San Onofre Nuclear Generating Station (SONGS):
Effect on Beaches and Bluffs
The object of the program was to assess the impact of the San Onofre Nuclear Generating Station (SONGS) construction on nearby beaches and bluffs.
The study conducted by CE provided basic information about the long-term oceanographic conditions at the site, including coastal setting, littoral cell processes, existing beach conditions, longshore transport of sand, rates of sand supply from local cliffs and rivers, wave climate, tides, sea level, rainfall, and drainage. This information was used to form the basis of preliminary projection of future beach behavior and an assessment of the probability of flooding the site with and without the current sea wall.
In 1964 and 1974, during construction activities at SONGS, coastal bluffs were excavated creating temporary laydown pads for protection against waves. The effects and transport of the sand pads were monitored from 1964 to 1994 and on 2001.
Coastal bluffs at San Onofre are composed of Quaternary marine and nonmarine sediments resting on Miocene marine rock. Locally the Miocene rock is faulted and highly sheared. The Pleistocene sediments are unconsolidated to poorly consolidated and form nearly horizontal layers. Locally, along the beach, and in gullies and canyons, perpendicular to the coast, the sediments form relatively steep to near vertical cliffs.
Historic records and review of aerial photos indicate the upper Quaternary sediments, that primarily compose the coastal terrace and sea cliffs, are erodible and subject to local surficial failures. Significant erosion and slope instability appears to be related to above average rainfall years associated with intense and prolonged rainfall and the rise of groundwater.
Natural sediment is delivered to San Onofre beaches and the inner continental shelf by local streams and erosion of coastal bluffs. Therefore, the bluffs are an important source of sediment for beach replenishment and protection. Beach and bluff changes have been monitored intermittently at San Onofre since 1945. Coastal bluff erosion is estimated to provide about 300,000 yd3/yr of sediment to southern California beaches annually.