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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
Alternative 4 Planned Coastal Retreat
An assessment of the rates of the coastal erosion along the southern California coastline in
general, and along the Solana Beach segment in particular, is a very complex task. The rates
vary greatly along the coast, depending upon the variety of natural geological and hydrological,
oceanographic, meteorological/climatic, and other processes operating in the natural (prior to
development) coastal environments. Furthermore, in highly developed coastal San Diego
County they are greatly influenced by anthropogenic (man-induced) factors, such as
construction of the structures interfering with the sand supply, over-irrigation and improper
drainage, disturbance of the natural soil and vegetation cover, and others. The southern portion
of the Solana Beach coastline is especially heavily developed with high-density condominium
complexes built during the 1970s. Some of the condominiums constructed prior to Proposition
20 of the California Coastal Zone Conservation Initiative of 1972 were built as close as 5 feet
from the edge of the bluff.
After 1972, when geologic reports became a requirement prior to the development of the coastal
areas, retreat data reported for the coastal San Diego County are controversial and incomplete.
The low quality data were often attributed to the lack of understanding of the processes causing
the erosion, as well as the bias on part of the private consultants favoring a certain point of view
(Gayman, 1985).
Very few scientific studies with the objective of measuring erosion rates were conducted in the
area. In 1983, the National Ocean Survey (NOS) section of the National Oceanic and
Atmospheric Administration (NOAA) conducted a study of the southern California coastline
based on detailed cartographic data over the past 100 to 130 years. Unfortunately, the
produced maps were too controversial. Part of the problem was in plotting errors, lack of
adjustments for seasonal changes, and errors in elevations. In some areas, the shoreline
known to be erosional (losing sand) was interpreted to be accretionary (gaining sand) based on
NOS data.
In 1994, the state-of-the art softcopy photogrammetric and geographic information system (GIS)
imaging laboratory (Coastal Geology and Imaging Laboratory, CGIL) at University of California
Santa Cruz (UCSC), funded by the Federal Emergency Management Agency (FEMA), used
high-precision mapping techniques to determine accurate long-term recession rates along the
San Diego County coastline by eliminating mapping errors (Benumof and Griggs, 1999). A
mean bluff recession rate for the Solana Beach segment was reported to range from 0.19 to
0.36 feet per year.
It is important to understand the mechanics of the coastal erosion to accurately evaluate its rate.
As it was discussed in the previous section, a typical Solana Beach seacliff is formed primarily
by two geologic formations: Torrey sandstone in its lower part, and the Bay Point Formation
terrace deposits comprising its upper part, or bluff. Retreat of the resistant lower cliff occurs
mainly due to the wave action and marine erosion. Erosion of the relatively soft Bay Point
Formation, which lies generally beyond the reach of wave action, is caused primarily by
subaerial and other non-marine processes. The edge of the bluff thus recedes significantly due
Project No. 323530000
Page 3-27
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