Document Type

Thesis

Date of Degree Completion

Spring 2023

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Lisa Ely

Second Committee Member

Carey Gazis

Third Committee Member

Breanyn MacInnes

Abstract

Large wood (LW) restoration projects were recently implemented in the Upper Yakima Basin following the destructive logging practices of the early 20th Century, which stripped Upper Yakima River tributaries of LW. The removal of natural LW increased incision, isolating channels from floodplain aquifers, and degrading resident and anadromous fish habitat. Returning streams to their natural state through instream LW installations is believed to increase floodplain groundwater storage by decreasing channel incision, increasing floodplain-channel connectivity, and raising the water table elevation. Additional storage in floodplain aquifers can help combat the adverse effects of climate change, namely decreasing snowpack and earlier melting. Storing infiltrating snowmelt and river water during peak flow in shallow floodplain aquifers could allow the natural release of groundwater as baseflow through the dry summer. Taneum Creek, Indian Creek, and Teanaway River have established LW projects and are candidates for floodplain aquifer storage. However, a regionally wide spread gray silt layer could affect potential aquifer transmissivity and storage capacity. Through fieldwork, mapping, and grain-size analysis, the groundwater storage volume was quantified taking into consideration the effects of the stratigraphy on groundwater storage, recharge, and flow. Volume estimates indicate a potential floodplain aquifer capacity of 1,040-1,990 acre-feet in the North Fork Teanaway watershed and 352-1,320 acre-feet in Taneum Creek.

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