The URL can be used to link to this page

Resolution No. 14-42 CITY OF TIGARD, OREGON RESOLUTION NO. 14- V-2 A RESOLUTION TO ACCEPT THE RIVER TERRACE STORMWATER MASTER PLAN WHEREAS, the City of Tigard annexed the River Terrace area west of Bull Mountain in 2011 and 2012; and WHEREAS,the City of Tigard does not have an existing Stonnwater Master Plan,and WHEREAS,the City of Tigard has completed a Stonnwater Master Plan specific to the River Terrace area, contributing to the city's broader goal of completing the River Terrace Community Plan and meeting state requirements for public facility planning,and WHEREAS, stonnwater public facility projects have been identified as part of the River Terrace Stonnwater Master Plan,and WHEREAS,a comprehensive funding strategy for all public facility projects in River Terrace will be developed as part of the River Terrace Community Plan.This strategy will include a list of projects to complete in the near term and their respective funding sources. NOW,THEREFORE, BE IT RESOLVED by the Tigard City Council that: SECTION 1: The City of Tigard River Terrace Stormwater Master Plan (Exhibit A) is hereby adopted. SECTION 2: The projects identified in the River Terrace Stormwater Master Plan shall be included in the comprehensive funding strategy for all public facility projects in River Terrace. SECTION 3: This resolution is effective immediately upon passage. r PASSED: This day of 2 11e'V /er2gl4. UA Mayo City of Tigard ATTEST: � ae�- City Recorder-City of Tigard RESOLUTION NO. 14- Page 1 River Terrace Stormwater Master Plan Otak Project No. 16851 Prepared for: City of'figard 1 Septen-iber 5, 20 14 46 y E Acknowledgements RIVER TERRACE Stormwater Master Plan Otak Project No. 16851 Prepared for: City of Tigard Prepared by: Kevin Timmins, P.E. Project Manager Ashley Cantlon, P.E. Stormwater Engineer Otak, Inc. 808 SW Third Avenue, Suite 300 Portland, OR 97204 September 2014 Table of Contents Section I—Introduction and Background.....................................................................................I Introduction......................................................................................................................................1 Goalsand Objectives......................................................................................................................2 DesignStandards.............................................................................................................................3 BackgroundInformation................................................................................................................4 Existing Conditions and Key Findings.........................................................................................4 Section 2—Stormwater Management Strategy............................................................................7 WaterQuality Strategies..................................................................................................................7 SiteScale LIDA...........................................................................................................................8 StreetScale LIDA.......................................................................................................................8 NeighborhoodScale LIDA.......................................................................................................9 Regional Stormwater Facilities................................................................................................10 WaterQuantity Strategies.............................................................................................................11 RegionalDetention...................................................................................................................11 High-Flow Conveyance................. Section 3—Stormwater Concept Plan and Estimated Costs................................................. 13 StrategyArea A..............................................................................................................................13 StrategyArea B...............................................................................................................................13 StrategyArea C...............................................................................................................................14 EstimatedCosts.............................................................................................................................15 Implementation..............................................................................................................................17 Maintenance....................................................................................................................................22 Section 4—Stormwater Calculations..........................................................................................23 ImperviousArea............................................................................................................................23 DownstreamAnalysis...................................................................................................................24 Regional Stormwater Facilities for Water Quality....................................................................25 Regional Stormwater Facilities for Water Quantity..................................................................26 High-Flow Conveyance................................................................................................................27 River Terrace Stormwater Master Plan i otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014 September\FINAIrRiverTerrace_SWMP_090514.docx Table of Contents Continued Tables Table 2.1: Recommended Strategies for Different Areas of River Terrace.............................7 Table 2.2: Examples of Site Scale LIDA.......................................................................................8 Table 2.3: Examples of Street S cale LIDA..................................................................................9 Table 2.4: Examples of Neighborhood Scale LIDA.................................................................10 Table 2.5: Examples of Multi-Functional Regional Stormwater Facilities.............................11 Table 3.1: Stormwater Infrastructure Total Cost Summary.....................................................16 Table 4.1: Summary of Impervious Area Reference Calculations...........................................24 Table 4.2: Impervious Percentage by Land Use........................................................................24 Table 4.3: Summary of Water Quality Calculations for Regional Water Quality Facilities.25 Table 4.4: 25-yr Peak Flow(cfs) Discharges from Regional Detention Facilities................26 Table 4.5: Summary of Regional Detention Facility Sizes........................................................27 Table 4.6: 25-yr Peak Flows (cfs) at Site Discharge Locations to T7,T8,&T9...................28 Figures Figure 1: Proposed Zoning(assumed for runoff calculations) Figure 2: Existing Drainage Basin Diagram Figure 3: Stormwater Management Strategy Areas Figure 4A: Stormwater Concept Plan Diagram (Strategy Area A) Figure 4A1: Stormwater Concept Plan Diagram (Strategy Area A: South) Figure 413: Stormwater Concept Plan Diagram (Strategy Area B) Figure 4C: Stormwater Concept Plan Diagram (Strategy Area C) Figure 5: West Bull Mountain Soil Infiltration(GeoDesign,2009) Attachments :attachment A: Background Information Attachment B: Cost Estimate Attachment C: XP-SWMM Model Schematic and Input Data Attachment D: West Bull Mountain Hydrologic/Hydraulic Analysis Figures (HDR,2008) Attachment E: Drawings from Roy Rogers Road Improvement Project River Terrace Stormwater Master Plan otak L:\Project\168(X)\16851\Reports\StormwatefMasterPlan\Final-2014_September\FINAI,River rerrace_SWMP_090514.docx Section I—Introduction and Background Introduction The West Bull Mountain Concept Plan was completed by Washington County in October 2010. Subsequently,the City of Tigard annexed the area and renamed it River Terrace. The city is working to complete the required planning process to allow development to begin. Part of the planning process involves master planning of utilities,including stormwater management infrastructure.This master plan contributes to the city's broader goal of completing a River Terrace Community Plan. River Terrace Study Area (outlined in yellow) W h o f O Ir IP tat It YLL C GAAROL S I °A KR • BULL SWMCDONALOSI • EAOOWg 4 SW•ONIIIA RD C C A t rl•ELr• ND RD SW nLIRMAM RD E a s K i n y : C SW SW TUALATIN RO Oytl I h 3 tt7 1 T u a I at 111 >RD SW NYBERCX t FRQS) The River Terrace Stormwater Master Plan (SMP)includes and refines the strategies and best management practices previously developed in the West Bull Mountain Stormwater Infrastructure Plan(SWIP) in response to stakeholder input and discussions with the project design team. The purpose of the River Terrace SMP is to: • Describe the stormwater management strategy for River Terrace. • Show how the strategy is to be applied during development of River Terrace. • Provide a cost estimate for the regional (i.e. public) stormwater management infrastructure. • Provide recommendations for implementation. • Provide recommendations for maintenance. • Document supporting calculations. River Terrace Stormwater Marler Plan 1 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAL-RiverTerrace_SWMP_090514.doca Section I—Introduction and Background Continued The study area for the SMP is based on the River Terrace area annexed by the City of Tigard in 2011 and 2013.The assumptions about land use,road locations,and site layout used to perform supporting calculations for this document reflect the adopted land use and proposed zoning in place at the time the calculations were performed (May 2014).The proposed land use and zoning assumed in development of the River Terrace SMP is provided in the attached Figure 1. Goals and Objectives The following stormwater management goals were developed during the West Bull Mountain SWIP and were carried forward into the development of the River Terrace SMP. • Restore/enhance vegetated corridors • Protect water quality • Preserve existing hydrology • Promote safe and long-lasting stormwater facilities • Balance the use of regional and on-site stormwater management • Preserve existing mature vegetation • Maximize use of multi-benefit facilities to create community amenities • Promote partnership with other public service providers The following stormwater management objectives support these goals and have been incorporated into the River Terrace SMP based upon the needs and characteristics of each drainage basin in the study area. • Regional facilities should be developed wherever possible to minimize the total number of facilities needed in the area. Low Impact Development Approaches (LIDA) for water quality and existing wetland areas for water quantity should be proposed wherever practicable. • Regional facilities should be dispersed to contribute to stream flow at multiple locations. • Regional facilities should be well-defined and accessible to maintenance crews to ensure longevity. • Regional facilities should be designed as community amenities that provide aesthetic, educational,and/or recreational benefits in addition to stormwater management. • Open conveyance elements should be used to enhance"key"pedestrian routes along streets or stream corridors. • Increased conveyance between the River Terrace study area and the Tualatin River should be utilized to minimize erosion and slope instability in steeper areas (e.g. high- flow bypass pipe and/or stream restoration). River Terrace Stermrater Master Plan 2 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAIrRiverTerrace_SWMP_090514.docx Section I—Introduction and Background Continued • LIDA (e.g. eco-roofs, flow-through planters,etc.) should be limited to flow-through type facilities unless geotechnical evaluations can demonstrate that infiltration is not expected to contribute to slope instability. • Impervious area should be minimized wherever practicable to minimize stormwater runoff(e.g. clustered development,"skinny" streets,reduced parking,etc.). • Regional water quantity/water quality facilities should be located along Roy Rogers Road,the proposed interior street parallel to Roy Rogers Road,or in/along existing drainages or wetlands whenever possible. Design Standards The stormwater infrastructure strategies recommended in this plan are based upon Clean Water Services (CWS) Design and Construction Standards and the CWS Low Impact Development Appmacbes(LIDA)Handbook. In addition,this plan reflects the City of Tigard's intention to adopt new design standards for the River Terrace study area in collaboration with CWS.The need for these new standards is based upon the following: • The city's recent experiences dealing with channel stability problems elsewhere on Bull Mountain,and the presence of similar drainage channel conditions in the River Terrace study area. • The city's decision to develop a new continuous simulation model for the River Terrace study area. • Anticipated changes to CWS's Design and Construction Standards to address pending requirements under their National Pollutant Discharge Elimination System (NPDES) permit. • The community's desire to preserve and protect existing natural resources in the River Terrace and Bull Mountain area. At a minimum,the new design standards will include the following: • Requirement to minimize stormwater impacts caused by development through use of best practices for water quantity management, even when a downstream analysis shows that the downstream system has adequate conveyance capacity.A new continuous simulation model will be developed to aid in the implementation of a flow-duration based design standard for design of water quantity management facilities. • Development of a minimum facility size standard for regional water quality and quantity (i.e. detention) facilities to allow flexibility in the implementation of this plan. • Allowance for smaller regional facilities in locations not anticipated by this plan where it can be shown that development of the recommended regional facility is either not timely or feasible and the proposed facility meets the minimum facility size standard. River Terrace Stormvater Master Plan 3 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINA1-Riverl'errace_SWMP_090514.docx Section I—Introduction and Background Continued • Allowance for interim facilities where regional facilities are recommended in instances where it can be shown that development of a regional facility is not timely and the proposed interim facility meets the minimum facility size standard. • Requirement to design regional stormwater management facilities as community amenities that provide aesthetic,educational,and/or recreational benefits. Background Information :1s part of this SMP,the project team reviewed seven key documents prepared for the River Terrace study area that provided background information about site conditions.A complete review of the data and relevant conclusions for each of the seven documents are provided in Attachment A of this SMP. These documents are as follows: 1) West Bull Mountain Hydrologic and Hydraulic Analysis(HDR Inc.,March 2008) 2) West Bull Mountain Natural Resources Inventory Technical Report(Pacific Habitat Services, April 23,2008.) 