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Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 18
3.2.3 Wave Setup
Wave setup results from superelevation of the water surface over the normal surge
elevation due to onshore mass transport of the water by wave action alone. Wave
setup is a function of both the stillwater level, and the elevation and slope of the
shore platform. For the San Diego area, the typical maximum range in wave setup
would likely vary from 2 to 1 foot, which would be added to the extreme water
elevation resulting from storm surge and astronomical tide.
3.2.4 El Nio
Large-scale, Pacific Ocean-wide warming periods occur episodically and are related
to the El Nio phenomenon. These meteorological anomalies are characterized by
low atmospheric pressures and persistent onshore winds. During these events,
average sea levels in southern California can rise up to 0.5 foot above normal. Tidal
data indicates that six episodes (1914, 1930 through 1931, 1941, 1957 through
1959, and 1982 through 1983, and 1997 through 1998 - mild El Nio-type
conditions were also reported in 1988 and 1992) have occurred since 1905.
Further analysis suggests that these events have an average return period of 14
years, with 0.2-foot tidal departures lasting for two to three years.
The added probability of experiencing more severe winter storms during El Nio
periods increases the likelihood of coincident storm waves and higher storm surge.
The record water level of 8.35 feet, MLLW, observed in San Diego Bay in January
1983, includes an estimated 0.8 foot of surge and seasonal level rise (Flick and
Cayan, 1984), which set the stage for the wave-induced flooding and erosion that
marked that winter season.
3.2.5 Design Stillwater
For design of coastal structures, a conservative high sea level is determined that
accounts for all of the factors that may increase sea level during the design life of
the structure. This should include tides, storm surge, wave setup, and the increase
in sea level that may occur during the design life of the structure. For the Solana



 


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