THE IN-SITU PASSIVE ACOUSTIC MEASUREMENT OF SHINGLE MOVEMENT UNDER WAVES AND CURRENTS - INSTRUMENT (TOSCA) DEVELOPMENT AND PRELIMINARY-RESULTS

An instrumented platform (TOSCA) is described for monitoring coarse-gr ained sediment transport in high (wave and tidal) energy environments. The system consists of a number of sensors which measure: instantaneo us current velocities at three levels; sea surface elevation; and self -generated noise (SGN) caused by intercollision of particles in transi t. SGN is related to transport rates, on the basis of laboratory calib ration; this, in turn, allows a correlation with simultaneous near-bed shear stress to be established. During the field measurements, PC-bas ed real-time data transmission is realised through the use of a (buoye d) radio telemetry system. TOSCA has been deployed in eastern Christch urch Bay, southern England. Burst data were collected every 2 h, over 10 min, with a sampling frequency of 5 Hz. The data sets obtained perm it detailed investigations into near-bed flow structure and shingle mo vement, on time-scales comparable to those of the turbulence.