3) Regional Landslide Hazard Mapping, West Bull Mountain Planning Area,Washington County, Oregon (Draft DOGAMI,March 31,2008) and ADDENDUM to Regional Landslide Hatiard Mapping, West Bull Mountain Planning Area,Washington County,Oregon (DOGAMI,April 21,2008). 4) Report of Prrhmnag Geological Evaluation West Bull Mountain Planning Arra(GeoDesign,Inc., April 21,2009) 5) Roy Rogers Road Improvements S W Beef Bend/Elsner/Scholls-Sherwood Roads(CH2MHill, November 1999) 6) Roshak Pond Overview— West Bull Mountain Planning(Washington County Department of Land Use and Transportation Planning Division,November 5,2008) 7) West Bull Mountain Siormwater Infrastructure Plan(Otak,February 2010). Existing Conditions and Key Findings A basic understanding of existing conditions was useful in developing this SMP and as a starting point for future development of the River Terrace study area. Key findings regarding existing study area conditions are as follows: • The River Terrace study area is drained by nine small drainage channels. Figure 2 shows the existing drainage basins.A small area at the north end drains towards Scholls Ferry Road. • Culverts under Roy Rogers Road have capacity for existing flows. • Culverts under Beef Bend Road for drainages T8 and T9 are under-capacity for existing flow rates.Conveyance improvements are needed to handle future flow rates from new development. River Terrace Stormmater Master Plan 4 otak L:\Project\168(X)\16851\Reports\StonnwaterMasterPlan\Final-2014_September\FINAL Riverl'errace_SWMP_090514.docx Section 1—Introduction and Background Continued • Fish passage requirements to modify existing culverts for fish passage will need to be evaluated at the time of design and implementation of improvements to Roy Rogers Road and Beef Bend Road. • The natural resources identified were used as a constraint to define buildable lands during formation of the concept plan for West Bull Mountain and was carried forward into the River Terrace SMP. Several culvert barriers and enhancement opportunities were identified for consideration during development of River Terrace. • The existing drainage channels in and downstream of the River Terrace study area are steep and have a high potential for channel erosion due to the fine sediment characteristics of the area and the velocity conditions that exist in these steep drainages. • The infiltration potential is poor in the River Terrace study area.The results of geotechnical drilling and laboratory testing confirmed that the area is underlain by clayey residual soils derived from the underlying basalt bedrock. • The effects of infiltration on slope stability for developed conditions are expected to be problematic given the steep terrain and proximity to shallow bedrock. Therefore, infiltration of stormwater is not recommended.LIDA facilities called for in this SMP shall be flow-through type facilities that are constructed with an under drain and do not rely on infiltration of stormwater. • Site specific geologic and geotechnical conditions will be important to evaluate during the design and construction of stormwater management facilities in the River Terrace study area. The Roshak irrigation pond,located in the northern part of the River Terrace study area along the T2 drainage,has a capacity of approximately 20 acre-feet. • Pond levels are maintained seasonally by pumping groundwater.The berm that forms the pond is comprised of a layer of soft to medium stiff silt Missoula Flood deposits and a layer of soft to medium stiff clay and silt derived from the basaltic residual soil. The pond is not identified in the County's acknowledged 1983 Goal 5 Program;however,it is identified in the County's 2005 Tualatin Basin Goal 5 Program as Class I and II Riparian and Riparian Impact Area. • The natural resource inventory for West Bull Mountain (Pacific Habitat Services,2008) identifies the pond as a jurisdictional water body by the Oregon Department of State Lands (DSL) and/or Corps of Engineers and would,therefore,be treated by CWS as a water quality sensitive area requiring a vegetated corridor. • The actual location of the vegetated corridor is determined when a development application is submitted,and depending on slope may be between 50 and 200 feet. Therefore,only a vegetated corridor proxy has been mapped around the perimeter of the pond at this time.The vegetated corridor proxy is an estimated location of the vegetated River Terrace Stormwater Master Plan 5 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAIrRiverl'errace_SWMP_090514.docx Section I—Introduction and Background Continued corridor based upon the wetland inventory and the adjacent slopes (Pacific Habitat Services,2008). • Modifications to the pond,including its removal,are expected to require permits from Oregon DSL and/or Corps of Engineers. • Change in water rights or use of the existing water rights associated with the pond would require coordination with Oregon Water Resources Department. River Terrace Stormvater Master Plan 6 otak U\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAI-Ric,erTerrace_SWMP_090514.docx Section 2—Stormwater Management Strategy Stormwater management infrastructure is needed to protect the water quality of downstream natural resource areas,the downstream receiving waters from increased rates of erosion caused by additional water quantity,and the built environment from flood damage during large storm events.The recommended Stormwater Management Strategy takes a comprehensive approach to incorporating stormwater management into the landscape of River Terrace.The SMP makes use of existing site topography,natural systems,and site design to efficiently and effectively manage stormwater quantity and quality. There are three combinations of water quality and quantity management strategies applied to the River Terrace study area,as shown in the attached Figure 3 and summarized in Table 2.1. The water quality and water quantity tools that are recommended for each of the strategies are the focus of this section of the River Terrace SMP. Table 2.1: Recommended Strategies for Different Areas of River Terrace Strategy Water Quality Water Quantity Area \ Combined Regional Water Quality Treatment and Water Quantity Detention Facilities Street Site and Neighborhood Scale 13 Regional Water Quantity Detention Facilities Low Impact Development Approaches C Street,Site,and Neighborhood Scale Downstream Conveyance Improvements Low Impact Development Approaches (High-Flow Bypass/Stream Restoration) Water Quality Strategies Best management practices (BMPs) are required to manage the transport of stormwater pollutants from River Terrace development to downstream receiving waters. Source control measures (i.e.proper management and disposal of household and animal waste) that reduce or eliminate the possibility of stormwater contact with pollutants are the most effective BMPs. However,not all contact with pollutants can be eliminated with source control BMPs and other management practices to meet water quality requirements are needed. It is recommended that water quality treatment in River Terrace is managed using Low Impact Development Approaches (LIDA) at a variety of scales (i.e. site,street,and neighborhood) and multi-purpose regional stormwater facilities that offer community benefits in addition to stormwater management. River Terrace Stormwater Master Plan 7 otak L:\Project\16800\16851\Reports\Stormwater114asterPlan\Final-2014_September\FINAL Riverrerrace_SWMP_090514.docx Section 2—Stormwater Management Strategy Continued LIDA,as described in the LIDA Handbook (CWS,2009),includes such things as infiltration planters,vegetated swales,and eco-roofs. LIDA facilities can be engineered to treat stormwater runoff and reduce stormwater volume from smaller, frequent rain events by encouraging retention within the facilities. It is recommended that the use of LIDA in River Terrace is limited to treating stormwater runoff and not retaining it due to poor soil infiltration and the potential for slope instability.All LIDA facilities should be sized per CWS Design and Construc7ion Standards in combination with the LIDA Handbook (CWS,2009) and designed to manage site runoff from all impervious surfaces generated by the water quality event. Site Scale LIDA Site scale refers to parcel by parcel LIDA on the buildable land shown in the River Terrace study area that is not planned for public right-of-way.Photographs of examples are shown in Table 2.2. Table 2.2: Examples of Site Scale LIDA k � Eco-roof Infiltration Basin Flow-Through Planter Site LIDA facilities should be designed as flow-through type facilities with an underdrain to minimize the occurrence of infiltration[ and an overflow to direct larger storm flows to a safe location,such as an open space area,the street gutter,or some other engineered stormwater conveyance feature. Street Scale LIDA Streets are a major source of urban stormwater pollution. Street LIDA refers to facilities located within the public right-of-way designed to treat runoff from streets,sidewalks,and trails. Street LIDA facilities can be located in many different places,including but not limited to sidewalk furnishing zones,planter strips,or curb extensions. These facilities can be I Infiltration potential is poor due to clayey soils.Infiltration is also potentially problematic for slope stability given the steep terrain and proximity to shallow bedrock. River Terrace Stormwale r Master Plan 8 otak 1-:\Proiect\16800\16851\Reports\StunnwaterMasterPlan\Final-2014_September\FINALrRiverTerrace_SWMP_090514.docx Section 2—Stormwater Management Strategy Continued located adjacent to the street with curb inlets that allow runoff to pass through the curb into the LIDA facility.Photographs of examples are shown in Table 2.3. Table 2.3: Examples of Street Scale LIDA 6;h;h I k 4� - Planter Box Curb Extension Linear Swale Public rights-of-way can also operate as a collection and conveyance system to transport stormwater from both streets and adjacent sites to a downstream destination.The conveyance facilities need to be capable of managing large storm events that exceed the capacity of LIDA facilities and route them to a safe location for discharge to the natural drainage system. The conveyance system will be a combination of street gutters,pipes,culverts and open channels.The use of street gutters and open channel conveyances should be maximized. Flow splitter manholes are recommended for portions of the River Terrace SMP,to maintain low flow contributions to the small natural streams near their headwaters and direct high flows to a bypass conveyance system,described later as part of the water quantity management strategy for River Terrace. Neighborhood Scale LIDA Neighborhood scale refers to LIDA applied to a collection of parcels and/or portions of right-of-way that cannot,or are not proposed to,be managed using Site or Street LIDA. Stormwater runoff in these situations is collected and routed to a LIDA facility down the block.This type of LIDA might occur at the end of a street,at a street corner,or adjacent to a neighborhood park. Photographs of examples are shown in Table 2.4. River Terrace Stormwater Master Plan 9 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_Septembcr\FIN AI-River'l'errace_SwMP_090514.docx Section 2—Stormwater Management Strategy Continued Table 2.4: Examples of Neighborhood Scale LIDA Infiltration Basin Vegetated Swale Extended Detention Pond Neighborhood UDA facilities should be designed to make efficient use of the landscape, enhance site design,and be a neighborhood amenity(not an isolated eye-sore hidden in the comer) and have an overflow to direct larger storm flows to a safe location,such as an open space area,the street gutter,or some other engineered stormwater conveyance feature. Regional Stormwater Facilities Regional stormwater facilities collect runoff from large areas,often under different ownership,are located at a low point,and are the last line of defense before stormwater is discharged to a natural drainage system. Regional stormwater facilities reduce the overall number of facilities that need to be maintained and can be a large enough feature in the landscape that they can provide additional benefits beyond just stormwater management. Regional facilities can provide water quantity,water quality,or a combination of both. Regional facilities recommended for River Terrace provide water quantity,or they provide a combination of both water quantity and water quality. Regional stormwater facilities use LIDA principles (i.e. bio-retention) applied at a larger scale. Regional stormwater facilities for water quality in River Terrace are required to be vegetated facilities and integrated with the area as a community amenity.Examples of community amenities that could be provided by a regional facility include aesthetics, education,recreation,and habitat. Stor mwater facilities and open water can enhance parks and recreational areas. Some facilities are only needed during heavy and infrequent storm events,and can be designed to have other uses at other times (as seen in the basketball court photo below). The placement of regional stormwater facilities along Roy Rogers Road can also function as a buffer between traffic and River Terrace development,and as a transitional landscape along the urban/rural interface. River Terrace Stormwater Master Plan 10 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINALrRiver7'errace_SWMP_090514.docx Section 2—Stormwater Management Strategy Continued Photographs of examples of multi-functional regional facilities are shown in Table 2.5. Table 2.5: Examples of Multi-Functional Regional Stormwater Facilities Y I 31 N err �ilrr lig.. Mimic Natural System:Wetland Passive recreation: Outdoor Seating Active Recreation: Basketball Court Water Quantity Strategies A stormwater water quantity management strategy is required everywhere in River Terrace to mitigate for potential flooding and erosion impacts that would otherwise result from increases in stormwater runoff volume,rate,and duration due to development in River Terrace. There are two water quantity strategies recommended in the River Terrace study area: regional stormwater detention and high-flow conveyance improvements extending downstream to the Tualatin River.The location for application of each strategy in River Terrace is described previously in Table 2.1 and on the attached Figure 3. Regional Detention Regional stormwater facilities for water quantity in River Terrace are required to be vegetated facilities and be integrated with the site as a community amenity,just like the regional facilities for water quality. Regional detention facilities shall be combined with the regional water quality facilities whenever possible. However,there are two locations where existing wetland areas are recommended to be modified to provide regional water quantity benefits,in which case water quality requirements have to be achieved before stormwater is discharged to these wetland areas. Regional detention facilities will need to be sized per the design standards described in Section 1 of this plan once they are adopted by the city. However,these standards could be superseded by future changes to the CWS Design and Construction Standards that are more stringent than those described by this plan and subsequently adopted by the city. River Terrace Stormwater Master Plan 11 otak L-.