APWA’s Kansas City Metro Chapter Awards City of Olathe Project of the Year

The City of Olathe and Affinis were awarded the Kansas City Metro Chapter of American Public Works Association’s Public Works Project of the Year Award for their Stagecoach and Sleepy Hollow Stormwater Improvements project. Thoughtfully designed, the final solution protects homeowners and increases roadway safety.

The City of Olathe, Kansas was experiencing significant flooding concerns in the Stagecoach and Sleepy Hollow neighborhoods. The existing stormwater system was inadequate, impacting homes and streets within the project limits. To reduce the flooding frequency, with the help of the Johnson County Stormwater Management Program, they decided to upsize pipes, rehabilitate select pipes, and increase inlet capacity. Managing the stormwater would create safer streets and reduce flooding impacts for residents.

The existing storm sewer network alignment was between homes and through backyard areas following the low elevation from E. Sunvale Drive to E. Sheridan Bridge Lane. The overflow path was between homes and in backyards. Feedback from residents, provided in the 2019 Preliminary Engineering Study (PES), showed there was significant street ponding at low points, and bypass flow, from these low points, was moving between homes and in backyards during heavy rain. The failing corrugated metal pipe (CMP) segments were contributing to the problem, and multiple constructability concerns needed to be addressed.

Affinis was selected by the City for the project in 2021. We started by surveying the area to collect information about the site, which we used to evaluate and model the existing system. Using PCSWMM, a node-link advanced modeling software, a model of the existing condition was created that showed flooding in more than 10 homes within the project area and five areas of excess street flooding. A hydraulic model of the proposed improvements was developed to upgrade the system and significantly reduce flooding problems per current City of Olathe, Johnson County, and APWA 5600 design standards.

Our solution involved a comprehensive upgrade of the existing stormwater system and addressed the failing CMP segments. Special structures were designed and implemented to increase system capacity. The ultimate solution included upsizing storm sewers with reinforced concrete box (RCB) culverts and reinforced concrete pipe (RCP), CMP segment rehabilitation using centrifugally-cast concrete pipe (CCCP) lining, and in-situ PVC pipelining when in conflict with houses and other utilities, and inlet/structure replacement.

This complex project included agency coordination with the Kansas Department of Health and Environment for a notice of intent, the City of Olathe for a floodplain development permit, and the Johnson County Stormwater Management Program for funding assistance. It also required design considerations to eliminate the need for a United States Army Corps of Engineers (USACE) permit or a Federal Emergency Management Agency (FEMA) Letter of Map Revision (LOMR).

The Stagecoach and Sleepy Hollow Stormwater Improvements project provided substantial benefits to the community and residents. Upgrading the stormwater system significantly reduced flooding of streets and homes, providing relief to more than 10 homeowners and eliminating excess street flooding in five areas, allowing for the safe passage of motorists and emergency vehicles. The use of CCCP and PVC lining extended the life of existing pipes, increased capacity, and addressed constructability concerns. The improvements not only enhanced the functionality of the stormwater system, but also contributed to the overall safety, well-being, and quality of life for the neighborhood and its’ residents.