Development of a Conceptual Site Model for Evaluating Seawater Intrusion under Sea Level Rise Scenarios Using Analytical Methods

Island County is located in the Puget Sound of Washington State and includes several islands, the largest of which is Whidbey Island. Central Whidbey Island was chosen as the project site, as residents use groundwater for their water supply and seawater intrusion near the coast is known to contaminate this resource. In 1989, Island County adopted a Saltwater Intrusion Policy and used chloride concentrations in existing wells in order to define and map “risk zones.” In 2005, this method of defining vulnerability was updated with the use of water level elevations in conjunction with chloride concentrations. The result of this work was a revised map of seawater intrusion vulnerability that is currently in use by Island County. This groundwater management strategy is defined as trigger-level management and is largely a reactive tool. In order to evaluate trends in the hydrogeologic processes at the site, including seawater intrusion under sea level rise scenarios, this report presents a workflow where groundwater flow and discharge to the sea are quantified using a revised conceptual site model. The revised conceptual site model used several simplifying assumptions that allow for first-order quantitative predictions of seawater intrusion using analytical methods. Data from water well reports included lithologic and well construction information, static water levels, and aquifer tests for specific capacity. Results from specific capacity tests define the relationship between discharge and drawdown and were input for a modified Theis equation to solve for transmissivity (Arihood, 2009). Components of the conceptual site model were created in ArcGIS and included interpolation of water level elevation, creation of groundwater basins, and the calculation of net recharge and groundwater discharge for each basin. The revised conceptual site model was then used to hypothesize regarding hydrogeologic processes based on observed trends in groundwater flow. Hypotheses used to explain a reduction in aquifer thickness and hydraulic gradient were: (1) A large increase in transmissivity occurring near the coast. (2) The reduced aquifer thickness and hydraulic gradient were the result of seawater intrusion. (3) Data used to create the conceptual site model were insufficient to resolve trends in groundwater flow. For Hypothesis 2, analytical solutions for groundwater flow under Dupuit assumptions were applied in order to evaluate seawater intrusion under projected sea level rise scenarios. Results indicated that a rise in sea level has little impact on the position of a saltwater wedge; however, a reduction in recharge has significant consequences. Future work should evaluate groundwater flow using an expanded monitoring well network and aquifer recharge should be promoted by reducing surface water runoff.

‘All of this Belongs to Us’: Land, Horses, and Indigenous Resistance on the Yakama Indian Reservation, 1900-1950

In the early 1900s, the Yakima Indian Agency welcomed non-Native ranching operations onto Yakama tribal lands, taxing rangelands, and resulting in widespread overgrazing. By the 1920s, agency concern for the welfare of ranchers facilitated a need to gain access to tribal grazing lands sustaining Yakama horses. As a result, agency officials launched systematic assaults on Yakama horse herds, citing horses as culprits of overgrazing and land degradation. However, Yakamas showed little interest in removing their horses, and instead actively opposed settler encroachment on tribal grazing lands. Through analyzing archival sources, conducting interviews, and reviewing scholarly sources, I argue that Yakamas and settlers used horses as a terrain of struggle, whereby they asserted competing claims to Indigenous lands and resources. Examining horses as a tool of resistance provides a useful lens for understanding forms of Native opposition to colonial hegemony, while interrogating problematic tropes settlers utilized to justify divesting Native communities.

Migration and Residence Patterns of Salmonids in Puget Sound, Washington

Thesis (Ph.D.)--University of Washington, 2016-08