\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAI-Rii�erTerrace_SWMP_090514.docx Section 2—Stormwater Management Strategy Continued High-Flow Conveyance The southern part of the River Terrace study area is located on steep terrain,along small drainages with small drainage basins,and where regional water quantity (i.e. detention) facilities would be difficult to construct. As a result,the water quantity strategy for the southern portion of the area includes the use of flow splitters at stream crossings to continue low flow discharges to the stream channels and a high-flow bypass conveyance system to safely convey the additional stormwater runoff down the south side of Bull Mountain and beneath Beef Bend Road. On the south side of Beef Bend Road,it is a short distance to a nearby Tualatin River meander bend.The high-flow conveyance system could either be in the form of a bypass pipe,stream restoration,or a combination of both.Any high-flow conveyance system utilizing a restored stream channel should be designed to handle and remain stable under future flow rates. 2 Infiltration potential is poor due to clayey soils.Infiltration is also potentially problematic for slope stability given the steep terrain and proximity to shallow bedrock. River Terrace Stormwater Master Plan 12 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAI-River I'errace_SWMP_090514.docx Section 3—Stormwater Concept Plan and Estimated Costs A Stormwater Concept Plan was prepared for each of the three recommended stormwater strategy areas.The recommended stormwater strategy areas are described below, summarized in Table 2.1,and shown in the attached Figures 4A,4A.1,4B,and 4C. The Stormwater Concept Plan schematically represents the specific stormwater infrastructure needs for River Terrace. It also includes the recommended drainage basin boundaries and stormwater conveyance assumptions used in the calculation of stormwater flows and facility sizes. Calculations performed to estimate facility sizes are presented later in Section 4 of this plan. In general,the conveyance of stormwater runoff throughout the River Terrace study area is assumed to follow closely with the street, trail,and public right-of-way network. Strategy Area A • Water Quality = Regional Water Quality Treatment Facility • Water Quantity = Regional Water Quantity Detention Facility The Stormwater Concept Plan for Strategy Area A is shown in the attached Figures 4A and 4A.1.There are a total of 11 regional stormwater management facilities recommended to meet both water quality and quantity requirements for 253 acres (49%) of the River Terrace study area. Stormwater in this area will be collected and conveyed in storm pipes that are typically located within the road network to the low points in their respective basins.These pipes will discharge to regional facilities located along Roy Rogers Road and existing local drainages. Strategy Area A is recommended for one small area on the south side of the River Terrace study area,next to SW 150 'Avenue,because it cannot be conveyed across the slope to connect to the high-flow conveyance system recommended for Strategy Area C. Strategy Area B • Water Quality = Street,Site,and Neighborhood Scale LIDA • Water Quantity =Regional Water Quantity Detention Facility The Stormwater Concept Plan for Strategy Area B is shown in the attached Figure 4B. LIDA facilities are recommended for water quality treatment in this area. LIDA facilities will be constructed and paid for by development as streets and neighborhoods are built.Two regional stormwater management facilities are recommended to meet water quantity requirements for 72 acres (14%) of the River Terrace study area.These two facilities are recommended within existing wetland areas and shall be designed to provide for enhancement and restoration of these areas. River Terrace Stormwater Master Plan 13 otak I.:\Project\16800\16851\Reports\StottnwaterMasterPlan\Final-2014_September\FINAIrRiverTerrace_SWMP_090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued Strategy Area C • Water Quality = Street,Site,and Neighborhood Scale LIDA • Water Quantity =Downstream Conveyance Improvements (High-Flow Bypass/Stream Restoration) The Stormwater Concept Plan for Strategy Area C is shown in the attached Figure 4C. LIDA facilities are recommended for water quality treatment in this area.LIDA facilities will be constructed and paid for as streets and neighborhoods are built. No infiltration or detention facilities are recommended in this area.Water quantity requirements will be met through downstream conveyance improvements. Stormwater will be collected and conveyed in storm pipes that are typically located within the road network where it will be routed through two flow splitter manholes along the T8 and T9 drainages. The flow splitters will be designed to allow low flows to continue into each drainage channel and to route high flows into a high-flow conveyance system to a single off-site improvement along the T8 drainage.A single off-site improvement is recommended in order to limit the amount of stormwater infrastructure outside the Urban Growth Boundary(UGB). Stormwater must receive treatment for water quality before reaching the flow splitters or entering the conveyance system. The T8 high-flow conveyance system will bring stormwater down the hill and beneath Beef Bend Road.A high-flow bypass pipe is recommended from the T8 flow splitter to Beef Bend Road for the following reasons: • the presence of steep terrain and erodable soils • the ability of piping to handle the combined runoff from both drainage basins more safely than a restored stream at this location • the proximity of future right-of-way adjacent to the T8 drainage channel that could readily accommodate piping,thus eliminating the need,expense,and challenge of acquiring additional land or easements for conveyance outside the UGB. Once the bypass pipe is beneath Beef Bend Road, stream enhancement and restoration of the T8 drainage is recommended all the way to the Tualatin River to accommodate future stormwater runoff from River Terrace and the urban reserve area south of River Terrace. Alternatively,a high-flow bypass pipe could be constructed adjacent to the T8 drainage all the way to the Tualatin River. These high-flow conveyance improvements are recommended to meet quantity requirements for 191 acres (37%) of the River Terrace study area.A conceptual design and alternatives analysis is needed for each conveyance proposal to determine the preferred alternative. River Terrace Stormwater Matter Plan 14 otak 1.\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAL,River l'errace_SWMP_090514.docr Section 3—Stormwater Concept Plan and Estimated Costs Continued While on-site detention was considered in this area,downstream conveyance improvements in the form of a pipe and/or stream restoration are recommended by this plan for the following reasons: • Geologic conditions strongly suggest it is better to convey the water to the Tualatin River than hold it higher up on the mountain. Piped conveyance would provide the most direct route for water to the Tualatin River. • Until such time as the UGB is expanded to the south,piped conveyance would allow farm land to remain in agricultural use. • When considering land costs,piped and/or stream conveyance may be less expensive than on-site detention. Estimated Costs LIDA facilities applied at the site,street,and neighborhood scale are not illustrated on the Stormwater Concept Plans and are not included in the Stormwater Cost Estimate. It is expected that these water quality facilities will be constructed and paid for by development as individual sites are developed.An analysis of cost to implement LIDA facilities was performed for Clean Water Services (WRG,December 2008) and concluded that costs to implement LIDA are often site-specific,and may or may not result in lower construction costs when compared to the cost of a conventional design approach. Costs associated with stormwater management for Arterial and Collector Streets are included in the transportation infrastructure cost estimate. Costs associated with stormwater management for Neighborhood Routes and Local Streets are assumed to be part of the costs to develop individual sites. Costs for regional stormwater facilities were determined according to estimates for facility size(footprint and volume).Assumptions and calculations used to estimate facility sizes are presented later in Section 4 of this plan. The following assumptions were made about the size,geometry,and needs of the regional stormwater management facilities to derive planning level cost estimates. • Regional stormwater facilities for detention and water quality were based upon meeting the detention standard. Excavation volume estimates assumed 5.5 feet of storage depth with 3H:1 V side slopes plus an additional one foot for freeboard. • Regional water quality facilities were assumed to fit within the space required for meeting the detention standard. • Land area required to locate a regional facility was assumed to be 110 percent of the facility footprint to construct.This extra space is for extra land area needed to match surrounding grades and to provide for facility access. River Terrace Stormwater Master Plan 15 otak L:\Project\16800\16851\Reports\StoffnwaterMas[erPlan\Final-2014_September\FINALRiverTerrace_SWMP_090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued • Sizing of regional stormwater facilities for detention where combined with wetland enhancement was based upon an estimate to construct a similarly sized detention facility outside of a wetland area,but spread out over a larger footprint to minimize inundation depths (1.5 feet) that would be tolerable in a wetland enhancement design and shallower side slopes (5H:1V). • Facilities sized to meet the new detention standard may result in a larger detention storage volume.Volumes calculated for the River Terrace SMP were increased by 25% to account for the potential increase. Costs for inlet/outlet pipes,manholes,inlets, flow splitters,and flow control devices in the right-of-way were based on recent bid tabulations. The total estimated cost for stormwater infrastructure for the River Terrace study area is summarized below in Table 3.1.A construction contingency was included in the cost estimates to account for uncertainties that are inherent in the planning stages for stormwater infrastructure.The contingency includes,but is not limited to variability in actual quantities, miscellaneous items such as fencing or signage,and unknown phasing for implementation. The estimate for land acquisition costs assumes purchase of land or easements for regional stormwater facilities and for high-flow conveyance improvements.The high-flow bypass pipe recommended between River Terrace and Beef Bend Road is assumed to be located within a future right-of-way,the cost of which is included in the transportation infrastructure costs. High-flow conveyance cost estimates are based upon a high-flow bypass pipe.An alternatives analysis is needed to determine the feasibility of stream restoration versus high- flow bypass pipe and should include a cost comparison. Table 3.I: Stormwater Infrastructure Total Cost Summary Construction $9,910,000 Engineering/Permitting $5,160,000 Land Acquisition $5,560,000 Total $20,630,000 A detailed breakdown of the Stormwater Infrastructure Total Cost Summary is provided in Attachment B. River Terrace Stormwater Master Plan 16 oak L:\Project\16800\16851\Reports\StormwaterMasterillan\Final-2014_September\F1NA1rRivei rerrace_SWMP_090514.doex Section 3—Stormwater Concept Plan and Estimated Costs Continued Implementation It is anticipated that implementation of this SMP will begin shortly after its adoption but will occur over time as development occurs. It is also anticipated that certain aspects of this SMP will be challenging to implement due to existing conditions, facility costs,and the regional approach to stormwater management recommended by this plan. Implementation challenges and strategies for the whole of River Terrace and each of the three Strategy Areas,to the degree that they can be anticipated and described,are included below. Pursuant to the recommendations and intentions described in this SMP,implementation of this plan hinges on the city developing and adopting new stormwater design standards and a continuous simulation hydrologic modeling tool. New stormwater design standards for the River Terrace study area would amend the City of Tigard Public Improvement Design