The Challenge
Located in the Chesapeake Bay Watershed, Howard County’s MS4 permit places stringent requirements on municipalities to reduce stormwater pollution into local waterways and the Bay. In addition to water quality concerns, the historic community of Ellicott City has experienced intense flooding in recent years, prompting urgent action from the County to mitigate flood risk. The County was tasked with treating stormwater runoff from approximately 2,000 acres of impervious surfaces by the end of 2019, and complying with future stormwater targets in the next cycle of their MS4 permit.
The Results
Opti technology increased wet weather capture and retention time, mitigating the impacts of downstream flooding. In addition to flood mitigation, Opti provided $14,000/yr in cost savings to landowners paying Watershed Protection Fees, and delivered an additional 19.4 acres of water quality credits towards Howard County’s MS4 permit. Based on one year of data, Opti’ adaptive control system outperformed traditional passive management by 2.3−3.9X.
The Solution
As part of the Clean Water Howard initiative, the County implemented Opti technology at two existing stormwater ponds located on both commercial and public property. Opti predicts and responds to the weather forecast, enabling the system to maximize storage capacity and retention time in each pond. Opti adaptively controls the outlet structures of the ponds, enabling it to draw down volume ahead of wet weather, mitigate peak flows during storms, and retain water for up to two days after the storm.
Watershed Flow Reduction
After a year of adaptive management at the two Ellicott City ponds, Opti performed an assessment for Howard County. Maryland Department of Natural Resources (DNR) provided support for the project through the Chesapeake Bay Implementation Grant (CBIG), which are EPA funds the DNR administers on behalf of the State of Maryland. Over 1,400 sites were evaluated and ranked based on their downstream flood mitigation potential, providing a critical knowledge base for expanding adaptive stormwater management on the watershed scale. The top six highest-ranked ponds were chosen for further analysis.
