Black Hawk Lake Urban Watershed Project
This project targets stormwater runoff priority areas in two locations in the northern reaches of the Black Hawk Lake watershed. Practices will include installation of a wetland, bio-swale and rain garden, which were selected to address nutrient and other water quality concerns. This project and associated partnerships will build on existing water quality efforts targeted toward lake improvement and focus on the importance of the Iowa Nutrient Reduction Strategy.
After working with the project partners including the regional IDALS Urban Conservationist to identify urban stormwater runoff priority areas, the proposed WQI project will target the northern reaches of the urban section in the Black Hawk Lake Watershed. This area is comprised of two sites near the intersection of County Highway M-54 and Highways 71 & 175. The first and priority location will be on the Evapco Inc. campus. Currently stormwater runoff from the approximately 25 acres of predominately impervious surface leaves the campus and enters a drydetention basin. Dry-detention basins are designed for flood control measures and provide minimal water quality benefits. The project is proposing to rehab the existing basin into a stormwater wetland that will capture and filter stormwater runoff from the campus. The final design of the wetland will focus on increasing the residence time of water and promotion of anaerobic conditions to maximize the nitrogen removal. A forebay will be installed to capture sediments entering the wetland, which will aid in the capture of phosphorus.
The second location is south of Highway 71& 175 in the west ditch of M-54. Along with the stormwater runoff from the above mentioned dry-detention pond, stormwater enters the ditch from the approximately 65 acre watershed and flows towards the lake where it enters a storm sewer intake. This intake discharges directly into a small DNR owned marina connected to Black Hawk Lake without any treatment. This watershed is predominantly agriculture fields with some urban components draining into the ditch. The project is proposing to install an approximately 1,000 linear foot bio-swale in the ditch. The bio-swale will capture and infiltrate stormwater as it flows throughout the swale. At the end of the bio-swale around the existing intake a rain garden will be installed as a final filtration practice. The two practices will work in conjunction to treat the stormwater from the remaining area.