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 Solana Beach Coastal Preservation Association
August 20, 1998
Project No. 1831
Page 48
were evaluated, specifically addressing the distance to the failure scarp from both the top-
of-slope and from the face of the lower near-vertical seacliff. Factors of safety are also
shown for the various slope geometries. Recognizing that upper bluff failures propagate
in much the same fashion as that shown on Figure 10, slope geometries exhibiting factors
of safety greater than 1.25 should be viewed as unsusceptible to upper-bluff failures.
Recognizing also that progressive collapse of the bluff top is episodic in nature, only those
areas where relatively steep upper bluffs currently exist are susceptible to bluff-top
collapses, triggered by either progressive marine erosion undermining the lower seacliff, or
from other subaerial factors.
8
SHORELINE AND COASTAL BLUFF PROTECTION
The progressive loss of the transient sand beach, resulting from the cumulative effects of
sand removal in the urbanizing coastal watershed, has caused a dramatic increase in the
rate of marine erosion, with the majority of the study area experiencing upwards of 8 to 10
feet of retreat in the last 15 years. Marine erosion has typically manifested itself in the
formation of sea caves and/or notches, where the notch or overhang eventually collapses
once it extends beyond bluff-parallel fractures in the Torrey Sandstone, typically on the
order of 6 to 10 feet back from the face of the cliff. Although the formation of sea caves
may appear to be more problematic, they have more inherent stability than the notch due
to their arching effect. The notch without the benefit of any subjacent lateral support
shears off as a large slab, as has occurred throughout the majority of Reach 4. Significant
failures within the lower sea cliff have undermined and destabilized the base of the upper
sloping terrace deposits, with some of the worst upper-bluff failures below the lots at 261,
367, and 371 Pacific Avenue. Elsewhere, where significant notches still remain, as in the
vicinity of 205 to 231 Pacific Avenue, and 235 to 265 Pacific Avenue, additional failures will
further destabilize the upper bluff (as in the vicinity of 255 to 265 Pacific Avenue) and
otherwise destabilize an area that is currently relatively stable (211 through 231 Pacific
Avenue).
The 1997-98 El Nio storm season has caused significant erosion of the coastal bluff
throughout the study area; however, a serious problem still remains. With the almost total
loss of the protective sand beach in this area, these sea cliffs continue to experience a
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