A NORTHERN CHANNEL ISLANDS HISTORICAL SHORELINE ANALYSIS THROUGH GIS

Global climate change is increasing global sea level at an accelerating rate. It is estimated that more than half the world population lives and works within 200 km of the coast, therefore projected increases in sea level rise will endanger livelihoods through exposure to storm surges, saltwater inundation, and increasing rates of erosion. Historical shoreline analyses can be used to understand how coastlines have evolved to present conditions, and inform how they may change under increased sea level in the future. Previous studies on historical shorelines analysis have focused on soft-sediment, human-modified coastlines, in which erosion has been identified as a problem, and analysis is performed in order to inform engineering and development projects. Therefore the Northern Channel Islands were chosen as a study site representing a hard-sediment, unmodified coastline in order to understand natural dynamics between geology, hydrology, and resulting coastal morphology. A historical shoreline analysis of the Northern Channel Islands was conducted through the Digital Shoreline Analysis System extension of ArcGIS in order to understand the effects of sea level rise on island morphology over time. It was determined that sea level does not control island size, as Santa Cruz, Santa Rosa, and San Miguel Islands experienced significantly different amounts of change over the 84 year study period (ANOVA, F2,85=6.522, p=0.002). Santa Cruz Island experienced erosion at a rate of 0.16 ± 1.13 meters/year, Santa Rosa Island exhibited net accretion at a rate of 0.015 ±1.0 meters/year, and San Miguel Island had the greatest amount of change with a rate of erosion of 0.72 ± 1.64 meters/year. In order to understand the variation between the islands, the geology, the direction of waves relative to shore, and area of watersheds were analyzed as factors to understand the differences, but statistically none of these variables were significant. Nonetheless, The DSAS analysis indicates that contrary to public conception, sea level rise is not the dominating control on the Northern Channel Islands rate of change on the century time scale. Future historical shoreline analysis should examine longer data sets of hard sediment coasts in order to further elucidate physical controls on island and coastal dynamics.