USING FENCES TO CREATE AND STABILISE SAND DUNES

Brian B. Willetts, Christopher J. Phillips

Abstract


Coastal sand dunes act as a barrier to wind and sea, as a reservoir of sand available to supply areas of eroding coast, and as a trap for mobile sand which would otherwise be blown inland and become a nuisance. Breaches of the dune system and areas bare of vegetation should be avoided or repaired in order to protect the stability of the dunes and so enable these useful functions to be sustained. The agents of initial damage to the dunes are water, which undermines them, and animals (including man) which damage the protective vegetation by grazing or trampling. Of these, man has recently assumed predominant local importance because of the popularity of sea-side holidays and of the land-falls of certain marine engineering works such as oil and gas pipelines and sewage outfalls. The need is therefore increasing for active dune management programmes to ensure that under these accentuated pressures, the coast retain an equilibrium comparable with that delicately balanced equilibrium which obtains naturally at a particular location. Such management programmes are already established in many countries. They tend, however, to be empirical and based on local experience (often of a very small number of people) because the difficulties of generalisation render transfer of information and technique meagre. Accounts of management techniques can be found in the literature (e.g. ref 1) but in most of such papers great emphasis is placed on vegetative restoration. Whilst this is the best way of re-introducing a lasting stability, it is often not a practical way of beginning the restoration of a deteriorating situation. The sand movement or the season may be such that planting alone is unlikely to be successful. It is the authors' opinion that, of the techniques at present available, the placement of porous fences provides the most effective means in relation to cost of creating and stabilising sand dunes (and should normally be supplemented by plantings). The object of this paper is to present a simple numerical model of dune formation at a fence. The model is based on what is known of the physics of air and grain movements near the fence, and the purpose of approaching the problem at such a basic level is to seek sufficient understanding to enable information and prediction methods to be transferred from person to person and applied at different sites. This requires that the processes which take place at the fence be better understood than at present.

Keywords


dune; dune stability; fence created dune

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