Using GIS to Index Fish Stranding and Trapping

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Mitigating Stranding and Trapping Effects on Fish Species During Hydroelectric Operations
Seattle City Light (SCL) is relicensing the operations of the Boundary Hydroelectric Project (Project) on the Pend Oreille River. The Pend Orielle River is located in Northeast Washington and is home to varied and important fish resources. These resources can be negatively affected by receding water levels either from Project operations or from natural reductions of inflow. When these conditions exist, fish may become stranded in shallow sloping shoreline areas (< 4%) or isolated in pools that become disconnected from the mainstem flow.
SCL is funding a study which was designed to develop an index model of relative stranding and trapping effects based on various scenarios of project operations and natural flow patterns.
This poster demonstrates the geoprocessing tools and methods used to identify potential stranding and trapping areas. The areas were periodically examined in the field during water drawdown events to measure actual fish stranding or trapping. Site-specific information, such as substrate and presence of macrophytes (aquatic plants), was also noted. A hydraulic routing model, which was developed separately, was used to determine when areas would be dewatered and the duration of trapping at specific pools. Applying assigned multiplication factors to the analysis, along with the hydraulic routing model, produced the stranding and trapping indices for each scenario. These resulting indices were then available for management personnel and interest groups to examine and compare the relative effect of various operation scenarios on fish stranding and trapping.

Morgan Omdal - Tetra Tech

Mr. Omdal is a GIS Coordinator and Project Manager for Tetra Tech in their Seattle, WA office. He has 5 years of applied environmental science and GIS experience and is Tetra Tech’s Deputy Project Manager for Forest Service GIS task orders under the Forest Service GIS Data Services Contract. Mr. Omdal’s past employers include The Nature Conservancy of Oregon, Colorado State University, Turnstone Environmental, Inc. and The Washington State Parks and Recreation Commission.

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