Table 30 (Continued)
Date
Construction and Rehabilitation History
The total cost of the repairs was 9,300. These repairs were
1962
required to prevent continued erosion (up to 60
in places) of
(Cont)
the channel banks and possible flanking of the jetties. In general,
to
ft mlw and
the top elevations for the jetties varied from
mlw. (The seaward 80 to 1 0 ft of each had
0
averaged about
subsided to the extent that they were not considered active parts of
the jetties.) Prior to the repairs, about 85 percent of the jetty
wing extensions were below design grade, and there were several
Thus, because of insufficient height
beaches below mhw
and general permeability of the design cross section, waves passed
over and through the jetty extensions causing continued bank ero-
sion. The maximum width of the "keyhole" cut was 3,000 ft, and the
width of land between the Gulf and jetty embayments was 500 and
250 ft on the east and west sides, respectively. Hydrographic sur-
veys made from time to time showed that severe erosion was taking
place along the toes of the jetties and their extensions. The loss
of bottom material, as great as 30 ft in sections, was undermining
the jetties and was felt to be the major cause of jetty subsidence.
Also, a possible factor in the subsidence of the jetty extensions
was that these sections were placed without any foundation blanket
material. For these reasons the repairs incorporated a foundation
blanket and a wider cross section with smaller core material and
were placed on the landward sides since smaller quantities of stone
were required and the potential for undermining would be less. At
this time it was suggested that an experimental berm (toe apron) of
stone be placed along a section of one of the jetties where under-
mining was occurring. This section would be periodically monitored,
and its effectiveness in arresting the undermining could be
evaluated.
A 100-ft-long experimental rock berm was placed along the toe of the
1965
west jetty wing (beginning 30 ft landward of the jetty angle and
extending landward). The berm was approximately 5 ft thick, 40 to
and was composed of
60 ft wide, had a design side slope of
A
well-graded quarry stone varying in weight from 100 to 2,000
total of 1,710 tons of stone was placed at a cost of ,600. The
berm was monitored by underwater inspections and surveys for
18 months following placement. During this time the berm maintained
its integrity, even along sections where scour was evident.
jetty consisted of placing 10- to 15-ton
1966
Rehabilitation of the
existing structure. The outer 80 ft of the original structure (con-
sidered destroyed) was not repaired. The toe berm was placed along
the seaward 650 ft of the channel side (and included the existing
100-ft-long experimental berm) and along the seaward 200 ft of the
(Continued)
(Sheet 4 of 6)
90
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