88th Avenue - 87th Street to 111th Street | Cook County Highway Department

Knight provided design engineering services for the reconstruction and widening of 88th Avenue from 111th Street to 87th Street in Cook County, Illinois across the municipalities of Hickory Hills and Palos Hills. Numerous existing drainage problems existed which Knight was charged with mitigating. Existing problems included undersized sewers and ditches, inadequately sized detention facilities, nonexistent emergency overflow routing, and flooding of private properties and the roadway. The proposed roadway would also require its own additional detention due to roadway widening from two to three lanes.

Knight studied the project area and the entire up and downstream watershed to better understand how the roadway’s drainage system operates. Large offsite areas were draining into the 88th Avenue drainage system undetained. This proved to be a large contributor to the roadway and private property flooding. Knight incorporated a multifaceted approach to address this and all of the existing drainage problems and address the increase in impervious area due to the roadway widening. Knight created a new detention basin in a digressional area, where FEMA previously bought out and razed three flood prone residential parcels. Offsite drainage areas were captured through the use of high capacity inlets. Overflow structures would release to ditch systems, below the roadway elevation, to provide relief to the sewer system before it would flood the roadway. The proposed storm sewers were designed for the 100 year storm where there was no overflow routing available. Additional in-line detention was provided in sewers to mitigate the increase in peak discharge due to widening. Construction of this project was completed in 2013 and has functioned well during past major storm events.