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Home My WebLink AboutStudies APPLICANT 9/10/2021Stormwater Management Plan and Drainage Study 197516 1h Street Springfield, Oregon For Moore Residential Trust 1955 161 Street Springfield, OR 97477 PR dtP916 P9 DIGrrALLY SIGNED OREGON 30,2 EXPIRES: 12/31/21 August 16, 2021 ENGINEERING= Si=I977 civil - transportation structural - geotechnical SURVEYING w .eranchEngineering.com Contents Page No. lA 2.0 Existing Conditions.._.__._1 2.1 Topography 1 2.2 Soils 1 2.3 Existing Storm System 1 3.0 Proposed 1 4.0 Stormwater Constraints_m._______.__.___._.__._.__...._______.__ 1 5.0 Proposed Development Stormwater Description.._ _—__2 6.0 Facility 2 7A................... —2 8.0 3 Appendices Description Appendix A Stormwater Management Drainage Basin Map Appendix B Site Soils and Map ® Branca &glneerft Inc 1.0 INTRODUCTION This Stormwater Management Plan (SWMP) report has been prepared for the analysis of partitioning a lot located at 1975 IV Street, Springfield, Oregon The subject site is located at the southeast comer 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 nearbypublic stomtwater systems located on S Street and 16- Street. 2.0 EXISTING CONDITIONS The site is located in Sprimilield, 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 sugject site is flat, but dues generally slope from its southeast corner to its northwest comer (the S Street and 16' Street Intersection) at approximately 0.596 The subject property has two trees located in from of the existing home, two trees located at its rear, and a hedgerow at Its southwest comer. 2.2 SOILS The Natural Resources Conservation Service (MRCS) 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-dralned silty and clayey alluvium ands in Hydrologic Soil Group Q the soil has a limiting drainage capacity between 020 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 and information is provided in Appendix B 23 li1HSTMG STORM SYSTEM There is currently a public pipe network for smrmwater located within the 160 Street right-of-way. It appears that roof drams for the existing bome 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 lfi- Street. 3.0 PROPOSED DEVELOPMENT A three -petrel pardtionis proposed. Parcel l will consist of 4,506 square feet (0-10 scres), 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 pmpffty- Parcels I and 3 will he analyzed as each having a single-family, residence meeting the conditions of the City of Springfields Engineering Design Standards and Procedural Mam od, Chapters 3 and 4. A Basin Map is shown in Appendix A 4.0 STORMWATER CONSTRAINTS Currently, all stormwater nimoff flows to the public pipe network in 16m 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 stormwi ter will need to be treated and piped, whether through direct connection to the network or through downspouts into the paved area of 16m Street. Considering that most treatment facilities are 2-3 feet deep prim to discharge, it maybe 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 curnect to the network 5.0 PROPOSED DEVELOPMENT STORMWATERDESCRIPTION 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 Sro®water Management Manual. Itis intended that forme constructionpermit applications for a home will need to treat 50%of all non - rooftop impervici s surfaces runoff before it is discharged to the public pipe network. Each parcel is treated as a separate basin. The basin characteristics me listed in the table below- Parcel 2 was not analyzed as it is already developed. Basin Description Imperviousrooftuparea Impervious non-rooftoparea Perviousarea Parcell 2,000 400 2,106 Pared 3 3,500 400 2,300 The basis 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 otherxim- rooftop impervious surfaces (patios, etc.) and 2,000-sf for Parcel 1 and 3500-sf 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 conceptofwhatmay actually be built, it is not possible to provide system or sizing details whichwill have beneficial meaning in the future. Due to the nature of the site and the available hod 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 Stormtvater 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 miniumm sized (5 -foot wide) rain garden near the edge of the driveway would be sufficient to treat eachbasm. 