transport was much higher as a result of the steeper beach slope and much more
energetic swash zone that developed for waves having longer periods. In the
midsurf zone, the local rates of LST were similar for the two wave cases.
As was found for the concrete-beach experiments, there was a region of the
movable-bed beach that was characterized by a reasonably high degree of
alongshore uniformity in waves, currents, and sediment concentration, between Y
(alongshore) coordinates of 15 and 30 m. The downdrift boundary is not perfect
though, and imperfections lead to sand trap efficiencies that are not 100 percent.
Slight accretion or erosion anomalies developed adjacent to the downdrift
boundary, and these anomalies must be accounted for in deriving estimates of
LST rates. Accurate and dense survey data are required to compute the
corrections. Errors associated with sand bypassing the traps were rather small.
The steadiness of mean flow conditions, quality of the sensors, and
repeatability of the measurements allow accurate data sets to be acquired, not
only of wave, current (at one depth), and water elevation parameters, but also the
vertical structure of the mean current and sediment concentration fields.
Sediment concentration measurements were more variable than wave and current
measurements, probably because of the small differences in local morphology
that exist throughout the beach. Mean values computed from several adjacent
transects are recommended for characterizing the vertical structure of sediment
concentration. Overall, steadiness and repeatability of the hydrodynamic
conditions allowed high-quality data sets of suspended sand concentrations and
longshore sediment transport rates to be acquired.
The LSTF has proven to be an excellent and robust facility, and so far has
yielded unprecedented measurements of surf zone sediment transport processes
in a laboratory setting, including sand transported in suspension. The potential
for making R&D advancements through the use of the facility is quite high.