A GIS-BASED APPROACH TO COASTAL CHANGE ASSESSMENT IN SANTA CRUZ COUNTY

Along the tectonically active Santa Cruz County coastline, the natural processes and human activities influencing coastal change are dynamic, complex, and often difficult to quantify. The advancement of Geographic Information System (GIS) technology continually offers new tools and methodologies for measuring coastal change and assessing relationships between rates of change and other spatially and temporally variable coastal parameters. Using modern GIS-based analytical tools, this study explores the spatial relationships between long-term rates of coastal cliff retreat, and potential forcing factors such as shoreline orientation, wave climate and lithologic variation along the coastline.

For this study, existing shoreline vectors derived from aerial imagery were imported into a GIS and used to calculate long-term cliff retreat rates using the Digital Shoreline Assessment System (DSAS). The calculated rates were averaged over morphologically defined coastal sections and statistically compared to shoreline orientation, wave climate and other locally variable coastal characteristics (e.g. morphology, geologic structure) to investigate correlative trends.

Previous coastal change research conducted along this section of coast indicates that rates of cliff erosion vary alongshore with average retreat rates between 7-15 cm/yr. While this variability has been qualitatively attributed to the influences of local wave climate, geology, coastal configuration and degree of armoring, the use of GIS provides a means by which these relationships can be statistically quantified.

This research tests the utility of GIS for coastal change assessment and offers a new approach for visualization, interpretation and correlation of multi-source coastal data. Findings of this research are important for defining coastal hazards and have valuable applications for coastal planning and resource management.