Long-Term Volumetric Sediment Contribution from Landslides: Big Sur Coastline, California

Along the Big Sur coastline in central California, the rugged Coast Ranges descend abruptly into the Pacific Ocean, creating one of the most extreme coastal slopes in the conterminous United States. Weak rocks and steep topography provide ideal conditions for frequent large landslides, which contribute a substantial portion of material to the overall littoral sediment budget. Little is known about the nearshore sediment budget in this area, including the amount, rate and frequency of input to the system from coastal landslides. Adjacent to the Big Sur coastline is the Monterey Bay National Marine Sanctuary (MBNMS), a protected area of coastal waters and home to a variety of aquatic species. The California Department of Transportation (Caltrans) is exploring solutions to the problems faced with keeping slide-prone coastal Highway 1 open and safe while minimizing impacts to the MBNMS below the road. As a contribution to developing a highway management plan, and in order to advance the fundamental understanding of processes along this stretch of coastline, we have developed a technique to quantify the historic volume of sediment that enters the littoral system from coastal slope failures. A pilot study was conducted as a means to test and refine the technique along the Big Sur coastline. Digital photogrammetry is used to produce Digital Terrain Models (DTMs) from historical and recent aerial photography. The DTMs are then subtracted to quantify amounts and identify areas of volume loss and gain along the coast during the period spanned by the aerial photographs.