The threshold of sand motion under wave groups

The critical condition for general motion of a sand bottom under sea states of random waves is analysed through an experimental investigation carried out in a wave tank by adopting both proper wave groups able to describe the sea states in a synthetic form and the spectral waves associated with thes e groups. The analysis of the results obtained shows an analogous behaviour as regards the general motion, thus the mathematical models available for regular waves may be used to characterize the critical condition under sea states. Further experiments already scheduled, will help to confirm the pre sent results.