Standards and be applied during the city's development review process. These amendments are more fully described in Section 1 of this plan.The new continuous simulation hydrologic modeling tool would be made available to the development community and city review staff to ensure that the new flow duration based design standard was being met. Once developed,it would also be used to confirm or revise the sizes of the regional facilities recommended in this plan. In addition to this SMP,the following documents will serve to guide the implementation of stormwater facilities in River Terrace: CWS Low Impact DevelopmentApproacbes Handbook, CWS Design and Construction Standards,and City of Tigard Public Improvement Design Standards. Additionally,the West Bull Mountain Natural Resources Inventory Tecbnical Report(Pacific Habitat Services,2008) should be consulted for natural resource enhancement and restoration opportunities that could be implemented with the required stormwater facilities. River Terrace Existing Conditions • Geology: River Terrace has some challenging site topography and potential geologic constraints,such as shallow bedrock and landslide hazards. • Soils:River Terrace soils are poorly drained.The introduction of stormwater could contribute to an increased risk of landslides. Challenges and Strategies During the course of developing this plan, the development community expressed concerns about the recommended regional stormwater management approach based on their experiences in North Bethany.These concerns include: River Terrace Stormwater Master Plan 17 otak L:\Project\16800\16851\Reports\StortnwaterMasterPlan\Final-2014_September\FINAI-RiverTerrace_S"P_090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued • More coordination and cooperation: Several regional facilities serve more than one property owner. If a property owner is ready to develop but does not have a regional facility located on their site and adjacent property owners are not ready to develop or are otherwise uncooperative,development can be delayed if the property owner ready to develop has to: (1)wait for an adjacent property owner or the city to build the facility, and/or(2) obtain permission from an adjacent property owner to cross their property to connect to the facility. • Prevailing wage:Because regional facilities are publicly funded,they must be constructed using"prevailing wage rates."As a result,publicly funded projects can be more expensive to build than privately funded projects. • Timing of and access to funds:Regional facilities are expected to serve more than one development,yet they will be needed when the first development occurs.This means that someone needs to provide upfront funding,with the expectation that subsequent development would reimburse the original funder. However,subsequent development may not occur in a timely manner,and developer stakeholders reported that it is difficult for them to obtain funding from lenders for a facility that serves more than one development. • Size and location:While regional facilities may require fewer acres overall,they require large, consolidated acres of land as compared to the traditional site-specific approach. This land is then unavailable for private development.With the traditional approach, stormwater facilities could be smaller and tucked away on otherwise unusable portions of a site. The following existing conditions and strategies have been identified to address these and other concerns raised by stakeholders. • Less coordination and cooperation: The River Terrace study area is topographically different from North Bethany. It is bisected by several small drainage channels and roads,resulting in the creation of numerous small drainage subbasins. North Bethany has only three drainage channels by comparison.This translates into potentially fewer coordination challenges because there are fewer parcels of land that drain to each of the recommended regional facilities. Moreover,of the 13 recommended regional facilities outside of the high flow conveyance area,6 serve subbasins under the control of a single property owner. • Implementation flexibility (smaller facilities):The city is committed to developing a minimum facility size standard as part of the package of new stormwater standards it intends to adopt for this area.The purpose of the minimum facility size standard is to provide facilities that will function without greater than typical maintenance and to allow for flexibility in the implementation of this plan.As long as a facility meets the minimum size standard and associated community amenity design guidelines,the city intends to River Terrace Stormwater Master Plan 18 otak U\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAILRiverTerrace_S"P 090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued allow multiple smaller facilities in lieu of any of the recommended regional facilities in this plan provided that: o their location meets with city approval; o they meet the City Stormwater Design Standards;and, o they do not prevent or otherwise make it more difficult for properties owned by others to implement the recommended regional stormwater solution. • Implementation flexibility(interim facilities):The city is open to the installation of interim facilities that do not meet the minimum facility size standard in instances where it can be shown that development of a regional facility is not timely or practical provided that: o its design and location meets with city approval; o appropriate provisions and safeguards are put in place so that it will be properly maintained over time; o downstream piping from the interim facility is designed and located such that a connection to the future regional facility is practicable. o it is designed to meet the City Stormwater Design Standards;and, o it does not prevent or otherwise make it more difficult for other development to implement the recommended regional stormwater solution. In addition to constructing the interim facility,the property owner would be required to contribute its fair share toward the construction of the future regional facility. The interim facility would need to be removed once the regional facility was operational, which would free up the land upon which it was located for development. • Implementation flexibility(re-use facilities):The city will consider allowing stormwater re-use facilities,e.g. cisterns,that capture and re-use Stormwater on site provided that: o their design and location meets with city approval; o appropriate provisions and safeguards are put in place so that they will be properly maintained over time; o they meet the City Stormwater Design Standards and applicable building/plumbing codes;and, o they do not prevent or otherwise make it more difficult for other development to implement the recommended regional stormwater solution. Stormwater re-use facilities could either be proposed as an interim or a permanent solution and,where approved as a permanent solution,could serve to reduce the size of the downstream regional facility. • Funding strategy:The River Terrace Funding Strategy for stormwater is being developed with the goal of mitigating some of the funding challenges inherent in the regional Stormwater management approach. Near term funding priorities will likely focus River Terrace Stormwater Master Plan 19 utak L:\Project\16800\16851\Reports\StonnwaterMasterPlan\Final-2014_September\FINAIrRiverTerrace_SWMP 090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued on those regional facilities that serve more than one property owner and that are in areas anticipated to develop in the near term. • Integrated design:Through the city's development review process,property owners will be encouraged to coordinate the design of the regional stormwater facilities with the design and construction of other required or needed improvements,such as roads,parks, and natural resource mitigation,in order to reduce overall costs. Strategy Area A Challenges and Strategies Strategy Area A does not have any specific challenges or strategies beyond those described above for the whole of River Terrace. Additional Studies/Actions Needed The following additional studies and/or actions are needed to advance the implementation of stormwater infrastructure in Strategy Area A. • City:A full package of new stormwater design standards and guidelines. • City:A new continuous simulation hydrologic modeling tool. • City:A life cycle cost comparison study that evaluates the cost of constructing and operating a few regional stormwater facilities versus many smaller facilities.This study will help the city develop a minimum facility size standard. • City and/or Developer: Geotechnical analysis of specific site conditions by an engineer, including depth to bedrock to inform the grading plan and recommendations for design, such as whether a liner is needed to discourage infiltration. There is potential that some regional facilities located along Roy Rogers Road may need to be relocated to the west side of the road due to proximity to bedrock. Strategy Area B Challenges and Strategies In addition to the challenges and strategies described above for the whole of River Terrace, the following challenges and strategies apply specifically to Strategy Area B. • Infiltration:Pending further detailed study by a geologist or geotechnical engineer,it should be assumed that site conditions are not good for stormwater infiltration. LIDA facilities should be limited to flow-through types with an under drain and not rely upon stormwater infiltration. • Existing wetlands:There are extra permitting challenges associated with stormwater detention facilities located within existing wetlands. However,wetland restoration for River Terrace Slormwaler Marler Plan 20 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAI,RiverTerraee_SWMP_O9(614.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued water quantity management enhances a natural resource and occupies property that would be otherwise undevelopable or very expensive to mitigate. Additional Studies/Actions Needed The following additional studies and/or actions are needed to advance the implementation of stormwater infrastructure in Strategy Area B. • City:A full package of new stormwater design standards and guidelines. • City:A new continuous simulation hydrologic modeling tool. • City:A life cycle cost comparison study that evaluates the cost of constructing and operating a few regional stormwater facilities versus several smaller facilities.This study will help in the development of the city's minimum facility size standard. • City and/or Developer:A conceptual design and alternatives analysis,including an improved cost estimate,that evaluates the advantages,disadvantages,and permitting challenges related to the implementation of regional detention facility T2_6 as a wetland enhancement and restoration effort.The West Bull Mountain Natural Resources Inventory Technical Report(Pacific Habitat Services,2008) describes four opportunities along the T2 drainage,east of Roy Rogers Road,to restore and enhance the natural resources in this area. • City and/or Developer: Geotechnical analysis of specific site conditions by an engineer, including depth to bedrock to inform the grading plan and recommendations for design, such as whether a liner is needed to discourage infiltration. Strategy Area C Challenges and Strategies In addition to the challenges and strategies described above for the whole of River Terrace, the following challenges and strategies apply specifically to Strategy Area C. • Off-site improvements:Downstream conveyance improvements that are located outside the Urban Growth Boundary (UGB) shall address land use regulations from the Washington County Community Development Code Sections 340-4.1 and 430-105.3 through 430-105.7;Oregon Revised Statute 215.275;and Oregon Administrative Rule 660-33. • Integrated design:Design of high-flow conveyance improvements should be coordinated with the design and construction of other required or needed improvements,such as the proposed road connection to Beef Bend Road parallel to the T8 drainage in order to reduce overall costs and streamline the permitting process for improvements outside the UGB. River Terrace Stormwater Master Plan 21 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINAL-RiverTerrace_SWMP_090514.docx Section 3—Stormwater Concept Plan and Estimated Costs Continued • Detention and/or discharge: It may be possible on certain properties within the high- flow conveyance area to detain water in an existing wetland and/or discharge runoff directly into one of the existing drainage channels upstream of the high-flow conveyance system. Such proposals will be considered by the city provided that: o their design and location are approved by all applicable authorities; o they meet the City Stormwater Design Standards;and, o they do not prevent or otherwise make it more difficult for other development to implement the recommended regional stormwater solution. Additional Studies/Actions Needed The following additional studies and/or actions are needed to advance the implementation of stormwater infrastructure in Strategy Area C. • City:A new continuous simulation hydrologic modeling tool. • City:A conceptual design and alternatives analysis for the recommended high-flow conveyance system that evaluates the advantages,disadvantages,and permitting challenges of restoring and enhancing the T8 drainage versus installing a bypass pipe.A more detailed conceptual design and alternatives analysis will eventually be needed to support the land use process for construction of a public facility outside the UGB and for environmental permitting if work within a jurisdictional water or wetland is proposed. • City and/or Developer:A geologic evaluation of all potential high-flow conveyance alignments that identifies specific conditions,such as depth of bedrock,that could affect the construction or construction costs of the high-flow conveyance system. • City and/or Developer:Property owner outreach to acquire easements,land,and right- of-way for the recommended high-flow conveyance improvements. Maintenance The city will be responsible for inspecting and maintaining all regional,Neighborhood LIDA,and Street LIDA facilities. The city will also be responsible for inspecting and enforcing maintenance on all Site LIDA facilities.The city currently maintains neighborhood and street facilities throughout the city and will