STONE MOBILITY AND LONGSHORE TRANSPORT AT RESHAPING BREAKWATERS

Physical model tests have been performed in two different wave flumes to analyse the threshold of stone movement and quantify the frequency and length of displacements due to head-on wave attacks at a reshaping breakwater, Data on stone movements were obtained from the observatio n of cumulative displacements at the end of each wave attack and from video records during the attack. Threshold conditions, frequency of mo vement and displacement length are expressed as function of a suitably modified stability number. A simple model is defined relating longsho re transport due to oblique wave attack to stone mobility, The transpo rt model is based on the assumption that movement statistics is affect ed by obliquity only through the appropriate mobility index and that s tones move during up- and down-rush in the direction of incident and r eflected waves, Without any calibration, results compare favourably wi th experimental data available in literature in the range of low mobil ity conditions where movement statistics was observed. A calibration i s provided in order to obtain an accurate transport formula valid in a wide mobility range, i.e. for reshaping breakwaters and up to gravel beaches.