Determining Columbia and Snake River Project Tailrace and Forebay Zones of Hydraulic Influence using MASS2 Modeling [report]

Cynthia L. Rakowski, John A. Serkowski, Marshall C. Richmond, William A. Perkins
2010 unpublished
ph: (865) 576-8401 fax: (865) 576-5728 email: Available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Rd., Springfield, VA 22161 ph: (800) 553-6847 fax: (703) 605-6900 email: online ordering: This document was printed on recycled paper. Summary Fisheries biology studies are frequently performed at U.S. Army Corps of Engineers (USACE) projects along the
more » ... olumbia and Snake Rivers, and the results are presented relative to the "forebay" and "tailrace" regions. At this time, each study may use somewhat arbitrary locations (e.g., the Boat Restriction Zone) to define the upstream and downstream limits of the study. The arbitrariness of the delineations could create inconsistencies between projects and make it difficult to draw conclusions involving multiple projects. To overcome this concern, USACE fisheries researchers are interested in establishing a consistent definition of project forebay and tailrace regions for the hydroelectric projects on the lower Columbia and Snake rivers. The hydraulic extent of a project was defined by USACE CENWP (a) as follows: The river reach directly upstream (forebay) and downstream (tailrace) of a project that is influenced by the normal range of dam operations. Outside this reach, for a particular river discharge, changes in dam operations cannot be detected by hydraulic measurement. In other words, the hydraulic extent is the zone where the flow direction or velocity can be influened by how the flow is distributed through the powerhouse and spillway bays at a project, i.e., the percent of spill flow, the spill pattern, and the turbines that are operational. The purpose of this study was to develop and apply a consistent set of criteria for determining the hydraulic extent of each of the projects in the lower Columbia and Snake rivers. This was done in consultation with USACE and regional representatives, A 2D depth-averaged river model, MASS2, was applied to the Snake and Columbia Rivers. New computational meshes were developed for most reaches, and the underlying bathymetric data were updated to include the most current survey data. These computational meshes were sufficient to resolve each spillway bay and turbine unit at each project, and they extended from the tailrace of one project to the forebay of the downstream project. MASS2 was run for a range of total river flows and, for each total river flow, a range of project operations at each project. The modeled flow was analyzed to determine the range of velocity magnitude differences and the range of flow direction differences at each location in the computational mesh for each total river flow. Maps of the differences in flow direction and velocity magnitude were created. After reviewing the preliminary results, USACE fishery biologists requested data analysis to determine the project hydraulic extent based on the following criteria: • If mean water velocity is less than 4 ft/s, the differences in the magnitude water velocity between operations are not greater than 0.5 ft/s or the differences in water flow direction (azimuth) are not greater than 10°. (a) Brad Eppard, USACE, CENWP in "Project Boundaries for Bonneville, The Dalles, and John Day Dams," April 2010. iii
doi:10.2172/1007372 fatcat:6dj2jc2zkvao3exhx4vv2o4wjm