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DeKalb County, Georgia

Small community takes multi-pronged approach to reducing flood risks

The Drew Valley-Brookhaven watershed area of DeKalb County, Georgia faced repeated annual flooding. After a particularly heavy rainfall in 2003 left dozens of homes under water, citizens demanded action. County commissioners responded with a mitigation plan, largely supported by FEMA grants, to remove repeatedly flooded homes, upsize culverts and build a community detention pond. Halfway through the project, a 1-percent-annual-chance rainfall event occurred, and the pond alone prevented flooding to virtually every home.

Photo by Bill Higgins

Community facts

Source: US Census Bureau.

Mitigation actions

In 2002, the community approved a storm water utility fee, which covered the 25% match for the $3.5 million project. FEMA grants covered the rest. “For a lot of communities, the 25% local match is difficult,” says Duncan Hastie, associate VP of Dewberry, the flood mitigation design consultant. “Having that storm water utility fee was critical to pulling this off.”

During heavy rain, the detention pond reduces the flow of water from Poplar Creek into the culvert by as much as 70% to control the influx of water. Community meetings led to aesthetic improvements to the pond, including wrought-iron fencing, landscaping and trails. It is now considered a community enhancement rather than an ugly storm water installation. Homeowners cite proximity to the detention pond and its landscaping as an asset to their property values.

The community estimates that $826,000 of losses were avoided in September 2009 alone thanks to the pond, and that $600,000 of losses were prevented by acquisitions. Avoidance of losses is expected to continue over a 30-year period.

Benefits of mitigation

Economic benefits
$12.4 million
Total monetized benefits
Return on investment
Estimated return on investment
Benefit-cost ratio
Benefit-cost ratio of the DeKalb County projects
Source: Dewberry. Drew Valley Flood Mitigation in DeKalb County, Georgia – Risk map before its time.

Project challenges

Aligning expectations and educating homeowners was critical

In workshops with local businesses and homeowners, Dewberry, the flood mitigation design consultant, spent several hours explaining to residents why some solutions, such as moving creeks underground, were not feasible. This education process helped to create local buy-in for the project from the beginning.

“This is the first time our engineer has ever heard a resident say that they wanted to live next to a detention pond”
Duncan Hastie, associate VP, Dewberry

Future considerations

Landscaping of land near flood detention pond.
Photo by Bill Higgins
Many more homes remained dry during a 1-percent-annual-chance rainfall event thanks to the newly built detention pond

After the pond was finished in 2009, the area experienced another devastating flood. Despite the fact that culvert construction was not yet complete, the detention pond saved almost every home from flooding. The only properties damaged were in the highest-risk area of the floodplain where homeowners had declined buy-outs.

Flood mitigation resources

Below is a non-exhaustive list of other flood mitigation information resources.