The City of Sumner in Bremer County, Iowa, has experienced multiple flood events over the past several years. In 2018, the City hired MSA to complete a comprehensive study of one of the major watersheds draining the City and to design a stormwater management system to protect downstream areas of the City from 100-year flooding. MSA’s study of the system identified that most of the flows originate from two primary subwatersheds: a northern watershed confined to a narrow valley and an eastern watershed that collected runoff in a wider, flatter expanse.

MSA’s design of the proposed solution worked with the natural topography of the northeast quadrant of the City to create three separate detention basins. Stormwater from an approximately 285-acre watershed is captured by the stormwater detention system. The three basins combined cover 17 acres and provide approximately 86.4 acre-feet of storage. The basins were constructed in 2020.

A temporary connection allows the detention basis system to slowly drain into an existing 30” storm sewer that runs under Walnut Street. Design has been completed on permanent discharge from the three-cell stormwater detention basin system using a combination of drainage ditches and box culverts to convey stormwater to the Little Wapsipinicon River. MSA is currently assisting the City in acquiring funding to complete the final phase of the project.

The City of Sumner stormwater detention basin project was selected by the American Council of Engineering Companies (ACEC) of Iowa to receive a 2022 Engineering Achievement Award in the category of Special Projects.