Description and Evaluation of Program USM

USM is a hydraulic‐simulation computer program developed by the U.S. Bureau of Reclamation to analyze unsteady‐flow conditions in canals. The program USM uses the method of characteristics to solve the complete Saint Venant equations for unsteady flow in open channels. This solution method yields accurate numerical results but sometimes requires more computer execution time than other methods. USM analyzes canal systems with a variety of structural boundary conditions, including check gates, weirs, siphons, and pumps. Check gates can have either manual or automatic gate control. Branching canals, supercritical flow, and channel dewatering cannot be analyzed. This paper describes the model and compares its strengths and weaknesses with those of other models. Several test data sets compiled by the ASCE Task Committee on Irrigation Canal System Hydraulic Modeling were used in the evaluation. USM simulation results are compared to field data collected from the Central Arizona Project canal system.