The Toppenish Creek basin comprises only 10% of the Yakima River subbasin, but contributes 20% of the Yakima?s summer steelhead run (Mid-Columbia ESU, Threatened, March, 1999). The Toppenish Simcoe-Unit (Unit) of the Wapato Irrigation Project (WIP) diverts streamflow from Toppenish Creek and its tributaries to irrigate roughly 2,000 acres. In doing so, these and other private diversions can desiccate long reaches of streams, killing juvenile steelhead. Land status, water use and the extent of steelhead utilization within the Unit must be determined to identify parcels of land with water that can be leased or purchased to return diverted streamflow into natal streams, maintaining aquatic species assemblages. In addition, a comprehensive accounting of the Unit will allow us to identify possible sources for water substitution, leaving flows instream for aquatic species. The main objectives and approach of this Project are to monitor all steelhead life stages as to location and timing of habitat utilization, quantify and locate all sources of diversion and augmentation, model consumptive use, and identify land status. This will lead to the development of an adaptive Management Plan and decision support system to actively pursue lands available for acquisition to return irrigation water for instream use. If land acquisition is not possible, we hope to work with landowners to restrict diversion timing to periods when surface discharge is not limiting (spring runoff), or identify alternative water sources for substitution. We expect that providing perennial flow to all stream reaches in the Project area will have a positive effect on steelhead populations, measured by yearly spawner surveys and juvenile censuses. By FY2002, we will have completed four seasons of field data collection, the Project GIS, and the Project Management Plan. Integrating Project products and those of other activities in the basin will supply us with a decision support system to begin implementing and adaptively evolving the Management Plan early in FY2002.Restore instream flow to dewatered Project streams by system modifications, water substitution, and land purchase or lease
