Sand transport in the Bristol Channel east of Bull Point and Worms Head: a bed-load parting model with some indications of mutually evasive sand transport paths

Abstract

We shall mainly consider the additional arguments put forward by Harris and Collins (this issue) in favour of substantial easterly sand transport in the nearshore zone of the Bristol Channel east of Bull Point and Worms Head and will conclude, on the available evidence, that the proposed nearshore sand transport routeways are neither continuous nor important. A few available examples suggest that some local exceptions may occur where the mean rather than the maximum shear stress determines the net sand transport direction. These are limited largely to the nearshore zone. In broad terms, therefore, the bed-load parting model is necessary to explain both the existence of the sand sheet west of the Bristol Channel with its west-directed sand waves, and the infill of the Severn Estuary, with an intervening zone of scour and non-deposition. Thus, the central part of the Bristol Channel is almost clear of sand not because of a present shortage of sand but because sand has been continually swept from it. The bed-load parting model and the mutually evasive sand transport system are not exclusive of one another. Bed-load partings exist mainly offshore, while the mutually evasive system is found mainly in sand-choked estuaries.