Hybrid Modeling of a Gauging Station Rating Curve

The accuracy of river flow data is very important for most hydrological studies. Even so, the uncertainty of these data is often neglected. The uncertainty can be significant since the flow is rarely measured directly, but rather indirectly through pre-defined functions of the river stage to discharge relationship or rating-curves. The uncertainty is even more prevalent when the rating curve is extrapolated beyond the available stage-discharge pairs (or gaugings) that form the basis for the rating curve. In an on-going case-study, a hybrid modeling technique is utilized to produce synthetic gaugings for the extrapolation of a rating curve. The control at the gauging-station is at a bed-rock drop where the hydraulic conditions is known to be demanding, especially at high flows. The hybrid modeling is a combination of an original approach to physical modeling and a 3-dimensional Reynolds-averaged Navier-Stokes model of the same geometry. The physical modeling makes use of large-scale computer numerical control (CNC) milling technique in a plastic foam material to provide a high-detail geometry from a point cloud. A combination of survey techniques including terrestrial and aerial laser-scans, sonar and total station point measurements are used to produce the necessary detail in the geometry. This paper describes the on-going research project, and presents temporary results of the hybrid modeling.