STORM AND SURFACE WATER SYSTEM PLAN January 2016 CHAPTER 6 CURRENT CONDITIONS - STATE OF THE STORM AND SURFACE WATER SYSTEM This chapter describes the state of the natural and constructed storm and surface water system as it exists in the first decade of the 21st century. Existing or baseline conditions of the storm and surface water system are described and used to evaluate the system that forms the basis of the Storm and Surface Water Basin Plan recommendations. This chapter is organized into three major categories 1) Flood Protection, 2) Water Quality Protection, and 3) Fish and Wildlife Habitat. Storm and Surface Water System Plan recommendations are based on analyses of each of these categories. Existing Conditions of the Storm and Surface Water System Background The City of Bellevue is part of the larger Puget Sound drainage basin. Located in the Lake Washington/Cedar/Sammamish Water Resource Inventory Area, stormwater originating in Bellevue either drains to Lake Sammamish east of the city or Lake Washington to the west. Lake Sammamish itself is a tributary to Lake Washington via the Sammamish River. Lake Washington drains to the Puget Sound via the Lake Washington Ship Canal (Ship Canal) at Montlake, then to Lake Union, and eventually through the Hiram M. Chittenden Locks (Ballard Locks) in Seattle to the Puget Sound. The storm and surface water system in Bellevue consists of a Historic logging in western Washington created series of open streams, a network of pipes, long-term impacts to streams and watersheds. storage facilities, lakes, ponds, wetlands, collection, and treatment facilities all in a mix of public and private ownership. As described in the City’s original Drainage Master Plan (KCM-WRE/YTO 1976), the mosaic of public and private drainage system components work together to perform the system’s critical functions of conveyance, flood protection, and environmental protection. Bellevue’s storm and surface water system is a direct result of the topography, current and historic land uses, regulations, and geology of the area. The city covers approximately 32 square miles. There are about 79 miles of streams within the city limits; approximately 13 miles of large-lake shoreline (Lake Washington and Lake Sammamish); and 3 small lakes (Larsen Lake, Lake Bellevue, and Phantom Lake). Figure 6-1 shows the open channel stream system in Bellevue, including the 26 drainage basins. Chapter 6 - Current Conditions - State of the Storm and Surface Water System 6-1 STORM AND SURFACE WATER SYSTEM PLAN Bellevue Storm Drainage Basins City of Bellevue Storm and Surface Water System Plan GIS Services Swan Lake Yarrow AVENUE NE116TH LAKE WASHINGTON BLVD NE BLVD WASHINGTON LAKE 108THAVENUE NE Bay 132NDAVENUE NE VALLEY140THAVENUE NE CREEK AVENUE NE 148TH Fairweather 405 YARROW NE 40TH ST POINT ¨¦§ K Bay E Cozy CITIES CREEK E Cove Y R AR C NE NORTHUP WAY RO GOFF Y 520 W E ! CR CREEK L EE L K A V 116TH AV AV NE 116TH 520 ! NE 30TH ST K 134TH AVENUE134TH NE E BELLEVUE-REDMOND ROAD E ARDMORE NE 24TH STREET R NE C 24TH STREET NE 24TH F SEARS STREET WEST F O CREEK TRIBUTARY G NE 20TH STREET G AV NEAV O NORTHUP F NE ROAD NE F C WAY 104THAVENUE NE (BELLEVUE WAY) Clyde AVENUE100TH NE NEAVENUE 112TH REDMOND 108THAVENUE NE AV MEYDENBAUER R Loch E NE 14 ST 120TH 92NDAVENUE NE BELLEVUE-REDMOND NE 12TH ST 130THAVNE E 400 PKWY CREEK 124TH AV NE K 173RD ROSEMONT Lake K NE 10TH ST Bellevue E NEAVENUE STURTEVANT AVENUE NE RE DRD L 132ND NEAV NE 8TH ST S WILKINS LAKE WASHINGTON BLVD NE CREEK OLD BEL NE 8TH STREET E AVENUE NE Y K NE 8TH ST CLYDE CREEK SAMMAMISH C E NE 110TH AV NE 106TH NEAV R E E BEACH NE 4TH ST R 148TH E C KELSEY W LAKE K NE 2ND ST Y 405 Y 120THNEAV Meydenbauer E AVENUE 164TH R CREEK S MAIN STREET 156TH ¨¦§ A Bay L MAIN T STREET E U 114TH AV SE K B I 116TH 140THAVENUE NE R T T Larsen S Lake BLVD Lake E BELLEVUEWAY L a W 112TH AVE SE 112TH k ST e SE 8TH ST HILLS R AV SE 108THAVE SE HI NORTH Sammamish iCl 8TH lsH SE CAo nRn SAMMAMISH e LAKE Dc t So Lake rC R 164TH E SE E Washington K SE 16TH ST 104THAVSE 145TH PL SE BELLEVUE MERCER RICHARDS Phantom AVENUE Lake SLOUGH118TH AV SE CREEK SE 22ND ST 123RD AV 123RD AV SE 168TH AV SE ROAD WAY SE 24TH ST ROAD EAST PY KAMBER PHANTOM SE 26 SE CREEK SPIRIT 156TH CREEK ST BEAUX RIDGE RICHARDS ARTS 128TH SE AV SE 90 EASTGATE WAY §¨¦ SAMMAMISH SE 36TH ST VASES 34THA C STREEK SUNSET W LAKE COAL CREEK CREEK VASA NEWPORT SE FACTORIA BLVD SE WAY CREEK SE K V 150TH AV SE A 90 E S E A §¨¦ 124TH AVSE NEWPORT R SE COAL CREEK C C R S SOUTH I E Lake W PARKWAY E SE 148TH AV SAMMAMISH E K L Washington DRIVE WAY AV 164TH AV SE AV 164TH