improved rates are illustrated in Figure 6, which shows calculated versus measured transport rates
using the CERC formula with calibrated K-values. Additionally, CERC formula estimates using
K = 0.39 and estimates from Kamphuis (1991) are included. The figure indicates that the Kamphuis
equation, which includes wave period, which influences breaker type, predicts measured rates well,
and the CERC formula gives reasonable estimates if K is calibrated, and it is applied to similar
breaker types.
25000
K=0.39
Calibrated K
Kamphuis (1991)
Pf
P di i
20000
15000
10000
5000
0
0
1000
2000
3000
4000
5000
6000
7000
8000
Measured Transport Rate (m3/yr)
Fig. 6. Comparison of calculated to measured transport rates
Cross-Shore Distribution Of Longshore Transport Rate
Ongoing research in the LSTF includes investigation of the cross-shore distribution of longshore
sediment transport. Longshore sediment flux was calculated from the rate of sand collected in each
trap, and plotted as a function of distance from the shoreline in Figure 7 for the experiments listed in
Table 1. The figure indicates that there are three distinct zones of transport; incipient breaking zone,
inner surf zone, and swash zones.
Incipient Breaking Zone
At incipient breaking, a substantial peak in transport occurs for Test 3, the higher-
energy plunging-wave case. However, an increase in transport is not observed in the other three
cases. The absence of peak in transport for the spilling cases can be explained as a function of
breaker type. Turbulence associated with spilling breakers remains close to the surface in the bore.
The jet associated with the large plunging waves penetrated deep into the water column, impacting
the bed, and caused sand to be suspended and transported by the longshore current (Wang et al.,
2002b). It is interesting that a peak is not evident with Test 6. A possible explanation is that the
approach slope to the breakpoint bar is much gentler than observed in Test 3, and the waves are
weakly plunging. Further research will investigate the amount of sediment suspended, and thus made
available for transport by longshore currents at the Test 6 breaker line.
Smith et al
9
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