Industry paper

Integrating engineered and nature-based solutions for riverbank stabilization

Authors: D. Loizeaux, J. Hill, M. Patton and J. Hoilman

Adding resilience to flood defense structures is critical to mitigating the impacts of climate change and natural disasters. Integrating engineered erosion control systems with nature-based infrastructure provides an effective solution for hazard mitigation that yields environmental and economic benefits. This presentation will highlight how Engineered Earth Armoring Systems can be combined with vegetation to provide resilient and long-term flood mitigation. It will also highlight fieldwork from a bank stabilization project on the Des Moines River. Palo Alto is the 13^th largest agricultural-producing county in Iowa, with an estimated $468,000,000 in crops and livestock reported in 2017. The West Fork of the Des Moines River cuts diagonally through the County, providing drainage for approximately 4,660 square kilometers of farmland. During rain events, the river would often flood this area, causing erosion on an upstream bend. The flooding impacted nearby roadways and a historic bridge, resulting in a nearly 40-kilometer detour for travelers. Between 2006 and 2019, flooding events caused severe bank erosion to occur on the river bend. Along roughly 215 linear meters of riverbank, up to 65 m of horizontal erosion occurred, losing over 1.25 hectares to erosion within this timeframe. If an erosion control solution was not implemented, then the historic bridge and surrounding roadway would continue to be at risk. The Sioux City Natural Resource Conservation Service (NRCS) and Palo Alto County originally considered the use of rock riprap or gabion hard armoring to control the erosion, but ultimately looked for a more cost-effective, nature-based solution. A combination of the Engineered Earth Armoring Systems was used to stabilize the bank and protect against scour, erosion, and surficial slope instability while promoting vegetation.