Coastal Processes: Cabrillo Beach, CA

Cabrillo Beach is named for the first European, Juan Rodriguez Cabrillo, to sail up the California coast. Originally this area was a rocky beach and wetland area, but this began to change with the construction of the San Pedro Breakwater in 1899. Sand was added to the area after the completion of the breakwater. Local residents liked this new beach, and Cabrillo Beach officially opened to the public in 1928. Shortly thereafter, the first grunion run was spotted.

Image from: Los Angeles City Lifeguard Association

The new Cabrillo Beach consisted of three beaches, all in one location: an Inner Beach, located inside the breakwater; an Outer Beach, located outside the breakwater and facing the open ocean; and a Natural Beach, a remnant of what the area looked like prior to 1899.

Breakwater: A breakwater is a structure = typically made of rocks) that is designed to protect a harbor or coastal area from waves. The result is a quiet water environment with low energy, minimal waves and no longshore current.

Wind Waves: are formed as wind moves over the ocean’s surface, causing the energy to be transferred from the atmosphere to the water. Friction causes the water to move ever so slightly to the right. Thus, wave trains move slightly to the right of the wind direction.

Sand movement along beach
    Swash and backwash – As waves move onshore = swash), they bring a bit of sand with them; as they pull back = backwash), they take a bit of sand with them. This zig-zag, back and forth motion of the waves and sand is called longshore drift.

    Longshore current - is a current that moves down beach and is caused by waves hitting beach at angle. It flows parallel to the shore and transports sediments down the coast.

Submarine Canyons: These canyons form in the continental slope as the result of river erosion. The ocean is not moving compared to the river, so when a river enters the ocean it carves a gouge in the continental shelf and slope. When the longshore current encounters a submarine canyon, the sediment in the current is funneled down the canyon and into the deeper parts of the ocean. In this way excess sand is removed from the coastal region.

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