Table 27
George Island Jetties
George Island, Florida, SAM
Date
Construction and Rehabilitation History
In
local interests cut a channel through
George Island to
1957
provide a direct route to the Gulf from Apalachicola (Figure 4 )
In April 1957 the Corps completed the existing projects with the
construction of two rubble-mound jetties on the Gulf and dredged the
channel to a depth of 1 ft (Figure 43, inset). The east and west
0
jetties, 900 and 1,030 ft long, respectively, and spaced 400 ft
apart, were built out to the -10 ft mlw contour. Approximately
70 ft of the landward end of each jetty flared away from the chan-
nel. The design cross section (Figure 43, inset) had a crest width
of 14 ft, a crest elevation of
ft mlw, and
side slopes.
On the seaward end of each jetty the side slopes changed to
via a 100-ft-long transition section. Minimum cover stone sizes
were 6 and 1 tons on the trunk and
0
sections, re-
spectively. The core stone weighed from 25
to 2 tons, and the
2- to 2.5-ft-thick foundation blanket used 15- to 200-lb stone. The
stone size was selected using Hudson's slope stability formula, a
ft mlw storm surge level.
maximum wave height of 13.7 ft, and a
Figures 44a and 44b are photographs of the jetties taken before and
shortly after the completion. "Keyhole" erosion on the landward
side of the jetties (the jetties and the crescentic erosion yielding
the silhouette of a giant keyhole) can be seen in the
tion photograph
The jetties and channel were surveyed in early 1977. The east jetty
showed substantial l o s s of material over 250-ft section at the
1978
ward end, the outer 50 ft was at or below mlw, and the remainder
ft mlw. The landward 350 ft of the east jetty
varied from
to
ft mlw except for the flared portion which was
was typically at
ft mlw. The west jetty was in good condition except for minor
at
to
ft
sections and the landward 150 ft which varied from
mlw. In 1978 the jetties were rehabilitated. A total of 4,700 tons
of 3- to 6-ton cover stone were placed as required at low sections
to bring the jetties up to the previous design elevations.
1985
The jetties are presently in good condition. The major problem, at
present, is the keyhole erosion that has been removing material at
an apparently constant rate since jetty construction (and is ex-
pected to continue). The proposed solution is to purchase title to
additional land on both sides of the channel.
78
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