One-Dimensional Modeling Techniques for Three-Dimensional Grade Control Structures

Generally constructed with materials from the proximal environment and promoting a more natural aesthetic within a stream, rock-weir grade control structures have recently become popular in-stream alternatives. Energy expenditure through rock weirs is increased from in situ, primarily one-dimensional (1D) conditions owing to strong velocity gradients and turbulence losses. Flow modeling methodologies utilizing a 1D assumption are not directly applicable for representing hydraulics through rock weirs; however, such models are readily implemented in engineering practice. An approach altering parameters and cross section configurations within a 1D model, Hydrologic Engineering Center River Analysis System (HEC-RAS), was developed to approximate hydraulic conditions associated with A-shaped, U-shaped, and W-shaped rock-weirs using data from a near-prototype physical model. Manning's n roughness values were adjusted for minimum energy variance and calibrated to serve as a turbulence model. Predicted total mechanical energy head and water surface elevations were approximated within a mean reach-averaged cross section absolute error of 0.013m. The developed methodology may be implemented in streams with similar dimensions and flow characteristics to the laboratory, and provides an approach for rock-weir field design.