the vertical pipe that allows water to enter the vertical pipe and leave the manhole at a controlled rate. The size of the holes and the elevation of the holes control how fast water can leave the detention gallery and how much of the detention gallery is used during various storm sizes. The top of the vertical pipe is left open as an emergency overflow. The emergency overflow lets stormwater bypass the flow control orifices during extremely large storms that would otherwise overwhelm the system. A flow control manhole also contains a sump, which is a depression located below the inlet and outlet pipe that helps trap sediment and floating debris, and keeps the orifice from clogging. Impermeable Liner: a PVC or HDPE membrane used to waterproof the flow-through planter. Manhole (MH) – a cylindrical underground structure that is used for maintenance and access of the storm system. It has a manhole cover and frame at the ground surface and includes a ladder that allows maintenance personnel to enter the manhole. Outfall (OF): the downstream open end of a stormwater pipe. It typically has either rip-rap or a concrete pad to prevent erosion from occurring when water leaves the pipe and may have a screen or grate to prevent rodents from entering the pipe system. Outlet Protection: a layer of large rip-rap rock positioned at the piped inlet to the vegetated infiltration basins to dissipate energy and resist the eroding action of the flowing water. Overflow/Beehive Inlet (BH): a vertical pipe with a beehive grate that extends approximately 6 inches above the soil surface, depending on the planter design. It allows stormwater from large rain events to enter the downstream storm system. The grate prevents debris and rodents from entering the piped storm system. Perforated Pipe: pipe that has small holes in it which allows ground water and infiltrating surface water to enter the pipe along its length. Piped Storm System: consists of all underground pipes that connect the inlets to the stormwater planter, and ultimately to the existing storm system. 4 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Rain Garden: an engineered planter that filters pollutants out of stormwater as it passes through engineered growing medium prior to infiltration. The rain garden contains an overflow inlet structure that conveys stormwater from large rain events to the public storm system and rip-rap protection at piped inlets to prevent erosion and damage to the planter soil and vegetation. Rip-Rap: a layer of irregularly placed stones or rocks positioned on the bank or at the inlet and outlet of a rain garden to resist the erosion from water flow into or out of the facility. Inspection/Maintenance Schedule The whole system shall be inspected and maintained quarterly and within 48 hours after each major storm event. For this Operations & Maintenance Plan, a major storm event is defined as greater than 1.0-inches of rain in 24 hours. All components of the storm system as described below must be inspected and maintained frequently or they will cease to function effectively. The facility owner must keep a log, recording all inspection dates, observations, and maintenance activities. Receipts shall be saved when maintenance is performed and there is a record of expense. Inspection/Maintenance Procedure Individual Components The following components shall be inspected and maintained according to the table: Component Component Part Observed Condition Maintenance Action Season Catch Basin Piping Debris and garbage build- up Clear piping to facility when blockage occurs. All Cracked Drain Pipe Repair/seal cracks. Replace when repair is insufficient. All Trap/Outlet Hood Debris and garbage build- up Clear hooded outlet. All Sump Depth of accumulated sediment has reached 1/3 of capacity Remove sediment using vactor truck (manholes) or shovel (area drains and catch basins only). All Structure Walls Cracks Repair/seal cracks. Replace when repair is insufficient. All Cover Missing cover Replace missing cover. All Cracks in grates Replace cracked grates. All Uneven cover Remove debris from frame/collar and ensure cover is level and secured. If settling has occurred so that cover is no longer level with surrounding grades, adjust rim to remove tripping hazard. All Flow-Control Manhole Piping Debris and garbage buildup Clear piping to facility when blockage occurs. All Cracked drain pipe Repair/seal cracks. Replace when repair is insufficient. All Flow-Control Device Debris and garbage buildup Clear debris from orifices, overflow inlet, and associated piping. All Covers or vertical pipe are not tightly secured Ensure seals are intact and flow control device is securely attached. All 5 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Component Component Part Observed Condition Maintenance Action Season Cracked pipe Repair/seal cracks. Replace when repair is insufficient. All Sump Depth of accumulated sediments has reached 1/3 of the capacity Remove sediment using vactor truck when sediment accumulation exceeds 8-inches of depth or otherwise restricts flow into the flow-control device. All Structure Walls Cracks Repair/seal cracks. Replace when repair is insufficient All Manhole Cover Missing cover Replace missing cover. All Cracks in grates or manhole cover Replaced cracked manhole cover All Uneven cover Remove debris from frame and