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HomeMy WebLinkAboutStudies APPLICANT 10/25/2022Stormwater Management Plan and Drainage Study 1975 16th Street Springfield, Oregon For Moore Residential Trust 1955 16" Street Springfield, OR 97477 �p PROFF�_ �y �NGINfF9 0� 69162PE DIMALLY SIGNED OREGON �FNEE CL�� EXPIRES: 12/31/21 August 16, 2021 ENGINEERING. -- Since 1977 civil - transportation structural geotechnical SURVEYING www.BranchEngineering.com Contents Page No. 1.0 Introduction............................................................................................................... 1 2.0 Existing Conditions.................................................................................................1 2.1 Topography 1 2.2 Soils 1 2.3 Existing Storm System 1 3.0 Proposed Development......................................................................................... 1 4.0 Stormwater Constraints........................................................................................ 1 5.0 Proposed Development Stormwater Description.......................................2 6.0 Facility Sizing............................................................................................................2 7.0 Maintenance...............................................................................................................2 8.0 Conclusion..................................................................................................................3 Appendices Description Appendix A Stormwater Management Drainage Basin Map Appendix B Site Soils and Map © Branch Fngineermg, Inc. 1.0 INTRODUCTION This Stormwater Management Plan (SWMP) report has been prepared for the analysis of partitioning a lot located at 1975 16- Street, Springfield, Oregon. The subject site is located at the southeast corner of the 16- Street and S Street intersection The subject property is identified as Tax Map 17-03-25-24 Tax Lot 2300. The stormwater runoff will be directed to the nearbypubhc stormwater systems located on S Street and 16- Street. 2.0 EXISTING CONDITIONS The site is located in Springfield, Oregon in the Q Street neighborhood area and consists of 0.41 acres of private property. The site is flat with minimal ground cover. A home is located centrally on the subject property. 2.1 TOPOGRAPHY The subject site is flat, but does generally slope from its southeast corner to its northwest corner (the S Street and 16m Street intersection) at approximately 0.596 The subject property has two trees located in front of the existing home, two trees located at its rear, and a hedgerow at its southwest corner. 2.2 SOILS The Natural Resources Conservation Service (NRCS) Web Soil Survey maps the subject site as containing a single soil type: Malabon-Urban land complex (76). Malabon-Urban land complex is described as a well -drained silty and clayey alluvium and is in Hydrologic Soil Group C; the soil has a limiting drainage capacity between 0.20 and 0.57 inches per hour. The typical profile of the soil type has silty clay loam between 0-12 inches, silty clay from 12-42 inches, and clay loam from 42-60 inches. A soils map and individual soil information is provided in Appendix B. 2.3 EXISTING STORM SYSTEM There is currently a public pipe network for stormwater located within the 16- Street right-of-way. It appears that roof drains for the existing home currently drains to splash blocks. A small ditch is located along the northern edge of the subject property and ends in a culvert at the southeast corner of the 16- Street and S Street intersection; this culvert connects into the public pipe network on 16 - Street. ¢jt1»;ZII10M D11311 DVI DI ICI] WS I WN I A three -parcel partition is proposed Parcel l will consist of 4,506 square feet (0.10 acres), Parcel 2 will consist of 7,063 square feet (0.16 acres), and Parcel 3 will consist of 6,200 square feet (0.14 acres). Parcel 2 will encompass the improvements already on the property. Parcels 1 and 3 will be analyzed as each having a single-family residence meeting the conditions of the City of Springfield's Engineering Design Standards and Procedural Manual, Chapters 3 and 4. A Basin Map is shown in Appendix A. CKl�'VC0MT►hY:TlIIIKK 112KI0tL\112YK Currently, all stormwater runoff flows to the public pipe network in 16- Street. The public pipe network is located under the sidewalk on 16- Street and is approximately 3-4 feet below the surface. In order to direct flows to this network all stormwater will need to be treated and piped, whether through direct connection to the network or through downspouts into the paved area of 16- Street. Considering that most treatment facilities are 2-3 feet deep prior to discharge, it may be necessary to use infiltration treatment facilities, surface treatment facilities, or position the treatment facility as close to the public pipe network as possible to ensure that the facility can effectively connect to the network. 