Fig. 12. Za. Test 6N: distribution of regular wave height

Hamilton_Ebersole_ce_2001
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13

magnitude of the longshore current at x s 4.1 m at

transect Y31 is caused by the small flow reversal

region further upstream, close to the shoreline. It is

interesting to note that just offshore of the peak

longshore current, the measurements suggest a slight

flattening of the longshore current distribution. This

observation is qualitatively consistent with the pre-

sent understanding of the interaction of the undertow

with the longshore current, see Putrevu and Svend-

sen Z1992..

Fig. 13 quantifies longshore uniformity of the

hydrodynamic processes in the irregular wave exper-

iment. As was found for the regular wave case, all

three hydrodynamic parameters tend to approach a

minimum asymptote, once the length of the testing

region is reduced to approximately 12 m, starting at

Y19 and extending upstream to Y31. The values of

the standard deviation in the irregular wave experi-

ment are significantly less than in the regular wave

experiment, especially for the wave and current data.

Perhaps the regular wave forcing generates a basin

response that does not occur when using irregular

wave forcing.

Fig. 14ac illustrates the high degree of longshore

hydrodynamic uniformity for the irregular wave case.

Fig. 14a shows that the significant wave height is

very uniform in the alongshore direction. The signifi-

Fig. 12. Za. Test 6N: distribution of regular wave height. Zb. Test

6N: distribution of mean water surface elevation. Zc. Test 6N:

distribution of mean longshore current.

Fig. 12b shows that the longshore variation in mean

water surface elevation is approximately "0.0015

m. This value is comparable to the elevation toler-

ance of the bridge support rails. Therefore, it can be

Fig. 13. Test 8E: longshore uniformity of hydrodynamics.