Literature about wandering channels on salt marshes is quite incomplete, especially on the mudflat. This phenomenon is illustrated in this work through the example of the Couesnon river in the inner part of the Mont-Saint-Michel bay. The Couesnon channel wanderings were studied with an aerial photos and satellite images dataset from 1969 to nowadays. Topographic surveys were conducted with aerial and terrestrial laser techniques, in order to characterize: i) sedimentary grounds evolution under tidal channel influence, from 1997 to 2010; ii) sedimentary balance evolution. Those evolutions were linked to different measured physical processes: tide, flow, wind and swell. The role of the 18.6 year lunar nodal cycle on the Couesnon channel dynamic is highlighted. Sedimentary inputs force the channel to the East on ascending phase, while the Couesnon river adopt a NNW axis position (or more to the west) on a descending phase. Due to the sedimentary inputs decrease, the channel is influenced by extern parameters: flow, discharge and intern one: slope. The global accretion of the system, about +100 000 m3/yr is not linear. Negative sedimentary balance occurs. Sedimentary balances vary in space and time. The surface erosion is mainly due to the ebb strengthening induced by channels presence. This work allows the realization of a global hydrosedimentary functioning scheme of the inner part of the Mont-Saint-Michel bay.
Sedimentary grounds evolution under the influence of wandering channels around the Mont-Saint-Michel monument