How subsoil morphology and erodibility influence the origin and pattern of late Holocene tidal channels: case studies from the Belgian coastal lowlands

This paper aims at a better understanding of the late Holocene re-entrance of the tidal system in the Belgian coastal plain after a 2–3 ka years long period of peat growth. The re-entrance was associated with the development of deeply incised tidal channels. The initial cause of the re-entrance, still a missing link in the understanding of the late Holocene coastal change, is investigated by focusing on the specific location of the young tidal channels. The research, though based in the western Belgian coastal plain, is relevant to the lowlands of the southern North Sea and English Channel. The investigation combines stratigraphic, radiocarbon and sedimentological data, together with maps showing the morphology of the pre-Holocene surface, the distribution of the Holocene deposits and the erosional surface produced by the late Holocene channels. It appears that the young channels re-occupied the same position as their early and mid Holocene predecessors. The re-entrance of the tidal system began by a removing of the upper part of the older channels which originated from the mainland. Once the channels were cleaned of sediment, tidal waters could re-enter and rework the easily erodable sand of the older channels and Pleistocene deposits.