Porosity and Flow Drag in HEC-RAS

Abstract Submission: Simulating flow through porous features like rubble mound structures or large woody debris in surface water models can be challenging. Previous versions of the Hydrologic Engineering Center River Analysis System (HEC-RAS) simulated these features either with terrain modifications (which could be limited vertically but completely excluded flow) or ineffective flow areas (which reduce conveyance but cannot be limited vertically). The latest version includes the advantages of both of these options without the liabilities. HEC-RAS Version 6.6 can simulate two-dimensional (2D) flow through porous regions with linear and quadratic flow drag. These features allow HEC-RAS to simulate a wide range of ecological and engineering features including flow through rubble mound structures, vegetation, natural and anthropogenic woody debris structure, among others. Porosity and flow drag are implemented in all of the HEC-RAS diffusive wave and shallow water equation solvers. HEC-RAS adopted a general approach for flow drag and porosity based on subgrid and lumped parameters instead of feature specific geometry and physical properties such as stem diameter and density for vegetation. This allows users to apply the feature to a wide range of physical situations and compute parameters outside of HEC-RAS. The equations are solved with a mixture finite-difference and finite-volume methods with an implicit time stepping scheme. The presentation will include a brief description of the theory, data requirements, and example results from verification and validation datasets as well demonstrate the utility of these tools with example applications.

Learning Objectives/Expected Outcome (Optional) :