Eastbank Aquifer near Rocky Reach Dam Completed

9722-D2N - Assessment of Ground-Water Temperatures near Rocky Reach Dam, Douglas County, Washington - Phase 1 and 2 - Completed FY2008

Problem - The Eastbank aquifer system near Rocky Reach dam is the water source for a fish hatchery operated by the Public Utility District No. 1 of Chelan County (PUD) to compensate for fish losses from Rocky Reach and Rock Island Hydroelectric Projects. The aquifer system also supplies water to about 50,000 people. A recent study concluded that ground-water temperatures have been increasing and because hatchery well water is already marginally too warm for growing salmonids, future increases could result in the need to find different approaches for supplying appropriate water. Future increases in ground-water withdrawals could possibly further increase temperatures, if they resulted in increased flow from the Columbia River to the aquifer during times of the year when river temperatures are higher. One approach for possibly avoiding or minimizing future increases in temperatures is to optimize ground-water pumping. Understanding how ground-water resources may be managed to avoid or minimize increases in ground-water temperatures while temperatures in adjacent surface-water bodies may be increasing is important for aquifer systems throughout the United States.

Objective - The objective of phase 1 of the study is to improve the understanding of the hydrologic and thermal conditions of the Eastbank aquifer system and the processes that affect those conditions. The objective of phase 2 is to determine if the water resources of the Eastbank aquifer system can be managed such that the hatchery can be supplied with appropriate water throughout the year. Phase 2 will be conducted if findings of phase 1 indicate it is warranted.

Relevance and Benefits - This study is consistent with the national USGS mission and goals and water-resources issues identified in the USGS Washington Water Science Center Science Plan. Specifically, the study addresses the following issues in "Strategic Directions of the Water Resources Division 1998-2008": effects of urbanization and suburbanization on water resources (issue 1); effects of climate on water-resource management (issue 7), surface-water and ground-water interactions as related to water-resources management (issue 8), and hydrologic-system management, including optimization of ground-water and surface-water use (issue 9). Phase 1 of the study will improve the understanding of the hydrologic and thermal conditions of the Eastbank aquifer system and the processes that affect those conditions and phase 2 will show how different ground-water-management strategies coupled with possible increases in Columbia River temperatures due to climate change and other factors may affect future ground-water temperatures. Findings of phase 2 will have transfer value for aquifer systems throughout the United States.

Approach - The objective of phase 1 will be met by evaluating existing data and studies and identifying data gaps, designing an updated data-collection program, collecting new data, and developing and publishing a conceptual model of the Eastbank aquifer system. The objective of phase 2 will be met by creating a 3-dimensional transient (time-varying) ground-water flow and heat-transport model of the Eastbank aquifer system that can be used to a) simulate the effects of different water-management strategies on water levels and temperatures of the aquifer for both current and possible future Columbia River temperatures, and b) identify water-management strategies that may avoid or minimize future increases in ground-water temperatures.