PLT20 - Muscatine Island Levee Incorporates HydroTurf for Overtopping Resilience

Abstract Description: Levee superiority is critical in the Upper Mississippi River floodplain, where many of the levees that protect infrastructure, industry, agriculture, and communities are constructed with hydraulically dredged sand. Sand levees are unable to withstand the erosive force of an overtopping flood event. The Muscatine Island Levee Improvement Project had two important goals: increase the upstream freeboard of the levee system while also creating a hard point for the most likely incipient point downstream. The hardened reach utilized HydroTurf®, which had not been used on levees in the Upper Mississippi.

HydroTurf® is an advanced revetment solution engineered to protect embankment dams and riverine levees from erosion caused by overtopping events. It includes an impermeable geomembrane incorporating an engineered turf with a high strength cementitious infill, resulting in a reinforced high-strength concrete matrix. The system provides a durable and impermeable barrier against erosive forces.

The Muscatine Island Levee directly safeguards 30,000 acres of land encompassing over $1 billion in property including heavy industry, regional power plants and transmission network, water supply, wastewater treatment, and transportation infrastructure for thousands of residents. When a sand levee overtops, the floodwaters can quickly create a scour hole hundreds of feet wide. This results in a multi-million-dollar levee repair project on top of the billion-dollar cleanup and reconstruction effort within the protected area. To mitigate this, the incipient point was designed to withstand the flow in a controlled manner and minimize interior damages from flooding.

Hydraulic modeling of the Mississippi River was performed using HEC-RAS to determine impacts of the project up and downstream and to select the proper location for the incipient point. The reach was iteratively sized using a 2D flow area and modeling overtopping scenarios across the 1000-foot segment of levee. To fit the structure within the levee footprint, a trough-like shape was designed to collect and slow the overflow of floodwater and direct it to the drainage ditch network. HydroTurf® was selected to armor the surface of this structure instead of concrete hard-scape or riprap due to overtopping velocity performance, comparable cost, low maintenance, and the desire for a natural grass look at a location tucked between multiple state wildlife areas. Construction was completed in 2024, and the District is now more prepared and resilient in the event of an extreme flood.