Supply, Distribution, and Transport of Suspended Sediment in a Macrotidal Environment: Bristol Channel, U.K.

Abstract

Various independent sets of data are used to investigate near-surface suspended sediment concentrations. The data include satellite (LANDSAT) imagery, field verification and near-synoptic surveys of specific areas and integrated, longer-term, surveys of the Channel. The information is used to identify areas of high turbidity, which relate to tidal and wave resuspension of the mobile sediments within the Estuary and Channel system. Thematic maps produced from the satellite imagery are comparable directly with the survey results and are combined with them, through a radiance/loge concentration relationship. Derived estimates of material present within the waters of the Channel range from 4.5 × 106 t to 13.4 × 106 t. Fluvial contributions are estimated to be of the order of 1.6 × 106 t/yr. Other evidence is available for the supply of material from the Celtic Sea. Isopleths of suspended sediment concentration are used to infer residual water and fine-grained sediment transport directions; these are compared with a more general model, which includes observed and predicted near-bed sand transport directions.Key words: Bristol Channel, Severn Estuary, suspended sediment, satellite imagery, sediment budget, sediment transport, residual water movement