continue to refine its operation and maintenance procedures. The maintenance of Site LIDA facilities will be the responsibility of the property owner or homeowner's association.The city should expand its existing stormwater education and enforcement program to include residential property owners to ensure that all affected property owners are notified of proper operation and maintenance procedures for LIDA facilities,especially when properties change ownership.The city could require that operation and maintenance procedures are recorded with the property title. River Terrace Stormwater Master Plan 22 otak L:\Project\16800\1 6851\Reports\StormwaterMasterPIan\Final-2014_September\FINALRiverTerrace_SWMP_090514.docx Section 4—Stormwater Calculations There is a strong correlation between impervious area and stormwater runoff.The first step toward sizing water quality facilities and estimating site runoff is to estimate the amount of impervious area associated with the various types of development planned for the River Terrace study area.Actual imperviousness will vary throughout the River Terrace study area and will need to be recalculated as development occurs.Assumptions about impervious area used for this SMP are documented in this section. Several calculations were made when developing this plan and the cost estimates. Calculations include: • Sizing of Regional Stormwater Facilities for Water Quality • Sizing of Regional Stormwater Facilities for Water Quantity • Use of High-Flow Bypass Conveyance Pipes The engineering analysis and calculations completed for this stormwater management plan should be considered preliminary.Additional engineering analyses will be required during future detailed design phases of either public infrastructure or private development projects to verify the assumptions made in this planning level analysis. Impervious Area There are four types of residential land uses being mapped for the River Terrace study area: low-density,two levels of medium-density,and high-density with a small amount of neighborhood commercial. Non-residential development such as schools,a fire station, various parks,greenways,and other open space areas are likely to have a different impervious area than was assumed for this plan,and will result in a different runoff volume and rate than rates calculated during this analysis. After expected densities were determined for the various development zones in the River Terrace study area,two sources were consulted to determine appropriate assumptions for percent impervious area relative to development densities.The multiple sources include: • An impervious area study from Clackamas County. • Measurements based on aerial photographs for recently completed Tigard and Bull Mountain neighborhoods in proximity to River Terrace study area. Clackamas County Water and Environment Services (%ES) published a study of impervious surfaces as part of the Damascus area Urban Growth Boundary (UGB) expansion.The WES study analyzed the impervious area percentages of a number of neighborhoods representative of current and future development in the Damascus area.Three of the neighborhoods studied are comparable to the 7 and 12 unit/acre figures assumed for River Terrace medium-density residential zones,with densities ranging from 9.6 to 14.8 units/acre. River Terrace Stormwater Master Plan 23 otak L:\Proiect\16800\16851\Reports\StonnwaterMasterPlan\Final-2014_September\FINALRiverTerrace_SWMP_(19)514.docx Section 4—Stormwater Calculations Continued These neighborhoods have a total average density of 10.9 units/acre and are 54 percent impervious.Only one neighborhood in the study had a comparable high-density residential zone,with a density of 25.5 units/acre and 62 percent impervious.Two neighborhoods in the study seem to correspond to the mixed-use designation,although with much lower residential density than identified for the River Terrace study area.These had an average density of 13.6 units/acre and 62 percent impervious area.Three areas were designated as schools,with an average of 31 percent impen-ious area. A summary of these findings are presented below in Table 4.1. Table 4.1: Summary of Impervious Area Reference Calculations Reference Source Description Density Impervious Area (units/acre) N Medium Density 10.9 54 Residential Clackamas County WES High Density Residential 25.5 62 Schools N/A 31 Mixed-Use 13.6 62 The complete list of proposed land uses in the River Terrace study area is shown in Table 4.2 alongside the impervious percentage assumed for stormwater calculations in this plan. The proposed land uses for River Terrace are mapped in the attached Figure 1. Table 4.2: Impervious Percentage by Land Use Land Use Impervious Percentage Community Commercial District 70 Future Right-of-way 70 Existing Right-of-way 70 Low Density Residential (4.5 Dwelling Units/Acre) 45 Medium Density Residential(7 Dwelling Units/Acre) 50 Medium Density Residential(12 Dwelling Units/Acre) 55 High Density Residential (25 Dwelling Units/Acre) 65 Downstream Analysis Stormwater from the River Terrace study area drains to eight small drainages.A small area at the north end of the site flows to (drainage basin Tl) SW Scholls Ferry Road and east to SW Barrows Road.The rest of the site drains to one of the other seven small tributaries to the Tualatin River.Tributaries T6 and T7 are not expected to receive additional flows from the River Terrace Stormwater Master Plan 24 otak 1-\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\FINA1,RiverTerrace_SwMP_090514.docx Section 4-Stormwater Calculations Continued River Terrace study area,and are therefore not included in the analysis for this plan. The need for water quantity management in the West Bull Mountain SWIP was based upon a preliminary downstream analysis. Subsequently,the City of Tigard intends to adopt new water quantity standards for River Terrace. (See Section 1 for more detail.) New standards will require that stormwater facilities be designed to match post-development flow durations to mitigate downstream flooding and erosion from new development in the River Terrace study area. Regional Stormwater Facilities for Water Quality This SMP calls for the treatment of site runoff to be handled using a combination of regional water quality facilities,and LIDA. Site,Street,and Neighborhood LIDA will be sized as part of future public or private development projects. Regional stormwater facilities that are recommended to provide water quality treatment are assumed to fit within the footprint of the facilities sized to meet water quantity requirements.Water quality volume and flows were calculated for the regional facilities that will provide water quality treatment. The water quality volume and flow were calculated based upon current Design and Consttrrctian Standards. The current standards use impervious area draining to the facility. Impervious area requiring treatment was calculated for each of the subbasins based on land use assumptions within each drainage basin.The calculation of impervious area,water quality volume and water quality flow are reported below in Table 4.3. Table 4.3: Summary of Water Quality Calculations for Regional Water Quality Facilities Contributing Facility Basin Area Impervious Water Quality Water Quality Flow (cfs) ID Area (acres) Volume (cf) (acres) WQSMB 10.41 6.45 8,426 0.59 WQ2_5ac 32.89 18.71 24,447 1.70 WQ2_5b 31.51 17.29 22,595 1.57 WQ2_7a 37.67 22.09 28,869 2.00 WQ2_7b 16.76 11.09 14,491 1.01 WQ3_2a 33.42 18.05 23,588 1.64 WQ3_2b 7.27 3.80 4,964 0.34 WQ4_4a 28.82 15.35 20,063 1.39 WQ4_4b 14.95 7.55 9,860 0.68 WQ5_6c 25.49 13.98 18,268 1.27 WQ10_3a 4.5 2.25 2,940 0.20 River Terrace Stormwater Master Plan 25 otak LAProjeet\16800\16851\Reports\StormwaterMasterPlan\Final-2014_September\F1NAl-RiverTernce_SWMP_090514.docs Section 4-Stormwater Calculations Continued Regional Stormwater Facilities for Water Quantity An XP-S)X MM model was developed for the River Terrace study area to predict existing condition runoff rates. The model was then modified to simulate future flow rates due to build-out of the River Terrace study area based upon proposed land uses. Regional stormwater facility volumes were estimated for each of the recommended locations based upon current CWS Design and Constniction Standards that require peak flow matching. The estimated facility designs were tested using the XP-SW'MM model to demonstrate that the current standard was being satisfied. Application of the new design standard is assumed to require some additional storage volume in each facility.An additional 25 percent was assumed for cost estimating purposes.A new hydrologic modeling tool will be needed to perform continuous simulation calculations and complete the design of the regional water quantity facilities under the new standard. Table 4.4 summarizes 25-year peak flows for select discharge points (or nodes),under existing,developed without detention,and developed with detention conditions as predicted by the XP-S\X'NfM model. Table 4.4: 25-yr Peak Flow (cfs) Discharges from Regional Detention Facilities Facility ID Existing Future Future W/Detention WQSMB 5.7 10.1 5.6 WQ2_5ac 77.1 143.0 67.7 WQ2_5b 75.67 170.8 74.7 WQ2_7a 10.4 35.7 9.3 WQ2_7b 10.8 16.6 10.8 T2_6 50.5 75.2 49.1 WQ3_2a WQ3_2b 44.1 49.0 44.0 WQ4_4a WQ4_4b 69.1 91.4 68.5 T5_6b 7.9 26.7 7.0 WQ5_6c 32.8 37.0 24.0 WQ10_3a 33.8 39.3 33.3 A schematic of the XP-S\X'NIM model along with supporting background information is provided in Attachment C. Depending on implementation sequencing, the regional facility T2_6 should be designed to provide maximum stormwater storage. Storage above and beyond what is required of this SMP could be used to reduce the size of the regional stormwater facilities located downstream or to manage flow durations from offsite upstream areas that were previously River Terrace Stormwater Matter Plan 26 otak L:\I'roiect\168(1)\16851\Reports\Stormwatcrhlasterplan\Final-2414_Scptembcr\FINAI-Ricer'l'crrace_SWhdP_Q9{)514.docx Section 4-Stormwater Calculations Continued developed under past standards. Table 4.5 summarizes contributing basin,peak inflow and outflow estimates,and peak storage and estimated required storage volumes for each regional detention facility. Table 4.5: Summary of Regional Detention Facility Sizes Peak Storage Facility Contributing Peak Inflow Peak Peak Storage Volume w/ ID Basin Area cfs) Outflow Volume Correction for (acres) (cfs) (cubic yards) New Standard (cubic yards) WQSMB 10.41 10.1 5.6 1,257 1,571 WQ2_5ac 32.89 39.1 5.0 7,928 9,910 WQ2_5b 31.51 29.3 8.4 4,190 55238 WQ2_7a 37.67 35.8 9.3 4,508 5,635 WQ2_7b 16.76 16.6 10.8 918 1,148 T2_6 97.0 77.9 49.1 5,364 6,705 WQ3_2a 33.42 30.9 13.3 2,938 3,672 WQ3_2b 7.27 6.7 3.5 579 724 WQ4_4a 28.82 26.6 16.0 2,430 35038 WQ4_4b 14.95 13.6 6.6 1,593 1,992 T5_6b 29.59 27.2 7.1 3,731 4,664 WQ5_6c 25.49 23.7 21.2 534 667 WQ10_3a 4.50 4.1 0.6 25876 Recommended LIDA facilities are not expected to have a significant effect on detention sizes and were therefore not included in the model.The use of LIDA is only proposed upstream of two of the regional water quantity facilities.The effects of LIDA on these two facilities could be performed as part of the design phase to account for any reduction in the size of the regional stormwater facilities that might result. High-Flow Conveyance Regional water quantity for development in the portion of the River Terrace study area draining to the T7,T8,and T9 drainages are recommended to use downstream conveyance improvements to manage water quantity.The XP-SWMM model was used to predict existing and future stormwater runoff for these drainage basins and to estimate the size of the required high-flow conveyance pipes. River Terrace Stormwater Master Plan 27 otak L.\Project\16800\16851\Reports\StormwaterMasterPlan\Final-2014_5eptember\FINA1rRirerTerracc_SWMP_090514.docx Section 4—Stormwater Calculations Continued Figure 4C shows flow from T7 will be conveyed to T8.Figure 4C shows that flow-splitter devices will be necessary at T9 to divert high flows from their existing drainage course to the discharge point into T8. 2,100 feet of 36-inch storm sewer pipe is estimated to provide this bypass between T9 and T8.Approximately 3,800 feet of 48-inch storm sewer shall convey increased flows from T7,T8 and T9 to the Tualatin River. The high flow bypass pipes were sized using the XP-SWMM model and the following set of assumptions: • Flow from T7 was sent to T8. • Flow splitter in T8 and T9 were assumed to engage during flows higher than the 2-year, 24-hour storm event at their respective reach locations. • Bypass pipes sized to convey the future 25-year flows. Table 4.6 summarizes the 25-year peak flow rates predicted by XP-SWMM under existing conditions and for future conditions in the drainage channels that drain the southern portions of the River Terrace study area.The Existing Conditions column in the table below is the calculated flow rate in the drainage channel where it leaves the River Terrace study area boundary.The Future Conditions column is the flow rate at the same location in the drainage channel after the upstream area is fully developed.The Future with Bypass Pipe column is the flow rate at the same location in the drainage channel after the upstream area is fully developed and after the high flows have been diverted to the bypass pipe. The Flows in Bypass Pipe column are the combined flows in the bypass pipe. Table 4.6: 25-yr Peak Flows (cfs) at Site Discharge Locations to T7, T8, & T9 Drainage Existing Future Future with Flows in Bypass Channel Conditions Conditions Bypass Pipe Pipe T7 4.7 12.8 0 N/A T8 (north) 91.6 158.9 83.0 118.4 T8 (south) 99.7 149.8 93.7 118.4 T9 28.5 65.0 28.4 37.0 Alternatively to piped conveyances,open channel conveyance improvements could be constructed. For example,restoration of the T8 drainage between Beef Bend Road and the Tualatin River could be designed in a manner that accommodates the increased flows from the River Terrace study area. River Terrace Stormwater Master Plan 28 otak L:\Project\16800\16851\Reports\StormwaterMasterPlan\]sinal-2014_September\FINAL ffiverTerrace_SWMP_090514.docx Figures SW SCHOLLS FERRY RD -.� ' Z .�r t' 'moi yr tar � r:, r � e• a'r y.r� r 3.3+, C"+-F'r- c7��'.=�•'7t' ER i ■ ,� ��'''.' C""'Ai' ir• tins 4 i a► �' Ix i Lk r■ s /. rc; SW BULL MOUNTAIN R ■ ■ r ■ ■ ■ ■ S ■ 'r ■ Ufa � :!. ` - r+ ■ t". .,.