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Saltmarsh - value for sea defence
The value of saltmarsh for sea defence has been assessed in relation to the
standard of defence required for earth bank sea walls in Essex (National
River Authority 1992).
| Width of saltmarsh |
Height of sea bank |
Costs Relative to a 3m sea bank |
|
80 metres
|
3 metres
|
1
|
|
30 metres
|
5 metres
|
X2
|
|
0 metres
|
12 metres
|
X12
|
Comparative costings also give an indication of saltmarsh value. Based on these
estimates a 30m wide saltmarsh might be valued at £1.4 million per ha.
at 1995 prices. When figures are calculated for their value to the maintenance
of existing sea walls (which is the usual situation in Essex) the value is still
£6000 per ha (King & Lester 1995).
Saltmarshes have also been shown to help reduce wave and tidal energy:
- For example the passage of waves through salt marsh vegetation in the USA
can reduce wave height by up to 71% and wave energy by 92% (Frey
& Bason 1978);
- Studies in North Norfolk suggest that the saltmarsh surface can reduce
wave energy by 50-100% (Möller et al. 1996);
- Studies in the Wash have quantified the attenuation
of wave energy.
Caution: The figures given in the Table above are based on relatively
old information. Whilst this does not alter the general proposition that saltmarshes
are important for sea defence, the ratios of costs may need to be reassessed.
References
Frey, R.W. & Bason, P.B.
1978.
North American saltmarshes.
In: Coastal Sedimentary Environments, ed.Davis, R.A.A.Springer, Berlin, 104-164.
King, S.E. & Lester, J.N.
1995.
The value of saltmarsh as a sea defence.
Marine Pollution Bulletin, 30/3., 180-189.
Möller, I., Spencer, T. & French, J.R.
1996.
Wind wave attenuation over saltmarsh surfaces: preliminary results from Norfolk, England.
Journal of Coastal Research, 12/4., 1009-1016.
National River Authority
1992.
East Anglian Salt Marshes.
National Rivers Authority, Peterborough.
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