Dredging, navigation and revetment construction • Sediment extraction • Turf cutting • Hay making • Reed cutting • Samphire gathering • Spartina

Sediment extraction

Although not an activity occurring today, many marshes in southeast England may have been adversely affected by former sediment extraction principally for brick, tile and pipe manufacture. Saltmarsh has also been excavated as ‘borrow pits’ for embankment construction, to provide moorings and to create oyster pits. The total amount of material removed has not been quantified, but probably runs into many millions of tons. The effects of this have been not only to directly reduce the area of vegetated marsh remaining, but also to disrupt the natural pattern of marsh drainage. Estimates suggest that some 40% of the area of the saltmarsh in the Medway Estuary has been lost in the last 100 years as a result of extraction which took place between 1840 and 1910. Whilst some of this loss may be attributed to the rise in relative sea level which is occurring there, as on the rest of the east coast, undoubtedly the reinforcement of an ebb-dominant regime and the subsequent loss of sediment from the system may be equally or even more important.

At the time of publication of the Estuaries Review (Davidson et al., 1991) extraction of other types of sediment was taking place; in 11 out of 155 estuaries this was thought to involve commercial quantities. In sites like the Ribble Estuary (Lancashire) and the Taw Torridge (Devon), where sand is extracted at the mouth of the estuaries, changes in the sedimentary patterns are occurring, but it is not clear what impact these have on the development of the saltmarsh.