Document Type

Thesis

Date of Degree Completion

Winter 2022

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Lisa Ely

Second Committee Member

Carey Gazis

Third Committee Member

Breanyn MacInnes

Abstract

Numerous stream restoration projects in the Yakima River Basin in Washington have placed large wood (LW) into tributary channels. One intended effect is to divert water onto floodplains to increase groundwater (GW) recharge and seasonal storage in shallow alluvial aquifers during spring high flows with the intention of releasing GW into streams during the drier summer months. Large wood was emplaced in the Indian Creek tributary of the Teanaway River in Kittitas County, Washington beginning in 2016. Potential changes in the groundwater recharge in the adjacent floodplain before and after the LW installation were investigated through stratigraphic analysis, stream-flow modeling, and GW levels in six piezometers installed in 2014 and 2018. Stratigraphic descriptions of the stream banks reveal a ubiquitous silt/clay dominant layer (60-90 cm thick) at a depth of 1 meter or less, overlying a sand and gravel layer (15-50 cm thick), a clay/silt layer (~30 cm thick), and another sand and gravel layer. These relatively continuous clay layers extend at least 2.2 km upstream from the mouth of Indian Creek on both sides of the channel. Similar clay units have been mapped in the region as glacial drift or lacustrine deposits. The measured stream flow and GW levels in the monitoring wells before and after the LW emplacement show no detectable effect of the LW on seasonal or longer-term GW levels. Data loggers show that GW levels return to baseflow within days of monthly precipitation exceeding 70 mm, suggesting GW flow within the permeable sand and gravel layers beneath or between the clay/silt layers. Available data show that the highest spring GW elevations precede peak stream discharge, indicating that the peak streamflow is not a significant source of GW recharge. A 1-dimensional hydraulic model run with and without channel obstructions at spring monthly average discharge and peak discharge suggests that the water surface elevation may increase ~10-50 cm within and upstream of LW. This assessment of stratigraphy coupled with GW data and stream-flow model can provide insight into the effectiveness of GW recharge from LW restoration projects in similar settings within the region.

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