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Raingardens

Raingardens. Managing Stormwater Runoff in Urban Areas Julie Gibson Leslie Newton December 4, 2001. What is a ‘raingarden’?.

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Raingardens

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  1. Raingardens Managing Stormwater Runoffin Urban Areas Julie Gibson Leslie Newton December 4, 2001

  2. What is a ‘raingarden’? Definition: A constructed depressional area that is used as a landscape tool to reduce direct drainage into streams and rivers using vegetation and soils to treat stormwater and remove pollutants. • Also called a “bio-retention” area • - Can be thought of as a miniature, artificial riparian buffer

  3. Problems with stormwater runoff • More flooding during storms—less base flow during dry periods • Increases in: • erosion & sedimentation • chemicals & metals in streams • nutrients • harmful bacteria & other pathogens • potential harm to plants & animals

  4. Why do we need rain gardens? • Avoid direct drainage • Remove water pollutants • Chemicals (fertilizers) • Gasoline/oil • Sediment • Aesthetics

  5. Direct drainage(the ‘ugly’ picture) Stormwater Streams & Rivers

  6. Indirect drainage(the ‘pretty’ picture) Stormwater Raingarden Streams & Rivers

  7. Pollutant removal mechanisms Source: NCCES 6/01 Hunt.

  8. Location • Strategically placed to intercept water runoff • Engineered on a graded slope no greater than the angle which can be retained by vegetative cover or other adequate erosion control devices or structures • Size based on area of drainage

  9. Process • Water collects & ponds in rain garden • Water infiltrates & percolates through mulch, sand layer, and through root system • Filtered water drains through outlet into stream or groundwater

  10. Design Elements • Grass buffer strip • Surface mulch layer • Planting soil • Sand bed • Gravel underdrain system • Overflow storm drain • Plants

  11. Grass buffer strip • The surface of the grass buffer strip slows water as it enters the rain garden and filters particulates from the runoff

  12. Summary of design parameters Source: NCCES 6/01, Hunt.

  13. Soil Mulch layer • Provides area for plant growth • Maintains moisture & avoids surface sealing • Filter for fine particles in suspension • Allows for microbial community breakdown of pollutants Planting soil • Provides region for water & planting material above • Soil pores provide additional storage for water volume • Soil particles adsorb pollutants through cation exchange Sand Bed – optional (12” deep) • Keeps finer soil particles from washing out through the underdrain system • Provides aerobic sand filter as final “polishing” treatment media Gravel Underdrain System • Collects & distributes treated excess runoff • Helps keep soil from becoming saturated

  14. Planting Soil Bed • Minimum 4 feet deep • non-hydric top soil (A horizon) • uniform composition • At least 10 to 25 % clay • Sandy loam or loamy sand texture • Objects > 1 inch removed for plant growth • Free of invasive/exotic plant parts • Tested to meet NCDA recommendations for hardwoood trees • Lime & fertilizer tilled into top 6 inches as needed

  15. Gravel Underdrain System • Gravel layer 8 inches deep • 4 to 6 inch perforated piping system

  16. Overflow storm drain • Drains stormwater that overflows ponding limits

  17. Plants • Endure prolonged direct sunlight • Quick transpiration rates • Withstand ponded periods for up to 3 days • Provide shade for herbacious ground cover • Native species – adapted to site • Dependent on season of planting • Diversity will help to increase resistance to pests & diseases

  18. NC Plants for Raingardens

  19. Cost Source: NCCES. 2001.Hunt

  20. Why build a rain garden and not a treatment wetland? • Smaller in size • Less expensive • Higher success rate • Low maintenance • Safe for children • Easy and effective way to meet EPA regulations requiring communities to improve the quality of storm water runoff

  21. Local Raingardens • Carpenter Village – Morrisville • Environmental Demo Showcase House – Morrisville (Carpenter Village) • Rocky Branch Project – NCSU (Motor Pool) • Unnamed raingarden – NCSU Library

  22. “Nonpotable water” Environmental Demo House – Carpenter Village

  23. Other Resources • Design of Stormwater Filtering Systems. Chesapeake Research Consortium. (December 1996). Chapter 6: Key Design Elements of Bioretention Systems.  • Earthtech. (January 29, 2001). Preliminary design of bioretention area for the Rocky Branch restoration and greenway project. Raleigh, NC. •  Ferlow, Donald L. “Development-Related Storm Runoff Renovation.” Constructed Wetlands for the Management of Stormwater Runoff. Cornell Cooperative Extension. August 20, 1997. •  House, C.H.1995. “Engineered Environments: Mimicking Nature to Clean Our Waters.” WaterWise, NC Sea Grant College Program. Vol.3, No.1. •  Hunt, William F. (2001). Designing Rain Gardens (Bio-Retention Areas). North Carolina Cooperative Extension Service. Raleigh, NC. • Hunt, William F. (2001). Designing Stormwater Wetlands for Small Watersheds. North Carolina Cooperative Extension Service. Raleigh, NC. • Rain Garden/ Bio-Retention Areas. (2001). Port Towns Community Development Corporation. http://www.porttowns.com/special/rain.html

  24. Questions?

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