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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 20
Continuous sea level records exist from a tide gauge in San Diego Bay beginning in 1906,
and from a gauge at La Jolla beginning in 1924. Figure 8 shows a plot of yearly mean sea
level at La Jolla based on data published by the National Ocean Service (NOS). The
straight line represents a least-squares fit of the data and indicates a mean rate of sea level
rise of 0.64 feet (19.5 centimeters) per century. The shaded areas above the trend line
correspond to above-average sea level episodes corresponding to major El Nio events
(Quinn, et al., 1978). The highest sea levels in La Jolla were observed on January 29, 1983
(7.71 feet MLLW), and August 8, 1983 (7.81 feet MLLW). These episodes were part of a
run of El Nio and storm-influenced extreme events that occurred during the 1982-1983
storm season. [The 8.35-foot extreme tidal level recorded in San Diego Bay during this
same period is due to the tidal amplification that occurs within the sheltered bay location.]
Considerable effort has gone into estimating future sea level rise, as this has a significant
impact on coastal erosion. The Marine Board Committee on Engineering Implications of
Changes in Relative Mean Sea Level, under the direction of the National Research Council,
has conducted extensive studies evaluating future changes in sea level (Marine Board,
1987). Representatives of Scripps Institute of Oceanography in La Jolla also participated
on the Marine Board . The Marine Board=s best estimate for local relative sea level changes
affecting San Diego was 16 centimeters per century, taking into account crustal
subsidence/uplift. The Marine Board further concluded that tide gauge records contained
substantial long-period fluctuations (5-100 years), which indicate that accurate
extrapolation of small sea level rise values from the data is very difficult. Determining
changes in rates of rise is even more difficult. Figure 9 has been reproduced from the
Marine Board study, depicting sea level elevations versus time for relatively stable crustal
areas. One should not lose sight of the fact that, excluding the relatively recent sea level
records that have been measured for at most the last 90 years, the majority of future sea
level predictions are predicated on relatively coarse sea level data extending back for
thousands of years before the present.
The reality is that estimated future sea level rise is critically important to estimating future
shoreline erosion, as sea level rise drives coastal erosion. Given a known rate of sea level
rise, in its simplest form, the amount of erosion in a given time is equal to the amount of
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