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A detailed analysis of blow-outs in coastal foredunes

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dc.contributor.advisor Bate GC, Prof en
dc.contributor.author Ferguson MV en
dc.date.accessioned 2016-09-22T13:19:00Z
dc.date.available 2016-09-22T13:19:00Z
dc.date.submitted 1994 en
dc.identifier.uri http://hdl.handle.net/20.500.11892/157466
dc.description.abstract The causes of blowouts on coastal foredunes have been well documented in the literature. Most of these causes are related to some form of disturbance which leads to vegetation destabilisation, loss and sand mobilisation. This study had indicated that some causes may be attributed to the wind acting on irregularities in the dune ridge, causing "gaps" or corridors which allow sand to move inland. <br><br> In the study area there are a large number of blowouts through the single foredune ridge. References, as long ago as 1855, indicate that the foredune area had the same irregular topography and was probably blown-out. This was long before the present heavy human utilisation commenced. This area is presently heavily utilised by people on an irregular but intensive basis and access to the foredune area is not only uncontrolled, but not even discouraged by local authorities. <br><br> The blowouts across the foredune ridge are predominantly orientated at a deflection between 0&deg; and 20&deg; from right angles to the coastline. They do not conform to classic blowout definitions given in the literature as they do not appear to be the result of net sand erosion, i.e. a loss of sand from the area. There are indications that the area is no longer an accretion system. Rather, it appears to be tending towards a sedimentary transport system. The evidence for this is that pulses of sand blown from the beach are channelled through the "blowout" areas of the partially vegetated hummocks. These unvegetated areas form tongues of sand which are slowly enlarging and forming a continuous connection between the beach and the lowland area behind the foredune ridge. The sand hummocks covered with vegetation show indications of lateral erosion on their edges. This erosion of the hummocks is clearly related to the wind patterns of the area and the conclusion is that these blowouts are formed as a result of natural causes (i.e. strong onshore wind, low rainfall or low net moisture balance, together with an abundant supply of sand). The impression gained by comparison with other less blown out foredunes is that human activities aggravate the situation because they cause destabilization of the vegetation. Hence, the combination of natural environmental conditions super-imposed with human trampling, is accelerating the process of destabilisation. <br><br> The wind acts in both an onshore and an offshore direction and results in sand movement landwards and seawards between seasons. The net result is a very slow deterioration of the physical foredune ridge. <br><br> The evidence also shows that onshore and offshore winds almost balance the net sand transport but with landwards movement the greater. This implies that the system is degrading. The possible consequences of vegetation destabilisation and disappearance may be an accelerated sand movement in a landward direction each season than at present. <br><br> Wind regimes and disturbance factors appear to be causing a slow migration of sand together with a slow but constant reduction of vegetation in the foredunes along the length of the study site. The lowland area is zoned by the Port Elizabeth Municipality for future housing developments and increased recreational facilities are to be provided. This sand movement inland is a potential hazard to further developments in the area. Several management proposals are given in the Conclusion which should ensure a reduction of disturbance to the foredune complex. A theory is proposed in the discussion for the origin of the blowout features in the foredune ridge in relation to human disturbances and climatic conditions - both past and present. en
dc.language English en
dc.title A detailed analysis of blow-outs in coastal foredunes en
dc.type Masters degree en
dc.description.degree MSc en


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