Beachface slope, swash climate and its relationship with the morphodynamic stage

Abstract

The uprush and backwash of a wave (swash climate) at the beach face, as well as the duration of this process, depend not only on wave characteristics such as height and period, but also on the beach-face slope, which in turn is partially conditioned by the sediment grain size. As a general trend, the coarser the grain size, the steeper the slope, and faster the uprush and backwash cycle (swash regimen) is completed. This cycle is partially related to the morphodynamic characteristics of a beach, passing through dissipative, intermediate, and reflective stages as the beach face slope increases. Observational data along the beaches of the Doce river delta, Espírito Santo - Brazil, showed a correlation between beachface slope, morphodynamic state and swash regimen, with some variations along the study site. Dissipative and saturated swash regimen were related to beach face slopes lower than 3°, while the reflective stage and more complete swash regimen were related to slopes higher than 5.5°. The flow regimen of extreme states often shifts from dissipative or reflective to intermediate morphodynamic state and vice-versa. The results herein provide an objective physical framework to morphodynamical comparative studies and potential implication for benthic ecological studies.