Evaluation of Stream Grade Control Structures in Loess Soil Region

Grade control structures are used extensively to control river channel degradation. Although their use is widespread, the durability and performance of these structures, namely, sheet pile, H-pile, rock sill, and concrete block weirs have not been systematically evaluated. In this study, stream grade control structures in a loess area (western Iowa) were quantitatively evaluated with a performance number system to determine their field conditions and durability. For these evaluations, two dimensionless parameters (erosion control ratios and discharge ratios) were developed to correlate field observations and measurements. Structures that experienced small flows performed relatively well, whereas those that carried large discharges had poor performance. The stability of riprap decreases as the discharge ratio increases. Better riprap performance was obtained at structures with greater erosion control ratios. Based on these evaluations, problems associated with the structures were identified. In-channel movement of rock riprap was found to be a prevalent problem. Considerations for future designs and construction are recommended. The evaluation method and procedure can be applied to loess soil regions in the central United States and other regions worldwide. The information gathered can be used to guide field surveying and modeling studies.