The Challenge: Following the 2008 Midwest flood, the Army Corps of Engineers (USACE) conducted a study to estimate the frequency and magnitude of flows along the Des Moines and Racoon Rivers. Based on the results, the Des Moines Downtown Levee Local Flood Risk Management System (along the Des Moines and Racoon Rivers) did not provide reliable risk reduction against the revised 100-year flood, thus affecting the system’s accreditation status by FEMA and impacting the City’s flood hazard mapping.
The Solution: JEO’s Water Resource team was hired as part of the team tasked with addressing system deficiencies and providing more resilient flood risk reduction infrastructure. In partnership with Stantec, our team addressed levee deficiencies in Phase B (segments of the Raccoon River from the SW 3rd St. bridge to Fleur Dr. on the left bank and from SW 3rd St. to SW 7th St. on the right bank). Design efforts provided for the increased elevation of the earthen levee and floodwall along the Raccoon River. The project improvements include an earthen levee raise, cast-in-place retaining walls and floodwall raises, gatewell structural modifications, a stop-log closure structure at SW 5th Street, storm sewer improvements, and riprap placement. With the earthen levee raised, the levee along the north bank of the Raccoon River will be improved to accommodate a potential ten feet wide multi-use trail on top of the levee.
Project Benefits: The team provided a full complement of design services, including civil analysis/design, structural analysis/design, and plan production. Improvements also required detailed and extensive coordination with the USACE for a Section 408 Authorization for a significant modification to the federal flood control project. The team is currently providing on-site construction observation and administration, including preparing as-built documentation and materials testing. After construction is completed in 2023, project enhancements will improve flood risk reduction in an important area of Des Moines.
Following the completion of the construction phase, a new Operation and Maintenance manual will be prepared, including detailed record drawings. These documents will support the FEMA accreditation process, ensuring the Des Moines Levee Flood Risk Management system will continue to be shown as providing risk reduction on future floodplain maps.