ERDC/CHL CHETN-I-67
June 2003
CGWAVE SENSITIVITY: Because the local interest was in the areas near the CD and the PP, two
transects (T1 and T2) were selected between these two facilities and the breakwater entrance (BE).
Figure 4 shows the orientation of these two transects for both existing and authorized model layouts.
The T1 is 481 m (1,579 ft) long between the CD and the BE and T2 is 673 m (2,207 ft) between the
PP and the BE.
The CGWAVE model has options to include bottom friction (BF) and wave breaking (WB). The
first step in the model calibration was to run some test cases to quantify their effect on the predicted
wave heights H inside the harbor. Thus, the T = 6 sec waves traveling to the west (i.e., θ = 180 deg)
were run for base cases (a) without BF or WB (none), (b) with WB only, (c) with BF only, and
(d) combined BF and WB (BFWB).
Figure 5 shows the wave height predictions along T1 and T2 for each of the four sensitivity
parameter combinations. As expected, wave height was larger for the "none" case (i.e., linear mode)
without BF and WB. Of course, in the linear mode, model predictions would be unrealistic as these
two wave phenomena are present in nature and would naturally limit the wave heights. Inclusion of
BF was more significant than WB. Even though the difference between BF and BFWB was slight, it
was decided to include the combined effects of both phenomena in comparison of the two
configurations.
with three wave gages (Figure 6). A NORTEK Aquadopp directional wave gage (PUV-type)
measured incident wave conditions outside the breakwater in an average depth of 2.2 m (7.2 ft) mlw.
Two unidirectional pressure gages measured transformed wave conditions inside the breakwater in
1.7 m (5.6 ft) mlw (Gage 215) and 1.3 m (4.3 ft) mlw (Gage 212). Gage 215 lay on transect T1. The
sampling frequency was 4 Hz, with a sampling interval every 3 hr, for all three gages.
Figure 7 is a time series of incident wave period, significant wave height, and wave direction.
Measured PUV wave directions were converted from wave direction from which waves travel,
measured clockwise from north, to CGWAVE conventions. Figure 8 shows transmitted wave
heights for Gages 212 and 215. Since this was a milder time of the year and there were no major
storms, incident wave conditions were fairly benign (i.e., in the range of T = 2 to 5 sec, Hs < 0.5 m,
and average wave direction of 118 deg or waves traveling to north-northwest. The transmitted wave
heights were even smaller, with a maximum of 0.31 m (1.1 ft) and averages of 0.06 m (0.2 ft).
Because these waves were small, it was difficult to compare them to CGWAVE predictions. A few
limited comparisons were made and are shown in Figure 9 for the two transmitted gage locations.
Measured incident wave parameters ranged from 2.03 ≤ T ≤ 4.75 sec, 0.07 ≤ Hs ≤ 0.27 m, and 135 ≤
θ ≤ 221 deg. An attempt was made to select the largest wave period and height combinations. An
equivalent significant wave height and exact wave period and direction were used as input to
CGWAVE. The model predictions were averaged over a 30-m (100-ft) square box around each field
gage location (Figure 6) to allow for location anomalies and the contouring algorithm in the model.
Considering that CGWAVE was designed for wave periods of the order of 5 sec or larger, the
agreement was good.
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