The design of hydraulic structures such as bridges on distributary flow areas and alluvial fans require methods that can adequately determine discharges at the structures. Flow conditions on distributary flow areas such as alluvial plains (Slopes) and alluvial fans are quite complex and require the application of unsteady flow hydraulics and sometimes need multi-dimensional flow analysis. The primary objective of this work has been to explore the use of the U.S. National Weather Service DAMBRK model, to describe the propagation of unsteady flows on distributary flow areas. The DAMBRK model was applied to several hypothetical situations to determine the capability of the program to describe unsteady flows. A distributary flow area below the McDowell Mountains in Scottsdale, Arizona, was modeled using the DAMBRK code. The flood plains computed using DAMBRK are compared with the flood plains using the FEMA method.