Hydraulic transient modeling was performed during a comprehensive evaluation of an existing raw water transmission system. The existing system is comprised of three cast iron pipelines and one steel pipeline and is supplied by five large pumping units. Pressure transients are controlled in the system by timed closure discharge valves at the pump station and by three tanks. Proposed improvements to the system include rehabilitation of the cast iron lines and steel pipelines with HDPE and Ductile Iron slip-linings respectively. The existing and rehabilitated systems were modeled using a Method-of-Characteristics based program, and the existing surge control devices were found to be adequate in both cases. General confirmation of the transient model was found by comparison of model output to measured field data during a normal pump shutdown. Some sensitivity was found to the pre-trip air volume in the hydro-pneumatic tank. Includes tables, figures.