City of Overland Park Reduces Flooding for Local Neighborhood with Storm Sewer Repairs

The City of Overland Park, Kansas wanted to address street and structure flooding issues and upgrade infrastructure in one of its residential neighborhoods. The Walmer Street Major Storm Sewer Repair (MSSR) project was designed to achieve these goals while minimizing impacts to homeowners.

A part of the city’s CMP replacement program, our team was responsible for replacing an undersized corrugated metal pipe (CMP) in a two-block stretch. This CMP ran through the backyards of 29 homes and would flow over 97th Street through these backyards during anything more than a 4-inch rainstorm. With heavier rain, the backyard overflow would cause flooding in up to 12 homes.

The project began with a preliminary engineering study (PES) in which our team evaluated the existing system’s performance. From this evaluation, we determined the project was eligible for Stormwater Management Program (SMP) funding. Based on our analysis, we knew the area needed greater storm sewer capacity through these backyards to eliminate flooding up to the 100-year storm event.

Multiple proposed alternatives were considered in the PES. The most cost effective and least impactful alternative was to replace the old CMP with a double 8×4-foot reinforced concrete box (RCB) in the same location, tying into the channels on the upstream and downstream ends.

With the PES complete and the concept confirmed, we moved into final design for this project. From the beginning of our design effort, we worked extensively with utilities to identify where conflicts were present and relocations needed. Two significant relocations were necessary:

1. Evergy had overhead power running through the entire length of the project area. We worked with them to design a permanent relocation that allowed for construction to proceed and minimized impacts to residents.
2. While the CMP had just enough clearance over the top of Johnson County Wastewater (JCW) facilities, the proposed RCB was in conflict. We designed a sewer relocation to avoid that by running the sanitary sewer parallel to the new RCB, tying into a deeper and lower sanitary sewer line in 99th Street.

Working with property owners in the project area, keeping them informed, and accommodating reasonable requests was important to the city and the Affinis team and critical to the success of the project. As the design proceeded, we accounted for all items that would be impacted by the project: fences, flower gardens, trees, and all other landscaping features were surveyed and included in the plans. The design called for the removal and reset or replacement of these items. This included small tasks like edging around flower gardens and larger ones, such as planting trees. Any ground disturbed was replaced with sod.

The improvements made in the Walmer Street project offered flood relief to the residents in the project area. It also provided the city with quality infrastructure which will last for the next 50 years and makes maintenance of this system easier by including RCB access points and removing the debris-collecting trash rack on the upstream end of 97th Street.