Depth-averaged flow computation at a river confluence

A depth-averaged elliptic computational model in curvilinear coordinates is presented for velocity and depth computations in shallow water river confluences of any geometry. The pressure correction equation has been used with SIMPLE or SIMPLE-like procedures in depth-averaged models to date; here this is replaced by a depth correction equation to improve the convergence. This is a significant enhancement to the SIMPLE procedure when applied to depth-averaged flow computations of river elements with irregular bed topography. First, the model is validated using laboratory measurements from a flat-bed confluence with flow recirculation. Second, it is validated using laboratory measurements from a confluence with irregular bed topography derived at the dynamic equilibrium of a movable bed experiment. Next the model is employed to simulate the complex confluence flow at a bend of a river with a floodplain. The model predictions give satisfactory agreement with field observations. Though the flow in the scour hole region of a river confluence is three-dimensional, if proper parameters are used to represent bottom friction and mixing, a depth-averaged model can be used to obtain sufficiently accurate velocity and water surface elevation information for the design of flood control measures in shallow water river confluences.