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Low Impact Development in COMPREHENSIVE Flood Risk Mitigation Planning

Low Impact Development in COMPREHENSIVE Flood Risk Mitigation Planning. Lisa Hair, PE, USEPA 2012 USACE Silver Jackets Workshop. Reduce Federal Expenditures And Improve Resiliency. Flood mitigation activities are FEMA, USACE Protection of Water Quality is EPA’s goal

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Low Impact Development in COMPREHENSIVE Flood Risk Mitigation Planning

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  1. Low Impact Development in COMPREHENSIVE Flood Risk Mitigation Planning Lisa Hair, PE, USEPA 2012 USACE Silver Jackets Workshop

  2. Reduce Federal Expenditures And Improve Resiliency • Flood mitigation activities are FEMA, USACE • Protection of Water Quality is EPA’s goal • Resiliency includes water supply assurance and adaptability to growth and climate Small storm retention in local ordinances for new development can help achieve these.

  3. LID reduces urban pollutants 2007: EPA Commissioned National Research Council to review Stormwater Program Result: Current methods not effective Runoff volume control needed - not just concentration of pollutants in runoff

  4. Low Impact Development” (LID) • Natural approaches - infiltration and evapotranspiration – and harvest-and-use • Distributed small-scale hydrologic controls retain rainfall close to the source • Replicates the pre-development hydrologic regime:reducing runoff volume compared to impervious surfaces Modified from Prince George's County, Maryland. Larry Coffman et al. (1999).

  5. Adaptable LID Practices Reduce the Impact of Imperviousness

  6. Imperviousness = Higher Flood Peaks Impervious Surfaces Increase Need for Mitigation • USGS equations predict increases in flooding with watershed imperviousness The National Flood Frequency Program, USGS, 2002

  7. Comprehensive Flood Risk Mitigation Starts with Stormwater Ordinances Motivated by, flooding, drought, stream erosion, beach or shellfish contamination –not usually water quality!

  8. “But we have detention pond requirements”: Why Detention Does Not Work Limiting flow rate with larger volumes extends the duration of that “peak” flow Extending hydrograph duration results in overlap and more flooding, scouring

  9. Proven Benefits of Flood Reduction,Cost savings, Environmental Nashville: USACE, Mill Creek – LID could reduce flood losses (reservoirs unacceptable); save endangered species as a side-benefit Omaha: Papio Creek Watershed Plan - LID adoption multi-jurisdiction for flood control; WQ side-benefit IL: Kane, Lake Counties - LID adopted for flood control; WQ and Groundwater Recharge side benefits Maricopa County (Phoenix) - LID for flood control since 1985; groundwater recharge side benefit MN: Capital Region Watershed District - LID cheaper flood control option; water quality improvement for popular lake Los Angeles’ Sun Valley Watershed - LID flood control benefits changed LA’s approach to overall stormwater management NC: Asheville Flood Task Force - Ordinances adopting LID for flood control, will see WQ benefits

  10. Small storms cause repititive losses - How much flooding can LID reduce? • Typical LID design retains 0.5 to 2”; can be designed for more • Flood reduction effect is large for small events • Not noticeable at major storms such as >5” • BUT – 80% to 90% of annual rainfall is <1.5” • AND - 80% to 90% of annual pollution is reduced

  11. Calculate Benefits $$ EPA modeled HUC-8’s from 2018 to 2040: Adopted LID practices on new development and redevelopment: • Annualized Avoided Losses, • San Antonio, TX: $6 M/yr • Richmond, VA: $2M/yr • EPA is not proposing LID for flood control, these are side-benefits to LID for water quality Atkins, 2012

  12. USACE Approach for Reducing Future Federal Expenditures • Policy Guidance Letter (PLG 52) requires recipients of Corps projects to protect against future flood risk Adoption of local ordinances for “no net increase in runoff” from new development is recommended

  13. FEMA NFIP looking to LID for Resiliency and Environment • FEMA CRS scoring credits for LID • NFIP EIS alternative: integrating future conditions –biggest impact may be future imperviousness • FEMA has LID in “Model Ordinances” for environmental protection, and funded LID pilots because of repetitive losses

  14. Conclusions • LID is necessary for water quality/stream health • Cost-effective for small storm flood reduction • Adds community resiliency via groundwater recharge, maintaining stream baseflow, enables growth w/o flood damage increase, eases climate change impacts • Reduces future federal expenditures, protects existing federal investments in flood control • LID is essential part of comprehensive mitigation planning – include LID in alternative selection

  15. For more information Google EPA Green Infrastructure

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