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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 34
rule. The age of the slope can be estimated from the angle of the slope
(Wallace, 1977).
As part of the aging process, the near-surface portion of the bluff develops a
weathering profile (pedogenic soil) that may form on at least part of the
slope. The relative development of the weathering profile is thus an
indicator of slope age. For coastal bluffs, the rate of marine erosion of the
seacliff limits the development of a weathered soil horizon on the upper
sloping surface.
5.3
Anthropic Influences
Human activity significantly influences shoreline changes, both directly, by erosive activities
along the bluff top and seawall building at the base of the bluff, and indirectly, exemplified
by the pervasive impact of activities in the upland watersheds, such as periodic burning of
surface vegetation by fires, the construction of dams and sand mining.
Until recently, longshore transport annually moved on the order of 200,000 to 300,000
cubic yards of sand through the Oceanside Littoral Cell, which encompasses some 52
miles of coastline terminating at the La Jolla Submarine Canyon (Nordstrom and Inman,
1973; USCOE, 1987, 1991). Under these natural conditions, a relatively persistent sandy
beach was maintained since available longshore transport energy was not sufficient to
cause a long-term beach deficit. It has been estimated that about 500 to 900 feet of
shoreline erosion has occurred in the Solana Beach area in the last 6,000 years. This
erosion occurred in the presence of beaches maintained by abundant sediment sources
from rivers and the coastal bluffs themselves.
Since the 1940s, approximately 40 percent of this sediment-producing watershed has been
dammed (Nordstrom and Inman, 1973; COE, 1987, 1991), and concurrently large
volumes of river sands have been mined from the lower reaches of North County rivers for
use in the construction industry. This human activity in the last 50 years has resulted in a
pervasive long-term sediment deficit (Inman, 1976; USCOE, 1991). The current sediment
deficit has essentially denuded the shore platform of sand, resulting in an underwater
topographic environment somewhat different than what has typically existed in recent
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