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Low Impact Development and Stormwater Management in Pennsylvania

Low Impact Development and Stormwater Management in Pennsylvania. Catherine Chomat, P.E. F. X. Browne, Inc Brian Oram, PG Wilkes University Dr. Robert Traver, P.E. Villanova University. Impacts of Stormwater Runoff on Aquatic Ecosystems. Impacts of Stormwater Runoff on Aquatic Systems.

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Low Impact Development and Stormwater Management in Pennsylvania

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  1. Low Impact Development and Stormwater Management in Pennsylvania Catherine Chomat, P.E. F. X. Browne, Inc Brian Oram, PG Wilkes University Dr. Robert Traver, P.E. Villanova University

  2. Impacts of Stormwater Runoff on Aquatic Ecosystems

  3. Impacts of Stormwater Runoff on Aquatic Systems • Historical Perspective • EPA 2000 Water Quality Report • Water Quality-Ecosystem Impacts

  4. Wastewater Treatment • Since 1970… • STP Construction $239 Billion • STP Operations $234 Billion • EPA Needs Survey • $84 Billion Needed for new STPs for • year 2008

  5. Wastewater Treatment • Populations Served by STPs • 1972 85 million people • 1988 150 million people • From 1972 to 1988… • 4000 new sewer systems • 2000 new STPs

  6. Wastewater Treatment • 1988: Less than 1% of U.S. Population discharges untreated wastewater • Meeting Effluent Criteria • Industrial 93% • Municipal 87%

  7. Summary of Quality of Assessed Rivers, Lakes, and Estuaries

  8. Leading Causes and Sources* of Impairment in Assessed Rivers, Lakes and Estuaries

  9. Development Activities Site Clearing and Grading Tree Removal Loss of Natural Depressions (Storage) Loss of Topsoil/Humus Loss of Pervious Area/Percolation Increase in Impervious Area Increase in Runoff

  10. Development Impacts on Water Quality • Watershed Hydrology • Stream Geometry • Degradation of Aquatic Ecosystems • Pollutant Export During Construction • Pollutant Export After Site Development

  11. 1. Watershed Hydrology • 1.Reduced Infiltration • Increased Peak Discharges • 2-5x Predevelopment • Increased Volume of Runoff • Moderately Developed – 50% more runoff • Decreased Time of Concentration • “Time Runoff Reaches Stream” as much as 50% lower • Increased Flooding • Frequency & Severity • Bankfull conditions: • Natural…Once every 2 years • Developed…3-4 times per year • Reduced Base Streamflow Due to Loss of Groundwater • Higher Runoff Velocity

  12. Changes in Hydrology Due to Development

  13. Hydrology Changes Due to Development

  14. Parking Lot vs. Meadow ParameterParking LotMeadow Runoff Coefficient 0.95 0.06 Time of Concentration (minutes) 4.8 14.4 Peak Discharge (cfs) 2-Year 4.3 0.4 100-Year Storm 12.6 3.1 Runoff Volume (cu. ft.) 3,450 218 Runoff Velocity 2-Year Storm (fps) 8 1.8

  15. COMPARISON OF RUNOFF VOLUME BETWEEN UNDEVELOPED AND DEVELOPED CONDITIONS

  16. 2. STREAM GEOMETRY • Channel Widening • Developed Area Streams: 2 to 4 times original size • Streambank Erosion • Increased Pollutant Loads • Increase in Floodplain • 3. Undercut Streambanks • Siltation of Stream • Stream Bedload • Substrate Changes (Biota Changes)

  17. Physical Impacts of Impervious Cover

  18. DEGRADATION OF AQUATIC ECOSYSTEMS • Cumulative Effects • Scouring • Sedimentation • Velocity • Streamflow • Organic Matter - Biochemical Oxygen Demand • Dissolved Oxygen • Nutrients • Toxics • Chlorides

  19. DEGRADATION OF AQUATIC ECOSYSTEMS • Temperature • Increase in % Impervious  Increases Temp. • Adverse Impact on • - Algae • - Macroinvertebrates • - Fish

  20. Temperature % Impervious Area

  21. DEGRADATION OF AQUATIC ECOSYSTEMS • Fish and Macroinvertebrates – • Decrease in • …Diversity • …Populations • …Clean Water Species • Increase in Pollution Tolerant Species

  22. 3. Degradation of Aquatic Ecosystems • URBAN RUNOFF POLLUTANTS • Sediments • Nutrients • Bacteria • Organic Matter • Hydrocarbons • Metals • Toxic Chemicals • Chlorides

  23. SEDIMENTS Produced by: Construction Erosion Developed Area Erosion Washoff Streambank Erosion Problems: Turbidity Reduced Light Penetration Clogging of Gills/Filters (Fish & macroinvertebrates) Reduced Spawning Habitat Destruction Nutrients Metals Toxics Metals and Phosphorus Attach to Sediments

  24. NUTRIENTS Nitrogen (TN, NH3, NO3, Organic-N) Phosphorus (TP, PO4, SRP) Eutrophication of Lakes, Impoundments & Large Rivers PROBLEMS: Excessive Algae and Aquatic Weeds Dissolved Oxygen Depletion Taste & Odor Problems Fish Kills Loss of Recreation Toxins Increased Water Treatment Costs

  25. Wet vs. Dry Weather

  26. Stream Hydrograph Total Phosphorus Concentrations

  27. Stream Hydrograph Total Suspended Solids Concentrations

  28. BACTERIA Always Found in Urban Runoff Often Exceed Health Standards More Developed – More Bacteria Older Developed – More Bacteria Special Problem Areas: Combined Sewer Areas Sewer Overflow Areas

  29. ORGANIC MATTER Biochemical Oxygen Demand (BOD) of Stormwater Runoff is High Causing: Decreased Dissolved Oxygen Stressed Aquatic Life Fish Kills Older, highly impervious areas – Highest BOD

  30. Dissolved Oxygen in Stream 0.4 Inches of Rain

  31. HYDROCARBONS Oil & Grease – Hydrocarbons Sources: Parking Lots Roads Gas Stations

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