Calculation of stage-discharge relations for gravel bedded channels

Abstract

A method for calculating stage-discharge relations (rating curves) in gravel bedded streams is presented and applied to five reaches at U.S. Geological Survey (USGS) gaging stations. The approach, which builds on the work of Kean and Smith (2005), uses a fluid-mechanically based model to convert measurements of stage into flow and boundary shear stress fields as appropriate for determining water discharge. The model does not use site-specific empirical roughness coefficients, such as the Manning coefficient, but rather determines channel roughness from field measurements of the channel geometry and the dominant physical and biological roughness elements in the modeled reach. The approach is fully compatible with current USGS-style river gaging procedures and can be used in conjunction with or instead of the standard empirical gaging methods. When used in parallel, the theoretical rating curves produced by the model are in good agreement with direct measurements of discharge made by the USGS. The results of our analyses indicate that the theoretical rating curve approach has the potential to substantially reduce the number of measurement visits, and therefore costs, required to develop rating curves for gaging stations. Owing to this lower cost, it is well suited for regional hydrologic studies in which rainfall distributions are measured in space and time and are compared with measured discharges on the links of the river network. In addition, our method is ideally suited for sites, such as remote locations, where it is difficult or impossible to define a complete rating curve using conventional methods alone.