DeKalb commissioners hear Snap Finger watershed inspection findings; Arcadis recommends targeted rehab and pond decommissioning pilots

DeKalb County commissioners on Tuesday received an in-depth update on the Snap Finger Creek watershed from Arcadis, the county's engineering consultant, who described field inspections, condition findings and early recommendations for detention-pond decommissioning and targeted rehabilitation.

"We're doing pole camera inspections" and deploying a small, caged drone that captures high-definition video plus LIDAR and thermal data to build a digital profile of culverts and pipes, Arcadis presenter Rich Bruel said. The team has mapped roughly 11,000 stormwater assets in the Snap Finger watershed, prioritized about 1,100 as highest-consequence for failure and is inspecting that subset in the field.

Bruel said inspectors have focused on the highest-risk classes of pipes — those beneath single ingress/egress roads and major collectors — and that the early field work has shown a nontrivial number of assets in poor or inoperable condition. "Of the higher-consequence assets we've looked at so far, about 10% are in very poor or inoperable condition," he said, urging careful modeling before committing to replacements.

Using a desk-based review of roughly 218 county-owned or county-maintained detention ponds in the watershed, Arcadis identified about 64 ponds (about 29%) as potential candidates for decommissioning because they provide little detention benefit. The firm proposed an additional nine ponds as candidates for water-quality retrofits and nine for consolidation.

As an illustrative case, Arcadis examined two ponds in a townhouse community the consultant called the Royal Town Park. Bruel said one pond (Pond B) produced little benefit to downstream detention and was recommended for decommissioning, while the other (Pond A) could be converted into a bioretention basin with underdrain and filter media to provide water-quality improvements.

"It's one of those opportunities where we're doing a lot of maintenance and not really getting anything for it," Bruel said of the ponds under review.

County and Arcadis staff emphasized that decommissioning is not a simple abandonment: the process would include breaching dams, grading and specific construction to remove persistent water-holding function while avoiding new downstream impacts. Commissioners also raised local concerns — property ownership (HOAs), maintenance responsibilities and potential resident pushback — and asked staff to include public outreach in any decommissioning plan.

Anwar Ahmed of Arcadis described how the Snap Finger work will inform a countywide watershed-prioritization framework. The firm layered three data sets — conduit risk scores, projected increases in impervious surfaces from the county comprehensive land-use plan and FEMA flood-loss areas — to rank 24 watersheds and recommended grouping the remaining watersheds into three study groups. Ahmed estimated a ballpark cost of about $1,000,000 for a stormwater master plan for each of the three watershed groups, but said that number is preliminary.

Commissioners pressed staff on model validation and resident experience. One commissioner requested that the inspection video be distributed so elected officials can see culvert conditions for themselves. "Before we make any firm... go out and start building stuff, I'd want to get some confirmation on that," Bruel said, noting the team would corroborate model outputs with on-the-ground information.

Staff and Arcadis said funding sources have not been finalized and that options will be studied (utility fee structures, loans or other mechanisms). They also said any decommissioning on privately owned ponds will require negotiation with property owners or HOAs and that municipal coordination will be needed where watersheds cross city boundaries.

The presentation concluded with commissioners thanking Arcadis for the work and asking staff to circulate inspection videos and forthcoming cost-estimate details. Next steps: staff will continue inspections and modeling, provide cost and savings estimates for decommissioning or retrofit options, and bring pilot recommendations (Royal Town Park bioretention and decommissioning measures) back to the commission for consideration.

Votes and formal actions taken by the panel during the meeting were recorded separately (see the "Votes at a glance" note below).