01/30/2009
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CSE
–S&W–DEW [DRAFT]
Accreted Land Management Plan
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2253 [30 JANUARY 2009]
Town of Sullivan’s Island, SC
6.0 MANAGEMENT ALTERNATIVES
The team of CSE–S&W–Dewberry has evaluated the accreted land (AL) area of Sullivan’s
Island and has described its history, present condition, and expected future changes with
respect to the shoreline, dunes and vegetation, as well as the flood potential under 10-year
and 100-year storm events. The AL area comprises nearly 190 acres of low dunes and swales
that have formed within the last ~70 years. Excess sand supplied by way of littoral transport
from Isle of Palms and Breach Inlet accounts for the buildup of the AL area. Average shoreline
change has been ~10 ft/yr with the likelihood of continued accretion through 2050 even under
probable SLR scenarios (Kana et al 1984, IPCC 2007).
Regardless of the future rate of accretion, the existing land is expected to remain stable (with
occasional flooding and inundation during major storm events) and to continue to support a
diverse vegetative community. With upward of nine distinct vegetation habitats, from grass-
lands to forests, there will be a continued shift from pioneering, low species (eg – dune
grasses) to shrub vegetation and, ultimately, maritime forest.
The future transformation of the AL can be seen by visiting the east and west halves of the
area (Fig 6.1). Land west of the Charleston jetty (referenced as Reach B herein) accreted rap-
idly between the 1940s and 1970s and is well established today. Its predominant vegetation
is early maritime forest with a dense canopy of trees reaching more than 40 ft in height. By
comparison, the eastern half of the AL (Reach C – east of the jetty) did not begin accreting
rapidly until the 1970s. As a result of its younger age, vegetation tends to be dominated by
shrubs and small trees reaching heights of the order 15–25 ft. Pruning along some sections
of Reach C has maintained a shrub/tree height of the order 5–10 ft. If left to natural succes-
sion processes, Reach C will likely look much like Reach B two or three decades from now.
Nearby undeveloped barrier islands also offer examples of how the Sullivan’s Island AL will
look decades from now. Bull Island and Capers Island exhibit densely vegetated beach ridges
extending over 1,500 ft inland (Fig 6.2). Both of these islands have been erosional during
much of the 20
th
century (Kana and Gaudiano 2008). However, in earlier times, accretion
allowed similar vegetation succession. Interior sheltered areas representing former shorelines
were transformed from grasslands to maritime forest, and the forest continued to mature long
after the accreted shorelines began to retreat. This, of course, accounts for situations where
mature trees can be seen perched along eroding escarpments or littering the beach with their
exposed root masses (Fig 6.2). In short, the AL is sufficiently wide to provide sheltered interior
areas where trees can mature over many years before erosion poses a direct threat to the
land.