A sand budget for the Santa Barbara Littoral Cell, California

The coastline of California has been divided into a set of distinct, essentially self-contained littoral cells or beach compartments. These compartments are geographically limited and consist of a series of sand sources (such as streams and eroding coastal bluffs), that provide sand to the shoreline; sand sinks (such as coastal dunes and submarine canyons) where sand is lost from the shoreline; and longshore transport or littoral drift that moves sand along the shoreline. A regional understanding of littoral cell boundaries and sand budgets can be an important tool in coastal engineering and land-use management decisions. Many harbors function as efficient sediment traps, such that average annual long-term dredging volumes should be a valuable tool for approximating littoral drift rates at specific locations within littoral cells, as well as changes in these rates over time due to natural or human impacts on the sediment budget. The Santa Barbara Littoral Cell contains three harbors with long-term dredging records and essentially unidirectional littoral drift, which provide an excellent opportunity for testing this concept. The littoral drift rates determined using this approach show a significant downdrift increase (from ~ 300,000 yds3/yr at the Santa Barbara harbor to ~ 1,000,000 yds3/yr at Channel Islands harbor) and are compatible with the fluvial sediment input and other components of the littoral sediment budget. Despite the damming of the four major rivers discharging into the Santa Barbara Cell, and the apparent reduction in fluvial sediment supply, there has been no systematic or significant reduction in the dredging rates at any of the harbors. Long-term dredging rates can provide useful and valuable information for better quantifying littoral cell budgets and also for documenting changes in these cells.