ERDC/CHL CHETN-I-67
June 2003
was the important wave process that contributed to this result for typical daily wave conditions of
0.30 to 0.61 m (1 to 2 ft).
They found that waves traveling to the southwest were the worst-case conditions for waves in the
vicinity of the CD. CHL also found this to be true due to the geometry of the harbor and wave
Finally, OCTI believes that some of the locals' concerns about larger waves may come from locally
generated waves in the creek that travel to the south. This is a condition that may occur daily and
can produce waves as large as 0.61 m (2 ft). Unfortunately, the breakwaters at the harbor entrance
are not designed for waves from this direction, so no amount of gap closure would alleviate this
wave condition. Because these waves develop by the wind blowing over a suitable fetch length, the
only type of protection that could be afforded would require some type of jetty(s) along the northern
side of the entrance channel inside the harbor or a detached breakwater inside the harbor north of the
PP and/or CD.
SUMMARY: This technical note has described results from the CGWAVE numerical model study
for predicting wave heights in Tedious Creek Harbor, MD. A new breakwater was constructed with
an existing as-built gap of 122 m (400 ft) between the breakwater sections on either side of the
entrance. An authorized gap of 91 m (300 ft) was originally proposed, but not constructed due to
geological and construction concerns. Wave height predictions from the CGWAVE model were
compared between the two configurations.
A series of nine regular wave conditions with wave periods of T = 6, 10, and 16 sec, wave directions
of θ = 135 (NW), 180 (W), and 225 (SW) deg, and incident wave height of H = 1 m were selected as
representative wave conditions in Tedious Creek. Predicted wave heights were compared along two
transects (T1 and T2) from the breakwater entrance (BE) to the county docks (CD) and to the public
piers (PP) and 11 rectangular boxes in the vicinity of the CD (four boxes) and PP (seven boxes).
The two transects give a general overview of wave heights inside the harbor, but exhibit significant
variability due to the changes in water depth along each one. Averaging wave height in the smaller
boxes in the vicinity of the CD and PP provides a reasonable way of quantifying the differences in
wave energy in the areas of concern to the local residents.
For the existing configuration, larger wave heights occur to the north for northwest waves, to the
west and vicinity of the PP for west waves, and to the southwest and vicinity of the CD for
southwest waves. For both transects, the largest wave height was less than 0.78 m (2.6 ft) and the
average wave height was less than 0.31 m (1.0 ft). The maximum wave heights in any box for any
wave condition were less than 0.37 m (1.2 ft) and 0.30 m (1.0 ft) for the PP and CD boxes,
respectively. Finally, the 95 percent confidence intervals for average wave height inside all boxes
for all wave conditions are 0.16 0.02 m in the PP area and 0.16 0.03 m in the CD area.
For the authorized configuration, the narrower gap reduces waves traveling to the southwest more
than to the west along both transects. The difference in wave height for waves traveling to the west
and waves traveling to the southwest decreases as wave period increases, however. The effect of the
smaller gap was minimal on overall wave height reduction, in agreement with OCTI's results. The
largest wave height along the two transects was 0.86 m (2.8 ft), with an average slightly less than the
existing configuration. The difference in maximum wave heights is probably due to reflections at
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