FMA Conference – September 2014
Abstract
The “Matrix”
HEC-RAS Model Optimization for Large Network Systems
Michael C. Nowlan, P.E., CFM (Wood Rodgers), Ashok Bathulla, P.E. CFM (Wood Rodgers), Rajmani Subedi, P.E. CFM (Wood Rodgers), Yiguo Liang, P.E. PhD (DWR)
916.326.5277
The Central Valley Floodplain Evaluation and Delineation Program has developed one of the largest channel network models utilizing the HEC-RAS program (developed by the US Army Corps of Engineers) for analyzing over 900 miles of the major connected rivers and streams in the Sacramento River watershed. HEC-RAS is an extremely powerful computer software program, utilized by the vast majority of floodplain managers and believed by many as the “One” for solving one-dimensional open-channel hydraulic problems in the world we see and experience. The development of a dynamic Sacramento River watershed model using HEC-RAS has required significant refinement to substantially control model run-time and reduce computational error.
As part of the effort in optimizing the Sacramento River HEC-RAS model, we sought out the oracle living inside the matrix (Mr. G.B.), who has deepened our understanding of the computational matrix and shared methods for refining computations to obtain more “reality-based” results. After successful attempts to reduce iterations, we are prepared to share what we have learned regarding the importance of understanding how selected parameters and geometric settings influence system computations. We will discuss key input parameters and their influences on the model, including effective/ineffective flow area settings, hydraulic property tables, geometric discontinuities, various coefficients, dampening factors, and even stream reach ordering logic.