5.0 PROPOSED DEVELOPMENT STORMWATER DESCRIPTION As discussed in the Proposed Development section above, the stormwater facilities will be designed to meet the City of Springfield's Engineering Design Standards and Procedural Manual, Chapters 3 and 4, which dictates that development is held to the design standards of the City of Eugene's Stormwater Management Manual. It is intended that future construction permit applications for a home will need to treat 50% of all non - rooftop impervious surfaces runoff before it is discharged to the public pipe network. Each parcel is treated as a separate basin. The basin characteristics are listed in the table below. Parcel 2 was not analyzed as it is already developed. Basin Description Impervious rooftop area Impervious non -rooftop area Pervious area Parcell 2,000 400 2,106 Parcel 3,500 400 2,300 The basins are intended to be representative of a future home and associated improvements. It is somewhat arbitrarily assumed that the future homes will have up to 400-sf of driveway and other non - rooftop impervious surfaces (patios, etc.) and 2,000-sf for Parcel 1 and 3500-8f for Parcel 2 of rooftop (these areas are based on Springfield Development Code Section 3.2-215). 6.0 FACILITY SIZING The stormwater facilities for any future development will need to be sized based on the amount of impervious area of the home and associated improvements. Without any concept of what may actually be built, it is not possible to provide system or sizing details which will have beneficial meaning in the future. Due to the nature of the site and the available land for a stormwater treatment facility, any number of options can be analyzed. For the purposes of this report a standard approach of sizing a facility using the simplified method in the City of Eugene's Stormwater Management Manual will be sufficient. With the assumed size of the impervious area as seen in the previous section, and given that a rain garden for water quality has a sizing factor of 0.05, Parcels 1 and 3 will each need an area of 10 square feet minimum would be needed to treat the runoff. This implies that a minimum sized (5 -foot wide) rain garden near the edge of the driveway would be sufficient to treat each basin Due to the shallow depth of the public pipe network, this facility could be designed as an infiltration facility. Based on experience working with Malabon-Urban land complex, a 10 square foot facility could treat and infiltrate all stormwater during the water quality event with a 0.50 in/hr infiltration rate. 7.0 MAINTENANCE The facilities will be maintained privately since they receive water only from private improvements and will be constructed under a Building Permit. Maintenance will be per the City of Springfield's Engineering Design Standards and Procedures Manual, Appendix 3A through 3A-4. Repairs to storm facilities shall be made in accordance with City of Springfield Public Works Department. 8.0 CONCLUSION Feasibility has been established for the stormwater system outlined herein for the Moore Partition It will be necessary to refine the design and calculations at the time of construction permitting. APPENDIX A Stormwater Management Drainage Basin Map •II nip°rtev[I� LEGEND :c .p,.«nl•.I ,Y SO0.V EYING W PROPERTY LINE RIGHT-OF-WAY LINE ^.."•^.^E^9 ''^•••'^ 4P — - — CENTERLINE rise c a.__ r r -...—...- DITCH — FENCE mr — EDGE OF ASPHALT PAVING :.e -- — —— --- CURB — -- :r�.m.�--�..-----0"•--- __ 'S' TREET 45 a —nom CONTOUR LINE _ P —_ _ __ [ ! W. --ww-- WASTEWATER SEWER LINE 0 3u•'•"s-.-3"""P -sr-- - STORM SEWER LINE pp�c��• WATER LINE PROPOSED WASTEWATER SEWER LINE PROPOSED ROOF DRAIN (ASTM D-3034) —w— PROPOSED WATER LINE (! ' PROPOSED UNDERGROUND WIRES (ELECTRIC. TELEPHONE AND CABLE TV) �o MANHOLE CURB INLET STREET LIGHT A PAPOWER POLE b rii'a+rns a STOP SIGN uHaz[ ro -..r .. PI8C6 8 WATER VALVE mw mNea -' rosa aF g FIRE HYDRANT Lu • �p m WATER METER m GAS METER O MAIL BOX O m `_A DECIDUOUS TREE v EVERGREEN TREE rn z z 'ipN ;, tTxcr / 0 CONCRETE W O O GRAVEL = F M BUILDING a o szao er I\caa O HEDGE J F N Qu IXe H z ,L-------� N w mz9 � I�amtur Z F n N ..: � GRAPHIC SCALE Am 10,1011 Ilm ..I 20 0 10 20 40 e4no prymnn 2146fi ( IN FEET I STORMWATER BASIN MAP TAX MAP 17-03-23-24 TAX LOT 2300 APPENDIX B Site Soils and Map m 11 'ry Sod Map—Lane County Area, Oregon 3 3 M pSmE: 1:327Rpnflad In Apnh d(&Sx IV)9Aek. N a a a is n A p 5 30 ® 9 Nw p�J Via: wm hHUv Cunrrmontlrata: NG584 FAge Sa:IIIM Zone 10N YJG539 ❑5W Natural Resources Web Soil Survey &1&2021 �i Conservation Serme National CooperaWe Soil Survey Page 1 a 3 Soil Map—Lane County Area, Oregon _SD, Natural Resources web Sol Survey &162D21 alaill Conservation Service National Cooperative Sail Survey Page 2 of 3 MAP LEGEND MAP INFORMATION Area at Wake. tA09 Spoil Area The sal surveys that comprise your AOI were mapped at Areaalnteresr(AQII Q army Spa 1:20,090. Soils Very Sony SpaWaming: Soil Map may not be valud al Mrs scale. 