THE EFFECT OF OFFSHORE DREDGING ON COASTLINES

Abstract

The South of England is well endowed with land deposits of river gravel and sand. Nevertheless, the demand for aggregate and the need to conserve agricultural land have increased to the point where in 1976 sea dredged aggregate was accounting for 11% of the total sand and gravel production. In addition to this annual home consumption of about 12 million tonnes of dredged aggregate a further 3.5 million tonnes was exported to Europe in 1976. Understandably, authorities responsible for coast protection and sea defence view the increase in the removal of marine deposits with concern and a system of licensing by the Crown Estate Commissioners who are responsible for the sea bed from high water to the UK Continental shelf limit has been developed over the years. Dredging by port authorities within their area ofjurisdiction, for navigational purposes, is outside this licensing system. Within the three mile limit local authorities have powers under the Coast Protection Act to regulate dredging. In 1976 a report by an advisory committee to the Department of the Environment1-1^ recommended, among other things, that further studies should be carried out by HRS aimed at reviewing the existing constraints on marine dredging for gravel. In general, the material which is sought for construction purposes is a 60% shingle, 40% sand mixture, but sand is also needed for reclamation fill and for industrial purposes. The areas dredged at present are shown in Figure 1. This paper deals briefly with the licensing procedure and at some length with the involvement of the Hydraulics Research Station in assessing how dredging might affect the coastline. The effect on fisheries, navigation, coastal ecology, and other interests is considered by other organisations. Very little is known of the criteria applied to offshore dredging by other countries, apart from Germany, but with the increased exploitation of the sea bed it is important that information gained by other countries should be used to improve our existing criteria. .