Kuriyama-Ozaki (K&O) Data
Kuriyama and Ozaki (1993; "K&O") carried out field measurements of
the longshore current at Hazaki Oceanographical Research Facility (HORF)
located on the Japan Pacific coast. The HORF research pier is 427 m long,
and the current measurements were made from the HORF pier by using a
float (compare Kraus and Sasaki 1979). The float measurements were
calibrated by comparing them with those from an electromagnetic current
meter. The beach at HORF, having a mean slope of 1/60, often includes
several longshore bars, leading to complex wave transformation with
shoaling, breaking, and reforming taking place.
Measurements were carried out for 4 years starting on 5 January 1987. If
bars where present, the measurements showed that 85 percent of the time the
peak in the longshore current distribution was on the shoreward side of the
bar crest. Kuriyama and Ozaki (1993) presented three cases of the longshore
current measurements in detail, taken during March and April 1989. The
significant wave height was also given at a few cross-shore locations based
on measurements with ultrasonic wave gages. Here, one case recorded on
28 March 1989 will be employed to test the capability of NMLong-CW to
simulate the current over a complex beach profile. Wave measurements
carried out in the offshore at a water depth of 23.4 m served as input to
NMLong-CW, and the significant wave height was Hs = 2.6 m and significant
wave period Ts = 8.86 s. The wave angle at breaking was observed along the
pier, and for input to the model an angle was selected in the offshore (α =
27 deg in the water depth 23.4 m) that produced the measured value at the
point of observation. A representative beach profile was obtained by taking
the average of five profile surveys along lines located around the pier (lines
spaced 10 m apart over a total distance of 50 m). This averaging produced a
more smoothed beach profile shape than, for example, the individual profile
surveyed along the line that spanned the pier (appeared to be somewhat
modified by scour).
Figure 42 shows the calculated (with and without the roller model) and
measured distribution of the longshore current together with the
representative beach profile. Two longshore bars are identified with a
marked trough in between. Breaking on the seaward side of the bar yields
two peaks in the longshore current distribution, in agreement with the
measurements. The seaward-most peak has the correct magnitude, but is
located somewhat seaward of the measured peak, whereas the shoreward-
most peak is a bit higher than the observed one, although in the correct
location. Addition of the roller model significantly improves agreement with
parameter was set to Λ = 1.0.
Figure 43 compares calculated and measured significant wave height.
The significant wave height was computed in the same manner as for the
CHL-I data. The entire series of waves from the Monte-Carlo simulation was
saved at each cross-shore location, and the significant wave height was
determined as an average for the one-third highest waves. At the two most
seaward measurement locations, the calculations markedly overestimate the
recorded heights. This is probably because the energy dissipation for the
waves propagating from the offshore to the profile in the nearshore being
modeled is underestimated (for example, friction in the bottom boundary
63
Chapter 6 Verification of Longshore Current Model
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