Beach Width and Climate Oscillations along Isla Vista, Santa Barbara, California

摘要

Santa Barbara County beaches adjacent to the University of California, Santa Barbara (UCSB), and Goleta Beach, 11 mi west of the Santa Barbara harbor, suffered dramatic erosion during the El Nino events of 1982-83 and 1997-98 and never fully recovered. This study analyzed a 70-yr record of beach width changes along a 9-km shoreline segment near Isla Vista, California. Results show an oscillation in beach widths as opposed to a long-term narrowing as predicted based on sand supply reductions. The oscillations of beach width relate to different phases of the Pacific Decadal Oscillation (PDO) Index. During positive PDO phases, El Nino-like patterns of increased precipitation and stream flow narrow beaches while during negative and calmer, drier PDO phases, beach widths widen. Results also indicate significant variability in the beach widths along the study area. Parts of the Isla Vista, UCSB, and Goleta Beach shorelines show significant changes to beach widths, the majority of these areas (59%) correspond to shore protection structures or other human alterations. Significant narrowing of beach widths over the 70-yr record were observed at 77% of the transects intersecting shore protection structures, primarily because of placement losses. El Ninos play an important role in decreasing beach widths (widths narrow by >50%) with all of the narrowest beaches occurring after the major events of 1982-83 and 1997-98. The 1982-83 El Nino was the key event resulting in the largest beach width changes, especially along Isla Vista, UCSB and Goleta Beaches, where beach widths have never recovered to pre-1982-83 levels. Beach widths following the 1997-98 El Nino did recover to post-1982-83 levels. The volume of sand removed from the beaches during the 1982-83 event was estimated to be around 385,000 ml From 1993-1995, sand volumes dredged annually from Santa Barbara harbor show a 74% increase above long-term averages (230,000 m~3/yr) which match the volume loss at UCSB and Goleta Beach, providing some evidence of a 1.7-km/yr (1 -mi/yr) alongshore transport rate of littoral sands. Including beach width measurements in shoreline change assessments provides additional information on beach processes, storm response, and human alterations that can aid coastal management decisions.