and large amounts of stone (during and after the
have been required to keep these jetties above mean high water (mhw). The
only remaining jetty with a concrete cap is the South Pass east jetty. Land-
ward extensions have been made to at least one jetty at the following
projects: Bayou Fontanelle (part of the Empire to the Gulf of Mexico Waterway
Projects), Grand Isle, Bayou LaFourche, and Calcasieu Pass. Plastic filter
fabric has been tested on sections of the jetties at Tiger Pass and Baptiste
Collette Bayou.
5. The structures are fairly low crested, being built or maintained at
to
ft mean low gulf
Typical design crown widths
elevations from
are from to 14 ft. Design side slopes were
on most of the older
(or
usually has been used on the newer designs
structures, while
and repairs. Cover stone sizes typically have been 1 to 6 tons with a maximum
of 1 tons used at the seaward ends of the South, Southwest, and Calcasieu
0
Passes jetties. Several of the more recent repairs and designs have called
for graded stone, typically 0 to 5,000 lb, placed by clamshell bucket. (The
stone.) Shell or
most recent repairs to Southwest Pass used 2- to
crushed bedding stone materials have been used as a core and bedding material,
acting as a filter layer for the larger stone. Advantages of shell are its
availability, lower cost than stone (per unit volume), and lower specific
gravity.
6. Seven of the projects have had repairs since they were constructed
originally (chronologically, the oldest projects). Southwest Pass jetties
have the most extensive repair history. South Pass jetties have not required
maintenance since 1970, and the channel has not been dredged since 1977. The
majority of repairs were needed due to overall subsidence of structures.
Steel sheet-pile jetties were constructed originally at Bayou LaFourche but
were badly damaged within a year and had to be supplemented at the base with
rubble stone. The projects at Grand Isle, Bayou LaFourche, and Mermentau
River have had direct involvement by local or State interests in either their
original construction or subsequent repairs.
General design of the structures has been concerned principally with
their settlement. The structures are not designed for hurricane conditions,
although they have been exposed to hurricane conditions in the Gulf of Mexico
since construction. None of the structures have been model tested for stone
slope stability. Hudson's equation and depth-limited wave heights are used
9
Previous Page