0 Soil Map Unit Polygons 9 VJrf S p a Enlargement of maps bethe scale of mapping can cause ,.,. Soil Map Unic Lines md Sell of the etail of mapping and accuracy of soil 4 Other line placement. The maps do not show the small areas of Map Unit Points contrasting soils that could have been shown at a more detailed Special Line FeaturesSoil Special Point Features scale. Lg Blowout water Features Streams and Canals Please rely on the bar scale on each map sheet for map ® Borrow Pit measurements. Trenspartatian Clay Spot Rails Source of Map: Natural Resources Conservation Service 0 Closed Depresdan Web Soil SurveyURL: Interstate Highways Coordinate System: web Mercator(EPSG:3B5]) Gravel Pit US Routes Maps from the Web Soil Survey are based on the Web Mercator Gravely Spa Major Roads projection, which preserves and shape but schdistorts and area, projection that preserves area, such as the ion that ® Landfill Local Roads Abersdistance o Albers equal-area conic projection, should be used if more Lava Flow accurate calculations of distance or area are req uired, Background aga Marsh or swamp . Aerial Photography This productis generated from the USDA­gRCS tended data as of Ne version date(s) listed below. .�. Mine or Query Soil Survey Area: Lane County Area, ® Miscellaneous Ydscer un11,20M Survey Area Data: Version 1l, Jun 11, 2020 ® Perennial VMmer Sail map units are labeled (as space allows) for map scales y, Rock Outcrop 1:50,099 or larger. A Saline Spot Dates) aerial images were photographed: Jun 12, 2019i 19, 2019 Sandy Spot The odhophoto or other base map on which the soil lines were Severely Eroded Spot compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor Sinkhole shifting ofmap unit boundaries may be evident, �p Slide or Slip Sodic Spot _SD, Natural Resources web Sol Survey &162D21 alaill Conservation Service National Cooperative Sail Survey Page 2 of 3 Sal Map�ane Connly Area, Oregon Map Unit Legend LSIA Natural Resources Web Soil Survey &1(=1 iMi Conservation Serme National Cooperative Soil Survey Page 3 of3 Map Unit Symbd Map Unit Name Acres in AOI Percent of AOI 76 Malabori lrban land cornplex 0.4 100.0% Totals for Area of Interest 0.4 100.0% LSIA Natural Resources Web Soil Survey &1(=1 iMi Conservation Serme National Cooperative Soil Survey Page 3 of3 Map Unit Description: Malabon-Urban land complex --lane Cmnty Area, Oregon Lane County Area, Oregon 76—Malabon-Urban land complex Map Unit Setting National map unit symbol. 238t Elevation. 300 to 650 feet Mean annual precipitation: 40 to 60 inches Mean annual air temperature: 52 to 54 degrees F Frost -free period. 165 to 210 days Farmland classification. Farm land of statewide importance Map Unit Composition Malabon and similar soils. 50 percent Urban land. 45 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Malabon Setting Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across -slope shape: Linear Parent material. Silty and clayey alluvium Typical profile H1 - 0 to 12 inches. silty clay loam H2 - 12 to 42 inches: silty clay H3 - 42 to 60 inches: clay loam Properties and qualities Slope: 0 to 3 percent Depth to restrictive feature: More than 80 inches Drainage class. Well drained Capacity of the most limiting layer to transmit water (Ksat): Moderately high (0.20 to 0.57 inlhr) Depth to watertable: More than 80 inches Frequency of floodirg: None Frequency of ponding: None Available water supply, 0 to 60 inches. High (about 11.4 inches) Interpretive groups Lard capability classification (irrigated): 1 Lard capability classification (nonirrigated): 1 Hydrologic Soil Group: C Forage suitability group: Well drained < 15% Slopes (G002XY0020R) Other vegetative classification. Well drained < 15% Slopes (G002XY0020R) Hydric sal rating. No LSM Natural Resources Wiab Soil Survey 8/16 21 it Conservation Serves National Cooperative Soil Survey Page 1 ort Map Unit Description: Malabon-Urban land complex --lane County Nes, Oregon Description of Urban Land Interpretive groups Land capability classification (irrigated): None specified Lard capability classification (nonirrigated): 8 Hydric sal rating. No Data Source Information Soil Survey Area: Lane County Area, Oregon Survey Area Data: Version 17, Jun 11, 2020 LSM Natural Resources Mb Soil Survey Ill1&2021 211 Conservation Service National Cooperative Soil Survey Page 2 ort