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For additional information about this project, visit Ecology’s website.

Case Study: Water Rights Support for Regional Water Supply from Lake Tapps

Client: Puget Sound Energy (PSE) Location: King & Pierce Counties, WA Contact for water resource projects: Tim Flynn

Project Background & Challenges

PSE has operated the Lake Tapps reservoir as a long-time hydropower source by diverting water from the White River, storing it in the lake, and then releasing it 21 miles downstream. When the hydropower project became financially unsustainable, PSE sought another revenue source to maintain the lake. Consequently, the utility decided to apply for both a new water right and a change in its existing rights. The objective was to allow water that was historically diverted for hydropower to be used for other purposes, including a new regional supply operated by the Cascade Water Alliance. PSE’s proposed change has engaged a broad spectrum of stakeholders — Native American tribes, lakeside homeowners, and downstream utility providers, as well as local, state, and federal agencies. Opinions differed widely on how best to balance these competing demands of maintaining instream flows, lake levels, and water quality.

Solution

Aspect is assisting Ecology and the Attorney General’s Office in processing this water right application. Ecology will use our expert review of the water quantity / quality evaluations to develop a Report of Examination either approving or denying the right. As part of this project, we have statistically analyzed streamflow records and run predictive models to evaluate the effects of implementing alternative targets for minimum instream flows and seasonal lake levels. We have also characterized the complex operations of the diversion, storage, and release facilities. In addition to reviewing the adequacy of the applicant’s analyses, our hydrologists also provide independent technical analysis and support the development of strategies that balance the conflicting demands of stakeholders and the greater public interest.