White River - Lake Tapps Climate Change Impacts

Background
Research Questions
Research Approach
Final Report/Thesis

Background

The Everett, Seattle, and Tacoma municipal water supplies provide the majority of water demanded in the Puget Sound Region. These systems are currently stressed by increasing municipal demands, instream flows, hydropower production, and flood control. Climate change will likely impact the demand and hydrologic signal in the future decades. Regional planners are seeking a new reliable water resource for the region. Cascade Water Alliance (CWA) represents eight municipalities and districts that have entered into a mutually beneficial agreement to provide their own source of water to meet their purveyor’s demands. CWA has signed a Block Contract with Seattle Public Utilities (SPU) which replaces individual contracts. This Block Contract will gradually reduce the amount of water purchased by CWA members from SPU. In the short term, the difference in supply will be provided by water purchased from Tacoma.  In the long term, CWA is seeking to purchase the water rights from Puget Sound Energy’s (PSE) White River Hydropower project so that it may be developed as a municipal water supply. As of June 2003, the Washington State Department of Ecology has granted PSE the rights to utilize Lake Tapps as a water resource, a step towards letting the water rights be sold. As of January 2004 PSE planned to no longer operate the Lake Tapps hydropower project due to economic inefficiency. Certain operations are still maintained to keep the lake level up and protect White River salmon.

The White River would be the 5^th major river used for municipal water in the Puget Sound. The White river watershed is the highest also, collecting snow pack and glacier runoff from Mt Rainier. This makes the White River unique in comparison to the other transient watersheds used for municipal supply.

Research Questions

Research Approach

These research questions will be addressed using the impact assessment method. A series of integrated models will be used to represent the physical hydrology and water resource operations.

The steps take in the impact assessment are as follows:

·     Downscaled general circulation model (GCM) output: information will be input to the hydrology model to produce climate change streamflow predictions

·     Historical temperature and precipitation data: this data will be input to the hydrology model to produce historic streamflow 

·     A distributed hydrology model: this model is a physical representation of the basin that outputs streamflows for given climate input (temperature and precipitation). The model is calibrated and validated to historic streamflow observations prior to generating future streamflow predictions.

·     A systems simulation model: This model represents the physical infrastructure which stores and conveys water from Lake Tapps.

Updated 05/13/2005