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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 32
5.2
Geomorphic Analyses
Geomorphic analyses include all factors that contribute to shaping coastal landforms.
Coastal erosion and coastal-bluff retreat are caused by both marine and terrestrial
processes. Surf action is usually the dominant marine agent producing both hydraulic
(wave) impact and abrasion. A basic understanding of the various geomorphic processes is
clearly a requisite to assess variations in shoreline erosion. Geomorphic analysis, including
coastwide geologic inventory, measurements of offshore bathymetry, and research to
determine historic climatic conditions permits assessment of likely future coastal erosion.
The relationships between the factors provide the coastal consultant the necessary tools for
evaluating future trends in coastal erosion.
Geomorphic factors that contribute to coastal erosion are mainly:
Climate. Long-term climatic and short-term meteorologic conditions
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produce large waves, the energy source causing coastal erosion. Storm
conditions may present a variety of wave directions, heights, and
frequencies.
Offshore Geology and Wave Energy. The amount of wave energy impacting
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a seacliff is locally controlled by the offshore seafloor bathymetry of the
shore platform, which is influenced by lithology and faulting. The shore
platform causes large, deep-water waves to break before reaching the
shoreline, thereby attenuating the amount of wave energy ultimately
impacting the seacliff. Variations in nearshore bathymetry also refract ocean
waves, locally focusing damaging wave energy onto certain coastline
segments (Munk and Traylor, 1947; Bradley and Griggs, 1976).
Clearly, the presence of Tabletop Reef shelters the northernmost portion of
the study area and causes refraction of incoming waves that may result in
increased erosion elsewhere along the coast.
Lithology and Structure of Coastal Bluffs. Lithology is the physical character
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of the rock, which provides the erosion resistance of the rock type.
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