Unsteady Flow Routing Using HEC-RAS (Version 3.0): Comparisons to the FLDWAV Model

The Hydrologic Engineering Center's River Analysis System (HEC-RAS) is a multifaceted software package capable of computing one-dimensional steady gradually varied flow profiles. The software, originally created in the early 1990s, is constantly being updated and modified. Some of the features that are currently included are: computations of the hydraulics of bridge waterways, scour computations at bridges that are due to contraction, piers, and abutments, in line weirs and lateral gated spillways, etc.

Unsteady flow computations has recently been added and is currently available in the latest beta version of HEC-RAS (Version 3.0). The one-dimensional solution of the Saint Venant equations using a four-point implicit method, similar to the scheme used the Center's version of the UNET program, is solved. The solution is built into the graphical interface and utilizes the same geometric editor and data files created for the steady flow computations.

Testing of the HEC-RAS beta version was performed by the authors on the Shaver Creek Watershed, located in Centre County, Pennsylvania. Sunny day dam breach failure was simulated for the Perez Lake Dam using HEC-1. The dam breach hydrograph was then routed downstream using the HEC-RAS computer model and the results compared to the National Weather Services DAMBRK model. Hydrologic methods were also compared to the results of the unsteady flow routing. 11 pp., 4 references.