Lisa Hair, PE, USEPA 2012 USACE Silver Jackets Workshop

 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.

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

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). Low Impact Development” (LID)

USGS equations predict increases in flooding with watershed imperviousness The National Flood Frequency Program, USGS, 2002 Impervious Surfaces Increase Need for Mitigation

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

Extending hydrograph duration results in overlap and more flooding, scouring Limiting flow rate with larger volumes extends the duration of that “peak” flow

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

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

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 EPA modeled HUC-8’s from 2018 to 2040: Adopted LID practices on new development and redevelopment: Atkins, 2012

 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

 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

 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

 For more information Google EPA Green Infrastructure