Friday, April 04, 2014
The Santa Monica littoral cell extends from Malibu south to the Palos Verdes Peninsula, shaping the western beaches of Los Angeles. As elsewhere on the southern California coast, sediment transport is generally from the northwest to the southeast.
Historically, the beach at Santa Monica was supplied by Malibu Creek and a number of other small streams in the northern part of the cell. These are streams dominated by big, but widely-spaced, flood events and sediment was probably delivered in big slugs. Development has altered runoff and more importantly, led to the construction of flood and debris control systems that trap sediment before it reaches the coast.
The Santa Monica Pier marks a significant geomorphic transition. To the north, the coast is backed by bluffs cut into a marine terrace composed of alternating marine and alluvial sediment. To the south, the bluffs disappear and the coast morphs into a long barrier beach (although this may be a little hard to see through the overprint of development). More on this in the next post on Venice Beach.
Early pictures of the bluffs show them eroding onto a relatively narrow beach. Perhaps at times in the past they were also a potential source of beach sediment? But the bluffs are now separated from the ocean by the Pacific Coast Highway and a wide beach created decades ago through some major nourishment projects.
An early breakwater - apparently part of a scheme to develop a boat basin (there have been some grand plans for the Santa Monica coastline that never materialized). The initial effect of the breakwater was for a salient (bulge) to develop on the beach behind it, but that feature is barely perceptible now that the breakwater has subsided and the beach has been widened so much by nourishment. The breakwater can still be seen in the aerial view and, if you look carefully, off the end of the pier in the photo below.