The City of Novi’s Stormwater Master Plan identified two regional detention basins (Taft Basin and Bishop Basin) that had inadequate storage, resulting in streambank erosion and excessive flows in down stream reaches. Field investigations of the basins indicated that this was due to sediment accumulation in the basins and an increase in peak flows. Therefore, Niswander Environmental and OHM, Inc developed a plan to retrofit the Taft and Bishop Basins to improve storage, water quality, and wildlife habitat.
Niswander Environmental conducted a hydrogeomorphic assessment upstream and downstream of each of the basins. This assessment provided the data required for the natural channel design and baseline conditions that will be used for evaluating the success of the restoration projects. Specifically, the assessment involved documenting existing conditions along the stream reaches and within the basins, including evaluating the degree of erosion, sediment accumulation, habitat conditions (flora and in-stream), soil types (bed and banks) and channel conditions (incision, bankfull depth, percent of vegetative cover, bank slope, bed particle size, etc). Niswander Environmental will continue to manage the sites through 2017.
The Taft Basin was enhanced by using natural channel design to create a low flow channel that would be capable of passing bankfull flows and transporting the normal bed sediment. The outlet structure was modified to reduce the peak flows and allow for the flood water to come out of the stream banks and fill the newly created floodplain wetlands. The new design resulted in a self-sustaining stream that not only improves flood storage but also allows for fish passage and creates valuable aquatic habitat. In-line stream structures were installed, and the floodplain wetlands were restored with native plantings. These improvements will help re-establish vegetation downstream of the basins in the coming years and will help improve water quality by reducing stream bank failure.
Restoration of basin included replacing the outlet with a new structure that increases flood attenuation and is maintenance free. Habitat improvements, completed in 2009, included removing invasive species, the creation of an emergent wetland shelf, installation of habitat structures, and enhancement of the basin’s riparian areas with native plantings.