Hydraulic Modeling of Large Roughness Elements With Computational Fluid Dynamics for Improved Realism in Stream Restoration Planning

Abstract

Many stream restoration design procedures are based on user experience in distributing standard stream design features into stream channel types based on a stream classification scheme. Computational fluid dynamics (CFD) models, increasingly used to represent stream flow fields, offer a more quantitative path forward. However, CFD models, in practice, parameterize roughness on too large a scale and therefore do not explicitly represent discrete features such as large rocks and large woody material whose placement is the focus of stream restoration activities. The Stream Habitat Assessment Package (SHAPE), made possible by rapid advances and availability of high-performance computing resources and increased sophistication of both in-house and commercial software, overcomes barriers that prevent the routine use of CFD modeling in stream restoration planning. Capabilities of SHAPE that improve stream restoration planning include (1) realistically representing natural streambeds from potentially coarse sets of field measurements, (2) easily deforming the streambed surface with a virtual excavator, (3) selecting complex objects from a library and embedding them within the surface (e.g., rocks and fallen trees), (4) successfully meshing the channel surface and its surrounding volume in accordance with established mesh quality criteria, and (5) sufficiently resolving flow field solutions. We illustrate these capabilities of SHAPE using a coarse set of field data taken from one of four study sites along a 1.5 mile stretch along the Robinson Restoration project of the Merced River, California, along with respective challenges, solution strategies, and resulting outcomes. Flow field solutions are conducted using parallelized finite element/volume solvers.