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Shingle sediment supply - a finite resource?
An important point to consider in relation to coastal
defence is that many of the beach-barrier systems on the modern coast
were initiated during the Holocene
marine transgression and are now responding to changes in sea level, storms
and tidal movement involving the reworking of an essentially finite sediment
supply (Pye 2001). This poses the most significant
management issue in relation to the sustainability of coastal shingle beaches
and structures, especially for sea defence purposes.
The situation in Start Bay (Slapton, Annex
02) is summarised in the Futurecoast
project as follows:
"There are no significant contemporary sources of material to this
coastline. Landsliding in the vicinity of Brixham can occur in response to easterly
storms and the removal of toe debris providing a local, although not significant,
source of beach material. Toe-trimmed headland slopes fringed by some raised
beach deposits are also potential sources in the north, but they are not presently
significant. This indicates that the sediments present in Start Bay were derived
from the seabed during the Holocene
period. This is consistent with the high proportion of flint pebbles (75%),
present on the barrier beaches, which have no local source." (Halcrow
2003).
A detailed study of the situation along the Channel coast (the INTERREG BERM
project) suggests that new material is available in areas where sea cliffs are
eroding, though even here the amounts are insufficient to maintain the beaches
in situ.
| General Guidance: This study has clearly identified the importance
of understanding the relict
nature of many of the shingle deposits that are present today. The conclusions
from Futurecoast
summarised in the report on Slapton (Annex
02), the continuing need for beach nourishment on the south coast
and the deficit of material identified for Dungeness (Annex
05 and in the summary
CHaMP report) and the situation at Cley (Annex 07) tend to confirm
the view expressed in 2.1 above that in many instances engineering solutions
to shingle erosion are unsustainable in the medium to long term. |
References
Halcrow
2003.
Futurecoast (3 CD set comprising reports and interactive map browser and two CDs with oblique aerial photography of the shoreline of England and Wales).
Department of Environment, Food and Rural Affairs.
Department of Environment, Food and Rural Affairs.
Department of Environment, Food and Rural Affairs.
Department of Environment, Food and Rural Affairs.
Department of Environment, Food and Rural Affairs.
Pye, K.
2001.
The nature and geomorphology of coastal shingle.
In: Ecology & Geomorphology of Coastal Shingle, eds.Packham, J.R., Randall, R.E., Barnes, R.S.K. & Neal, A.Westbury Academic and Scientific Publishing, 2-22.
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