Flow Around Submerged Barbs in the Raccoon River Iowa

The placement of bendway weirs (barbs) has beneficial effects on bank stability and river ecology by increasing the conveyance at the center of the channel. This study focuses on the Raccoon River, Iowa, USA, and specifically the stabilization of the north riverbank immediately upstream of the US-169 highway bridge. The integrity of the north bridge abutment, originally built in 1950, is in danger as the river continuously erodes the surrounding soils. The Iowa Department of Transportation (IDOT) proposed solution to the problem is to install a combination of barbs and bendway weirs on the north bank upstream of the bridge to stabilize the bank. Although many recent studies have focused on the flow effects and scour holes produced by the addition of barbs, few detailed design guidelines exist. The objective of this study is to employ fundamental knowledge to evaluate the effectiveness of the proposed IDOT design and eventually produce a comprehensive, non-site specific barb design to increase bank stability. The study utilizes a commercial Surfacewater Modeling System (SMS) software package with a 2-D solver to evaluate the large scale effects of the design. Quantitative and qualitative evaluation based on previous fundamental studies showed the IDOT design effectively reduced the flow-induced shear stress, velocity, and depth along the river bank. Results also showed the current IDOT design will produce adequate sedimentation between structures and effectively move the bank line back towards its historic location. Future results from the continuation of this study will help to further reduce the ambiguity of barb design.