Figure 82. Beach morphology after nearly 10 hr of wave activity for the plunging- breaker case (elevations are in meters)

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perturbation is greatest in magnitude and in terms of extent from the boundary.

The perturbation influences the orientation and crest elevation of the bar in this

region. A peak in the longshore transport distribution existed in the vicinity of

the bar for the plunging-breaker case. As was found for the spilling-wave case,

the magnitude and alongshore extent of the erosion perturbation was greatest in

areas where the LST rate was highest. For the plunging wave case there is

erosion of the shoreline along the updrift boundary, and the upper beach slope

contours are narrowed, as was seen for the spilling wave case. Foreshore and

shoreline erosion perturbations appear to extend further downdrift than was

observed in the spilling-breaker case, approximately to the 30-m alongshore

coordinate, consistent with the fact that high transport rates were evident in the

swash zone for the plunging-breaker wave case.

Unlike the spilling-breaker case, no well-defined undulatory morphologic

features existed at the point where the updrift erosion perturbations transition to

the section of beach having relatively straight and parallel contours. Bottom

contours in the vicinity of the bar show much more irregularity than offshore

contours in the same depths measured in the spilling wave case. The bar evolved

after remolding, and this evolution is believed to explain the lower degree of

repeatability in process measurements that were made for the plunging-breaker

case. With the exception of the bar region, beach contours are reasonably

straight and parallel between the alongshore coordinates of 15 and 30 m.

Along the downdrift boundary of the beach, a slight erosional perturbation

exists along the offshore end of the beach, as was seen for the spilling-breaker

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Chapter 10

Longshore Sediment Transport Experiments