Medium-term sedimentation on high intertidal mudflats and salt marshes in the Severn Estuary, SW Britain: the role of wind and tide

Six sites monitored monthly on salt marshes and mudflats in the middle and outer Severn Estuary gave potentially predictive–retrodictive relationships between the vertical response of the sedimentary surface (erosion/accretion), a factor reflecting tidal heights, and the wind-wave power-supply. The continuing rise of relative sea level in the area, at the rate of a few millimetres annually, is providing accommodation space at a pace low enough to permit the continuing vertical build-up of the salt marshes throughout the estuary. On the mudflats, wind and tidal conditions during the survey maintained an accretionary regime in the middle estuary but an erosional one in the outer part. The Severn Estuary is a system in delicate balance which is likely to respond dramatically to modest changes in the tidal and/or wind regimes.