Post-meeting Action Steps for Community Members and Neighborhood Associations
Consider 3 mitigation options and send emails, letters or calls noting your preferences to DeKalb CEO Michael Thurmond, Board of Commissioners, and Departments of Roads and Drainage and Planning and Sustainability (see email addresses below) through October. At some undetermined time in future, Commissioners will decide whether to fund mitigation measures using county’s storm water utility fund. Two other flood-prone communities in DeKalb that were also recently evaluated may seek funding from this same fund.
Meeting Conveners
Commissioner Jeff Rader and Staff of DeKalb’s Departments of Roads and Drainage and Planning.
Presenter
Sam Fleming, Dewberry Engineering
Full report to be posted on dekalbcountyga.gov
Presentation
Available here.
Study Purpose
To identify factors that cause repeated flooding at Briarcliff/Briarlake intersection and strategies to reduce flooding frequency due to overtopping of the south and north culverts and Greely Lake (marsh across from Echo Lake) that flow into Echo Lake. It examined impact of flooding and mitigation options on utilities (e.g., 30” diameter water main and gravity sewer under Briarcliff) and transportation (possible road blockage during construction). It did not directly focus on sedimentation into Echo Lake or Greely Lake or other parts of Echo Lake watershed. The study involved extensive site measurements in 2016 and hydrology modeling based on new, preliminary FEMA floodplain maps and estimates about future impervious surface area in watershed.
Key Findings
Echo Lake drains large watershed (> 1400 acres) of which > 12% is impervious surface. South culvert (near Echo Drive) overtops more often (1 in 5 chance in a given year) than north culvert (near Circlewood) (1 in 50 chance in given year).
Three possible flooding mitigation options and cost (which includes cost of any land purchase):
1.
Install 14 barrel culverts under Briarcliff to increase flow from Greely Lake into Echo Lake, install long, low wall along southwest corner of of Briarlake/Briarcliff intersection to block water flow from Greely Lake, but maintain current elevation of Briarcliff. This would reduce flooding by increasing water flow into Echo Lake through culverts and increasing retention capacity of Greely Lake. Would increase flood elevation at Greely Lake by ~ 9”, but this is not likely to increase flood risk of homes south of Greely Lake. Substantial adverse impact on traffic and utilities. Estimated cost: $1.4 million.
2.
Install 5 larger, barrel culverts under Briarcliff to increase water flow from Greely Lake into Echo Lake, install short weir wall on south side of Briarlake to block flow from Greely Lake, and raise elevation of Briarcliff by 3 ft. This would increase water flow into Echo Lake through the culverts and use elevated road to block flow from Greely Lake. Would increase flood elevation at Greely Lake by ~ 1.2 ft, but this is not likely to increase flood risk of homes south of Greely Lake. Substantial adverse impact on traffic and utilities. Estimated cost: $1.57 million.
3.
Rebuild dam on Simmons Lake (behind Lakeside High School) to form “dry retention area” in old Simmons lakebed/ravine (not to recreate Simmons Lake). Small opening at bottom of dam would allow passage of normal stream volume, but during peak flows that otherwise might cause floods, water would back up behind dam, and release very slowly over many days. Option includes low wall on south side of lowest point of Briarcliff to increase retention capacity of Greeley. No impact on utilities and traffic on Briarcliff. Would decrease flood elevation ~ 1 ft in vicinity around Echo Lake and Greely Lake. Would increase flood elevation slightly above Simmons dam, but this is not expected to affect homes near Simmons. 40% expected reduction in peak flows into Echo Lake would also reduce heavy sedimentation now flowing from Simmons Lake and prolong Echo’s ability to serve as retention basis for 1400 acre watershed. Estimated cost: $955,000
Next Steps
County will consider input from community residents, neighborhood associations, and a coalition of local schools that includes representatives of Lakeside High School.
Contact Information for Community Comments —
CEO Mike Thurmond
311CCC@dekalbcountyga.gov
404-371-2000
Commissioners —
Jeff Rader
jrader@dekalbcountyga.gov
District 2 (ELHA’s district)
Kathy Gannon
kgannon@dekalbcountyga.gov
Super District 6
Nancy Jester
njester@dekalbcountyga.gov
District 1
Larry Johnson
larryjohnson@dekalbcountyga.gov
District 3
Steve Bradshaw
srbradshaw@dekalbcountyga.gov
District 4
Mereda Davis
mdjohnson@dekalbcountyga.gov
District 5
Gregory Adams
gregoryadams@dekalbcountyga.gov
Super District 5
Roads and Drainage
Peggy Allen
pvallen@dekalbcountyga.gov
Planning
Andrew Baker
abaker@dekalbcountyga.gov