 Physical process models of channel reaches are generally well understood and will calculate the depth and area of inundation for given channel conditions and a specified flow rate, such as for use in floodplain mapping and flood insurance.Conversely, given the observed inundation area of a recent flood and the channel conditions, a model can calculate the flow rate.Applied to various potential channel configurations and flow rates, a reach model can contribute to selecting an optimum design for a modified channel.