Integrating Engineered and Nature-Based Solutions for River Bank Stabilization
(Print PDH from the February 2022 issue of Informed Infrastructure)
Course Information
Palo Alto is the 13th-largest agricultural producing county in Iowa, with an estimated $468 million in crops and livestock reported in 2017. On average, each farm in Palo Alto County covers about 435 acres, and each acre is essential for the farm’s livelihood. Simply put, land is important and losing it to erosion is not an option.
The West Fork of the Des Moines River cuts diagonally through Palo Alto County, providing drainage for approximately 1,800 square miles of farmland. 485th Avenue and 425th Street intersect along the West Fork of the Des Moines River and are connected by the Kirby-Flynn Bridge, a historic pin-connected Pratt high-truss bridge dating back to 1881. During rain events, the Des Moines River often would flood in this area, causing erosion on an upstream bend and floodwaters to inundate the bridge, resulting in a more-than 24-mile detour for local travelers.
Between 2006 and 2019, flooding events caused severe bank erosion to occur on the riverbend just upstream of the Kirby-Flynn Bridge. On this roughly 700 linear feet of riverbank, up to 215 feet of horizontal erosion occurred, losing more than 3 acres to erosion within this timeframe (see Figure 1). If an erosion control solution was not implemented, then the historic bridge and surrounding roadway would continue to be at risk. The 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.
Author
Drew Loizeaux, P.E., Engineering Services Manager
Learning Objectives
At the conclusion of this article, the reader should be able to understand the following:
• Learn the environmental considerations utilized in the Des Moines River Stabilization project.
• Learn how to specify and design engineered earth solutions in various site hydraulic conditions.
• Learn the geotechnical design principles in designing for erosion control.
• What are environmental and cost benefits of using HPTRM reinforced vegetation to mitigate the impacts of climate change and natural disasters.