Document Type

Thesis

Date of Degree Completion

Spring 2023

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Carey Gazis

Second Committee Member

Lisa Ely

Third Committee Member

Breanyn MacInnes

Abstract

In the Yakima River Basin in south-central Washington, increasing demands for water, overallocation of surface water, and a changing climate are leading to a loss of water storage and increasing water deficits in drought years. A warming climate has reduced snowpack in the Cascade Range, a vital reservoir for the irrigated agricultural industry which supports the basin’s economy. Managed aquifer recharge (MAR) is a sustainable and cost-effective approach for securing water supply by storing water underground for recovery during drought. Diminishing groundwater levels in regional basalt aquifers over the last several decades suggest there is significant storage available for intentional recharge of these aquifers.

This study focuses on the areas around Rattlesnake Ridge east of Yakima, Washington. The region consists of east-west trending folds and faults of the Yakima Fold Belt with bedrock composed of the Grande Ronde, Wanapum, and Saddle Mountain formations of the Columbia River Basalt Group, and sedimentary interbeds of the Ellensburg Formation. The basalt aquifers are targets for MAR due to the immense thicknesses and vast spatial extent of the formations, the water-bearing vesicular flow tops and interbeds, and the structural controls of the Yakima Fold Belt.

Informed by the 2011 study of the Columbia Plateau Regional Aquifer System by the U.S. Geological Survey, this research quantifies the groundwater storage available for MAR in the Wanapum and Saddle Mountain Basalt aquifers through reconstructions of subsurface stratigraphy and analysis of historical groundwater level changes. This research finds that there has been nearly 100,000 acre-feet of groundwater storage lost annually in the basalt aquifers of the study area in the last fifty years. Because the Wanapum aquifer is thickest (typically over 1,000 ft thick) and experienced the most groundwater storage loss, it is the best candidate for MAR in the study area, although all basalt aquifers are suitable for a successful MAR program.

Comments

This thesis research contributed to the Rattlesnake Ridge Managed Aquifer Recharge Investigation Study funded by the Yakima Basin Integrated Plan through the groundwater subcommittee.

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