January 13, 2004
14:36
WSPC/101-CEJ
00094
544
W. C. Seabergh & N. C. Kraus
sand tight to a length of 1,052 m, began in July 1978 and was completed in August
1980. Figure 7 shows the dual-jetty project. The bulbous right shoulder of the inlet
formed after construction of the south jetty, when wave activity was reduced in that
location. Previously, much sediment would enter the interior Banks Channel after
passing over the weir (interior channel at top of Fig. 7) and settle there to be dredged
for beach nourishment of Wrightsville Beach. Thus the deposition basin region was
not capturing sediment as designed because the sand typically moved over the weir
at the swash zone. This sand eventually formed a spit and required vessels entering
the inlet to make sharp turns in strong crosscurrents to remain in the navigation
channel. However, by using the sand spit as an extended deposition basin area, the
USACE Wilmington District has only had to dredge the deposition area every 3
to 4 years, and the dredging also keeps the spit from further encroaching into the
navigation channel [Government Accounting Office (GAO) 2002].
3.1.3. Ponce De Leon Inlet, Florida
Prior to 1968, Ponce De Leon Inlet had functioned as a natural passage through
the barrier islands separating the Atlantic Ocean from Halifax River and Indian
River North. The inlet became recognized as difficult and dangerous to navigate
with controlling depths over the ebb shoal of typically 1.2 to 1.8 m (King et al.,
1999). During 19681972, two rubble-mound jetties were constructed to provide safe
passage via a 4.6 m deep by 61 m wide dredged channel. The north and south jetty
have overall lengths of 1,234 m and 1,242 m respectively. A 549 m long weir of king
piles and adjustable concrete beams were constructed along the north jetty. The weir
section consisted of a 91 m landward length at +1.2 m mlw elevation, and seaward
a 457 m length at 0.0 mlw elevation. An impoundment basin to entrap material
Fig. 8. Ponce de Leon Inlet, Florida. Construction completed in 1972. Weir is located on the top
(north) jetty. Note spit development and channel migration into deposition basin in 1976.
Figure 8. Ponce de Leon Inlet, Florida. Construction completed in 1972. Weir is located on
the top (north) jetty. Note spit development and channel migration into deposition basin in
1976.
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