HR: 0800h
AN: H41C-0321    [Abstracts]
TI: Regional Long-term Coastal Change in Southern California
AU: * Hapke, C J
EM: chapke@usgs.gov
AF: USGS Pacific Science Center, 400 Natural Bridges Dr., Santa Cruz, CA 95060 United States
AU: Reid, D
EM: dreid@usgs.gov
AF: USGS Pacific Science Center, 400 Natural Bridges Dr., Santa Cruz, CA 95060 United States
AU: Weber, K
EM: kkonicki@usgs.gov
AF: USGS, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Morgan, K
EM: kmorgan@usgs.gov
AF: USGS Florida Integrated Science Center, 600 4th St. South, St Petersburg, FL 33701 United States
AU: Morton, R
EM: rmorton@usgs.gov
AF: USGS Florida Integrated Science Center, 600 4th St. South, St Petersburg, FL 33701 United States
AU: Sallenger, A
EM: asallenger@usgs.gov
AF: USGS Florida Integrated Science Center, 600 4th St. South, St Petersburg, FL 33701 United States
AB: The USGS National Assessment of Coastal Change project addresses issues that include the impact of severe storms, identifying coastal vulnerability, and the effects of potential accelerated sea-level rise. One of the principal tasks is to calculate long-term shoreline change rates using a method that is consistent and repeatable at a national scale. We have undertaken the analysis of the open-coast shorelines for California, Oregon and Washington. Methodologies that have already been developed for the Gulf of Mexico are applied to the West Coast and modified where necessary to adjust to the differences in coastal geomorphology between East and Gulf Coast-type shorelines and the variable geomorphology of the West Coast. In addition to measuring coastal change along linear and sometimes dune-backed beaches, the methods must also incorporate the means to measure long-term change along narrow beaches backed by cliffs, pocket beaches and headlands, and high-relief stretches of coast. For the completed analysis of Southern California, the dataset includes nearly 150 historical maps dating back as far as the mid-1800s. In addition, lidar data, collected for the entire U.S. West Coast in 1998, is used in the analysis. Three coastal change reference features are used for the Southern California analysis: high water line and mean high water shorelines for the sandy beaches, and the cliff edge. The long-term shoreline change rates for Southern California, generated using a linear regression method on four shorelines, are surprisingly low for a region that is generally thought to be experiencing widespread erosion. Our analysis for an approximately 120-year period shows that only 6% of the 277 km of coastline analyzed is undergoing long-term erosion, at an average rate of 0.4ñ0.2 m/yr. This pattern changes somewhat in the last 25 years, where the percent of eroding coastline increases to 21% and the average erosion rate is 1.1ñ0.2 m/yr. The highest erosion rates are in the northern portion of the region near Santa Barbara, and to the south near Oceanside. The completed cliff erosion rates for San Diego County indicate that of the 53 km of the coastline that are backed by cliffs, 34% are experiencing erosion at an average rate of 0.4ñ0.16 m/yr. Both the beach and cliff erosion analyses provide a regional perspective of coastal change trends for Southern California that had not previously been available and initial results suggest that the general trend is not long-term shoreline erosion.
DE: 4546 Nearshore processes
DE: 3020 Littoral processes
DE: 1800 HYDROLOGY
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting