USGS Washington Water Science Center
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9722-CK4 - Potential Effects of Increased Ground-Water Withdrawals on Streamflows in the Lower Skagit River Basin, Skagit County, Washington - Completed FY2010
Problem - State and local water-resource managers in the Lower Skagit/Samish basin face two water-availability issues that are common throughout Washington State. First, they must reserve water for domestic wells that are exempt from the water rights system without harming river and stream ecosystems in the lower Skagit River basin. Skagit County, which would be responsible for implementing the proposed reservation rules through land-use management, requires a scientifically credible basis for allocating reservations of any size. Second, water managers need to determine where ground-water pumping between the Skagit and Samish basins should be regulated as part of the Skagit River instream-flow regulations.
Objectives - This study has two primary objectives. The first objective is to evaluate the effects of potential ground-water withdrawals and consumptive use on streamflow in four tributary subbasins (the East Fork and mainstem of Nookachamps Creek, Fisher Creek, and Carpenter Creek). The second objective is to determine to the extent possible the location of the ground-water divide between the lower Skagit and Samish Rivers for the purposes of identifying areas where wells would be subject to reservations under the Skagit River instream-flow rule.
Relevance and Benefits - This study is consistent with the national USGS mission and goals and to water-resource issues identified in the Center's Science Plan. The study addresses surface-water and ground-water interactions as related to water-resource management, which is a priority issue for both the Strategic Directions of the Water Resources Division 1999-2008 and the Washington Water Science Center's Science Plan. The methods developed for this study will benefit other areas of Washington because of the widespread need to reserve water for domestic uses while maintaining streamflow to protect ecosystems.
Approach - The study has two components: 1) development of a numerical model to assess the effects of ground-water pumping on streamflow in four tributaries to the lower Skagit, and 2) construction of seasonal water-table maps for the area between the Skagit and Samish Rivers.