Loading...
HomeMy WebLinkAboutStudies APPLICANT 5/26/2022 (2)St®rmwater Management Plan and Drainage Study 824 S 70' Street Springfield, Oregon For 836 S 70'h, LLC 939 Riverstone Lane Springfield, OR 97477 'aFD PROFF ANG I N6 40 69162PE �2 OREGON EXPIRES: 12/30/23 May 26, 2022 EVIGINEERING= 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 2 3.0 Proposed Development.........................................................................................2 4.0 Stormwater Constraints........................................................................................2 5.0 Proposed Development Stormwater Description.......................................2 6.0 Facility Sizing.....................................................................................................................3 7.0 Maintenance........................................................................................................................3 8.0 Conclusion...........................................................................................................................3 Appendices Appendix A Appendix B Branch Enpneecin , Inc. Description Site Soils and Map Basin Map 1.0 INTRODUCTION This Stormwater Management Plan (SWMP) report has been prepared for the analysis of subdividing a property located at 824 S 70'" Street. The subject site is south of Glacier Drive, north of Ivy Street, and east of S 69" Place. The subject property is identified as Tax Map 18-02-02-23 Tax Lot 4300. The stormwater runoff will be directed to the public stormwater system within the S 70" Street right-of- way. 2.0 EXISTING CONDITIONS The subject property is located in Springfield, Oregon in the Hillside Development Overlay Zone and consists of 1.76 acres of private property. The subject property's southwesterly boundary abuts the northerly terminus of S 69"Place and the easterly boundary abuts the westerly margin of S 701h Street. The subject property is surrounded on all sides by fully improved properties. There are fences of various heights and character around the site where it abuts other properties. 2.1 TOPOGRAPHY The subject property is sparsely wooded with clusters of trees which have diameters at breast height ranging from 6- to 28 -inches and grassed slopes of up to 12.5 percent. The elevations on the subject property range from 710 -feet in the southwesterly corner of the site to 678 -feet in the northeasterly corner of the site. 2.2 SOILS The Natural Resources Conservation Service (MRCS) Web Soil Survey maps the subject property as containing approximately 92.5% of Urban land-Hazelair-Dixonvihe complex (127C) and 7.S% Hazelair silty clay loam (52D) which resides in the northeasterly portion of the property. Urban land-Hazelair-Dixonville complex can have key features of both Hazelair and Dixonville soil types, while Hazelair silty clay loam only has Hazelair characteristics. They are differentiated below: • Hazelair is described as a moderately well -drained colluvium derived from sedimentary rock and is in Hydrologic Soil Group D; the soil has a limiting drainage capacity between 0.00- and 0.06 -inches per hour. The typical profile of the soil type has silty clay loam between 0- to It - inches, silty clay from 11- to 15 -inches, clay from 15- to 36 -inches, and weathered bedrock from 36- to 46 -inches; 5 test pits were dug for the associated Geotechnical Report, and no bedrock was found. • Dixonville is described as a well -drained colluvium and residuum derived from basalt and is in Hydrologic Soil Group D; the soil has a limiting drainage capacity between 0.06- and 0.20 - inches per hour. The typical profile of the soil type has silty clay loam between 0- to 14 -inches, A ty clay from 14- to 26 -inches, and weathered bedrock from 26- to 36 -inches; 5 test pits were dug for the associated Geotechnical Report, and no bedrock was found. A soils map and individual soil information is provided in Appendix A. 2.3 EXISTING STORM SYSTEM There is currently a roadside ditch located on the westerly edge of the pavement inside the S 70th Street right-of-way. Additionally, a 36 -inch public stormwater line exists along the easterly edge of the same right-of-way. An 8 -inch public stormwater line also exists to the southwest of the site inside the S 691" Place right-of-way, but is uphill from the subject property, and continues westerly away from the site. 3.0 PROPOSED DEVELOPMENT An 8 -lot subdivision is proposed. Each lot ranges from 7,400- to 7,600 -square feet. It is intended to dedicate and extend S 69" Place (a public road) from its northerly terminus, curving through the site to intersect S 70" Street. Included within the dedicated right-of-way will be a 20 -foot -wide roadway with curb and gutters with a 4.5 -foot planter strip and 5 -foot sidewalk on both sides of the road. The dedicated road will include underground utilities for the lots on its northerly and southerly margin. Based on conversations