�...iA ROW41 .Ar On cubedvG—Eye River'lerraee StormLegend Nwater Master Plan n r- River Terrace Study Area Urban Reserves Figure 1: Existing or Future Street Proposed Zoning 0 1,600 Proposed d Zoning Sensitive Areas =Community Commercial District p (Assumed for RunoI.rii7 ®Significant Wetlands High Density Residential(R-25)� Feet ®inventoried Wetlands ®Medium Density Residential(R-12) A. ^^r»^=«»••^•»• Calculation =Natural Resource Buffers C_�]Medium Density Residential(R-7) p••^••=•M••»= m»•••d-•^m=mho Existing Drainageway F-1 Low Density Residential(R4.5) Tualatin River IJ t s-1�� III • j •r'•a �� ,,,� • `moi -I �"' +�I' - +h"� ,<�rpt-`" �'�' 3' r� •r t q- �' r� dam, orf✓,��7��j � � �' � ��'�:�''�s��'�`N�� ,.e1 FWFAIrf _ q :. .� t � y MAL;, //II�� • .moi" . 1 �� .„ 1►1 s107 y ,71 jw R. F ' rg NIS, �IMM� ;/�// ; �� ,. ,. � ` �—►'� �Vii► Drainageto River Terrace Stormwater Master Pla Figure 2: Legend V=Rwer Terrace Study Area Sensitive Areas Existing Existing Subbasin ,..,..,Significant Wetlands 1 C100 Omland Flow Direction . .. Basin DiagramOft.Contour Line ®.Natural Resource Buffers i,et —Existing Drainageway oaTualatin Riwer SW■fy/10LL■FERRY RD� + • •�.. `\ ■ _ ..'j.'-.^t +¢..`' erf.W.rt�y+ ,'�Yw•!Y^:j7JN`�•j-•�j �. %114; � �` {.�. /� .�..•4r � ,'; _ fat Y • � � F 'j K SW BULL MOUNTAIN RD t�� ice•J ..: Yy��.. It F. F y 2 •�� x , %< IrIt r tt T 6 y SW BEEF BEND RD � 00 River Terrace Stormwater Master Plan N Legend A Figure 3• @River Terrace Study Area Recommended Strategy, 0 16D Existing or Future Street =Strategy Area A Stormwater Management Senslti—Arsss Strategy Area Feet S ®Sig Wenands Strategy Areas ®Invent.neloned Wetlands Strategy Area C ®Natural Resource �Existing Orainagewsyay Tualatin River -w SW SCROLLS FERRY RD •- = t .. �1 Bast -•Basin Basin T2 6b r.. T-2 T25at 1 16.1ac W02 7a WQ2_5ac ..•.•.F W7b Basin t i T2-6a f++�+• :�a�l 26ac Basin ` >) act. . WQ32b Ba��„ T3 2b _ WQ3 2A 1 BBa�sin Tal eP 1 1 • SW BULL tMOUXTAIX RD w _ �1 ;I �Ta•ja -28:8 WQ4 4a asin Ta, W/a4_4b , . .^.... f ,rf£r Basing "I ; y T5 6b j Basin r 29.6ac / 75_6a 1 Basin ` * r/� f6.1ac T5_66c T5_6b / sin 25.5ac 8_4a AALNLMLft g.gac a Bsin. Basin T7 3a'``• Tg—� W055-6c �•1.4:38c Legend RieerTerraceStrxmw•aterManagement Plan rww0w& River Terrace Study Area Sensitive Areas Stormwater Conveyance Existing or Future Street ® Significant Wetlands Pipes Figure 4A: asins ® Inventoried Wetlands a' Q Proposed low Direct Natural Resource Buffers NotStreetLIDAA Stormwater Concept Plan �--- Overland Flow Direction 70 ft.Contour Line Existing Drainageway SwaleslDltches Diagram (Strategy Area A) WitStreet LIDA Regional Stormwater Facility N No Street LIDA Water Quality and Quantity n � Water Quantity Only 0 /V 1 000 ■ ■ 1 � Basin ; �1 jT9_3b / ■ Basin 18.6ac T9_3* j ■ Basin 25.4ac t ■ 8_4b ■ _2s0 _ sW Woodhue street 38 ■ M '1 t Basin ■ jf T9_4 f 13.3ac ■ ■ Basin r f TB-3b )! ■ asin 11.5ec ! ; .6ac ■ ■ —<< law Rosario Lane _a O SW Bee/Bend Road Ricer Terrace Stormwater Management Plan Legend River Terrace Study Area Sensitive Areas Stormwater Conveyance Figure 4A.1: Existing or Future Street Inventoried Wetlands Pipes Stormwater Concept Plan 0 Proposed Subbasins Natural Resource Buffers With Street LIDA -4---- Overland Flow Direction Existing Drainageway No Street LIDA Diagram (Strategy Area A) 10 ft.Contour Line N . Flow Splitter Device Regional Stormwater Facility ti Water Quality and Quantity o 400 Feet ■ Bassin WOSNB SMB t 1 � { t n�7! f Basin t 1 T3_6b Basin 1 T2 7ta 1 T2 5a 1 ` 37.7 c _ •/ 16-1 2.9ac * V r Basin 4 T2 5c ` Sac T2 6 $M2 7a WQ2 ac bb ti+r T 7 4 WQ2_7b � �6a .p Basin bac Basin T2 7b ; sh 31.5ac 1 WQ3�2b 3 WQ3 2A t Basin T1 2a 33�4ac �! 3 t '. f • SW BULL MOUNTAIN p0 a of ' ■ 1 Basi ! T4_ a' t/ 28.8 WQ4 4a Basin a T4_4b b WQ4'4b� .. I t I w t. Y2-- Easin a ',BasBasin f61ac T8_T56c58b I 19.9 �25.5ac \ 'zbac BasinsiT9 3 iBasin 25.4a�. W05 6c... n "' ,T8 3f i4.3ac { �I7.2ac Legend River 7crrace Stnrmwater Management Plan �� River Terrace Study Area Sensitive Areas Stormwater Conveyance Existing or Future Street tl® Significant Wetlands Pipes Figure 4B: ® Inventoried Wetlands a— Q Proposed SuDbasin5 With Street LIDA Stormwater Concept Plan '0----- Overland Flow Direction Natural Resource Buffers No Street LIDA 10 ft.Contour Line Existing Drainageway SwaleslDkches Diagram (Strategy Area B) With Street LIDA Regional Stormwater Facility N No Street LIDA � Water Quality and Quantity A �l Water Quantity Only o 1,100 Feel dry.- M Basin T4_4b 14.9ac Basin'; Basin 8 2 c T5 6b04 r, 29.6ac Basin n � ?5,6 Basin '6-tai Bps'n T5_6c T13_Bb . T8_4a - 25.5ac 19: Basin T.9-3a 5.4sc r.. 18` Q 1 Basin T9"4 1W21ace +qp. S' f. 1.9ec Si6ac b Basin TI 0-3b .. 4.5ec .il W010 3a 3 Approx.2.500 feet of high now bypass pipe between Ta and T9 drainages. Approx.3,900 feet of high now pipe between Beef Bend Rd.and the Tualatin River.Stream fy restoration to also be evaluated as an option. ao RD f� OD Ar b Proposed Outfall to Tualatin River Ricer Terrace Stormwater Management Plan Legend tri j River Terrace Study Area Sensitive Areas Stormwater Conveyance Figure 4C• O Proposed Subbasins ® Inventoried Wetlandspipes Stormwater Concept Plan Existing or Future Street Natural Resource Buffers with Street LIDA -�^^^ Overland Flow Direction Tualatin River = no Street LIDA Diagram (Strategy Area C) 10flContour Line Existing Drainageway Swales/Ditches Regional Stormwater Facility N Be with Street LIDA Water Quality and Quantity A . Flow Splitter Device Water Quantity Onlyfeet 0 1 000 dao.. Q s ti A<<QR Dq Z SW T WHEE SW SCHOLLS FERRY SW B �W ON !LL S RD SW FRIENDLY LN QZ SW LUKE N W W t7U DTR E R ti Q J S FIR REE RCb Q S BRISTL CONE WAY h � SW LEEDI G L SUNDEW DRco S S HL DR SW TUSCA Y ST Q z S MIL S -' W S BAKER LN 2 Q D qct � �9 � � W SW OLON R Q O � t2 L Q O SW B LL MOUNTAI RD = SW RAYL 3 S y Q y DFKA(B 7- SW BURGUNDY ST t to SW CABERNET R 3 to SW P L z J zz CA k � �S' A to tD y 2 b r` J z LASICH Q O Q SW BEEF BEND RD DRAFT LEGEND N West lull Mountain Planning Area Q West Bull Mountain Study Area n o 2.000 FIGURE 5 Soa Infiltration N Feel SOIL INFILTRATION Good Potential 1 INCH EQUALS 800 FEET Fair Potential Poor Potential Data m tns map a from Wasfangto Co,nty aro mottos 11._-G-,211.1 z el r HEIS dataOeSe.TMS INOrmalgn was love,opIm at mulbple ` r --- Water Scales arr0 acc—as.No warranty is oe wen mIs map A t t a c h m e n t A — Background Information • As part of this SMP,Otak reviewed multiple data sets and reports prepared for the River Terrace study area. Our review of the data and relevant conclusions are summarized for the following seven items. DOCUMENT 1: West Bull Mountain Hydrologic and HydraulicAnalysis(HDR Inc.,March 2008) The purpose of this study was to describe existing hydrologic and hydraulic conditions for the basins within the West Bull Mountain Study Area.The scope of work included creation of existing conditions hydrologic model (HEC-HMS) and Hydraulic model (HEC-RAS) and an evaluation of the conveyance capacity of streams and culverts under existing flow conditions,as well as the general potential for erosion in the streams. 1) Capacity of existing culverts was evaluated.Figure 4-1 from the HDR report shows the location of culverts considered to be under-sized in terms of capacity. 2) Flooding is most prominent along reaches T2A,T8,and T9 with localized flooding at several other locations,as shown in Figure 4-2 from the same report. 3) The report shows that the culverts modeled within the study area violate hydraulic criteria for fish passage crossings.However,most of the streams are steep and should be expected to have high velocities.According to Washington County (correspondence with Rick Raetz, former Washington County),culverts beneath Roy Rogers Road that were constructed circa 2001 during the most recent road improvement project were designed for fish passage. See discussion under DOCUMENT 5 for Otak's review of construction drawings provided by Washington County for Roy Rogers Road. The need to modify existing culverts for fish passage will need to be evaluated at the time of design and implementation of improvements to Roy Rogers and compared against fish passage requirements in place at the time. 4) The potential for channel erosion may be significant due to the fine sediment characteristics of the area and the velocity conditions that exist in these steep drainages. 5) Attachment D of this River Terrace SMP provides copies of both Figure 4-1 &Figure 4-2 from the HDR report. DOCUMENT 2: West Bull Mountain Natural resources Inventory Technical Dort(Pacific Habitat Services,April 23,2008.)A natural resources inventory was completed for the 712 acre West Bull Mountain Planning Area and the Stream Resources Study Area consisting of approximately 27,500 linear feet of designated streams and stream corridors in West Bull Mountain.The scope of services included the following: 1) Stream and buffer assessment using the Tualatin Basin Rapid Stream Assessment Technique (RSAT) to evaluate creek and riparian conditions; 2) Wetlands assessment including mapping all wetlands within the study area,assessing approximate size,Cowardin and Hydrogeomporphic (HGM) classifications,and Oregon Freshwater Wetland Assessment Methodology (OFWAM) analysis; 3) Wildlife habitat assessment by on-site and windshield surveys to determine the approximate size and type of all habitat features and use of the Wildlife Habitat Assessment(WHA) technique;and 4) Identification of potential stream enhancement,wetland enhancement/mitigation,and aquatic species barrier/passage projection. 5) Inventory data was compiled and stored in a GIS database for easy mapping. The natural resources identified were used as a constraint to define buildable lands during formation of the preliminary concept plans assumed for this SWIP. Several culvert barriers and enhancement opportunities were identified for consideration during development of West Bull Mountain.The findings of the Report were used to identify suitable context sensitive infrastructure placements. DOCUMENT 3: Regional Landslide Hatiard Mapping, West Bull Mountain Planning Area,Was County,Oregon (DOGAMI,Draft-March 31,2008) and ADDENDUM to Kegional Landslide Hatiard Mapping, West Bull Mountain Planning Area,Washington County,Oregon (DOGAMI,April 21,2008). These reports indicate that: • Forty-seven landslide deposits are located within the West Bull Mountain Planning Area (WBMPA) and 93 total landslide deposits within the approximately 13 square miles southwest quarter of the Beaverton quadrangle. • Eighty-three of these were classified as shallow,nine as deep,and six as debris flow deposits. • The average landslide area is approximately 20,000 square feet. • The average depth of failure for the shallow-seated landslides is 8.5 feet.Two square miles of the 13 are classified as highly susceptible,6.5 square miles as moderately susceptible,and 4.7 square miles as low susceptibility to shallow-seated landslides. • The average depth of failure for the deep-seated landslides is 26 feet. 0.03 square miles are classified as highly susceptible,2.5 square miles as moderately susceptible,and 10.5 square miles as low susceptibility to deep-seated landslides. These results suggest site specific geologic and geotechnical conditions will be important to evaluate during the design and construction of stormwater management facilities in the River Terrace study area. In addition,an assessment of the effects of infiltration on slope stability for developed conditions will need to be performed. . DOCUMENT 4:The Report of Preliminary Geological Evaluation West Bull Mountain Planning Area (GeoDesign,Inc.,April 21,2009)included the following discussion on soil properties and the use of Low Impact Stormwater Management. The NRCS SSUGRO database provides a mean value of the saturated hydraulic conductivity for all of the soil series mapped in the planning area. Unfortunately, the saturated hydraulic conductivity cannot be used as a direct measure of the infiltration rate used in stormwater infiltration facility design.The saturated hydraulic conductivity is measured using a laboratory apparatus that allows only unidirectional flow.Field-measured infiltration rates used in facility design allow for lateral flow of the infiltrating water.Consequently,the saturated hydraulic conductivity typically underestimates the actual infiltration rates measured in the field. However,measurements of saturated hydraulic conductivity were available throughout the planning area and could be used to provide a relative comparison of infiltration potential for the purpose of this planning evaluation. The soil properties (e.g.,liquid limit,plasticity index,ratio of sand fraction to fines fraction,and saturated hydraulic conductivity) and interpretive characterizations (depths to the impervious layer and groundwater) were used to evaluate the relative potential of each soil series for utilization in low impact stormwater management.The relative rating methodology assigns a low,medium,or high potential for each soil series based on these characterizations. Saturated hydraulic conductivity published in SSUGRO was used as a proxy for the long-term infiltration rate,and the primary factor considered in assigning the soil infiltration potential. Soil series with a reported saturated hydraulic conductivity below 0.1 inch per hour was considered to have a poor infiltration potential. Rates ranging from 0.4 to 0.7 inch per hour were assigned a fair infiltration potential,and conductivities exceeding 1.0 inch per hour were assigned a good infiltration potential. No soil series in the study area reported saturated hydraulic conductivity that fell within the range of greater than 0.1 and less than 0.4,and greater than 0.7 and less than 1.0. For all good potential soil series,the depths to the restrictive layer and groundwater exceeded 6.6 feet.The depth to the restrictive layer exceeded 6.6 feet for the soil series rated as fair infiltration potential,but groundwater depths were less than 6.6 feet.The potential was decreased by one range (for example,a good infiltration potential becomes a fair infiltration potential) for soil series where the reported slope exceeds 12 percent. It is the geotech's opinion that the issues of constructability and directivity to the groundwater flow paths for infiltration ponds constructed on sloping ground justified downgrading the potential for these areas. A copy of the GeoDesign map of the Bull Mountain Planning Area showing areas having poor, fair, and good potential for infiltration determined using this methodology is provided in the attachments as Figure 5. The