ensure cover is level and secured. If settling has occurred so that cover is no longer level with surrounding grades, adjust rim to remove tripping hazard. All Outfall Scouring/Erosion Add splash block/rock pads. All Sediment or debris buildup Remove sediment and debris to maintain at least 80% conveyance capacity at all times. All Overflow Inlets Piping Debris and garbage buildup Clear piping to facility when blockage occurs. All Cracked drain pipe Repair/seal cracks. Replace when repair is insufficient. All Structure Walls Cracks Repair/seal cracks. Replace when repair is insufficient. All Atrium/Beehive Grate Missing or cracked grate Replace grate. All Debris buildup on grate Remove debris on grate and in planter. All Sump (Type 2 Only) Depth of accumulated sediments has reached 1/3 of the capacity Remove sediment using vactor truck when sediment accumulation exceeds 8-inches of depth or otherwise restricts flow into the flow-control device. All Rip-Rap Aggregate Displaced rock aggregate Replace or refill ballast aggregate to 6- inch depth All Drainage Fabric Ripped or displaced fabric Repair, replace and/or re-set drainage fabric All 1. It is illegal to hose sediments through your system. Sediments often can be removed by hand. 2. Large facilities and underground facilities will need to be cleaned with heavy equipment, such as vactor trucks, by trained professionals. Inspection and Maintenance Logs Clean Water Services requires maintenance staff to complete inspection and maintenance logs. The logs shall be produced for: Infiltration/Flow Control All facilities shall drain within 48 hours. Date, time, weather, and site conditions when ponding occurs shall be recorded. Pollution Prevention 6 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL All sites shall implement best management practices to prevent hazardous wastes, litter, or excessive oil and sediment from contaminating stormwater. Contact Clean Water Services Environmental Services Program at 503-681-5175 or CWS main office at 503-681-3600 for immediate assistance with responding to spills. Record date, time, weather, and site conditions if activities are found to contaminate stormwater Vectors (mosquitoes and rodents) Stormwater facilities shall not harbor mosquito larvae or rats that pose a threat to public health or that undermine the facility structure. Monitor standing water for small wiggling sticks perpendicular to the water’s surface. Note holes/burrows in and around facilities. Record date, time, weather, and site conditions when vector activity is observed. Maintenance Record date, description, and contractor (if applicable) for all structural repairs, landscape maintenance, and facility cleanout activities. An inspection log has been provided as an exhibit below. Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Appendix D: Exhibits Exhibit A: Basin Map SW S T E V E S T R E E T BF WAT SW 84TH AVE 15' SANITARY SEWER EASEMENT EXISTING ONSITE WATER QUALITY FACILITY 20' STORM AND SANITARY SEWER EASEMENT PROPERTY LINE SHEET LEGEND 50 FT WETLAND BUFFER LINE SUB-BASIN A - ONSITE - FACILITY TREATED SUB-BASIN B - ONSITE - UNDISTURBED AND UNTREATED SUB-BASIN C - ONSITE - DISTURBED AND UNTREATED SUB-BASIN D - OFFSITE - DISTURBED AND UNTREATED SUB-BASIN E - OFFSITE - DISTURBED AND TREATED \\ C I V I L P D X 1 \ C I V I L - P R O J E C T S \ C \ P \ 2 0 2 4 \ 2 4 0 0 2 6 8 - S T E V E - S T - P A R K \ P R O J - I N F O \ P L A N N I N G - D E S I G N \ S T O R M \ B A S I N M A P \ 2 4 0 0 2 6 8 - B A S I N M A P . D W G 110 SE Main St., Suite 100 Portland, OR 97214 Ph: 503 222 5612 Fax: 503 222 2283 Email: info@greenworkspc.com LANDSCAPE ARCHITECTURE ENVIRONMENTAL DESIGN THESE DRAWINGS ARE THE PROPERTY OF GREENWORKS, P.C., AND ARE NOT TO BE USED OR REPRODUCED IN ANY MANNER, EXCEPT WITH THE PRIOR WRITTEN PERMISSION OF GREENWORKS, P.C. GREENWORKS, P.C. 2022, ALL RIGHTS RESERVED© Pr o j e c t : VERIFY SCALE: DRAWINGS ARE TO SCALE IF BAR MEASURES 1" 0"1/2"1" Checked By: Job No. Approved: Drawn By: Sheet No.of Date: Revisions: Sh e e t T i t l e : Su b m i t t a l : St e v e S t r e e t P a r k Ci t y o f T i g a r d 13 1 2 5 S W H a l l B l v d . Ti g a r d , O R 9 7 2 2 3 50 3 - 7 1 8 - 2 7 8 8 Ca r l a @ T i g a r d - O R . g o v 09/02/2025 200249.5 39 JZ JZ CL/SL 111 SW Fifth Ave., Suite 2600 Portland, OR 97204 O: 503.542.3860 F: 503.274.4681 www.kpff.com LA N D U S E A P P L I C A T I O N EXH 3 SCALE 20 1 INCH = 20 FEET 20 400 PR O P O S E D B A S I N MA P Project SiteA1A2A3A4A5A6 Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Exhibit B: O&M Inspection Log Private Water Quality Inspection Log Attention: This inspection log is to remain on site and must be made available upon request by District or City employees. Property description: Site address: Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Inspection Date: _________________ Inspected by: ___________________________________ Comments: ________________________________________________________ ________________________________________________________________ ________________________________________________________________ Steve Street Park | KPFF Consulting Engineers STORMWATER OPERATION & MAINTENANCE MANUAL Exhibit C: CWS O&M Manual Low Impact Development Approaches Handbook 97 98 Low Impact Development Approaches Handbook Low Impact Development Approaches Handbook 99