Identifying Stream Habitat Features with a Two-Dimensional Hydraulic Model

摘要

The Yakima River Basin Storage Study is investigating the need and benefit of increasing water storage in the Yakima Basin to provide beneficial flows for habitat and still meet irrigation demands. Presently, flow releases for irrigation do not coincide with the flows required for adequate aquatic habitat, in particular for salmonid fish species. The major thrust of the storage study is to shape annual hydrographs to more closely resemble the flow patterns that existed prior to regulation. With limited storage volumes in the basin, meeting the demands of both habitat and irrigation is challenging. This report details one aspect of the storage study, determining habitat availability at various flow rates using the two-dimensional (2-D) hydraulic model titled, Generalized Sediment Transport for Alluvial Rivers and Watersheds (GSTAR-W). The Ecosystems Diagnostic and Treatment (EDT) model is being utilized (Mobrand, et al., 1997) to assess the benefit of modifying flow releases at certain times throughout the year. EDT develops a working hypothesis to guide restoration efforts and includes an analytical model to quantify the biological potential of stream habitat for salmonid fish species (Greg Blair, Mobrand-Jones and Stokes, written communication). To address some of the more specific input needs for the EDT model, two-dimensional (2-D) hydraulic models were constructed and run over a wide range of flows for selected reaches of the Yakima and Naches Rivers. A two-dimensional model provides continuous hydraulic data over an entire reach of interest, as opposed to one-dimensional (1-D) hydraulic models, which provide cross-sectional average hydraulic properties at discrete locations. Outputs of the 2-D models are flow depth, depth-averaged velocity, water surface elevation and Froude number. Identification of pool, riffle and glide habitat types used the Froude number. Additionally, the quantity and quality of side channel habitat can be evaluated over the given range of flows. The 2-D models discussed in this report were run over a range of flows from the lowest anticipated discharge to approximately 130% of bankfull discharge. The model results can be displayed and mathematically manipulated in a Geographical Information System (GIS) to categorize areas for each EDT reach.