Late Flandrian shoreline oscillations in the Severn Estuary: change and reclamation at Arlingham, Gloucestershire

Abstract

Five morphostratigraphic units of estuarine alluvium in an erosively off-lapping relationship underlie the now almost totally reclaimed post-glacial wetland enclosed by the great bend in the upper Severn Estuary at Arlingham. The oldest unit is mud-dominated and includes peats, but the next, probably spanning the Medieval Period, sees the beginning of a substantial influx of sand into the upper estuary. The three youngest units are identifiable with the estuary-wide Rumney, Awre and Northwick Formations, which formed within the past 300 years in response to the repetition of a regional cycle of coastal movement that involved cliff cutting on the salt marshes and then the upbuilding of further mudflats and wetlands. The trend of relative sea level in the area has meanwhile continued upward. Piecemeal wetland reclamation, commencing not later than the Medieval Period, and possibly beginning in Romano-British times, has complicated the development of these morphostratigraphic elements. The reclaimed part of the salt marsh now has the form of an upward and outward flight of geomorphic surfaces that increase in elevation with declining age. Locally, where sea defences have been either abandoned or eroded in response to changes in the pattern of estuarine currents, renewed tidal siltation had led to the burial of soils formed on the reclamations.