Construction of this project included 12 terraced berms with a total length of nearly 1 mile, covering approximately 8 acres of open space hillside along the east side of Interstate 71/75 in Covington, Kentucky. This project demonstrates how green infrastructure techniques can be designed and constructed, even on steep topography (more than 120 feet of elevation change), to provide flow attenuation and reduce downstream combined sewer overflows (CSO).

The 12 interconnected terraced berms were constructed along existing 10-foot interval contours to collect, treat, infiltrate, and slowly release stormwater runoff that flows into an Interstate ditch and Sanitation District No. 1’s sewer system. Each terraced berm includes a bioretention soil mix planted with a variety of small vegetation plants and a variety of trees spaced 25 feet on-center. A detailed bioretention soil mix was specified to enhance the plant and tree growth while also providing stormwater reduction benefits. The reduction of stormwater will be achieved through infiltration, as well as evapotranspiration that is enhanced by the vegetation and trees within each terraced berm.

An underdrain system was designed to hydraulically connect the series of terraced berms in order to attenuate flow and help mitigate the impact on the sewer system from stormwater runoff from the project site. Compacted clay downslopes were also designed to provide slope stability for the terraced berms.

Performance monitoring of the terraced berms indicates that this project is removing 5.6 million gallons of CSOs annually.