The West Fork of the Des Moines River in Palo Alto County, had experienced years of erosion and flooding. From 2006 to 2019, the riverbank had receded up to 215 feet in the middle of the bend. Approximately three acres of soil had been lost during that timespan, and the receding shoreline was approaching an existing roadway. The historic Kirby-Flynn Bridge was also in jeopardy of approaching waters. This bridge is the only remaining pin-connected Pratt high-truss bridge in the U.S., and dates back to 1881.
The Sioux City Natural Resource Conservation Service (NRCS) wanted to stabilize approximately 865 lineal feet of the bank and reinstate channel alignment to what it was in 2006. Initially the project engineer considered using rock riprap, but wanted to find a more cost effective solution.
A combination of 2,940 feet of SCOURLOK® and 6,200 square yards of ARMORMAX® was selected because it provides long-term protection from erosion, promotes reinforced vegetation, and helps improve water quality at a lower cost than rock. Both systems are designed to resist extreme hydraulic stresses and are able to withstand wave action.
The design included two rows of SCOURLOK along the 2006 channel alignment with a benched area, protected by ARMORMAX, to the current bank condition. Additionally, an upper wall section with one row of SCOURLOK was installed to protect the current bank location.
Vegetation quickly established, providing a nature-based solution that will help improve water quality and reduce sedimentation. The combination of SCOURLOK and ARMORMAX will also prevent erosion caused by hydraulic and geotechnical forces for up to 75 years, protecting the Kirby-Flynn Bridge and maintaining the reinstated shoreline.
Editor's Note: Scranton Gillette Communications and the SGC Water Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the editorial teams of Water & Wastes Digest, Water Quality Products and Storm Water Solutions.
