Unsteady Flow Routing with the Hydrologic Engineering Center River Analysis System (HEC-RAS)

The Hydrologic Engineering Center (HEC) has added Unsteady Flow Routing capabilities to our river hydraulics software, HEC-RAS. The unsteady flow equation solver used in HEC-RAS is the UNET program, developed by Dr. Robert Barkau. HEC has developed a new geometry pre-processor for UNET that is based on the same hydraulic calculations that are used in the steady flow computations of HEC-RAS. This allows the user to enter data one time and perform either steady flow and/or unsteady flow analyses. Additionally, a post processor has been developed that takes the unsteady flow results and back calculates all the hydraulic properties that are available from the steady flow hydraulics. This allows the user to view the same types of output whether they run a steady flow or an unsteady flow solution. This paper presents the capabilities that have been added to HEC-RAS for performing unsteady flow computations. The unsteady flow pre-processor, hydraulic computations, post processor, and new output graphics and tables are described.