January 13, 2004
14:36
WSPC/101-CEJ
00094
546
W. C. Seabergh & N. C. Kraus
were constructed at a cost of .4 million. The north jetty, 1,053 m long, consists of
a 171 m long shoreward jetty trunk; a 411 m long armor stone weir section (crest
elevation +0.7 m mlw, set at mean tide level) (Weggel, 1981); a 503 m long seaward
jetty trunk; and a 46 m long head section. The north jetty (with the exception of
the weir section) and the south jetty are built to an elevation of 2.7 m above mlw.
The south jetty, 1,012 m long, consists of a 966 m long trunk and a 46 m long head
section. Also, a 2.4 m wide fishing walkway was constructed on the crest of the jetty
to an elevation +3 m mlw. Sand dikes composed of dredged material tied the jetty
roots into the existing dune lines. The seaward parallel sections of the jetties were
183 m apart with an entrance channel 91 m wide and 3.7 m deep at mlw between
them. The deposition basin was dredged to a depth of 6.1 m mlw with a capacity of
459,000 cubic meters. It was dredged adjacent to the low weir section of the north
jetty (Perry, Seabergh, and Lane, 1978). More than a million cubic yards of sand
from these two dredging projects were pumped to adjacent beaches.
The dominant direction of longshore transport was assumed to be southerly
when the inlet project was designed (Douglass, 1987), and the weir section was
placed on the north jetty. As of 1985, the jetties had no history of damage or repair
and appeared to be functioning properly (Sargent, 1988). Spit growth into the bay
along the inlet shoulder illustrates the usual path of sediment transport coming
over a weir. Predominant waves and longshore current move fine sand along the
swash zone, generating spit growth around the north shoulder of the inlet. Sediment
enters the shoreward portion of the deposition basin. The ebb current also carries
sediment from the edge of the spit entering the interior navigation channel into
the bayward end of the deposition basin, as can be noted in Fig. 9. According to the
USACE Charleston District, the project has performed better than expected because
planned 3-year maintenance dredging has been needed only once since the project
was built. District staff states the channel through the inlet has been kept open
primarily by the flushing action of the current flowing through the jetties (GAO,
2002). The shoreline adjacent to the weir has receded an average of 0.6 m/year since
1981.
3.1.5. Mouth of the Colorado River, Texas
The mouth of the Colorado River tended to skew to the west (left in Fig. 10), most
likely a response of the channel to spit growth from the east. As part of navigational
improvements dating 19881990, two rubble-mound jetties were constructed at the
mouth of the Colorado River, providing protection for the 4.6 m deep, 61 m wide
entrance channel, that discharges to the Gulf of Mexico. The west jetty is 442 m
long, and the east jetty, which contains a rubble-mound weir, is 808 m long. The
east jetty weir section begins 125 m from the landward end and extends 305 m
seaward. The crown elevations of the weir section and remaining jetty sections are
0.0 m and +2.4 m, mlw, respectively. The seaward ends of the east and west jetties
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