4.4 Biological Resources
expected unless sedimentation permanently buried a reef. Therefore, impacts to feather boa kelp were
considered significant if sedimentation was predicted to substantially bury reef, where the species occurs,
for several years.
Sea palms and sea fans also are considered relatively tolerant of physical stress, living in areas with very
strong waves and occurring from the low intertidal to subtidal. Their occurrence on low to high relief reefs
without interspersed sand patches suggests they may be less tolerant of sedimentation than surfgrass and
feather boa kelp. They also have a longer life span and take longer to reach sexual maturity. Given the
longer life spans of the species and suspected lower tolerance to sedimentation, impacts were considered
significant if sedimentation was predicted to substantially bury a reef where they occurred for greater than
one year.
Giant kelp forms persistent beds, but the extent of the beds may vary considerably year to year in response
to a variety of physical and biological stresses. Giant kelp, particularly in the microscopic and juvenile
stages, is considered highly sensitive to sand movement and disturbance and is one of the first species to
be eliminated under wave or sand scour stresses. Based on the naturally high seasonal variation in kelp bed
size due to a variety of factors, an impact would not be considered irreversible unless sedimentation
affected a substantial part of the historic kelp bed area and persisted such that recruitment potential would
be substantially affected.
Historic and Proposed Beach Replenishment Volumes. In the past 45 years, over 33 million cy
of sand has been artificially introduced to the Oceanside Littoral Cell, approximately 1.3 million cy of sand
has been artificially introduced to the Mission Bay Littoral Cell, and about one million cy has been
introduced to the Silver Strand Littoral Cell (Appendix D). Nearshore areas off Oceanside and Carlsbad
have been exposed to frequent and recent sedimentation from projects similar to, or in excess of, that
proposed with the Regional Beach Sand Project. This is also true for Imperial Beach. Less frequent
disturbance, but at similar to higher volumes, has occurred off Mission Beach. Areas that have been less
subject to sedimentation from beach replenishment occur between Leucadia and Torrey Pines.
Natural Sand Fluctuation. Beach profiles have been measured at various frequencies since the 1930s
at 50 transect locations between Oceanside and the U.S.Mexican border with most of the data being
collected since 1983. In shallow water the changes in sand level are related primarily to wave condition,
whereas changes in sand level in deeper water are more complex. Generally, larger waves in fall and winter
resulted in several feet of sand being removed from the nearshore and redeposited directly outside the cut
Regional Beach Sand Project EIR/EA
Page 4.4-29
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