REEK EWIS C L VILLAGE SE 405LK NEWPORT PARK DR SE ¨¦§WA SH HIGHLAND BLVD 119TH BLVD PKWY SE FOREST SE 60TH 160TH AVE SE LEWIS ST LAKEMONT SE 60TH ST DRIVE CREEK CREEK SE 62ND PL LAKEHURST COUGAR SE CO AL COAL 123RDSEAV C 112TH SE AV LAKEMONT BLVD SE WAY 116TH SE AV RE EK CREEK MT NEWCASTLE GOLF CLUB RD Legend NEWCASTLE WAY COAL Streams Lake LK WASH BLVD SE City Limits Bore n 116TH AVE SE 110TH PL SE COAL 5,200 The City of Bellevue does not guarantee that the information on this map is accurate or complete. This data is provided on an SE 88TH ST CREEK Feet "as is" basis and disclaims all warranties. Source: City of Bellevue SE PY Coordinate System: State Plane, Washington North Zone, NAD83 NSRS2007 (Bellevue) " SE 95TH WAY Date: 5/29/2015 File Name: V:\utpl\ArcGIS\Storm\StormwaterSystemPlan2015\StormwaterSystemPlanPartialUpdates2015\Bellevue_StormDrainBasins.mxd IT Department Figure 6-1. City of Bellevue streams and drainage basins. 6-2 Chapter 6 - Current Conditions - State of the Storm and Surface Water System STORM AND SURFACE WATER SYSTEM PLAN January 2016 Stormwater systems collect and convey the portion of total rainfall that is not otherwise lost to evaporation, plant uptake, or soil storage. The “excess” rainfall flows through pipes and streams while making its way to the receiving water body. Establishing the existing conditions of the storm and surface water system requires a brief discussion of the variables that contribute to the state of the system. The quality, volume, and rate of stormwater runoff is influenced by rainfall patterns, soils, geology of the area, land surfaces, vegetative cover, and social behavior. Appendix B-1 provides the Bellevue Stormwater Basin Fact Sheets for each drainage basin. Rainfall Storm and surface water systems are intrinsically related to climate. The timing and distribution of rainfall events in the Pacific Northwest have sculpted the physical, biological, and chemical balances of open stream systems. Bellevue receives on average 36.6 inches of rain each year (see Figure 6-2 Annual Rainfall). The historical Pacific Northwest rainfall pattern is distinctly divided into two seasons—a dry summer and fall followed by a prolonged rainy season in the winter. On average, 79 percent of the annual precipitation falls during the wet season from October through April (see Figure 6-3 Average Monthly Rainfall). Because most of the precipitation occurs during the winter months, plant uptake and evaporation have marginal effects on rainfall consumption. The remainder must either be stored in the soil profile or it becomes the source of water for streams. In October, when the rainy season begins, the soil profile has been largely depleted of excess moisture because the growing season has just ended. The availability of soil moisture storage is an important component for overall stormwater management. Flood control, water quality improvement, and habitat protection are directly affected by how much of the total amount of precipitation becomes stormwater runoff rather than being infiltrated into the soil profile, or lost to plant uptake and evaporation. What remains, the excess precipitation, becomes the stormwater runoff that the Utilities Department and private property owners are tasked with managing. Over the last few years, rainfall has not followed historical patterns. Staff will be monitoring rainfall to determine whether there are consistent changes in the timing or intensity of rainfall. Yearly Avg= 36.6 in. Wet Figure 6-2. Annual rainfall, Bellevue, WA, Figure 6-3. Average monthly rainfall, Bellevue, WA, 1981-2014. 1981-2014 Chapter 6 - Current Conditions - State of the Storm and Surface Water System 6-3 STORM AND SURFACE WATER SYSTEM PLAN 6-4 Chapter 6 - Current Conditions - State of the Storm and Surface Water System STORM AND SURFACE WATER SYSTEM PLAN Soils and Geology Soils and geology are important to surface water management because they directly affect the extent to which water soaks into the ground or runs off. The surface soils and geology in Bellevue were generally formed by glaciers, which receded approximately 10,000 years ago. Soils were originally mapped by the Soil Conservation Service (SCS) (Snyder et al. 1973). Most soils in Bellevue can be classified as glacial till, glacial outwash, or wetland soils. Till soils are generally compacted and do not readily allow water to infiltrate. Outwash soils mostly consist of sand and gravel, and tend to allow water to infiltrate. Wetland soils are generally at low elevations that receive water, and are saturated with water or ponded for most of the year.