Hydrologic Analysis of Stream Stabilization and Stream Grade Control Structures

Grade control structures, namely sheet pile, h-pile, rock sill, and concrete block weirs, are used extensively to control river channel degradation. Quantitative evaluations of these structures (such as in loess covered areas of western Iowa) can aid to determine their durability and provide guidance for future design. Although local geology and groundwater can affect field performance, streamflow rate is one of the most important factors because it represents the forces exerted on the structures. Structures that experiences different flows may perform differently, depending on the relationship between the stability of the structures and the external forces exerted on the structure, i.e., hydrologic and hydraulic conditions (flow rate and velocity). An objective evaluation of the durability and performance of grade control structures requires information on the flow that has passed through each structure. A comparison of historical flows to design flows is needed to correlate measured external forces and structure performance observed in field. In this study, a hydrologic analysis of stream stabilization and stream grade control structures is performed for drainage basins consisting of small streams and rivers in rural areas where no streamflow gauging stations are available. The reconstruction of streamflow history provides an estimate of the maximum historical discharge that can be compared with the design discharge. Historical flows are determined from precipitation data and drainage basin characteristics, using a computer simulation program (HEC-1). The model is validated using field data from western Iowa and can be applied to ungaged sites in other regions.