ERDC/CHL CHETN-III-66
June 2003
During the initial photogrammetric survey in January 1982, 111 dolosse distributed over the two
jetties were targeted to determine armor unit movement through photogrammetry. In addition,
photogrammetric maps were developed and plotted on transparent drafting material. They
documented the location, orientation, and elevation of about 57 percent of the armor units placed on
the jetties. The remaining dolosse were underwater or beneath the top layer of dolosse and not
visible in photography. A survey in September 1983 indicated that 65 percent of the targets were
within 0.09 m (0.3 ft), and 91 percent were within 0.3048 m (1.0 ft), of their initial positions. The
maximum vertical change was a drop of 1.28 m (4.2 ft) on a dolos at the head of the south jetty. The
largest horizontal displacement was nearly 1.83 m (6.0 ft) on the channel side of the south jetty head.
It was noted that storm events had occurred during the period between January 1982 and September
1983. A survey conducted in March 1984 revealed that the mean vertical displacement for all points
monitored on the two jetties was 0.05 m (0.15 ft), and only 10 percent of the monitored dolosse
experienced detectable horizontal movements, the largest of which was about 0.3048 m (1.0 ft) when
compared with the September 1983 data. This was a relatively storm-free period. Between March
and May 1984, the mean vertical displacement of all monitored dolosse was 0.14 m (0.46 ft).
Approximately 3 percent moved in excess of 0.3048 m (1.0 ft) vertically, with a maximum value
indicating a 0.61-m (2.0-ft) drop. The largest horizontal displacement was 2.13 m (7.0 ft) at the head
of the south jetty. Altogether, about 9 percent of the monitored dolosse moved in excess of 0.61 m
(2.0 ft) horizontally, with 31 percent moving up to 0.61 m (2.0 ft). About 60 percent experienced no
detectable horizontal movement. During this period (March through May 1984), an intense coastal
storm affected the mid-Atlantic states and exposed the jetties to what was believed their design wave
heights. A walking survey in May 1984 revealed four broken dolosse on the north jetty at the head
of the structure and one broken unit on the south jetty located near the head on the channel side of
the structure. Despite exposure to the design storm wave event, only five of the 1,326 dolosse
(0.4 percent) used in the 1982 rehabilitation had broken. Of the five broken units, only one had
experienced a horizontal displacement in excess of 0.61 m (2.0 ft) from its initial location. Others
had moved up to 2.13 m (7.0 ft), yet had not broken. This finding suggested that impact may be
more important than movement in dolos breakage. An armor unit may experience significant
impacts even with only small movements.
The May 1994 photogrammetric survey indicated that the targeted dolosse on the north and south
jetties had been dynamic since the initial monitoring ended in 1984. Horizontal movement had
ranged up to 2.01 m (6.6 ft) and vertical displacement (subsidence) as much as 1.62 m (5.3 ft).
Dolos movement on the north jetty was slightly greater than those on the south. From 1984 to 1994
about 73 percent of the targeted units on the north jetty and 86 percent of the units on the south jetty
had moved less than 0.3048 m (1 ft). Conversely, about 13 and 4 percent of the north and south jetty
units, respectively, had moved distances greater than 0.91 m (3 ft). With regard to el changes
between 1984 and 1994, 93 percent of the dolosse on the north jetty and 95 percent of those on the
south structure had subsided. Between 1984 and 1994, the average movements of horizontal and
vertical targets on the north jetty were 0.2743 m and 0.2438 m (0.9 ft and 0.8 ft), respectively; and
on the south jetty the average movement was 0.1828 m (0.6 ft) both horizontally and vertically. The
1994 broken armor unit survey revealed 17 broken/cracked dolosse as opposed to five in1984. Of
the broken/cracked units, nine were located on the north jetty and eight were situated on the south
structure. Pieces of the armor units were separated on 10 dolosse. Four dolosse were broken and
being held together by rebar, and four had only hairline cracks. Considering the types of breaks, the
majority (10 units) had shank-fluke breaks. There were five mid-shank breaks and two fluke-shank
breaks. There were nine angled breaks and eight straight ones. Fifteen of the 17 units were
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