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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
Terrace (190 Del Mar Shores Terrace). Also, gravel deposits were observed at the base of the
cliff below 629 West Circle Drive.
Artificial Fill
Compacted earth materials are encountered in the study area adjacent to the man-made
structures, such as seawall backfill, geogrid slopes, parking areas, riprap, and revetments.
They usually occupy relatively small areas along the coastline, except for the approximately
400-foot length of riprap below 190 Del Mar Shore Terrace.
Groundwater
Slight groundwater seepage was observed on the lower bluff face in the Torrey Sandstone in
areas of siltstone layers and lenses in several caves in the northern part of Solana Beach in July
2001. Groundwater also is found at Fletcher Cove immediately adjacent and north of the
existing stormwater discharge platform. No other areas of significant seepage were observed.
Groundwater is thought to be a main agent of subaerial erosion of coastal bluffs. Active
subaerial erosion usually occurs in areas supporting a flow of groundwater along the contacts of
lithologies of different permeabilities. Unlike in some other parts of the coast, the contact of the
primary Solana Beach cliff-former, Torrey Sandstone, with the overlying bluff top terrace
deposits, does not typically create a significant groundwater barrier. Subaerial processes may
have played an additional part in erosion of the channel fill deposits discussed in the previous
sections. Gaal and Kuhn (1985) indicated steady groundwater flow through the channel fill
exiting as seepage at the cliff below Del Mar Shores Terrace and Del Mar Beach Club
condominiums in 1976.
Groundwater flow in the lower sandstone cliffs occurs primarily along structural discontinuities
and is an important factor in cliff stability. Artim (1985) reports that examination of rock falls
after failure inevitably revealed the presence of water seepage near or at planes of failure.
The USACOE (1996) names the following as typical sources of groundwater: (1) natural
groundwater migration from highland areas to the east of the terrace; and (2) infiltration of the
terrace surface by rainfall, and by agricultural and residential irrigation water. Uncontrolled
irrigation water causes a rise in the water table, and, especially if accompanied by uncontrolled
surface runoff allowed to run over the bluff face, will promote slope failures and accelerate
erosion of the upper bluff.
Seismicity
San Diego is in a highly active seismic region. The San Diego area has experienced mild
earthquakes in recorded history, but none have been catastrophic. In 1964, three earthquakes
of magnitude 3.5 had epicenter locations in San Diego Bay east of the Naval Amphibious Base
(NAB) (City of Coronado, 1974). A magnitude 5.3 earthquake occurred 28 miles west of Solana
Beach on the Coronado Bank Fault in July 1986. With respect to local faults and fault zones,
Project No. 323530000
Page 3-10
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