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Shingle beaches - State 1, Erosional to State 2, Accretional
or semi-stable
Stabilisation of shingle beaches is normally associated with attempts to maintain
their coastal
defence capabilities. Thus the techniques employed involve the use
of engineered structures and/or beach nourishment. For both approaches the primary
aim is to maintain the beach in its existing position. The methodologies used
to create stability or at least hold the beach in a position where it affords
protection to the hinterland can be broken down into two basic approaches:
- Preventing erosion
Traditionally the approach adopted is concerned with 'improving' the sea defence
capability of the beach or structure by building groynes and breakwaters (coastal
defence structures). This may be accompanied by beach reprofilling.
- Promoting accretion
Promoting accretion requires there to be a suitable source of new material
to 'feed the beach'. This can include beach nourishment
using material derived from sources outside the sediment cell within which the
shingle structure exists. Other approaches are concerned with the reuse of material
by recycling
or 'by-pass' from the down drift to the updrift side where long shore movement
takes place.
 The direction
of movement is as shown in the Figure opposite. The preferred direction of movement
from a sea defence perspective is shown in the figure in blue. Note that in
a few cases, and for the restoration of more natural shingle forms, a reversal
of the process to restore shingle movement may be considered i.e. State
2 to State 1 by allowing natural processes such as realignment
to dominate.
Caption:
The principle route for creating or re-creating stability on shingle beaches.
Undertaking engineering works designed to prevent erosion can, potentially
at least, also provide the means for creating more stable areas where vegetation
becomes established. Both toe protection along the base of the sea walls and
breakwaters can be used to reduce scour. Buried revetments, e.g. at Sovereign
Harbour in Eastbourne have helped to build up the base of the beach. As a result
less material is needed to build the shingle up to a level suitable for flood
protection. The top of the ridge is broader, and hence more suitable for the
development of vegetation communities. At Pevensey investigations are taking
place into the use of tyre bales for a similar purpose. These may have the added
advantage that the bales are not solid structures and can provide gaps for the
shingle to penetrate and hold the beach together, as well as voids for root
systems.
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Summary guidance - creating stability, engineering approaches
It is clear that beaches can be stabilised using artificial structures.
Because these are associated with coastal protection measures, other activities
usually take place, such as beach replenishment and/or reprofiling. As
a result the establishment of new shingle communities is rare. The case
of Black
Rock where stable vegetated shingle developed following building
coastal protection structures may be an isolated example.
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