with staff at the City of Springfield, the site will not include on-site stormwater quality management facilities. Most treatment facilities require water to slowly move through a growing medium. Having water housed in facilities for longer time spans on slopes exceeding 10 percent may be harmful by promoting erosion and slides. It is assumed that individual lot improvements will either weephole/drain to the road or stub into the stormwater main. 4.0 STORMWATER CONSTRAINTS Connecting to the existing 36 -inch stormwater line within S 70'" Street will require an oversized manhole. The average slope across the site prevents the use of infiltration facilities to reduce stormwater discharge. S 69'" Place will be extending through the subject property. The easterly half on the existing improvements on S 69`" Place will drain to the site (see Appendix B for total basin map). S 69" Place extends approximately 420 -feet to the south. This accounts for approximately 6,720 -square feet of asphalt, 2,000 -square feet of sidewalk, and up to 22,369 -square feet of private residential improvements, which will be draining to the curb inlets being installed in this project. 5.0 PROPOSED DEVELOPMENT STORMWATER DESCRIPTION The proposed stormwater development for the subject property will consist of four curb inlets along the northerly portion of the road. The road will shed water to the north to match the existing direction of the slope on-site. Below is an explanation of what pipe size is required to convey runoff. The impervious surface of the proposed road consists of 9,022 square feet of asphalt and 4,236 -square feet of sidewalk. All the homes' impervious areas will be draining to the stormwater system as well as some of the pervious area on the south side of the road. If each lot maximizes its lot coverage, there will be an additional 20,874 square feet of impervious area and 19,423 square feet of pervious area entering the system. Utilizing the areas calculated in the last paragraph and in Section 4.0 above, the total flows during 2-, 10-, and 25 -year storm events are listed in the table below: 6.0 FACILITY SIZING All stormwater structures and pipes are to be installed per the City of Springfield's Engineering Design & Procedures Manual Chapter 4.00. 7.0 MAINTENANCE The facilities will be maintained publicly as they are located within the public right-of-way and are being installed through a Public Improvement Project (PIP). 8.0 CONCLUSION Feasibility has been established for the stormwater system outlined herein for the Tentative Subdivision. It will be necessary to update the design and calculations at the time of the PIP permitting. Flow (cfs) Depth of water in 12" pipe (inches) Pipe percent full 2 -year 1.20 3.2 27% 10 -year 1.61 3.8 32% 25 -year 1.82 4.1 34% 6.0 FACILITY SIZING All stormwater structures and pipes are to be installed per the City of Springfield's Engineering Design & Procedures Manual Chapter 4.00. 7.0 MAINTENANCE The facilities will be maintained publicly as they are located within the public right-of-way and are being installed through a Public Improvement Project (PIP). 8.0 CONCLUSION Feasibility has been established for the stormwater system outlined herein for the Tentative Subdivision. It will be necessary to update the design and calculations at the time of the PIP permitting. Site Soils and Map m o mRx dR P, Z rN 2 \ } \'6E J ! - Z 16 IL /;Q�)b2 C\\ dq !]#fes 2 =�sa..! {I!�■ § tg� #,0>+:,©A! �.{asxex Soil Map—Lane County Area, Oregon Map Unit Legend Map Unit Symbol Map Unit Name Acres to A01 Percent of AOI 52D Hazelair silty Gay loam, 7 to 20 0.1 7.5% percent slopes 127C (Urban land-Haze1air-0ixonAlle 1.81 92.5% complex, 3 to 12 percent slopes Totals for Area of Interest 2.0 100.0 Natural Resources Web Soil Survey 3/21/2022 Conservation Service National Cooperative Sail Survey Page 3 of 3 Map Unit Descripton: Hazelair silly clay loam, 7 to 20 percent slopes ---Lane County Area, Oregon Lane County Area, Oregon 52D—Hazelair silty clay loam, 7 to 20 percent slopes Map Unit Setting National map unit symbol., 237c Elevation: 200 to 2,000 feet Mean annual precipitation.: 30 to 60 inches Mean annual air temperature: 50 to 55 degrees F Frost -free period: 160 to 235 days Farmland classification: Farmland of statewide importance Map Unit Composition Hazelair and similar soils: 85 percent Minor components: 3 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Hazelair Setting Landform: Mountains, mountains Landform position (two-dimensional): Footslope Landform position (three-dimensional): Mountainbase Down-slope shape: Linear Across�fope shape: Linear Parent material: Colluvium derived from sedimentary rock Typical profile H1 - 0 to 11 inches: silty clay loam H2 - 11 to 15 inches: silty clay H3 - 15 to 36 inches: clay H4 - 36 to 46 inches: weathered bedrock Properties and qualities Slope: 7 to 20 percent Depth to restrictive feature: 20 to 40 inches to paralithic