New instrumentation for the investigation of sediment suspension processes in the shallow marine environment

An instrumentation system has been developed that continuously measures: flow velocity, water depth, and suspended sediment concentration profiles in the nearshore zone. The system consists of four components: (1) an array of electronic sensors, including: an electromagnetic current meter, a surface-piercing resistance wave gauge, and a five-element array of optical back-scatterance sensors; (2) a signal processing electronics unit; (3) a guyed mast support structure; and (4) a data acquisition system. The small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves (∼2 m). Results from an experiment on an exposed ocean beach on the coast of Washington, U.S.A., indicate that sand suspension events of long duration (15–40 sec) relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift. Work is now in progress to modify the system for self-contained operation on the continental shelf. Field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation.