The sediment budget of the erosional intertidal zone of the Medway Estuary, Kent

Abstract

A prolonged erosion of the broad salt marshes of the Lower Medway began around 1700 A.D. This trend accelerated rapidly between about 1860 and 1910 A.D. when the marsh clay was exploited by the brick and cement industries. In the late 1880's several enclosed marshes were breached by the tide and have remained derelict since. Recent measurements show that accretion on the shrinking areas of salt marsh surfaces is still proceeding. In contrast, the salt marsh creeks and cliffs, and the increasing areas of tidal flat surface are all eroding. Enough measurements have been made to confirm that the changes are proceeding in the same direction throughout the estuary, though at varying rates. Only for Stoke Marshes has sufficient data been assembled to compile a sediment budget, and this shows an annual deficit of about 160,000 tonnes. The deficit for the entire intertidal zone probably approaches 1,000,000 tonnes/yr. There is no evidence that this sediment is redeposited subtidally within the estuary. Erosional intertidal zones such as those in the Medway, Severn and Poole Harbour provide many contrasts with more widely described accretionary regimes, such as The Wash, Dee and Solway.