Project Summary
The Muscatine Island Levee District’s levee system protects nearly a third of the City of Muscatine, including 7,900+ acres of farmland, 2,200+ structures, the regional airport, water and wastewater infrastructure, two power plants, and an elementary school – representing roughly $850M in property and approximately 4,800 residents. With 14 of 20 flood crests since 2001 reaching moderate or major flood stage, the need for improvements was urgent.
Klingner delivered a two-pronged solution: raising a 3-mile at-risk levee segment to the 100-year plus 4.5’ of freeboard protection level, and developing a hardened overtopping reach approximately 7 miles downstream to create conditions for more controlled major flood events. Sand sourced from Deep Lakes Park was used to raise the levee crown, reducing permitting complexity and hauling distance while simultaneously creating new recreational ponds for the community.
The hardened reach was constructed using HydroTurf®, a geosynthetic revetment system, in what marked its first-ever application on an Upper Mississippi River levee. This extremely durable material blends into the landscape, preserving the area as an attractive landing spot for migrating waterfowl.
Klingner’s team spent four years vetting HydroTurf® before its application, including performing complex hydraulic modeling that showed likely overtopping velocities of approximately 21 ft/s – well within the product’s tested threshold of 40 ft/s. To prevent pressure buildup within the levee and promote drainage during prolonged major flooding, engineers developed 31 strategically-placed custom filters beneath the geosynthetic grid. A Penetrating Colloidal Concrete Treatment was also applied to the binder to promote durability through Iowa’s freeze-thaw cycles, supporting a projected 50-year lifespan comparable to concrete and articulated concrete blocks.
Geotechnical borings informed slope stability and seepage analyses as well as filter system design. Wetland constraints limited all design modifications to the landside of the levee, requiring close coordination with industrial landowners, removal of unused railroad infrastructure, and the purchase of 0.14 acres of adjacent property to achieve the optimal hardened reach configuration. Dual funding mechanisms, including EDA grant funds in Muscatine County and ARPA funds in Louisa County, required separate base bids and continuous compliance tracking throughout construction. A Section 408 permitting process with USACE added further complexity, ultimately establishing regulatory precedent for HydroTurf® in levee applications.
In a 700-year flood scenario, the improvements are projected to reduce recovery time from one year to one month. The hardened reach is anticipated to reduce floodwater flows by up to 98%, directing water to an existing pump station and buying critical time for evacuation and emergency response.