bedrock Drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 12 to 24 inches Frequency of flooding: None Frequency of ponding: None Available water supply, 0 to 60 inches: Low (about 4.8 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4e Hydrologic Soil Group: D Ecologicalsite: R002XC0100R- Claypan Low Hill Group Forage suitability group.: Moderately Well Drained < 15% Slopes (GO02XY0040R) Natural Resources Web Soil Survey 3/2112022 Conservation Service National Cooperative Soil Survey Page 1 of 2 Map Unit Description: Hazelair silty clay loam, 7 to 20 percent slopes --Lane County Area, Oregon Other vegetative classification: Moderately Well Drained < 15% Slopes (G002XY0040R) Hydric soil rating: No Minor Components Panther Percent of map unit: 3 percent Landform: Swales Hydric soil rating: Yes Data Source Information Soil Survey Area: Lane County Area, Oregon Survey Area Data: Version 19, Oct 27, 2021 USDA Natural Resources Web Soil Survey 3121/2022 21111111111 Conservation Service National Cooperative Soil Survey Page 2 of 2 Map Unit Description: Urban land-Hazelair-Dimnville complex, 3 to 12 pement slopes --Lane County Area, Oregon Lane County Area, Oregon 127C—Urban land-Hazelair-Dixonville complex, 3 to 12 percent slopes Map Unit Setting National map unit symbol. 2341 Elevation: 200 to 2,000 feet Mean annual precipitation: 30 to 60 inches Mean annual air temperature: 50 to 55 degrees F Frost -free period. 160 to 235 days Farmland classification: Not prime farmland Map Unit Composition Urban land: 35 percent Hazelair and similar soils: 25 percent Dixonville and similar soils: 20 percent Minor components: 3 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Urban Land Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 8 Hydric soil rating: No Description of Hazelair Setting Landform: Hills Landform position (two-dimensional): Summit, shoulder, toeslope Landform position (three-dimensional): Interfluve, nose slope, base slope Down-slope shape: Linear Across -slope shape: Linear Parent material: Colluvium derived from sedimentary rock Typical profile H1 - 0 to 11 inches: silty clay loam H2 - 11 to 15 inches: silty clay H3 - 15 to 36 inches: clay H4 - 36 to 46 inches: weathered bedrock Properties and qualities Slope: 3 to 12 percent Depth to restrictive feature: 20 to 40 inches to paralithic bedrock Drainage class. Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 12 to 24 inches l= Natural Resources Web Soil Survey 3/212022 Conservation Service National Cooperative Soil Survey Page 1 of 3 Map Unit Description: Urban land-Hamlair-Dixonville complex, 3 to 12 percent slopes --Lane County Area, Oregon Frequency of flooding: None Frequency of ponding., None Available water supply, 0 to 60 inches., Low (about 4.8 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated). 4e Hydrologic Soil Group: D Ecological site: R002XCOl OOR - Claypan Low Hill Group Forage suitability group: Moderately Well Drained < 15% Slopes (G002XY0040R) Other vegetative classification: Moderately Well Drained < 15 Slopes (GO02XY0040R) Hydric soil rating., No Description of Dixonville Setting Landform: Hills Landform position (two-dimensional): Summit, shoulder, toeslope Landform position (three-dimensional): Interfluve, nose slope, base slope Down-slope shape: Linear Across -slope shape: Linear Parent material., Colluvium and residuum derived from basalt Typical profile H1 - 0 to 14 inches: silty clay loam H2 - 14 to 26 inches: silty clay H3 - 26 to 36 inches: weathered bedrock Properties and qualities Slope: 3 to 12 percent Depth to restrictive feature: 20 to 40 inches to paralithic bedrock Drainage class: Well drained Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding.: None Available water supply, 0 to 60 inches: Low (about 4.6 inches) Interpretive groups Land capability classification (irrigated).: None specified Land capability classification (nonirrigated): 3e Hydrologic Soil Group: D Ecological site: R002XCO11OR -Low Hill Group Forage suitability group: Well drained < 15% Slopes (GO02XY0020R) Other vegetative classification: Well drained < 15% Slopes (GO02XY0020R) Hydric soil rating: No L6p,� Natural Resources Web Soil Survey 3121/2022 Conservation Service National Cooperative Soil Survey Page 2 of 3 Map Unit Description: Urban land-Hazelair-Dixonville complex, 3 to 12 percent slopes --Lane County Area, Oregon Minor Components Panther Percent of map unit: 3 percent Landform. Swales Hydric soil rating: Yes Data Source Information Soil Survey Area: Lane County Area, Oregon Survey Area Data: Version 19, Oct 27, 2021 usim Natural Resources Web Soil Survey 3/2112022 �� Conservation Service National Cooperative Soil Survey Page 3 of 3 APPENDIX B Basin Map ' ..:�':,+' .. "fit ''.f "` � - �- a�:.F• ,_ � r •. . ��'_ •� +"}lam h y rii T' >>ll�lL �{,1 r[§�p�g� 1 :L.1�r',t ': •. �i�- � 7 4 tip'' �Y� .✓ r �� ♦y.Y (• 00 44 Al IAI t. Tillit t r; �{ i+,•�" . t.. y�a4.. �: ♦ �J :' q v ,• f y IC