Document Type

Thesis

Date of Degree Completion

Spring 2020

Degree Name

Master of Science (MS)

Department

Cultural and Environmental Resource Management

Committee Chair

Karl L. Lillquist

Second Committee Member

Anthony Gabriel

Third Committee Member

Steven Hackenberger

Fourth Committee Member

Shane Scott

Abstract

In the Yakima Basin, managers are expanding reservoirs including Cle Elum Lake to increase the availability of water. The objective of this study was to examine areas prone to further shoreline erosion to inform resource management. This research included the use of airphotos and fieldwork to identify erosional shorelines. Erosion was verified in the field using a video survey as well as indicators such as shoreline slope, sediment size, and nearshore width. Near-term erosional segments were identified by more rapidly receding bluffs while long-term erosional segments included both bedrock cliffs and bluffs. Although most of the shoreline is depositional, near-term bluff erosion is most prevalent along the southeastern and northeastern shorelines while long-term erosion is mainly along the northwestern and southeastern shorelines. Potential erosion control variables were identified in the scientific literature and data representing them were acquired from fieldwork and outside sources. Geologic units and slope intervals are statistically significant variables in shoreline erosion. In the near-term shoreline erosion inventory, low bluffs with sandstone substrates make the largest contribution to the relationship between geologic units and erosional segments. An extensive cliff formed of intrusive igneous rocks is important to the relationship between geologic unit and long-term erosion. Although the nearshore and foreshore zones are largely below 36° reflecting the glacial origins of this basin, intermediate slopes between 11° and 36° and steep slopes between 37° - 49° are mainly responsible for the link between slope intervals and both bluff and cliff erosion. A Geographic Information Systems (GIS) model used these factors to predict relatively limited areas highly susceptible to future erosion, with near-term erosion risk mainly on the eastern and southwestern lakeshore while the southeastern and northwestern shoreline are most susceptible over the long-term. The product of this analysis were hazard maps indicating the relative risk of shoreline erosion. These maps formed the basis of policy recommendations including increased shoreline protection along southeastern shoreline and the implementation of a long-term monitoring program for shoreline erosion to support the management of cultural resources.

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