Fig. 1. An experiment in progress at the LSTF
Four wave generators were used to produce waves in the LSTF. The generators are
synchronized to produce unidirectional long-crested waves at a 10-deg angle to shore
normal. A digitally controlled drive servo electric system controls the position of the
piston-type wave board, and produces waves with the periodic motion of the board. The
system allows a variety of regular and irregular wave types to be produced. The generators
were oriented at a 10-deg wave angle for the present study, but they can be positioned to
produce waves from 0 to 20 deg from shore normal.
The beach was constructed using approximately 150 m3 of fine quartz sand having a
median grain diameter, d50, of 0.15 mm. It was desired to obtain an accurate rate of
longshore sediment transport and its cross-shore distribution with minimal longshore
variation and boundary influences. Therefore, straight and parallel contours were
maintained throughout the model to maximize the length of beach over which longshore
uniformity of waves and currents exist in the basin. Beaches having "three-dimensionality"
affect incident waves and, subsequently, the longshore currents and sediment transport
associated with the waves.
The model beach was of finite length and bounded at the upstream and downstream ends.
To minimize adverse laboratory effects created by the boundaries and to produce uniform
longshore currents across the beach, it was necessary to supplement wave-driven currents.
A recirculation system was installed which consisted of 20 independent vertical turbine
pumps placed in the cross-shore direction at the downdrift boundary. Flow channels were
placed upstream of each pump to direct flow to the pump, which externally re-circulated
the current to the upstream end of the facility, where it was discharged through flow
channels onto the beach. The objective of this system was to maximize the length of beach
Smith and Wang
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