Historic Flooding in Atlanta, September 2009Anne Larson Hall, Environmental Sciences, Emory University
"Epic flooding in Georgia, 2009," USGS Fact Sheet 2010-3107, confirms the level of destruction from floodwater experienced by Atlanta in September 2009. Although most residents in the U.S. are aware of the 100-year floodplain as a measure of flood risk for their homes, 18 streams in Atlanta experienced discharges much greater than the 500-year annual exceedance probability. Over the course of 3 days, 15-20 inches of rain fell. The major wastewater treatment plant for Atlanta, R.M. Clayton, experienced flooding and damage to critical infrastructure and discharged sewage directly into the Chattahoochee River. Directly across the river, R.L. Sutton wastewater treatment plant in Cobb County also experienced severe damage.
How does a major metropolitan area respond to and recover from a disaster of this magnitude? What policies build resilience in the face of unexpected severe weather-related events and protect critical infrastructure? Does our aging urban infrastructure exacerbate flooding?
It is estimated that impervious surface in the Metro area has increased by 20% from 2000-2010, and up to 71% in North Atlanta suburbs (AJC, 2010). Efforts to decrease stormwater volume include new legislation requiring less runoff, storm water utility taxes to pay for infrastructure and repairs, construction of bioswales, installation of porous pavement and storage features. Some infrastructure construction is still underway, for example, the 10 million gallon Peachtree Creek Capacity Relief Project.
Federal Emergency Management Agency (FEMA) and the Georgia Department of Natural Resources have revised flood maps for determining flood insurance rating and building requirements. Better detail is now available with the use of 2-foot contour interval GIS topographic maps instead of 20-foot contour maps.
Individuals with expertise/responsibilities in the following areas have helped create the case study:
- Georgia Water/Wastewater Agencies Response Network (GA WARN)
- Atlanta Regional Commission
- U.S. Geological Survey
- Federal Emergency Management Agency
- Department of Watershed Management (City of Atlanta and Metro Atlanta counties)
- Upper Chattahoochee Riverkeeper
- Georgia Department of Natural Resources
Key teaching points:
- Developing an understanding of the impacts of urban development on fluvial systems.
- Assessing the magnitude and impact of urban stormwater flow and the failure of wastewater treatment infrastructure during high flow events.
- Developing plans to decrease stormwater flow and to contain potential sewage overflows.
- The importance of using updated, accurate flood risk maps to alert utilities, businesses and residences of the potential risks of 100 and 500 year flood events.
How this example is used in the classroom:
This example leads into assignments analyzing Emory campus stream hydrographs using Septemter 2009 USGS gaging data. Students also calculate recurrence intervals, predict 100 and 500 year stream discharges, and
obtain flood risk maps for their residences.