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 stonowater during the water quality event with a 0.50 hVlw 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 Engin rung Design Standards and Procedures Manual, Appendbt 3A through 3A4. 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 APPENDIX B Site Sails and Map Soil Map- . Count' Ane, Oregon a �z MgSeg l:�Pp[1mmApfbK(65°v117dat e N 0 e v v a u w w w Nna9wreemp�om mnermN�aa:r.®e agem:ummcwwa�e NawnfR o. W Soil Survey Sl l6 l Cooean . SaMPe Naemul C Pentim Sou Survey No 1 of 3 O a 0 2 IL � goo w �gty o • � 3F22o m n 1 HN E� m eE E 'n_ffi _ m Em� tw o�9.RF K oo :- 5 5 @@ o E a•. � $E�Fa � � •�p85 � �� $ $ •��E 5•p @aIS E� n�o y n E zaE m� w m •m9n E_ �o - $ wE � vwi E m r'q w _ gg � c it m y • p$p� E m�p a� m$ EnE gmmm�3 $�R °i� E„ • �o F 5 I m3$ 2naR 8Em a m � $ •; 1 E 1 oINN ei:. SOY Map—lane County Area, Oregon Map Unit Legend NaNrel Remuma Web Soil Survey all52021 Conwnratloe Samoa NaOonN Coopere5ve Soil Survey Page 3 013 Map UnN Symbol Mep UnN Name Aaaablm pNoantof AOl lib Melabor ftnlorui plea 0.4 100.0% L. for Am oflnfalast OA 1WA% NaNrel Remuma Web Soil Survey all52021 Conwnratloe Samoa NaOonN Coopere5ve Soil Survey Page 3 013 Map unit neeaipEon: wnil omen IaM cooiplez—lane counlyMm, coition Lane County Area, Oregon 76—MalabomUrban land complex Map Unn $*" National map unit symbol., 230[ Elevation: 300 to 650 feel Mean annusl predppatlon: 40 to W inches Mean annual airtemperaaxe: 52 to 54 dogmas F Fmsf--free period: 105 to 210 days Familerd dassdlcation: Farmland of statewide importance Map Unit Composlllon Malabon and similar sops: 50 percent Urban [and: 45 percent Estimates am based on observations, desmpkws, and transects of Setting Landforn: Terraces Landform position fthreadineensiaeall Tread Lown -slope shape: Linear Acrossabpe shape: Unear Parent material Silly and clayey alluvium Typical profile Hf - 0 to 12 Inches: silly day loam H2 -12 to 42 Inches: sllty day H3 - 42 to 60 inches: day loam properties and qualities Slope: 0 to 3 percent Depth to resWc&e feature: More than 80 inches Drainage dans: Well drained Capacity of the mos6mlting layer to trdnamit water (tcsary: Moderately high (0.20 to 0-57 inlhr) Depth to water table: Mom than 80 inches Frequancyof600dir None Frequency, ofpmding: None Available water suppty, 0 to 60lnches: High (about 11A Intoes) Interpretive groups Land capability clasei6cation (hrigaMcq: 1 Lard cepabfnty dassificabon ihemodgated): 1 Hydrologic Soil Group. C Forage suitabifily group: Well drained <15%Slopes (Go02XY0020R) Othervegatadve dassification: Well drained <15%Slopes (G002XY0020R) Hydric soli mtirg: No Nations! Resources Web Soil Survey 8116=1 eonssrvmion Sam" Naboml CeopanaWo Soll Survey Page l d2 Map Una Oesvipbm: MalnbpMlrban land mmplax—Lana C *Ansa, Orgon Description of Urban Land Interpretive groups Land capabXW classi9catlon (nigated): None specified Land capabdily Gassdreallon (rmnlydgated): 8 Hyddc Solt raV% No Data Source Information Soil Survey Area: lane County Area, Oregon Survey Area Data: Version 17, Jun 11, 2028 Natural lteaouiem Web Stir Survey enwmi Coaeery . Service Nsripnal C P rale Sad Survey Page 2 aft