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 City of Solana Beach
Section 3
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Environmental Impact Analyses
to the change of the upper-bluff slope angle from an original 60 to 90 slope to an
approximately 35 slope. This retreat is significant, episodic, and often incorrectly attributed to
marine processes.
It is necessary to make a distinction between short-term (historical, cyclic) and long-term
(geologic, chronic), and site-specific and average, rates of erosion. Most often reported short-
term rates vary from 0 to 1.3 feet per year for the California coastline (Gayman, 1985). High
rates of erosion are generally reported in the areas of seacaves, where the nature of erosion is
episodic and its short-term rate is extremely high for the narrow zone of the collapsed cave.
The average rate of erosion would vary greatly depending on a percent of the shoreline
occupied by, for instance, seacaves or less resistant formations. The rates tend to increase
greatly following heavy winter storms, such as the 1982-83 El Nino episodes (being 100-year
events according to USACOE estimates). In 1970, a seacliff base recession study was
conducted along a 21-mile segment of coastline from Leucadia to Point Loma (Artim, 1985). A
total of 93 monuments were monitored from 1970 to 1982. The average rate of retreat was
reported to be 0.04 feet per year, but may be as high as 0.5 feet per year. The predicted future
rates should be based upon accurate determinations of erosion covering both short- and long-
term periods (Gayman, 1985).
The need for high quality, unbiased data is presently well recognized (Gayman, 1985).
Accurate estimates of the past rates of shoreline erosion are needed both for future planning
and establishing setback requirements for new developments, as well as for evaluating the
necessity and efficiency of shoreline protective measures or other alternatives (Gayman, 1985).
Monitoring of coastal erosion through remote sensing may be a future possibility.
Analytical Methods
A very thorough discussion of the analytical methods used to assess relative rates of coastal
erosion is presented in the USACOE (1996) geotechnical report for the reconnaissance study of
the Encinitas shoreline. USACOE groups the methodologies in the following five general
categories.
Historical Analyses use historical records, such as maps, aerial photographs, surveys, and
such. This method is proven useful in assessing the short-term retreat rates over relatively
narrow study areas.
Geomorphic Analyses take into account all geomorphic processes to assess variations in the
shoreline erosion. For instance, along a relatively geologically uniform section of the coastline,
such as the Solana Beach coastline, a rate of bluff retreat can be assessed qualitatively based
on variations in shape of bluff profiles along the coast.
Analyses of Human Activities are necessary considering the enormous human impact on the
coastline for the past 40 to 50 years.
Project No. 323530000
Page 3-28
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