Stormwater drainage management meets Garnavillo goals


November 2017 to October 2020


Undersized storm sewer, poor alignment and clay soils were causing flooding and drainage problems in the City of Garnavillo, Iowa. A primary drainage path flows through a residential area carrying flows from the state highway and large segment of the City's business district. The regular flow and clay soils created conditions which stayed wet, making yard maintenance difficult. Poor alignment and high velocities discharging from undersized culverts also increased soil erosion. City officials hired Fehr Graham to find solutions to better manage the stormwater runoff and help secure funding to pay for the fixes.

Our team suggested rain gardens and permeable pavers to the City Council and Public Works Department. With help from Fehr Graham, the City was awarded $210,000 from a Community Development Block (CDBG) grant and $80,000 from an Iowa Department of Agriculture and Land Stewardship (IDALS) grant. Both grants were reserved for water quality improvements. City officials were concerned about how long the permeable pavers would hold up with routine semitrailer traffic carrying heavy loads. Our team shared information on the pavers as well as personal experience with their installation which reassured the City that the pavers could handle the semitrailer weight.

Our project design included two rain gardens, a block with permeable pavers and improved downstream conveyance. Open drainage channels were also reshaped to address high velocities and erosion. Fehr Graham worked closely with the City and Amy Bouska, the area Urban Conservationist with IDALS, to ensure water quality was maintained and the City's goals were reached.

The project improved water quality and filtration and decreased soil erosion. Property owners can now enjoy their backyards without worrying about flooding.

» Assisted with grant applications.
» Coordinated with local and state agencies.
» Designed improvements.
» Prepared project easement plats.
» Prepared plans and specifications.
» Assisted with bidding the project.
» Provided construction phase survey and observation.