Measuring Longshore Sediment Transport in a Large-Scale 3-Dimensional Laboratory Facility

Aiming at improving present understanding on longshore sediment transport (LST), the U.S. Army Engineer Research and Development Center recently established a Large-scale Sediment Transport Facility (LSTF). The 3dimensional movable-bed facility has the capability of simulating wave conditions that are directly comparable to annual averages along many low energy coasts. Wave, current, and sediment concentration are measured accurately at numerous longshore and cross-shore locations and throughout the water column. Depth-integrated LST rate and its cross-shore distribution are measured with 20 bottom traps installed at the downdrift end. These, along with beach-profile data, allow detailed analyses of LST processes. This paper focuses on the methodology of designing and implementing LST experiments. Each experiment consists of a number of wave-run segments. Each segment has a specific objective. The first few segments are designed to accomplish two tasks before the actual LST measurement. One is to achieve proper pump settings for the circulation of breaking-wave-generated longshore current. The other task is to allow the beach to reach equilibrium state. Successful accomplishment of these two tasks is crucial to ensure longshore uniformity of hydrodynamic and beach conditions, and to minimize interactions at the lateral boundaries. LST measurement is then accomplished with at least four wave-run segments, including one focusing on measurements at maximum number of locations alongshore, one on measurement of vertical current profiles, and two repeated measurements to ensure data quality. The first phase of LSTF experiments indicated that the above procedure was successful and should be valuable to the design of future laboratory studies.