percent of the total transport. Additionally, the reduction in total transport between the higher and
lower spilling cases (Test 1 and Test 5) was a factor of 2.8, but the reduction in swash transport was
only 1.4. The reduction in total transport between higher and lower plunging cases (Test 3 and
Test 6) was 2.2, but the reduction in swash zone transport was again only 1.4. Although data are
limited, this implies that swash zone transport contributes more to the total transport rate for smaller
scales, and conversely, as incident wave height increases the contribution of swash transport to total
transport is less. The results indicate that the contribution of swash zone transport can be significant,
and total longshore transport estimates should account for transport in this region.
In addition, results from the present study have implications to field measurements of longshore
transport. Although swash zone transport measurements are difficult to obtain in the field, the results
indicate that it is necessary to include swash zone transport to obtain accurate measurements of total
longshore sediment transport. For example, if swash zone transport is neglected in the present study,
the overestimates of the CERC formula increase by 50 to 250 percent.
SUMMARY
Measurements of longshore transport rates were performed in a large-scale physical model for
four incident wave conditions that varied by breaker type and incident energy. Measured transport
rates were compared to estimates computed using the CERC formula and Kamphuis (1991)
equation. Additionally, the CERC formula, in particular the coefficient K, was evaluated. It was
found that the CERC formula overestimated measurements by a factor of 7 to 8 for spilling breakers,
and more than a factor of 3 for plunging breakers. The CERC formula is not sensitive to breaker
type, which was found to be an important factor to total longshore transport rates. If the coefficient K
of the CERC formula was calibrated using measured data and applied to similar breaker types,
differences were reduced to 10 percent or less. Estimates using the Kamphuis equation, which
includes wave period, that influences wave breaking, were good with differences ranging from 1 to
25 percent. The findings indicate that total longshore transport rate is a function of breaker type, and
the CERC formula performs well if K is calibrated and applied to wave conditions having similar
breaker type.
The cross-shore distribution of longshore sediment transport indicated three distinct zones of
transport: the incipient breaker zone, the inner surf zone, and the swash zone. A peak in transport
occurred for the higher energy plunging waves in the incipient breaker zone, indicating that the
breaker type suspends more sediment for transport. Transport in the inner surf zone was near
constant for three of the four wave conditions, indicating that energy is saturated and transport is
controlled solely by depth. The exception was lower-energy spilling waves. Swash zone transport
accounted for a significant percentage of the total transport, and future relationships should
incorporate swash zone transport.
ACKNOWLEDGEMENTS
The authors wish to acknowledge William Halford, David Daily, and Tim Nisley who provided
technical support for this study. The authors wish to thank Bruce Ebersole for review and thoughtful
discussion on the paper. Ping Wang was jointly funded by the U.S Army Engineer Research and
Development Center and the Louisiana Sea Grant College Program. Permission to publish this
abstract was granted by the Headquarters, U.S. Army Corps of Engineers.
Smith et al
11
Previous Page
