Breakwaters
Breakwaters are offshore, shore-parallel structures, generally constructed of rock rubble piles that are emergent (above the water) even at high tide.. Their purpose is to literally “break the water” by stopping (not just attenuating wave action).
Many breakwaters are constructed to create a harbor, such as Dana Point Harbor shown here. Harbor breakwaters are generally attached to the shoreline at one end.
Breakwaters that are not attached at one end have also been used to shield beaches from wave action and erosion.
Breakwaters may not be the best answer for San Clemente
Breakwaters do an excellent job of protecting coastlines from wave action. In most cases, too good of a job. Usually a salient (a portion of the beach protruding outwards) forms in the lee of the breakwater. If the breakwater is very effective, the salient can extend out and connect with the breakwater, and then is called a tombolo (a geologic word based on the Italian for a sand bar). A tombolo can also occur naturally, as happens behind Morro Rock or the Venice Breakwater shown here.
If a tombolo forms, then it effectively cuts off down-coast transport of sand, and could cause sediment starvation in the down-coast direction.
Submerged breakwaters may be a better alternative
Submerged breakwaters — also called Artificial Reefs — could be a better nature-based alternative for San Clemente. These are discussed in the following section.