Quantcast Impact of Long-Term Sea-Level Change

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Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 36
Preservation Strategy was the need to provide additional beach nourishment to
accommodate recreational demand, with the year 2040 total demand requiring an average
beach width of 325 feet.
Anthropic activities have also locally influenced rates of bluff-top retreat and bluff-slope
decline by uncontrolled and concentrated surface drainage, and by surface alterations
ranging from early farming to more recent residential bluff-top development (Kuhn and
Shepard, 1980; 1985).
In any assessment of future coastal erosion, one must address the impact of human
activity, and recognize that the historical database cannot simply be projected into the
future without considering human impact.
Human activities in the last 50 years have resulted in the progressive loss of the transient
sand beach, primarily from the cumulative effects of sand removal in the urbanizing
watershed. This has caused a dramatic increase in the rate of marine erosion not
previously observed during man=s initial habitation of the North County coastal area.
5.4
Impact of Long-Term Sea-Level Change
An entirely independent method of assessing the rate of coastal erosion is to consider long-
term (geologic) sea-level change, which is the major factor determining coastal evolution
(Emery and Aubrey, 1991). Sea level rise drives coastal erosion and has been discussed in
detail in Section 3.3.
Tectonic activity can also account for significant relative changes in sea level in a local area.
Past movement along the Rose Canyon fault zone and associated faults, which uplifted
Mount Soledad and formed Point La Jolla, also created a zone of structural weakness along
which the La Jolla Submarine Canyon has been incised. The Torrey Pines block, with its
relatively horizontally stratified Eocene-age formations and wave-cut terraces, has
experienced approximately 500 feet of tectonic uplift in the last 2,000,000 years, while the
tilted and uplifted Soledad Mountain block has undergone more than 800 feet of tectonic
uplift in the same period (Kern, 1977). The Eocene and Miocene shorelines shown on
Figure 12 show the major impact of tectonic sea-level change on shoreline erosion and
shoreline location (Howell and others, 1974). Differential tectonic uplift is responsible for



 


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