FIGURE 6.2 Large-scale landsliding along the Humboldt County, California, coast at Centerville. SOURCE: Copyright 2002–2012 Kenneth & Gabrielle Adelman, California Coastal Records Project, <www.Californiacoastline.org>.
Cliff and bluff erosion is not reversible. The most common human response has been to armor the cliff base with rock revetments (Figure 6.3) or seawalls (Figure 6.4). Ten percent of the California coastline has now been armored, including 33 percent of the coastline of the four most developed southern California counties (Ventura, Los Angeles, Orange, and San Diego; Griggs, 1999). Shoreline armoring also has increased over the past several decades in Oregon and Washington. Approximately one-third of the Puget Sound shoreline is now armored (Shipman et al., 2010). Despite this protection, coastal storm damage has increased over the past several decades because of intense development and the occurrence of a number of severe El Niño events, raising questions about the long-term efficacy of existing coastal protection structures (Griggs, 2005; Shipman et al., 2010). Moreover, while seawalls and revetments may provide current protection for oceanfront development and infrastructure, they are usually designed for a particular set of wave and sea-level conditions. If sea level increases substantially and wave heights continue to increase, the original freeboard will be gradually exceeded and overtopping will become more frequent.
Beaches respond quickly to the forces acting on them as waves and littoral currents easily move the sand. Along the west coast, beaches change seasonally in response to the different winter and summer wave climates. These fluctuations in beach width are predictable and temporary, and the losses of sand experienced each winter are normally recovered the following summer. Longer-term fluctuations in beach widths associated with the El Niño-Southern Oscillation and the Pacific Decadal Oscillation (PDO) also have been documented in southern California (Orme et al., 2011).