Metrics of Shoreline Armoring Impacts on Beach Morphology in the Salish Sea, WA
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Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Summer 2020 Metrics of shoreline armoring impacts on beach morphology in the Salish Sea, WA Hannah Drummond Western Washington University, [email protected] Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Environmental Studies Commons Recommended Citation Drummond, Hannah, "Metrics of shoreline armoring impacts on beach morphology in the Salish Sea, WA" (2020). WWU Graduate School Collection. 975. https://cedar.wwu.edu/wwuet/975 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. Metrics of shoreline armoring impacts on beach morphology in the Salish Sea, WA By Hannah Drummond Accepted in Partial Completion of the Requirements for the Degree Master of Arts ADVISORY COMMITTEE Dr. Andy Bach, Chair Dr. Eric Grossman Dr. Ian Miller GRADUATE SCHOOL David L. Patrick, Dean Master’s Thesis In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non-exclusive royalty-free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. I acknowledge that I retain ownership rights to the copyright of this work, including but not limited to the right to use all or part of this work in future works, such as articles or books. Library users are granted permission for individual, research and non-commercial reproduction of this work for educational purposes only. Any further digital posting of this document requires specific permission from the author. Any copying or publication of this thesis for commercial purposes, or for financial gain, is not allowed without my written permission. Hannah Drummond 8/7/2020 ii Metrics of shoreline armoring impacts on beach morphology in the Salish Sea, WA A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment Of the Requirements for the Degree Master of Arts by Hannah Drummond August, 2020 iii 1. ABSTRACT Coastal development, and the shoreline defenses that accompany it, makes it vitally important to understand the shoreline’s response to anthropogenic modifications. Armoring, or shoreline erosion control structures such as seawalls or riprap, is found on an estimated one third of Salish Sea shorelines and has been shown to degrade nearshore habitat. We compared physical beach characteristics from adjacent sections of armored and unarmored shoreline at a variety of locations in the Salish Sea to assess the effects of armoring on beach morphology. Nineteen sites, each a minimum of 500 meters in length, were selected from ten reaches sampled with boat-based LiDAR by the WA Dept. of Ecology Coastal Monitoring and Analysis Program. To assess data quality and select the best methodology for further analysis, beach slope and width measurements were compared between the point cloud and corresponding digital elevation model (DEM). Differences in the two data formats were found to be insignificant and the DEM was selected as the input data because use of the DEM is more efficient than the point cloud. Cross-shore profiles were generated from each DEM for each reach at 10-meter intervals alongshore. Estimates of beach slope, width, and toe elevation were extracted from the DEM along each profile in both the foreshore and backshore zones. Parameters were tested for significant differences between the armored and unarmored sections both regionally and within each site. The relationship between bluff or armor toe elevation and beach width and slope was also tested. Locally, direct impacts from armor covering the backshore habitat were more prominent than parameters that are suspected to be controlled by geomorphic processes. For example, backshore width and bluff or armor toe elevation were significantly different between armored and unarmored sections and correlated with each other but parameters such as slope or foreshore width that were not in direct contact with shoreline armoring did not show strong iv differences between armored and unarmored sections. The relationship between backshore width and toe elevation was consistent across all shore types and geographies. These results can be applied to restoration efforts by prioritizing armor removal projects where the armor toe is the lowest elevation compared to adjacent unarmored shoreline in order to maximize potential habitat benefits. v 2. ACKNOWLEDGEMENTS This thesis would not have been possible without the support from many people in the WWU and Puget Sound nearshore research community. First and foremost, I would like to extend my sincerest appreciation for my advisor, Dr. Andy Bach, who provided essential guidance through every step of the research process. I would also like to thank my committee members, Dr. Eric Grossman and Dr. Ian Miller, who provided thoughtful feedback and offered their expertise on numerous occasions. A special thanks goes to my supervisor, George Kaminsky of WA Dept. of Ecology, who played a crucial role in shaping the focus of this research, was always available to offer detailed feedback, and who, with the help from his team (Heather Weiner, Diana McCandless, and Amanda Hacking), provided the beach elevation data used in this study. The staff and instructors in Huxley College of the Environment were an essential resource. Dr. Andy Bunn offered specialized statistical advice and instructors of the GIS program including Dr. Aquila Flower, Dr. Michael Medler, Tyson Waldo, and Stefan Freelan all provided me with the technical skills required to complete and display this research. Ed Weber was also a valuable resource providing logistical assistance with everything from offering office space to engaging in practice presentations. vi CONTENTS 1. Abstract ................................................................................................................................... iv 2. Acknowledgements ................................................................................................................ vi 3. Table of Figures .................................................................................................................... viii 4. Introduction ............................................................................................................................. 1 4.1 Background ...................................................................................................................... 1 4.2 Study Area ........................................................................................................................ 3 4.3 Physical Environment ...................................................................................................... 5 4.4 Research Questions and Objectives ............................................................................... 10 5. Methods ................................................................................................................................. 11 5.1 Sites and Reaches ........................................................................................................... 11 5.2 Data ................................................................................................................................ 13 5.3 Beach Parameter Extraction ........................................................................................... 14 5.4 Analysis .......................................................................................................................... 16 6. Results ................................................................................................................................... 17 6.1 Site Variability ............................................................................................................... 17 6.2 Armored and Unarmored Comparisons ......................................................................... 18 6.3 Toe elevation correlations .............................................................................................. 24 7. Discussion .............................................................................................................................. 27 7.1 Direct Geomorphic Impacts ........................................................................................... 27 7.2 Impacts to Nearshore Processes ..................................................................................... 29 7.3 Sources of Error ............................................................................................................. 32 8. Conclusion ............................................................................................................................. 35 Appendix A: Choosing the Input Data Format ............................................................................. 37 8.1 Data Format Comparison Methods ...............................................................................