D.G. Hamilton, B.A. Ebersole r Coastal Engineering 42 (2001) 199218
concluded that there is no measurable longshore
gradient in the mean water level in this region. Fig.
12c shows that the degree of uniformity in the mean
longshore current is quite good. The reduction in
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-
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
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.