Table 2. Comparison between measured and predicted total longshore transport rate

zone 16 m from the shoreline (Figure 4). In this case, inner surf zone wave height is significantly

less than observed for Tests 1 and 3. The average beach profile of Test 1 was used as the initial

profile for Test 5, and little change occurred between the two profiles. During Test 5, erosion

occurred shoreward of 9 m from the shoreline and sand was deposited between 10 and 12 m from

shore, and seaward of 13 m. Figure 5 shows wave transformation and the beach profile formed

during Test 6. Waves shoaled to 0.21 m, 12 m from the shore, where heights sharply decreased.

Wave heights in the inner surf are similar to those of Test 1 and Test 3. A subtle breakpoint bar

formed under the plunging wave conditions.

Total longshore transport rate was computed by summing the sediment flux measured in all of

the traps. Measured transport rates are given in Table 2 along with the predicted values from

Equations 1 and 2. If the recommended K-value of 0.39 is used, the CERC formula (Equation 1)

over-predicts measured values from the spilling cases by a factor of 8 for Test 1 and nearly 7 for

Test 5. Estimates are greater than a factor of 3 for both plunging wave cases. The CERC formula

produced similar estimates for Test 1 and Test 3 because they have similar wave heights, although

breaker types differed. Measured transport rates were nearly 3 times greater for Test 3 (plunging)

than Test 1 (spilling). Results using Kamphuis (1991) (Equation 2) produced more consistent

estimates with the measured data; differences ranged between one percent for Test 1 to 25 percent

for Test 5. The improved estimates of Kamphuis (1991) can in part be attributed to the incorporation

wave period into Equation 2, which influences breaker type.

Table 2. Comparison between measured and predicted total longshore transport rate

CERC Formula (K=0.39)

Kamphuis (1991)

Experiment

Measured

m3/yr

Number

2,660

22,030

2,680

7,040

23,850

5,920

1,170

7,940

880

3,410

12,770

3,410

The results indicate that in addition to wave height, breaker type is a factor in estimating

longshore transport rates. Kraus et al. (1982) identified four different cross-shore distribution

patterns of longshore sediment transport from field measurements. Sunamura and Kraus (1985)

commented that the wave conditions during the experiment were a combination of spilling and

plunging breaker types.

Considering the role of breaker type in longshore transport rates, the CERC formula was

evaluated based on breaker type. If measured transport rates from Test 1 are used to calibrate the

CERC formula, K = 0.049. Applying this coefficient to the wave conditions of the lower energy

spilling case (Test 5) gives a transport rate of 1060 m3/yr, or a 9 percent difference from the

measured rates. Likewise, if the CERC formula is calibrated using transport rates from Test 3,

K = 0.119. Applying this coefficient with wave conditions of the lower energy plunging case

(Test 6), a transport rate of 3760 m3/yr is calculated, which is 10 percent of measured rates. The

Smith et al