INTRODUCTION TO SAND & MUD FLATS

Definitions and descriptions

Sand and mud flats develop in moderately sheltered coastal inlets and bays. They are covered twice daily by the tides. Finer sediments settle out in the quieter waters of the inner parts of estuaries and other tidal embayments to create mud flats. Sand flats tend to develop towards the outer more exposed shores and can form offshore banks and bars. They provide the substrate upon which saltmarshes (in estuaries and other tidal inlets) develop. Sandy foreshores also act as precursors to sand dunes.

Traditional management

Tidal flats are not managed in the same way as other coastal habitats, though there are traditional activities associated with resource exploitation.

Reasons to restore

Sand and mud flats have been damaged or destroyed by a variety of of human actions including the enclosure of tidal land. This has most frequently taken the form of port and harbour development. Exclusion of the tide followed by infilling (with dredged and other material including inert waste) has provided the foundations for sometimes extensive development. These losses are exacerbated in areas where sea level is rising as the shoreline is pushed landward. In areas where there is a fixed transitional boundary (as for example a sea wall) then there is an overall steepening of the foreshore and a reduction in the width of the tidal flat, another form of 'coastal squeeze'.

States and values

Tidal sand and/or mudflats exist to two basic states:

1. They are either accreting (State 1);
2. Or eroding (State 2).

For the purposes of the Guide these states are used to describe to the overall status of the tidal areas. Natural dynamics (due to changes in tidal regime or river channel movement) force periods of both erosion and accretion, which are a natural and necessary part of their development. Sand and mud flats have an intrinsic value. They can be extensive and contribute substantially, in some areas, to the wilderness quality of the coastal landscape. They support significant biomass resources (including invertebrate fauna, Zostera and algae). These in turn provide food for large wintering populations of waterfowl. The high productivity associated with the tidal waters and flats also helps to support a number of spawning and juvenile stages of some commercial fish species.

Guidance (routes to restoration)

Restoring the nature conservation value of the tidal flats for wintering waterfowl is a major requirement, especially where habitat has been destroyed as a result of development. Under these circumstances the provision of compensatory habitat may be part of the original permission for development. Three principle approaches to restoration can be identified for sand and mud flats, namely:

1. Move seaward (using a variety of techniques) by encouraging the accumulation of sediment on the foreshore including by the construction of polders;
2. Maintain the existing shoreline (by methods including beach nourishment);
3. Retreat landward through 'managed realignment'.

Key publications:

• Background documents: Descriptions of sand and mudflats are usually included within publication on estuaries and other tidal wetlands. The relationship with birds is dealt with in detail in the Estuaries Review (Davidson et al. 1991). The UK Marine SACs Project http://www.ukmarinesac.org.uk/, has publications that provide information relevant to the assessing the importance and management of sand and mud flats. ;
• Guides: A detailed review of the restoration of tidal sand and mud flats has been provided in English Nature Research reports No. 425 (Atkinson et al. 2001) obtainable in pdf format from the English Nature web site (http://www.english-nature.org.uk), under Publications, search using the report number, 425;
• Web sites: The English Nature Web site @ http://www.english-nature.org.uk includes a wealth of additional information including a report on Zostera and information on the pros and cons of using dredging for the restoration of sand and mud flats (and saltmarshes).

References

Atkinson, P.W., Crooks, S., Grant, A. & Rehfisch, M.M. 2001. The Success of Creation and Restoration Schemes in Producing Intertidal Habitat for Waterbirds. English Nature Research Report, 425 English Nature.

Davidson, N.C., Laffoley, D..d'A., Doody, J.P., Way, L.S. & Gordon, J. 1991. Nature Conservation and Estuaries in Great Britain. Nature Conservancy Council.