City of Portland Stormwater Management Manual sets a minimum infiltration rate of 2-inches per hour for all surface infiltration facilities.A field-measured infiltration rate may be a factor of two or greater than the saturated hydraulic conductivity. Consequently,rates of 0.4 to 0.7 inch per hour and 1.0 inch per hour were used to delineate areas of fair and good infiltration potential for planning purposes. Figure 5 shows that the infiltration potential is poor in most of the planning area except for the southern portion where there are areas having a fair infiltration potential.Areas of good infiltration potential are limited to one large area at the southern boundary of the planning area along SW Beef Bend Road.The results of geotechnical drilling and laboratory testing performed for this project confirmed that the areas having a poor infiltration potential are underlain by clayey residual soils derived from the underlying basalt bedrock and that the areas having fair to good infiltration potential are underlain by fine-grained Missoula Flood deposits.There was no explanation for the overall poor infiltration potential within the Missoula Flood deposits located in the northern portion of the planning area. DOCUMENT 5: Roy Rogers Road Improvements S.W1 Beef BendlElsner/Scholls-Sherwood Roads (CH2MHill,November 1999).The construction drawings for this project provide inventory and detailed information for the drainage structures under Roy Rogers Road that drain the River Terrace area towards the west.Relevant drawings from the plan set are included in Attachment E for future reference.A summary of the useful information provided on these drawings is as follows: • Ditches are used to route storm runoff down embankment slopes to the stream crossings. • Drainage T-2 crosses Roy Rogers Road under a bridge approximately 79 feet long and 43.3 feet wide. High water elevations shown on the detail sheets differ by 2.4 feet (0.75 meters).The greatest elevation shown is 236.3 feet(72.01 meters),and provides approximately 12.4 feet of clearance. • Three 18-inch diameter culverts 250.3 feet in length with a slope of 0.26 percent are used to pass drainage T-3 under Roy Rogers Road. • A 6'x6'concrete box-culvert 115.5 feet in length with a slope of 5.0 percent provides the crossing for drainage T-4.The box culvert is counter sunk two feet with concrete baffles to simulate a streambed for fish passage. • Drainage T-5 crosses Roy Rogers Road in a 160 foot long 48-inch culvert with a 9.8 percent slope and a 156.5 foot long 24-inch culvert with an 8.8 percent slope. DOCUMENT 6:The Roshak Pond Overview— West Bull Mountain Planning(Washington County Department of Land Use and Transportation Planning Division,November 5,2008) memorandum summarizes the known information regarding the Roshak Pond. The pond was enlarged from a smaller spring fed pond and now stores water for irrigation.The pond has a capacity of approximately 20 acre-feet,which is the maximum allowed per the water right certificate.During the irrigation season when the pond level decreases,the Roshak family pumps water from a well into the pond.A soil boring located in the berm of the pond in March 2009 as a part of the previously mentioned geotechnical report consisted of a layer of soft to medium stiff silt Missoula Flood deposits and a layer of soft to medium stiff clay and silt derived from the basaltic residual soil. The ground water in the boring was found at a depth of 3 feet which corresponded approximately to the water level in the pond. The pond is not identified in the County's acknowledged 1983 Goal 5 Program;however,it is identified in the County's 2005 Tualatin Basin Goal 5 Program as Class I and II Riparian and Riparian Impact Area. The natural resource inventory for West Bull Mountain(PHS,2008)identifies the pond as a jurisdictional waterbody by the Oregon DSL and/or Corps of Engineers and would therefore,be treated by CWS as a water quality sensitive area requiring a vegetated corridor. The actual location of the vegetated corridor is determined when a development application is submitted,and depending on slope may be between 50 and 200 feet.Therefore,only a Vegetated Corridor Proxy has been mapped around the perimeter of the pond at this time. The Vegetated Corridor Proxy is an estimated location of the Vegetated Corridor based upon the wetland inventory prepared for this project and the adjacent slopes. Modifications to the pond are expected to require permits from Oregon DSL and/or Corps of Engineers. Change in water rights or use of the existing water rights associated with the pond would require coordination with Oregon Water Resources Department. DOCUMENT 7:The West Bull Mountain Stormlvater Infrastructure Plan(Otak,February,2010) describes the stormwater management needs for the River Terrace study area,and includes a portion of Urban Reserve Area 6D.The West Bull Mountain Stormwater Infrastructure Plan(WBM SWIP) also documents the guiding input from project stakeholders that were considered in developing the recommended stormwater management concept that will be carried forward into the River Terrace SMP. The West Bull Mountain Stakeholder Working Group (SWG) put forth two Planning Goals relevant to the planning for West Bull Mountain stormwater management: • Equitable and Feasible Infrastructure Financing—Creation of an urban infrastructure financing plan will begin early in the process in order to ensure infrastructure is provided and financed in an equitable and feasible manner. • A Green Community—The West Bull Mountain Community Plan will endeavor to protect significant natural resources,preserve open spaces and habitat corridors,protect water quality by using a watershed approach,respect existing topography,and use sustainable planning practices to create a green community that is practical to develop. The West Bull Mountain SWG drafted and approved Planning Principles to guide the Concept Plan. Four of the principles are relevant to stormwater management: #5. Infrastructure Finance Certainty and Equity—Financing plans for infrastructure (water,sanitary sewer,stormwater,transportation,and parks) should begin early in the planning process and should create certainty for all parties. It should be equitably distributed according to the benefits of urbanization, proportionality of use,and based on a public/private collaboration that explores creative financing tools. #8. Preserve/Protect Natural Resource Corridors and View Corridors—The community plan will endeavor to preserve and protect existing natural resource corridors and minimize impact on habitat connectivity as well as protect the scenic views and natural beauty of the area. #9. Parks and Open Spaces in the Community—The plan should consider a range of parks,from tot-lots and ball fields to natural areas and community gardens, distributed within West Bull Mountain's neighborhoods. Conservation areas and open lands should be used to define and connect different neighborhoods,districts, and natural resource areas such as the Tualatin River National Wildlife Refuge. #15. Sustainability—Design and implementation strategies should allow the community to meet the needs of the present without sacrificing the ability of future generations to meet their own needs.The community plan should strive to achieve an ecological look and feel by integrating sustainable planning practices which may include Low Impact Development Applications. The following list of stormwater management strategies were put forth and considered while developing the SWIP and are carried forward in this Plan. • Restore/Enhance Vegetated Corridors • Protect Water Quality • Preserve Existing Hydrology • Promote Safe&Long Lasting Stormwater Facilities • Balance the use of Regional and On-site Stormwater Management • Preserve Existing Mature Vegetation • Maximize use of Multi-benefit facilities to create community amenities • Promote Partnership with Other Public Service Providers The following list of specific ideas and concepts were generated to accomplish the identified goals,principles,and stormwater strategies.They were considered part of the stormwater approach for West Bull Mountain and guided the stormwater management strategies applied throughout West Bull Mountain in the SWIP.The Low Impact Development Approaches Handbook and the Design and Constrmction Standards provide additional detail about each of the stormwater concepts considered. • Open conveyance elements to enhance "key" pedestrian routes along streets or along stream corridors. • Low Impact Development Approaches (e.g.,eco-roofs, ,flow-through planters,etc.). It is assumed that these would be limited to flow-through type facilities unless geotechnical evaluations can demonstrate that infiltration is not expected to contribute to slope instability. • Minimize Impervious Area(e.g.,clustered development,"skinny" streets,reduced parking, pervious pavement,etc.). • Regional Detention/Water Quality facilities parallel to Roy Rogers and/or a new interior street that is also parallel to Roy Rogers. • Re-use for irrigation. • Increased conveyance between site and the Tualatin River(e.g.,High flow by-pass pipe or stream restoration) Two alternative stormwater management concepts were developed for the study area and compared using a set of qualitative criteria. The final strategy was a hybrid,which made use of portions of each alternative. One alternative made use of regional facilities and was more applicable in some of the drainage basins,while the other was a better solution in other drainage basins that could make use of LIDA.The final strategy applies the best of both alternatives to match the characteristics and needs of each drainage basin.The WBM SWIP document should be consulted for further details on the alternatives analysis. Attach m e n t B — Cost Estimate 0 . RIVER TERRACE STORMWATER MASTER PI AN tormwater ManaaeMe it Infr r r imate(orepared in 14 lu a�n.,xu uu. .1 uxxn 9rl'raOounr Mm nn[IvtpNf9mo m-re\nm mvu num nrn rn.�b.ex.e iia a. ff29'_J 355 l9 "'A )95"r ^UO f 981 3109 S 99111/ 3': S'. _ 5 5 111.:1 t'S56 Jo0 f1' 1965; 121 1 f'.�.'. sl9 U'.- 31 51153_1 SL'1 w 155 {]:1116 3'l " 1' S ]0'19 121^S' f'• w w 31121 N! 5-9 - t31.M3 f6AU 315.528 32'81 il'3+' 33". SSAJ' w $" w w w fm'm ,nl IKIpEvf IIW,.nn.,� �.. 1' 1•.J.�•. S.I.^ sl6uw 3J0- f-.— 337.9W f1U:,. 3w— $..- 33."', 33,�SW w w w f1: i,xca.nnnlr..1„n.,.1,.i r. •. .:...:•: 51"•v... 5_15'96 t5,±'". 531,192 3/M”, 612P11 1 13Y2_ f6,,P 533}-0 3 .1 K'. I" 1" w s2wm Rom s.',1ro 3=• 3'.• s; 1.:• fJ,nm f=. w 1P0«, 31(;[rtl fln,«NI 31�' f1n;,. f1" w 1 fn f1I00W s5,rcu 3+••' S t' t 5:,500 f:. Y' 360Jo0 S14mo s¢ N,f,000 y;- f'_T', aiAJ1110LINN11012� $'` fd1.lIU1 3�. 530 VA S' 530000 �urtwwla.n En 1 f S" f-: s"J. f • y. • 5:•.., Hln,0110 s F. w w w w w fa.auo F: w t54oro w 3� s w su'6m w Y• w w 3� A, w SRo�'Sn W w w w M w w 5_- s2.%� w s w Fos.«n fsi2.4�; s"s',sao F. 3.. y. y,. y. y.. , {Cls' f1J1x- sis- s s S f• f9' sNs1 w• u95 l Ssssrwl Hr � 19J1 3. 1.1.0 ��,,,I.,•.•Ix�,ll.,.„lxrx 377s ,Iu f6Yl x9 s H9s___ la.vc. uu ur f9Hd2. 3=J, s S+_;:: SIJu: 5 Ul x wWJ H'll.lx: SIA3l,61M 5911.94 512x33'1 HJxn2 5X13.135 !1)3p61, 142,a61 H1/I,JG !41,]30 SI,UJ,2U flk,3,6J3 5!$02'249 11,—.It/ ff,159A>U - 3169,736 3 f+ 1+-1._N 1.'! tlNfl Stl 3rFlcle fi29'3 w>9]9) 5529'4 w f w 3 s sn w w t� w w is a. syr 3;1 S5„ ss;. W 33 iJs $07njn 1 HM,815 I 3W 1. a2- I.w,.JlmlJwin.:.�aw.�...w.elec<.u:.w..s.e. I_ a•r Jo1. r(!�Ch11,Er1tE RIVER TERRACE STORM\C A r[:R NIASrF:R PIAN Stormwater Manaaernent InfrastructurntitvEstimate III\t I,I�I'BIYII,IN I'NII AM„I\I %A7 RQ11Al27YANDDE WIONPOND 1,1:1156 I,IN WIND nI131-IAIINIAINVIIAN'l?, AQS11B \\'Q2_5AC \\Q2_5B R'Q27A R'Q2711 U'Q31.1 RQ3,.Z11 W'Q44{ U'QJ 3B %QS_cr; U`IO_l.i I__c 1'S cls 'r6/��.n1�1 IM I��n��ll) I'•I 1lnxer.RAgNI. 1:7 70,096 2317 14137 7206 7603 1730 5760 1287 Nil 2960 1116 1920 11190 6126 l' 9,563 436 2985 1492 1593 323 776 139 667 S10 157 262 - 11 OA10 2.026 1031 1.100 037 1.043 0250 0.671 0461 2DD 0.730 1.734 1.3V� 52,746 1 1969 9816 5324 U07 5046 1210 3216 966 1597 6393 Llr24 2 2 2 2 2 2 2 2 2 6 P.3 2 2 2 2 2 2 2 1 4000 5500 %-, 4000 4000 - 2.1x 2900 3000 17000 2 2 2 2 2 2 2 1 I 1 0 0 4 2 1,Z00.am IN, I_ 14 1.0 1.777 300 1874 893 1,710 Attachment B A t t a c h m e n t C — XPSWMM Model Schematic s B Out r —— •' t �Yt] 1�.. p xi .j SMB :l. -�-,•~" i �* aY R�• �► 7 VW11011•'FERRY Rb ■ i! 1I.' A - �•t•�'r J It y` l_4 - .xs •'.'�.r -�• ..r• -Sfr,_ ~•• t'. t '� • N • �'�1..' ,yM r 1 !So a .� Link20 1 �Node ... n� R,. �` R r No 21 20'in 18•. Hnk•17 nk) No all 1 e 11`+. 1t id•°ao'�' Node22 �, •_ ode e15 •! a ) t Node23 i T2_5 Node17 Y. --i- "` #• !► >, N'aeza IZ AL 7:M •, .i _ Node30 r •7 '! •"' ode31:A L. „i '�. •. . ` - Nodal ode31 3 �yt11133 U�3 t. 40428 Link a Until Noda306 T3 2 Node26 ��, � • .'tee r oag38., ■ _ ted► . a 3 ` .f,,tr Node39 ■ is ' .. oAeaO ridgy t • t -`tee \. No _. ■ �T fir• n 0 ■ ■ r .••�. v• � t� � it � � �-� N•aal�C�.p•�Y�r. Toil t T4_2 �,toin O .C• Vr �owtr�/Nod urs'•` �,, '.. No'de54� will Node53�.)j�M w►•' a ,4 _ 4 . T5 - v�k51 River•lerracc 5tormwatcr Maxtor Plan Legend O XPSWMM Node Street(Future) XPSWMM Sensitive Anas Existing Schematic •XPSWMM Runoff Node ®Significant Wetlands A T2,T3,T4,and SMB XPSWMM link ®Inventoried Wetlands N jr�MRlvw Terrace Study Area Existing Drainageway QF—HEC RAS XS Natural Resource Buffers ,.,..b,..eb.... Oo- mw,w.v.....�..�...w,.. ..o-... _xiating Sub-Basin Fse1 a T W F R Ask a J� T5 b sz Ilk -yNude60. ; LinY55>� � t aaD G •`• ,r ` 1 c w .70 .71� aRan �� •- noeerL . t ' i Rnrr Terrace�numuaw,lfastrr Plm Lp•na XPSWMMO XPSWMM r]E'.ON D,--B.— Noe• Existing Schematic •XPSWMMR.m Noes sD••ilFu<w N T5 WL a' «- f•XPSWMM U. aw.A.- RII lnwnbned Wedentls ,r...... r.....r.... e w r ® rrvx-.RTerrace SWdy Area.EFisti sourw Dren D � eanrey � �...�.. —NEC RAS XS Q Neiur•I ReBuffers F••1 1T-1—Rarer .pR■5 ■ ' � .K '• f - � - gip! TOB ♦rwa>timml�mmmmmm•ars,mmmmmm<,m^ - ,�•' �. .. Y ms.mmm<.�a.Vma.m� :■Its+t s. . Node64 Node65 Node66 w ' r a V - - �4� J 54 .'1 �'. . T8 4 9 3a.' i V10� T5_5 '-�- '� ''• -t j K -Node69 hNode70 as f a4 "'■ /'T�73Part atm�biJ Node71 - 'Node94 Node110 8 3 e -+ �Notle95 JI NOd@7 T10 -:Node96 _3 se as as as as as as as m m as Y v e75 T9t2.m isms-�_ Al'•�- F. •1n � yl 1Node112; - Node98 �.� , Node77 ^o J � Node99 f 1,2 99 Nod X100 Node114 __„�T10 2 e Nordee101 �Node115 Nodellbn ■HID RD RRRiii ` NO'de79 ; +� ~4 Node81, „ Node80� C 0 Node8200 River terrace StormwatCl i Master Plan XPSWMM Existing Schematic f m Node83 T8,T9,and T10 Node84 Nodpit Legend {��. �� ! r' ` S'.