Momentum transfer for practical flow computation in compound channels

A new theoretical 1D model of compound channels flows-the exchange discharge model-is presented. The interactions between main channel and floodplains are taken into account as a momentum transfer proportional to the product of the velocity gradient at the interface by the mass discharge exchanged through this interface due to turbulence. Geometrical changes in cross sections are also modeled; they generate a similar momentum transfer, proportional to the actual mass transfer. Both effects are incorporated into the flow equations as an additional head loss. This make the formulation suitable for stage-discharge computation but also enables practical water-profile simulations. The model is tested successfully against available experimental data for (1) stage-discharge relations; and (2) water-profile computation applied to a field case.