The distribution of sediment type and benthic communities in the central and eastern English Channel is shown to be polarised around a distinctive local hydrodynamic feature. The seabed in the region includes an extensive area of gravel substrate which is both an important habitat for benthic marine fauna and a valuable source of material for the marine aggregate industry. Effective management of the area is predicated on an understanding of whether it represents a single homogeneous unit, or several different units that may need to be managed in different ways. The aim of this study was to provide information that would inform such management decisions. Spatial patterns in gravel habitats and communities were studied by investigating the physical environment through modelled and empirical data, and the distribution of infauna and epifauna along an east-west trending transect. A common spatial pattern was observed in both physical and biological parameters, but rather than indicating a simple longitudinal gradient, there was a distinct polarisation around a central feature, a bedload parting (BLP) zone situated between the Isle of Wight and Cotentin peninsula. Sediments and communities at the eastern and western ends of the transect were more similar to each other than to those in the middle. The strong hydrodynamic regime in the BLP area controls sediment distribution, transporting finer material, mainly sand, away from the mid transect area. The pattern in sand content of the substrate mirrors the magnitude of the potential bedload transport, which is complex in this region due to the interplay between the M2 and M4 tidal constituents and produced a series of erosional and depositional zones. The structure of benthic communities reflected the local substrate and hydrodynamic conditions, with sponges observed among the stable substrates and stronger currents that characterised the mid transect area, while infauna became more diverse towards the ends of the transect where substrates were more mobile. We conclude that the area should not be considered as a homogeneous unit for management purposes, despite its apparent uniformity on contemporary seabed sediment maps.

Spatial patterns in gravel habitats and communities in the central and eastern English Channel

Marine sands and gravels currently contribute 24% (over 20 million tonnes/year) of the total sand and gravel aggregate consumption of Great Britain. To maintain or increase this contribution into the future, the identification, assessment and licensing of additional sand and gravel resource areas is of fundamental importance. Research into the Quaternary history of the continental shelf surrounding the UK assists in the prediction of sand and gravel resource locations. Similarly, resource assessment is significantly improved through an understanding of the origin and formation of these Quaternary deposits. Geological considerations also feature strongly in the management of existing dredging licence areas and in the acquisition of future licences from the Crown Estate. Precise resource assessment, coupled with accurate dredger positioning and track recording systems, minimizes the extent of dredged sea bed, thereby limiting environmental impact and improving the consistency of dredged cargoes. Also important is the need to overcome marine aggregate prejudice which arises from the perception by some customers that marine dredged sands and gravels differ markedly from those obtained onshore. Central to this issue is the argument that some of the most substantial marine deposits originated in subaerial environments at similar times and by the same processes as their present-day terrestrial equivalents, having been deposited in Quaternary cold climate fluvial environments.

The UK marine sand and gravel dredging industry: an application of Quaternary geology

Grain-size variability and formation process of lowstand river sediments in the Japanese Islands: A review and outlook

The extraction of marine sand and gravel has taken place in a number of countries around the North Sea, the Baltic Sea and English Channel for several centuries, but large-scale dredging for aggregates only began in earnest in the 1960s. Today, marine sands and gravels have an increasing role to play in maintaining European supplies of concreting aggregates as well as material for beach nourishment and constructional fill. The distribution of sand and gravel resources offshore is uneven. They vary in their thickness, their composition and grading, and their proximity to the shore. Many deposits lie in places that are currently inaccessible to the dredging industry. This paper outlines the production of marine sand and gravel in northern Europe and describes the distribution, composition and Quaternary origins of the most important marine sand and gravel resources in northern Europe. Examples are given for the UK, the Netherlands and Denmark, and in summary form for France, Belgium, Norway, Sweden, Ireland and Germany. Most marine sand and gravel deposits are of fluvial or glacial origin and have been reworked to varying degrees by marine and coastal hydrodynamic processes. They represent a range of former depositional environments, including fluvial channel-fill or terrace deposits, glacial meltwater plain deposits, seabed lag gravels and degraded shingle beach or spit deposits, as well as modern marine tidal sandbanks and sandwave deposits.

B. Larsen

Papers

Sources of sand and gravel on the Northern European Continental Shelf