Depth of disturbance in mesotidal beaches during a single tidal cycle

Variations in the disturbance depth were measured across four open mesotida l beaches on the Gulf of Cadiz coast of Spain during single tidal cycles, u sing rods and plugs of marked beach sands inserted in the foreshore. The st udied beaches show a wide range of morphological variations and are distrib uted along a broadly homogeneous straight coast where energetic conditions remain more or less constant. Several parameters like wave height, beach gr adient and grain size distribution have been compared with the variability of the recorded disturbance depth. As a conclusion, it is suggested that th e morphodynamic regime is the characteristic that best explains the spatial variation of the disturbance depth, as well as the different response of t he beaches under broadly similar energetic conditions. Three main morphodyn amic classes have been observed in the studied beaches: reflective, barred dissipative and dissipative. In each case the morphodynamic situation contr ols the distribution and relative intensity of wave processes acting across the beach profile and, hence, the different rate of disturbance depth. The morphodynamic study of a beach permits an initial prediction of its morpho logical response under variable wave conditions.