1.0 Introduction
Beach sand is a product of weathering of the land. The primary natural source for the region's beaches
is sediment carried from inland areas by rivers and streams. Over the past half century, human actions have
been the major influence affecting the shoreline. Through urban development activities, including water
reservoir and dam building, flood control systems and sand mining, natural sediment transport has been
hindered or eliminated. Most major coastal streams have at least one dam and reservoir. Much of the
fresh water that naturally flowed to coastal wetlands is diverted to farms and cities. These dams reduce
the size of flood flows and thus reduce the flushing of sediment from estuaries. They also trap sand that
would otherwise nourish coastal beaches. This beach sand is the primary buffer protecting seacliffs and
coastal development from erosion and storm damage. To offset the loss of natural sand sources no longer
reaching the shoreline, previous projects have built "manmade"beaches. Most of the sand for this purpose
has come from the massive harbor dredging projects in San Diego Bay and Oceanside Harbor. While the
likelihood is low that sources of sand as large as these dredging projects will be available in the future, sand
replenishment projects would help to offset the gradual thinning and disappearance of the region's beaches;
loss of environmental, recreational, economic, and aesthetic benefits; and the increasing destruction of
coastal property and development.
The natural sand cycle is a seasonal process. Typically for the San Diego region, beach sand loss occurs
in the winter due to large storms and waves, followed by a period of sand gain during the summer's gentler
storms and surf. During the winter, sand shifts from the beach above the mean sea level to the larger
portion of the beach offshore covered by seawater. These combined seasonal processes, including both
winter and summer sand shifts, comprise a complete sedimentation cycle.
A coastal segment that contains a complete sedimentation cycle is defined as a littoral cell. It is the dynamic
interface between the ocean and the land. Along the San Diego region's coast, there are three littoral cells
that cycle sand on and off the beaches (Figure 1-2). Bounded on one side by the landward limit of the
beach and extending seaward beyond the area of breaking waves, a littoral cell is the region where wave
energy dissipates. Littoral cells are physically interconnected; occurrences in one part of a littoral cell will
ultimately have an impact on other parts. The three littoral zones off of the San Diego region include the
southern half of the Oceanside Littoral Cell, the Mission Bay Littoral Cell, and the Silver Strand Littoral
Cell. The southern half of the Oceanside Littoral Cell stretches from Oceanside to La Jolla1 and includes
the shorelines of the cities of Oceanside, Carlsbad, Encinitas, Solana Beach, Del Mar, and San Diego. The
Mission Bay Littoral Cell includes Ocean, Mission, and Pacific beaches in the City of San Diego. The
1
The northern half of the Oceanside Littoral Cell extends from Oceanside to Dana Point in Orange County.
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Regional Beach Sand Project EIR/EA
99-69\SANDAG EIREA 3.4.wpd 7/17/00
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