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San Pedro Bay Delta, in Southern California Shore and Shore Use Changes During Past 1-1/2 Centuries from a Coastal Engineering Perspective

  • Author(s): Wiegel, Robert L.
  • et al.
Abstract

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 Bayl Corona del Mar bluffs at the southeast. The 30-mile long shore has been extensively modified by anthropogenic activities and by natural events which are described; 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 (Alamitos, Anaheim, Newport), development and operation of marinas and navigation channels, 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, Huntington 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 (quartz and some feldspar). The beaches and surf, which are easily accessible, are popular 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 1930's; these are documented. There have been extensive beach nourishment (replenishment) projects for many decades which have successfully mitigated negative effects of sediment trapping, coastal structures, and ground subsidence. Dates, quantities and sources of the sediment placed as nourishment are given. 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, 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 Lowlands Restoration Project. Its history and restoration (a modification of the original) is described. The largest seaport complex in the USA, 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 3 sections, with 2 navigation entrances). The region has become extensively urbanized; it is part of the Los Angeles (Coastal) Megacity.

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