ERDC/CHL CHETN-III-65
March 2003
Figure 2. View of Burns Harbor north breakwater trunk
el +12 in July 1999 versus 65.5 m (215 ft) (4.6 percent) in July 1994. In July 1999, concentrations
of low areas occurred between stas 8+40-15+65 and 30+70-37+80, however, sporadic areas of low
elevation were noted along the length of the structure. Both the 1994 and 1999 surveys revealed the
crest width less than the el 17 design and steep slopes (steeper than the 1V:1.5H design) on the
harbor side of the structure. A broken armor unit survey conducted during July 1999 revealed
225 broken or cracked armor stones above the waterline (versus 165 in July 1995). Of the 225
stones, 34 were located on the breakwater crest, 96 on the lake-side slope, and 95 on the harbor-side
slope. About 42 percent of the broken stones were observed on both the lake- and harbor-side slopes
in 1999 versus 57 percent on the lake side and 27 percent on the harbor side in 1995. The survey
revealed that between 1995 and 1999 most of the additional breakage occurred on the harbor-side
slope. The percent of broken armor units on the breakwater crest remained relatively constant at 15
to 16 percent for both surveys. In 1999, about 44 percent of the broken armor stones were located on
the eastern one-third of the breakwater versus 50 percent of the broken stones in 1995.
To minimize further breakwater damage and reduce transmitted wave heights in the harbor, a
submerged reef breakwater was constructed lakeward of the north structure during the construction
seasons between June 1995 and August 1998 by the U.S. Army Engineer District, Chicago. The
1999 periodic inspection of the breakwater not only determined changes in the armor unit field since
the previous survey, but established new base conditions since construction of the submerged reef
breakwater. Subsequent inspections will evaluate the effectiveness and analyze the performance of
the improved project.
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