Measurement techniques of shingle transport in the nearshore zone

New, innovative techniques are presented for the detection of shingle movem ent. A passive acoustic technique is used for the remote sensing of instant aneous gravel motion in shallow offshore areas. Noise created by the interc ollision of moving particles (self-generated noise, SGN) is proportional to the transport rate. This approach is used in conjunction with measurements of waves and currents in the benthic boundary layer, to study processes as sociated with shingle transport. The SGN method can be used in tidally-domi nated areas and those experiencing shoaling (nonbreaking) waves; its use in the surf zone (beaches) is limited, due to increased ambient noise levels caused by wave breaking. A new shingle tracing technique has been developed , based upon the implantation of a miniature electronic transmitter into a shingle particle (of the same shape and specific gravity as the indigenous sediment population). This "transmitting pebble" can be detected remotely o ver a beach, to depths of burial of up to 70cm, offering high (80%) recover y rates, Application of the techniques developed have demonstrated the enha ncing role of the waves in offshore shingle transport processes; modificati on of existing (steady current) shingle transport formulae are suggested, f or use in the marine environment. Longshore shingle transport, in the surf zone, can be calculated using the energy flux equation, originally derived for sand. The coefficient (K) is shown to be constant for gravel particle s izes (D-50 > 20mm) and equal to 0.017.