City of Kansas City, Missouri
2017-2019
A dozen residents of this north Kansas City Somerbrook subdivision contacted the city’s water services department in summer 2018, complaining that the yard erosion along an unnamed tributary to Fishing River had advanced so far that house foundation slabs were exposed and backyard fences and a retaining wall were in jeopardy of collapsing into the creek. The city initially estimated work to correct the grade and place erosion mats would cost around $260,000.
Following some initial study that resulted in additions to the scope of the project to extend the reach of the stream in question and also to design a repair for a failed retaining wall, WRS has developed preliminary design plans, specifications and estimates for a proposed solution to stabilize the stream and repair the wall, including a slope stability design. An analysis of aerial photography, land-use data, and soils data demonstrated that the stream through Somerbrook subdivision suffers the same consequence of development as many other urban streams: Before development, the land surrounding and under the housing was primarily agriculture, which allowed the stream to meander naturally.
WRS engineers used the HEC-RAS hydraulic model to study the flow patterns of water in the stream and define the ideal solutions to the erosion. The proposed improvements include using riprap grade controls to stabilize the channel grade and regrading the channel banks to a stable slope. The location and height of the grade controls reduce the velocities in the channel upstream of the grade controls by creating a backward condition. The placement of the downstream grade control also halts any potential future knickpoints from forming and migrating upstream. The drop across the grade controls makes up the total change in elevation along the channel and localizes the higher velocities to the grade controls. The bank reshaping is limited to the banks along the grade controls and the right descending bank upstream of the middle grade controls. They will be regraded to a 3-to-1 slope and replanted to provide further natural stability.
WRS was also integral in securing necessary permitting from the U.S. Army Corps of Engineers for the in-stream project improvements.
