San Pedro Bay Delta in Southern California: Shore and shore use changes during the past 1 (1/2) centuries from a coastal engineering perspective

摘要

The flood plain formed by detritus deposited by the Los Angeles, San Gabriel, and Santa Ana Rivers (and several streams) is a multi-river delta at the coast and shelf of San Pedro Bay, a hook-shaped bight in southern California. It is between Point Fermin (southeastern tip of Palos Verdes Hills) on the northwest and Newport Bay/Corona del Mar bluffs at the southeast. The 30-mile-long shore has been extensively modified by anthropogenic activities and by natural events; construction of dams for flood control (which also traps sediments), river mouth structures, ground subsidence owing to oil, gas, and water withdrawal; structures and dredging at the entrances of landlocked bays; development and operation of marinas and navigation channels; and encroachment by buildings and infrastructure. Sand beaches are along almost the entire shore: Long Beach Municipal Beach, Belmont Shore Beach, Seal Beach, Surfside Beach, Sunset County Beach, Bolsa Chica State Beach, Hun-tington Cliffs, Huntington City Beach, Huntington State Beach, Santa Ana River Mouth County Beach, West Newport Beach, Balboa Beach. The sand is light in color, and is mostly silicate. The beaches and surf are easily accessible and extensively used by residents and visitors. The natural supply of sediment to the coast became severely restricted, and beach erosion studies have been made since the 1930s. There have been extensive beach nourishment (replenishment) projects for many decades that have successfully mitigated negative effects of sedimentrntrapping, coastal structures, and ground subsidence. Beach profile surveys and "Clancy beach width" measurements made during many decades were used to evaluate the effectiveness of the Surfside-Sunset beach project (including West Newport Beach). The wave climate in the Southern California Bight is complex. Six different meteorological patterns are the sources of the waves; they include North Pacific storms, local seas. and southern swell that have traveled thousands of miles from storms in the south 40 to 50 deg. latitudes. The waves are affected (refraction, diffraction, reflection, shoaling) by the islands, banks, submarine canyons, and local bathymetry of the California Continental Borderland. Sources of wave measurements, analysis, storage, and retrieval are given. The region is subject to storm waves, floods, droughts, seawater intrusion. earthquakes, and tsunamis; some details of which are given. Damages caused by several severe wave events are described. A coastal lowland/wetland that was substantially impacted in the past century was restored recently, the Bolsa Chica Low lands Restoration Project. Its history and restoration (a modification of the original) is described. The largest U.S. seaport complex, by volume, is in the northwest part of San Pedro Bay. the contiguous Los Angeles and Long Beach Ports/Harbors: with 9.2 miles of breakwaters (in three sections with two navigation entrances). The region has become extensively urbanized; it is part of the Los Angeles (coastal) megacity.