over which waves and wave-driven longshore currents are uniform by continually re-
circulating wave-driven longshore current through the lateral boundaries of the facility.
Each pump included a variable speed motor to control discharge rates. The variable speed
motors were controlled remotely to allow a cross-shore distribution of longshore current.
A 21-m instrumentation bridge spanned the entire cross-shore of the beach and served as
a rigid platform to mount instruments and observe experiments. Each end of the bridge was
independently driven on support rails by drive motors, which allowed it to travel the entire
length of the wave basin. The bridge could be moved either manually or by entering the
desired longshore (Y) location on a PC in the LSTF control room.
INSTRUMENTATION
Time series of water surface elevations was measured using single-wire capacitance-type
wave gauges. Ten gauges were mounted on the instrumentation bridge to provide wave
heights as they transformed from offshore to nearshore. The cross-shore location of the
gauges could be repositioned on the bridge depending on the wave conditions.
Additionally, four gauges were placed in front of each wave generator to measure offshore
wave characteristics.
and unidirectional longshore currents. The ADVs were positioned at the same cross-shore
position on the bridge with the wave gauges, but separated by approximately 40 cm in the
longshore direction to prevent interference between the two instrument types. As with the
wave gauges, the ADV cross-shore location could be repositioned on the bridge.
The eight most offshore ADVs were down-looking three-dimensional (3D) sensors,
which sampled velocities in the x, y, and z directions 5 cm below the sensor. The first two
ADVs were two-dimensional (2D) side-looking sensors, which sampled velocities in the x
and y directions, also 5 cm from the sensor. The 2D sensors were used to allow
measurements in water too shallow for the 3D current meters.
All of the ADVs were mounted on vertical supports that allowed the vertical position of
the sampling volume to be adjusted. Typically, the ADVs were positioned vertically to
sample at a location that gave the average velocity in the water column. However, some
experiments were conducted in which the vertical position of the ADVs was varied to
obtain the velocity distribution through the water column.
An automated beach profiler mounted to the instrumentation bridge was used to survey
the beach. A mechanical spring-wheel system attached to a vertically mounted rod
followed the sand elevation as the system moved cross-shore along the bridge. The vertical
movement of the rod produced a voltage, which was recorded and converted to elevation.
The vertical resolution of the system was 1 mm. Horizontal positioning of the profiler was
controlled by the bridge position and a cross-shore motor mounted on the bridge. The
profiling system was amphibious to allow the entire beach to be surveyed without draining
the basin.
Survey data were obtained every 5mm in the cross-shore direction and every 0.5 or 1.0
m in the longshore direction. Initially, survey lines were taken every 0.5 m in the
Smith and Wang
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