�':, �I 1 of O XPSWMM Node ( No(de87 ` "� a h / {4; •XPSWMM RunoffNo,fe O♦ •`' r ..JI r':T'Y'si't.1''.��s, ..:T`:• if f,i " •'f)1}., t .0+ i ,r4 •ii�� r . •r XPSWMM Link ry r a�' �• tR~ < tt l (Hy rl;i�1 1 ppyy�,ac,, rm`:River Terrace Study Area x,cMrt em.t��-gti /Lr v }4;{, t_• / ger Y�h �, ,, A —HEC RAS XS /� •r'�aw" < 't`?� a IV`Il • E...lung Drainage Basin NoAe88 ♦ ':,1:"'� �. ; ,s, r,y'�F: Via' F y( Street(Future) h TSL1s V � �-�' '� ;' `( 1 r 1 '�SIr,�Y+,'M. ,1^ �• Jsy Wetlands +, +ai ,� • ' 1 �:,fir•/�+-y',s ,�-,. ,�. Sensitive Areas �fY �/ ir� „ �•-+ h �� '�.j R Inventoried Wetlands Link �84 f J -►r 790 Existing No Exis g Drainag"ay det -� ' + '-♦�-C� .. ��, i '• Natural Resource Buffers Noe89 �' � i i'[�;. Er �� • Tualatin River N to ,y.e 'fir A w• '1s ,- r v , 1,000 Feel , .rid•-�' 'i' r.j 'Y•'' ` XPSWMM NODE INPUT:EXISTING CONDITIONS MODEL (Cont.) Curve Time of Curve Time of Node Impervious Number Concentration Node Impervious Number Concentration Name Area(ac) % (CN) (min) Name Area(ac) % (CN) (min) SMB 0.5 100 98 5 T4_5 12.075 100 98 S 10.62 0 83 16.5 31.407 0 82 20.4 T10_2 3.286 100 98 5 T4_6 13.267 100 98 5 9.491 0 91 20 24.966 0 83 20.4 T10_3 6.56 100 98 S T5_4 1.02 100 98 5 37.792 0 81 20 30.56 0 78 2S.6 T10_4 5.465 100 98 5 T5_5 2.015 100 98 5 12.937 0 83 20.4 42.964 0 87 20.6 T2_4 9.957 100 98 5 T5_6 0.523 100 98 5 108.014 0 78 27.2 25.892 0 76 20 T2_5 3.72 100 98 5 T8_1 2.13 100 98 5 26.136 0 74 20 37.464 0 86 25 T2-6a 3.08 100 98 5 T8_2 1.595 100 98 5 11.45 0 85 20 35.661 0 85 25 T2 6b 22.563 0 77 24.9 T8_3 1.782 100 98 5 T2 7a 31.171 0 80 24.9 78.482 0 83 38.8 T2-7b 2.39 100 98 5 T8_4 4.026 100 98 5 17.38 0 84 20 51.429 0 78 20 T2_8 19.658 100 98 5 T8_5 4.109 100 98 5 35.099 0 84 20.4 23.879 0 74 20.4 T31 1.301 100 98 5 T8_6 0.398 100 98 5 88.417 0 76 26.3 9.185 0 70 20 T3_2 2.541 100 98 5 T8_7 22.14 100 98 5 30.757 0 82 20 62.463 0 83 20.4 T33 20.006 100 98 5 T9_2 0.841 100 98 5 45.502 0 83 20.4 21.473 0 82 20 T4_2 1.789 100 98 5 T9_3 0.974 100 98 5 51.93 0 80 25.2 36.632 0 76 10 T4_3 1.948 100 98 5 T9_4 0.298 100 98 5 25.531 0 73 18.4 14.161 0 83 20 T4_4 1.574 100 98 5 45.7 0 78 20 IF REff A .141i '�.� 'i'�f• -.l�yr .x Node399 - ..w 40 • �'� � Y `'fit+. ra T2_4 \• '�•a' Cel•�~��. T2 Sic 1"• ,? s s' c i �.• { n�'fTB �.Y.;Node 0 01-3 T2 SacDet - `[ e. ode21 $`Node20 Nod e395 dre�77de16 R f. Node23 Node394 I T2 7bDet v . }Y T2_5bDet - N0de397 f•' `t�'T'°h� y =�+. °I de24 `,j' 1 •Ra► (r�. ,, 1 ��AI -t it A _ ___ s Ry.•.. '� f i ^flit 2 Node393 T3_2bDet :?' `' L �' '•tom Node392 d&33 Node r is S -Link 4 H k2 N0 e306. + �_2aDet T32 Node26 Notle37: ,;:� tri-e ; l-�.; ,0� Node39 i• c•F'b Nodie.440 s It 4*s'e ,• -t i Notle41 r ode42 - � r -- v�w r 4` Node43 �^w mit w \ C � T : q AIN d5M1i7Ci"- N�( e45d5 t Nd e46 Y v T4 4aDet T4_61" - T4 0de390 '� ..�. .. 0 Node50 r n 6 Nod T'4�1 >� � Node51 Npd_. 91 • r ,c w"yA� 4bD'et 10 ? =1' #•• Node61 ; tiii d x � _ . - T ,�'Y _ - dam + •�.d.1� �1�� n'. �! . 5- bDet !.":� Ti'6a T5 6cDet • - rZ 4Y.� Node389 " Node388 T Ricer Terrace Stormwater Master Plan Legend O XPSWMM Node Street(Future) XPSWMM Senenlvs Ansae XPSWMM Runoff Node N Proposed Schematic ®Significant Wetlands I T2,T3,T4,and SMB OEM XPSWMM Link VIM Inventoried Wetlands A tr..River Terrace Study Area—Existing Drainageway 0 1.000 —HEC RAS XS Natural Resource Buffers Qlxu Proed Sub-Basin Feet el d:w...,,rw..,.wer.w,w.v...,e.a...a«e.` I ® ?` � _ ■ - | - � Psi • � i \ ea ; a ƒ © . . < } | \! / w:* � 22� ! � ` |�& | ■■ . \ \ O0 � . w a < �. . - < \ , _\ \ • � � \ . - s�� 222g ) §3r � � p6. r gat �' d y, ter rrT r <<� r r "RR;r 4+� - .'�.,.�u'tl�-+t11a� \� t-- 1 �. - � N. � ,��A/:'. - � ,. 11►f+ �♦ , r c t om' 8ei4 • (. .t, Node66 T5 6bDet '�%` j•-- 0T5 60 T8 481 'H... ' s Nod 7 s Node389r,'!�'Node3'88 .i"va"-�:�t' • - 7� f�j t T10.4 �'. V°51 T5.2i 1�.;'" r+•: A i ` _. _ �,c�, ��o T9_3a Node57.1 _ y ' �, -=�T,9 3b Node109 a y. T8�3fa"" No. 9. Node83 Un T73a Link313 .•'N w 7• e7 �R` c s t ai Node T5 ,T8_3b . e -' •at,4�ii1 ..• :JL 0de84 NodelliD T8_39 fNoCIt Tu0_3a o ---r:.. BYPLkdd62 Node402 BYPLin 361 y Node? Node401 Node96 J Notle75 TB_3a �Ne413 '�Node387 6 .. c o e764 Nod 112 t . o ,� �R� fes+" AF ! I •• _.. I 4 �'•ti 'S�;;, 'y _ qr t l Node113 C Node77 - C , wo r � C _ ' Link299 p Notl 0 'Notle114 T10_2---..._....-- AA •t,. t Node 115 Node 101 C 1Node116 j•.r i BEND RD --� ' NOdl7 • -�.. � rl l 0 7 Node81, I t t w•r {t n!� RINLr Icrracu Stormwatcr 5 de82 .J t, !(' < . MasterPlan XPSWMM r Existing Schematic - T8,T9,and T10 Y hode83 J r ` i {��r ♦ S Node84 r � Legend Q # 4„• _ ti, .N t+T8r2c XPSWMM Node ".� L•r 'i7� ,' .t T 4 t • rc v�f i• ` ,R � � ,` le IC •vim` XPSWMM Runoff Node ��Node87, ,i A• t t �- � r. srr XPSWMM Link tm j .y: -< `y” ••I• �fit.•s j„�f J• a'. .x mil. !/J. High Flow Bypass 'f�+w S ) ��r S� � h � River Terrace Study Area �ry ��; � �.` r —HEC RAS XS �'1C t c"Y r' : ? fr Y f"rel` r v � * Jt� ?� { QProposed Sub-Basin �v aFa � : 4 .�.. • :I tY !�' {f • Sheet(Future) TBi1._• .� �� ,��t��- •i,, t ,, �i• ry�{ t.: 7/� '7``�T"+C7v Wetlands t. + sj'^�-d i% ''##', �-�. �•� rT. 1 r '! ti r rr • Sensitive Areas aR C +moil"•.',i'. t 'A. T 'T` AL•' .1 f Inventoried Wetlands 4 if I.. fie` F } .Lti .t.7'- �.�•e Existing Drainageway ✓w, LIhk84 �9 1� ,mss Node9D� Natwal Resource Buffers r NOde89 Vr r+ €Y aSJ'f x•` t 4YM Tualatin RivNei < I �.�'�' �. !"•_' `_.'i; �t�t��.�' � a+�' I o00 ,. 4 « Fee, l svr •' a 7 J XPSWMM NODE INPUT:PROPOSED CONDITIONS MODEL (Cont.) Curve Time of Curve Time of Node Area Number Concentration Node Area Impervious Number Concentration Name (ac) Impervious% (CN) (min) Name (ac) % (CN) (min) SMB-Det 6.45 100 98 5 T4_6 13.267 100 98 5 3.96 0 85 10 24.966 0 83 20.4 T10_2 3.286 100 98 5 T54 0.874 100 98 5 9.491 0 91 20 26.171 0 78 25.6 T10_3 13.38 100 98 5 T55 0.166 100 87 5 16.75 0 81 20 4.972 0 87 10 T10-3a 3.35 100 98 5 T56a 3.06 100 98 5 3.35 0 85 10 3.06 0 85 10 T10_4 5.465 100 98 5 T5_6bDet 15.57 100 98 5 12.94 0 83 20.4 14.02 0 85 10 T2_4 7.119 100 98 5 T5_6cDet 13.98 100 98 5 77.31 0 78 27.2 11.51 0 85 10 T2 5 0 0 98 5 T73a 7.2 100 98 5 T2_Sa 18.71 100 98 5 7.07 0 85 10 14.18 0 85 10 T8_1 2.13 100 98 5 T2_SbDet 17.29 100 98 5 37.464 0 86 25 14.22 0 85 10 T8-2 1.595 100 98 5 T2-5c 4.5 100 98 5 35.661 0 85 25 4.49 0 85 10 T8_3 1.4 100 98 5 T2 6a 14.51 100 98 5 61.696 0 83 38.8 11.58 0 85 10 T8-3a 2.81 100 98 5 T2-6b 7.58 100 98 5 2.8 0 85 10 8.58 0 85 10 T8-3b 5.74 100 98 5 T2_7aDet 22.09 100 98 5 5.74 0 85 10 15.58 0 85 10 T8-3f 8.61 100 98 5 T2_7bDet 11.09 100 98 5 8.55 0 85 10 5.67 0 85 10 T8_3g 5.95 100 98 5 T2-8 19.66 100 98 5 5.91 0 85 10 35.1 0 84 20.4 T8 4a 9.54 100 98 5 T31 1.16 100 98 5 10.33 0 85 10 79.21 0 76 26.3 T8 4b 18.13 100 98 5 T3 2 0 0 98 5 20.04 0 85 10 T3_2aDet 18.05 100 98 5 T8_5 1.861 100 98 5 15.37 0 85 10 10.813 0 74 20.4 T3_2bDet 3.8 100 98 5 T8_6 3.69 100 98 5 3.47 0 85 10 4.51 0 85 10 T33 20.01 100 98 5 T8_7 22.14 100 98 5 45.5 0 83 20.4 62.463 0 83 20.4 T4_2 1.438 100 98 5 T9_2 0.453 100 98 5 41.74 0 80 25.2 11.56 0 82 16.5 T4_3 1.948 100 98 5 T93a 11.75 100 98 5 25.53 0 73 18.4 13.61 0 85 10 T4-4 0 0 98 5 T9 3b 8.88 100 98 5 T4_4aDet 15.35 100 98 5 9.72 0 85 10 13.47 0 85 10 T9 4 5.56 100 98 5 T4 4b Det 7.55 100 98 5 5.56 0 85 10 7.4 0 85 10 T4_5 12.08 100 98 5 31.41 0 82 20.4 A t t a c h m e n t D — Figures from West Bull Mountain Hydrologic and Hydraulic Analysis (HDR, 2008) Legend i - • Fish Barrier Capacity& Fish Barrier SCHOLISFERRY * Bridges Cross-Sections V! 711 . Planning Area Boundary e !j �� Watershed Boundary Stream Reaches Roads BMC_9 1 1 inch equals 1,500 feet IM fcE ; JA , ' � ' $AIC 18 11; 9AIC..1a _t i[[FItEIO � 1` s amc 12 do s' Summary of Problan Areas ONN COMPANY I Marry Sdnrfi,rr 1MM[diMwiiYiMy3Ma�t w0lriaMs MrIMY I Cb.ui v.ur trMoas L•\Project\14500\14588\Reports\Stotmwater\DRAFT-StormwaterInfrastructurePlan\Attachments\HDRFigure4-l.doc Legend N ChannelFlooding PlanningArea Bounds SCNOLISfERRY ry Watershed Boundary Stream Reaches Roads r-- 1 inch equals 1,500 feet _ A r ( -- I I Ulm S BEEF BEND �~ I. �C K 4 ' Flooding and Under Capacity Channels FIGURE 4-2 i LG Nest&d11.ta nla, Htc;Wo�y wnl HyNawc kalysis C ea,,V ate,Ser.r.ces ttVP.Ctt�1P.�1N1' SLe,,, ��i,-rrce•, L•\Proica\14500\14388\Reports\Storni%,stet\DRAFT-S PYati\r\rtachmcnts\old\HDRFigum4-2ca.doc A t t a c h m e n t E — Drawings from Roy Rogers Road Improvement Project X ui•rn.•5 P7./A M 00640 AW7 0 - fIIMCC AIR Cm Hm CA, a voiri'u•o i�"°ss'w,�"si piw w r w "'�I w wa..am arsr+w Yw +sa.o�P ra it '..�.11.a]nl ii �+%Yi�IatlY. �I •f '7 '�Vf �:a"�'iN'i�xrrPiMO'u..isn�n �-tt'' , •� - ei� .— IM• 0.1 1l rn SJNitAvHo Iiine SV r — -- - M7 to ow Ll — am k A . _.- ��R$ w ep W, Y a r 10 jig. �~rte° u� v5 1 Y ,� • t w 1 � � M • f p O V O ' 'any o i 'D0$ 0 r siiiro rww rwamYr■is rw rwYo V n r uw.�r uor.m o s.0 L m.ini w w.w r waao.al aau�ra _w.awe r m+ww waver w aiw w �i .mrur.ow w..vane r s.waI Ml Y SONIMVda 1-Ing SY ¢o W� JW W= �N 2 � m J 1 W O � WU mN -w.ra. ..rms'1 rpAAro'Aw7 - � 1 uo+ +40.3w dZl•r 3,wry o1 w+t15 ➢6p1 J6i,.sA1 LOAmJ'dwJ o!a V,rn+aJ rtl-O!d i+rPrraf��[� rf r62L+IVf- P'rl r Po!'rGCB+IDBS•4rB.S rrd L r r1'ir -IO.O.L' IS I- a s 'aPri IrO r�..ry rOaI,WS 21 fc{: f6i�0-1,YK Di 19Y.0.).DK��i`; � E f-r.Wzr rdry5 rr.W'mf rrazae'w Eq'Dis am r Cll -abrd•.g rp5 r OOf'm1 wa +�mjv lZ�k t 'y rYf'f'Z9p.o ors(9 ao1',DD+rA1,oAonAw7 rr Ddu r/af- rprraNYM a'als,o -K, Ile�u+rvrr-,5A-' .e�d',rrs rmAls woof r rbew.f.YK of bs9 _._w ws a` Cil r-�6q�ab ,rq •m'rwo7 Cr r 6'YZ-pd"Drs rues wu- oof•srf 41"91'AII rf 6wi9 0,446� rarml,raur7,Davy aMI.Ww'1-/our A_ae11-m 0 Nr M-9,9 i vi b-Is s 'Il 99 Y4S4C� rP-A�',K DrS'DNd hlrod Afl 16-6d'PS wS Vlv.11 IAMD7'Mr3 rYI161 O 16-99'Hf w5 111wIO.D1, •Z2! My r'DS a+4B Mr'Vf"6w7 +r-16d -ra.V colt 'a G91'IYS4.0.).'IS® q;fliDrl',rrv/rD.r-0.-Wl'pro7 •S9-NI,rJ Z rdll'ml NO OST!/"r17,Tf W-V AfA'RM'wNl MJ9 Yl vdm.0-7--6 o-w YK-5*"--1 AlJ, r-a+ s+Ywm<1 i¢1 Can ws U -MN-el >r DS rr-ez.M r+s r�+riO o1, zrero.r.as�i ,eOaK'rmier rrW,IM'rrDf Q '4-92'S-6Z 3 -A srsj A0 a d-IAemc.av,.iw wa„s uYr O 7 mii r .�p a I a.a,F6,n6© a w1 aD+s•n.n 0. � I u�ggy-ba IAYp 6r ouf'Irrl© � .,. I+A,irn'Irw7 +616 asrl•w.Ai c+Aon moJ rr ra1/r v IPr a/Z-00.0 ...15 1 ¢w.1 w-I/7'1wR7 frY•O.._YK /ro- MM'1'ws an Q ..� rS lir�wsMo .augtAAliM., O0OMd3HS-SllOH3S 9 u v ;' ro,■tew ZZ mw WOWS" /a3NS13/ON39 X338 59 •r. , ■orcin. a Yw zz m OYl/W -- •• a,aa w� ■ • F � x .�nr+ppp R 8 .. ..�.p p d C] �Q{a■, ac 1g€ c 3 ? $ as $ $! < � i e O's 0000 00 8 a O O ■roF �� MATCH LIME STA I"L" 1•310 SEE SHEET 7 i tj Pi ` � - - •.acs _. QQ S r•Jaa _ ?S 1.300 . - � l I� r I I" -1 a WJ +•fi ! W U _ 1*3 1.200 q .•}L7, Ll 110 4■91 urxwr Ri 1 •r�•r •q'ti +f, 'Pb �Pws" r•»� r•rm _ Y.Xf4nd GkvW t.100 � II21 Nit to to r z MATCH LINE STA "L"1.060 SEE SHEET S -- — Fpffia O0OM83HS-S11OH3S S. 'm /d3NS13/4N38 J338 L M Y•6uM •1Mr, g 8 d Y 8 g ; f � P o �ar9i:6 R as r¢f P C a siby e a ,>f MATCH LINE STa "L" 7610 SEE SHEET B : I . 1; '4 i 3E;d I.600il �. gr Iaa 'aa ulo4unon r IIn9'M*S Ma Ia500 � $ N _ ,= 1«400 =m— r k � k u MATCH LINE STA "L" 1.310 SEE SHEET 6 ) | MI ■ a ` qo g■ . § | �] �■ z % / | �� a s ! | kd w • b � ! �\ KI Is \| 1. I \ Kl1ih9 » Aw -��■ e @ t & & = c ¢ # ■ § w , � /� \� ! \ ■ § » ■ | ! � ! ■ � � � � : 9l p! \ \ 4/• q�2G ! ■ } \! » � .|. ! | „�.! �,■ � , � ! � � � � ' ;l �I � ,» �■ � ;■9®;! - ! ! |. | k • $ ! /� �k � � � /\■ Ef�� \ ■ ! | | ! | | @l All l eee«ee e @ e 69 a &@@+ � ` 226 . � EEe eEs£R � ! 2.&3-s 9@0 �:e Tnf+rrz� �,,,«�,., .c.. aooMa3HS SIloHJS at " AONSIVON38 3338 'M „ITN,7 '.NYllIY 0�IIM �Y}tQ6 p i( Y'�WIP ypypyy�� l C I - •- MI V R Yr I I I� I 'v I I I I i I g g' CI C wa. �•n is o,.ui..�npo OOOM83HS-SIIOHOS 6= /a3NS13i0N39 3339sgz8 ��}�y� uwpw wo,rrsn M UMb z �Qi�i-i O� P lAR � E MY!dad E R a sA�6L Y � R R b a� a it Aq *i¢r eek %„ caa bW e g 9' m QArg 8 3 ggt 9ggg gg gg � p{ 000® OD DO © iL�Ht MATCH LINE STA "L'1.820 SEE SHEET 9 13 i«800 — p pi 1«700 ; p !� ki Ya PATCH LINE STA "L" I-d10 SEE SHEET 7 ! I � I .wee TIIHMRND wu.�Milw a.olw•„ ,' = ,o 000M83HS-SllOHDS 6 n • �_ A W?N No,ww=/. /83NS13/0N39 A339 In MfMi�Z 7C"r— ouuaw a 1,!! f IE � h a 3WP! v+lP�+ S � Of � ►t •P.� �� +jP�b, $ �'� �8 .$� .:+;P�`R a A w�,��d .F� :cW F� y ry' i'`4 $ �'e4 �F�� &F,�'F adjF�,� � g� � ac -•6-F� 000 0 C-) 000 (bo® o o 0 o® 0 g G ® 7 0 ® 0 C YATCM 1.14E TSTA "L"2,020 5£E SHEET 10 g R R 2+00 1` i TAW 7 3 N � .gypAr ys - "� , a SSct ey J x900 t^ .aiiFit s +j I S C \\ IILA MATCH LINE STA "L" 1+820 SEE SHEET B wm I �;-s= OOOM83HS-SIIOHDS Bc II 59ZZ� rp "v,y. r. /83NS13/ON39 1339 wasua ro.'•tv�r i�ru �,rtary a,mss � ° 1IL a s if R 9 a b MATCH LINE STA -1 2+590 SEE SMEET 12 ; 069'6!'^47 YtffE7J'e 3 , h 2-500 $ N N r M U I G � P7 7 S ' r w : 1 41 2+400 I i_ T+400 t,l ^P 2.9r. AW MATCH LINE STA "L"2.310 SEE SHEET 10 R @ R 1: Z' E g|1 \/ �2 �g \ \■� k � , ! � ! ! �! © ' | /!5 q■ | \ � ! ` MITI, Ail mill! e & a @@e @t m&&A « | E 4 Q ]Rlf #k /#i . / 2#£| � 'l| � !om �! |;,.777 k r �■ , ■••� ;i°� ■ , 4 Z! | ! $ 3g kni eaae a S eee s E ` z&5 _� • _ASNWFON EE E@zEs e a ~� s�3-s N2D . . � � ' . sa-i -rye ruaY OFT ON a., n,YtY,.o O0OMtl3N5-5110HOS f� S9ZZ�� uwa�No,awsrr /tl3NS13/ON39 1338 ,IYISY11 41 YrYYM If �� .711Z1� 000000 O 0 0 ® O500 O D @ 00 6 0 HATCH L!N£ STA !;� :o-/ L nj•1 T o SEE SHEET JI i lip i�_k�a� pa coag 6 T� nr e Y a ' pi ]*100 a ;t ep i� N ' 3-000 1 i r 2 r 2-900 u �h MATCH LINE STA "L`2.890 SEE SHEET 12 I ,a is q s � i Bil�fe e ay ,Y co 113[rg{�$(Wi Q a 111111-4 TAW Iii Z iE, �i BF w (1= 1 I a� r� b f w N4 i dwaim -44 ! j I I w 74 01 I I I I I I I N I"as, N wa,IwdKvnw+ .w waver r.,ap sKa,w 2265 I „vwcror coDF BEEF BEND/ELSNER/ OD 13A�.vw SCROLLS-SHERWO � r,.rvn,r�rol uy.1l MI�N!IM L •1 00111 I m as o• of va vl oo - + -- - - - - -- — - -- - I vwgl r/wSln+jinr _ r » p _ . �m a a m a or a Is - m rm wsm..sr wMaMr�.w,r -- Z •'+�i n iu w.o w�i'lMwwreucTZ ilr a+� a K N p ri'rouf a a>w�. «a vM rn PC rn w tMri.l n3. HHt qp >h S• — _ ,�J,,. _ — oz SOMIAUG 111119 SV s x o m p p !i t 4 MAN t !' c� As 4qlI - - - K law I ` -1 2,0" .11 MA-w II C awl f I ,t t . 'J9d 000000.1 M•,d'•.S rvnlS 91.3.VI.M© '117J KSU/.i. e�! t11 xwe ao]Q .._.._�1•plap�jNg•M•S ...�i,,s a s N= •.uud na.r =151V v isr.t wj KWzsI.0 _v bIS ,x • 1 s�P 1 ).laacr.r _I.va Qs d 1Ull.B& `0p�mie •\ O(Z j WODi00y vorr'owJ© I•rMrAV J I - IluoehS.a0i:.Yl.rorlrw'a.l� `� • 001+ 4 R� �,�TIFIYIRMp w.wawu ms s¢ A r 000M83HS-SIIOHDS /d3NSI3/ON39 3339 �I 3 € 8aY Ali 42; 6'QMS � lF 3a is E� �gg� y3g 00 ',fp� OOOG 0 SO G J YArCH LIME STA '•L"3.460 SEE SFW 15 u u � II 3400 s _ Y ]+700 ,!I II y 'r h r I i ciyf:•srA SEf 13 5.170 .n.