Figure 94. Total LST rates computed with and without corrections to account for anomalous volume change adjacent to the downdrift boundary for the plunging-breaker case

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correction seems to be greatest just after the beach is remolded. The anomalies

in beach bathymetry appear to develop quickly after the beach is remolded, and

then with time, a near-equilibrium condition seems to develop in which the

anomalies don't grow as fast, or grow very little. Note the lower magnitude of

the correction prior to remolding that was done after T1h_case3, and the large

correction immediately thereafter in T1h_case4 and T1h_case5. Also note the

trend for the magnitude of the correction to decrease between the tests,

T1h_case8 and T1h_case10, after the beach was remolded prior to T1h_case8.

A similar result was found for the plunging-breaker case (Figure 94). The

beach was remolded prior to case T3g, and with subsequent runs, the magnitude

of the correction decreased. Again, the magnitude of the correction was as much

as 25 percent of the total volume that accumulated in the traps. For run

T3g_case3, malfunctions of the profiler precluded computation of corrections to

the trap weights.

Repeatability of LST Rates

Results shown in Figures 93 and 94 also illustrate the degree of repeatability

that can be expected in estimates of the total LST rate. Total transport rate

estimates for the spilling breaker case ranged from 2,350 to 2,950 m3/yr. Of the

nine estimates made under what were essentially the same forcing conditions, six

fell in the range from 2,600 to 2,850 m3/yr. The mean value for all estimates is

about 2,700 m3/yr, which implies that estimates of total LST are repeatable, to

within 10 to 12 percent, and more likely within about 4 to 6 percent for this wave

condition.

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Chapter 10

Longshore Sediment Transport Experiments