Date of Graduation

12-2023

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Kevin M. Befus

Committee Member

Barnard, Patrick L.

Second Committee Member

Covington, Matthew D.

Keywords

coastal groundwater hazards, groundwater, hydrogeology, sea level rise, Seattle, Washington

Abstract

Sea level rise (SLR) associated hazards, such as coastal flooding and erosion, are pressing issues of great concern for coastal communities across the globe. Shallow and emergent groundwater can contribute to groundwater hazards such as flooding, landslides, or damage to shallow infrastructure. This study investigates the shallow groundwater within Seattle, Washington, and projects how it will respond to SLR using interpolation and numerical groundwater modeling methods. Then, a geologic modeling method is presented as a preliminary investigation of heterogeneity and anisotropy within the aquifer system. In the results for the present-day interpolation, ~6 % of the coastal buffer –the total area within 1 km of the coast within the Seattle Municipal boundary– is modeled as emergent. This area increased to ~8% with 1 m of SLR and ~15% with 2 m of SLR. In the results for the present-day model, ~0.5% of the area within the coastal buffer is modeled as emergent; this area increased to ~3% with 1 m of SLR and ~7% with 2 m of SLR. These studies show that the low-lying Duwamish River Basin will likely experience the greatest exposure to shallow and changing groundwater levels. The models projected the extent of emergent groundwater to expand despite the overland inundation of low-lying areas and shallow groundwater by seawater. However, areas with shallow groundwater decrease with SLR. The results also show that the extent of emergent groundwater is greater than the area inundated by seawater in SLR scenarios for both the interpolation and numerical methods. The results show that the impact of shoaling groundwater hazards could exceed the long-term coastal inundation area, indicating that groundwater hazards associated with SLR must be accounted for in climate adaptation planning.

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