Stormwater Master Plan: Storm Sewer Capacity Study Washington Lee High School October 13, 2011 Department of Environmental Services
Goals Reduce the risk of potential stormwater threats to public health, safety, and property Develop system models that can assess the impacts of new development on system capacity Comply with State and Federal stormwater and floodplain management regulations Department of Environmental Services
Original stream network Only 28.5 miles left of original 50 mile stream network Storm sewer network 366 miles of storm sewers, ~ 10,000 catch basins
Modeling Approach Modeling pipes / box culverts 36 inches in diameter or larger Calibrating using June 2006 event Department of Environmental Services
Department of Environmental Services
Department of Environmental Services
Department of Environmental Services
Approximate water level in basement Department of Environmental Services
Department of Environmental Services
Design Storm • Storm drainage systems typically designed for the 10-year event • Use the June 2006 for calibration / prioritization (event of record – worst since Tropical Storm Agnes in 1972) • Evaluate appropriateness of the 10-year event at locations without overland relief. Department of Environmental Services
10 year flow = 7,540 cfs Department of Environmental Services
Capacity Projects in Progress 24 th St. N. at N. Sycamore St. John Marshall Drive and Lee Hwy. West Little Pimmit Run Phases I & II Spout Run Department of Environmental Services
Climate Change Department of Environmental Services
Impacts not associated with Capacity • Sea level rise (a separate analysis) • Wind damage • Increase in frequency of hurricanes and tropical storms • Increases in snowfall Department of Environmental Services
Arlington’s consultants estimate increases in 10-year precipitation of approximately 3% by 2050, and approximately 8% by 2100 Department of Environmental Services
Questions? Department of Environmental Services
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