Underwood Creek Rehabilitation and Flood Management Phase 1—Final Design and Construction: Milwaukee, Wisconsin

Underwood Creek extends eight miles upstream from its confluence with the Menomonee River, located near Milwaukee County Grounds (MCG), and is contained within in a highly urbanized watershed. Due to past flood management concerns, Underwood Creek has undergone considerable alteration that included floodplain filling, channel widening and realignment, and the installation of concrete lining along a significant portion of its length. These channel alterations have successfully reduced peak water surface elevations along Underwood Creek, but contributed to downstream flooding conditions. As a result, the Milwaukee Metropolitan Sewerage District (MMSD) initiated the MCG Floodwater Management Facility Project, which includes an overflow diversion structure on Underwood Creek and an approximately 900 acre-feet floodwater storage facility on MCG property. The MCG floodwater storage facility has provided an opportunity to rehabilitate approximately 6,600 feet of Underwood Creek watercourse through the removal of concrete channel lining; the development of a replacement bioengineered channel, with riffle and pool sequences; and the reactivation (lowering) and re-vegetation of the adjoining floodplain. The MMSD Underwood Creek Rehabilitation and Flood Management - Phase 1 Project addresses the design and construction of rehabilitation improvements along 2,200 feet of watercourse, and is scheduled for completion in mid-2010. Thirty years of stream flow gage records were evaluated to develop low-flow and bank full discharges, which served as a basis for the rehabilitated channel design. Bioengineered bank stabilization measures were developed that satisfy stability criteria immediately upon implementation, and will promote eventual establishment of dense streambank vegetation. An approximately 7 acre floodplain re-vegetation plan was created that contains wet meadow, shrub-carr, and floodplain forest wetland areas, which required design integration between the hydrologic and hydraulic watercourse analyses and the channel and floodplain grading plans. Backwater simulations for a wide range of design events were completed, providing assurance that the rehabilitated watercourse will function as intended over a variety of hydrologic conditions, given a highly urbanized watershed. Adopted rehabilitation goals included a desired increase in floral diversity as well as introduction of slope stability; provisions for shading of aquatic resources; methods to eradicate non-native species within the planting and seeding area and an abutting buffer zone; and perpetuation of Butler's gartersnake habitat.