Date of Graduation

5-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level

Graduate

Department

Graduate School

Advisor

Stephen K. Boss

Committee Member

Ralph K. Davis

Second Committee Member

John C. Dixon

Third Committee Member

Frank L. Farmer

Abstract

Discussions related to the adverse impacts associated with shore armor (i.e. seawalls and riprap) are a common topic within the coastal community. While many agree that the installation of these structures alters the shores geomorphic response, there is disagreement in the type and degree of response. Furthermore, studies that have delved into this topic have been conducted in numerous settings but have been confounded by a lack of data regarding shore morphologies prior to installation of these structures. At Yellowstone National Park, there is an opportunity to assess the impacts of shore armor quantitatively because the National Park Service requires detailed surveys in advance of all infrastructure improvement projects in an effort to determine the overall impacts of these projects on park environments relative to their benefits to park visitors and employees. The purpose of this study then was to contribute to this ongoing discussion of adverse impacts from shore armor by monitoring several non-engineered and engineered shore segments along the shore of Yellowstone Lake. For the purposes of this study, all shore segments that possessed shore armor (i.e. a seawall or riprap) were referred to as an engineered beach while any shore lacking a seawall or riprap was classified as a non-engineered shore segment.

This study began with an effort to determine if there were geomorphic differences between several non-engineered and engineered shore segments located along the western and northern shore of Yellowstone Lake. This effort was accomplished by measuring cross-shore profiles, dry-beach widths and conducting a grain size analysis of the dry-beach sediments. Results from the initial survey conducted in July-August 2005 established that there were significant geomorphic differences between the non-engineered and engineered shore segments of Yellowstone Lake. Visual observations combined with surveyed cross-shore profiles, grain size analyses and dry-beach width measurements revealed that the non-engineered shore segments were indeed geomorphically different from the engineered segments. That is, the non-engineered shore segments displayed relatively wider beaches composed of sand to fine gravel with gently sloping profiles whereas the engineered shores were typified with angular L-shaped profiles with narrow dry-beach faces. In addition to the geomorphic differences, visual observations and analysis of the data revealed that the engineered shores were indeed adversely impacted by the shore armor through the processes of placement loss and profile deflation.

A repeat survey was then conducted in the summers of 2006 and 2007 to determine the short-term variability of these non-engineered and engineered shore segments. Three years of data with a two-year interval indicated that there was a consistent difference in the geomorphology of the non-engineered and engineered shore segments. These differences were reflected in the cross-shore profile, the volume, and the dry beach width for all four study sites. In addition to these consistent differences, analysis of the data showed that the non-engineered shore cross-shore profiles fluctuated about a mean shape, whereas the volumetric calculations and dry-beach measurements showed that both the non-engineered and engineered shores experience annual variability in their shore morphologies. Insight into the short-term variability was an essential component for the third portion of the study, which was an investigation into the long-term response of the shore to the engineering efforts along the shore of Yellowstone Lake.

The third and final phase of this research was a long-term study of the shore responses to shore armor at Yellowstone Lake. This aspect of the study was intriguing because very few long-term studies focused specifically on shore responses to shore engineering exist. The methodology of this study incorporated the use of Historical GIS techniques to extract quantifiable data from construction drawings in order to be compared with the contemporary data collected from 2005 to 2007. Results revealed that, while both the non-engineered and engineered shore segments experienced a decrease in volume, the volumetric decrease was more pronounced for the non-engineered shores. The engineered shores indicated a smaller amount of volumetric change, suggesting that passive erosional processes and placement loss has had a long-term impact on the engineered shores in that the engineered structures have fixed the shoreline at these segments while the non-engineered shores are still able to adjust to changing conditions.

Upon completion of this dissertation research, it was concluded that the engineered shore segments of Yellowstone Lake exhibit morphological features similar to those associated with hard stabilization of marine and Great Lakes coastal settings and are suggestive of enhanced erosion and shore degradation at engineered shore sites when compared to adjacent non-engineered shore segments. Ongoing monitoring and repeat annual surveys of study sites enhance understanding of shore zone processes at Yellowstone Lake. Furthermore, results from this study may also aid in developing alternative strategies for protecting lakeside infrastructure while at the same time conserving lakeshore resources and preserving the quality of visitor experiences at Yellowstone Lake.

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