PSGB Ecosystem Conference The Effectiveness of LIDs in Reducing Stormwater Runoff February 9, 2009

1. PSGB Ecosystem ConferenceThe Effectiveness of LIDs in Reducing Stormwater RunoffFebruary 9, 2009 Doug Beyerlein, P.E. Clear Creek Solutions, Inc.

2. This presentation was originally given at the Puget Sound Georgia Basin Conference in Seattle, WA, in February 2009by Doug Beyerlein, P.E. Clear Creek Solutions, Inc.

3. Presentation Introduction Permeable Pavement Rain Gardens Impervious Runoff Dispersion Green Roofs Rainwater Harvesting Watershed Reforestation Summary

4. Introduction There is nothing magical about LIDs. Stormwater must go somewhere. Stormwater must either: Infiltrate into the soil. Evaporate/transpire into the atmosphere. Runoff.

5. Introduction Key considerations in LID effectiveness in the PSGB region: Type of soil: till or outwash. Type of vegetation: forest, pasture, urban.

6. Introduction LID hydrologic modeling requires continuous simulation: WWHM (HSPF) Continuous simulation hydrology models the entire hydrologic cycle for multiple years.

7. Introduction WWHM: Western Washington Hydrology Model • Developed for the State of Washington Department of Ecology. • Has the ability to model a full range of LID facilities and practices.

8. Summary

9. Permeable Pavement

10. Permeable Pavement Reduces Runoff Volume: • Evaporation. • Infiltration to native soil.

11. Permeable Pavement Flow Paths Evaporation from pavement Rain on pavement Surface Runoff Infiltration through pavement Infiltration to gravel subgrade Underdrain Flow Infiltration to native soil

12. Permeable Pavement • Reasons why permeable pavement is a good LID option in PSGB region: • Ratio of drainage area to infiltration facility area is 1 to 1. • Western Washington rainfall volumes and intensities are relatively low. • Subsurface storage provides water for long-term slow infiltration and evaporation.

13. Roof Runoff Dispersion Dispersion of impervious roof runoff on adjacent pervious lawn allowing some water to infiltrate before becoming stormwater runoff.

14. Roof runoff dispersion reduces runoff volume by slowing the runoff velocity and allowing: • Evaporation from adjacent pervious land. • Transpiration from adjacent pervious land. • Infiltration on adjacent pervious land.

15. Roof runoff dispersion reduces runoff volume by slowing the runoff velocity and allowing: • Evaporation. • Transpiration. • Infiltration.

16. Roof Runoff Dispersion Flow Paths Impervious Roof Surface Surface Runoff Pervious Surface Interflow Infiltration to Native Soil Infiltration to native soil is dependent on native soil characteristics.

17. Roof Runoff Dispersion • Reasons why impervious runoff dispersion is a good LID option in PSGB region: • Turns impervious runoff into pervious runoff. • Works best with outwash soils; less benefit with till/poor draining soils • Soil moisture storage provides water for infiltration and evapotranspiration.

18. Green Roofs

19. Green Roofs Reduce Runoff Volume: • Evaporation. • Transpiration.

20. Green Roof Flow Paths

21. Green Roofs • Reasons why green roofs are a good LID option in PSGB region: • Can be used in highly developed urban areas. • Soil moisture storage provides water for evapotranspiration.

22. Rain Gardens

23. Includes planter boxes

24. Rain Gardens Reduce Runoff Volume: • Evaporation. • Transpiration. • Infiltration to native soil.

25. WWHM Rain Garden Modeling Downstream control structure: Water infiltrates into the soil before runoff.

26. Rain Garden Flow Paths Inflow to Bioretention Facility Weir Flow Infiltration to Amended Soil Vertical Orifice Flow Underdrain Flow Infiltration to Native Soil

27. Rain Gardens • Reasons why rain gardens are a good LID option in PSGB region: • Regardless of volume reduction there are good water quality benefits. • Works best with outwash soils; less benefit with till/poor draining soils • Soil moisture storage provides water for long-term slow infiltration and evapotranspiration.

28. Rainwater Harvesting

29. Rainwater Harvesting Reduces Runoff Volume: • Storage for later application and evapotranspiration.

30. Rainwater Harvesting • Reasons why rainwater harvesting is a good LID option in PSGB region: • Can be used in highly developed urban areas. • Can reduce municipal water supply demand for irrigation.

31. Watershed Reforestation

32. Reforestation Reduces Runoff Volume: • Evaporation. • Transpiration. • Infiltration into soil.

33. Reforestation • Reasons why reforestation is a good LID option in PSGB region: • Works best with till soils; less benefit with outwash soils. • Soil moisture storage provides water for long-term slow infiltration and evapotranspiration. • Provides wildlife habitat. • Reduces carbon footprint.

34. Summary

35. Summary • In PSGB region: • Permeable pavement is the most effective LID to reduce stormwater runoff, regardless of soil type. • Roof runoff dispersion into outwash soil is the most effective LID to increase groundwater recharge.

36. AcknowledgementsSeattle Public Utilities provided much of the funding for the modeling of green roofs and rain gardens.Taylor Associates of Seattle provided info and photos of Seattle green roofs.The City of Portland, Oregon, Bureau of Environmental Services (BES) provided the Hamilton green roof monitoring data.

37. Questions?Contact: Doug Beyerlein 425.892.6454beyerlein@clearcreeksolutions.com