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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
Impact of Long-Term Sea Level Changes is considered when long-term rates of erosion are
evaluated.
Empirical and Analytical Techniques are numerical models developed to assess shoreline
erosion rates. The brief overview of these techniques is given in USACOE, 1996. The
landward long-term seacliff base retreat may be estimated based on the shelf-slope method and
littoral lens method (Zeiser Kling, 1994). A short-term landward retreat of a seacliff base may
be estimated for any beach width for a single storm of a certain recurrence interval using the
probabilistic method of Everts, 1991. The long-term down wearing (or vertical scour) rate of the
platform may be estimated as approximately 0.02 to 0.04 times the horizontal seacliff retreat
rate (Zeiser Kling, 1994).
The methodology used for the USACOE study was applied for the study of the northern part of
the Solana Beach shoreline by Group Delta (1998) and may be recommended for future
studies.
Rates of Retreat of the Solana Beach Coast
A summary of the geologic erosion rates and measurements of coastal bluff retreat, based on a
review of available geologic data, is presented in Table 3.1-2.
Everts (1991) developed an empirical method for the estimate of the long-term mean annual
rate of seacliff base retreat for the Oceanside littoral cell. The rate is considerably greater for
the cliffs more susceptible to wave attack due to the lack of protective beach buffer. The
historical beach profile data may be used to estimate seacliff erosion rates. The USACOE
survey in the Solana Beach area north of Fletcher Cove indicated that 100 feet of sandy beach
that existed during the 1957-60 survey disappeared by 1988. Using the Everts (1991) method
and the reasoning outlined in Zeiser Kling (1994) for similar conditions in the Encinitas area, a
mean long-term rate of retreat at Solana Beach corresponding to a mean long-term beach width
of approximately 80 feet, and a zero width beach, equals a retreat rate of 0.2 feet per year, and
0.36 feet per year, respectively. Erosion rates presented by reaches accepted from Group
Delta (1998) are presented in Figures 2-1 through 2-7.
Benumof and Griggs (1999) correlated long-term erosion rates for the Solana Beach Reach
obtained for FEMA's project (discussed in the previous section) with the quantitatively
characterized physical properties of the cliff-forming materials and erosional mechanisms
(primarily wave conditions). They concluded that, at Solana Beach, seacliffs are composed of
relatively high intact rock strength material and are relatively resistant to erosion; Solana Beach
cliffs are rated similar to the La Jolla cliffs composed of the older sandstones and siltstones.
Geological structure, particularly joint orientation, is of great importance for the seacliff stability.
Benumof and Griggs (1999) specifically noted for Solana Beach that even though large storm
waves occurring at high tides are particularly effective in causing basal cliff erosion, wave
energy reaching the cliff base is significant also during low tide conditions. They also concluded
that more resistant Solana Beach type cliffs do not contribute a significant amount of sediment
to the beach system.
Project No. 323530000
Page 3-29
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