The West Fork of the Des Moines River in Palo Alto County, Iowa, had experienced years of erosion and flooding. From 2006 to 2019, the riverbank had receded up to 215 feet (65.5 m) in the middle of the bend. Approximately 3 acres (1.2 ha) of soil had been lost during that time span, and the receding shoreline was approaching an existing roadway. The historic Kirby-Flynn Bridge was also in jeopardy of the approaching waters. This bridge is the only remaining pin-connected Pratt high-truss bridge in the U.S., and dates to 1881.
The Sioux City Natural Resource Conservation Service (NRCS) wanted to stabilize approximately 865 lineal feet (263.7 m) 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 Propex SCOURLOK and ARMORMAX was selected because it provided long-term protection from erosion, promoted reinforced vegetation and helped improve water quality at a lower cost than rock. Both systems are designed to resist extreme hydraulic stresses and can 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.
Palo Alto County, Iowa
Shorelines and waterways
Propex SCOURLOK and ARMORMAX