Internal architecture and evolution of bioclastic beach ridges in a megatidal chenier plain: wave flume experiments and field data

Forcing parameters of chenier ridges formation and internal structure are investigated using field data and wave flume experiments. This work focuses on modern, coarse bioclastic beach ridges such as those located on the uppermost part of the tidal flat in Mt. St. Michel Bay (NW France), in the context of a prograding megatidal chenier plain. These ridges migrate landward over the upper tidal flat and salt marshes by washover processes during coincidence of high spring tide and enhanced wave activity, until they are stabilized and integrated in the chenier plain. The internal architecture of these ridges has been investigated on the field using high-frequency ground-penetrating radar (GPR). Three types of ridges were identified, that represent a continuum of evolution between active transgressive, mature transgressive (Fig. 1), and mature progradational ridges (Fig. 2). Each type reflects major differences in external morphology and internal structure. The altitude of the banks regarding to the level of tidal flooding, as well as local sediment supply, are assumed to be important forcing parameters in chenier development and evolution.