Search

A simple empirical model is proposed for predicting extreme wave run-up on natural beaches during severe wave events (deep water wave heights H0 ≳8 m or return periods of about 50 years). The new model departs from traditional approaches that use the slope of the beach face βf and the Iribarren number ξ0 as parameters for predicting run-up and instead uses the distance offshore xh to water depth h to estimate a near-shore profile slope as S = h/xh, where the depth of closure is the proposed choice for h. Extreme run-up Rx is then expressed in terms of S as Rx/H0 = CS2/3. Observations from recent severe storm events in South Africa are used to estimate the dimensionless coefficient C≃7.5. The data are also compared with those of Holman [1986] and the results verify his regression equations and confirm they are valid for significant wave heights extending to 8.5 m for beach-face slopes around 0.1. The run-up predictions of Holman [1986], Nielsen and Hanslow [1991] and Stockdon et al. [2006] are compared to those of the proposed new model. The results suggest that the new model reduces the uncertainties in predicting wave run-up on natural beaches compared with previous models, and thus enables improved estimates of extreme wave run-up and the upper limit of beach change for coastal planning and management.

Although blowouts in sand dunes have been extensively studied elsewhere, little is known about those within the Holocene dune fields of the Maputaland coastal margin in KwaZulu-Natal, on the east coast of South Africa. Research in this paper involved measuring, describing and analysing wind flow patterns at a single blowout near Mabibi and related the results to the wind dynamics. From this, a preliminary hypothesis of blowout formation was made. Topographic steering through both the logarithmic spiral form of the bay adjacent to the blowout and the morphology of the dune had a significant influence on wind patterns in both pre-and post-frontal wind conditions. As the blowout widens, further channelling accelerated a jet around the headland, which would ultimately result in complete breakthrough of the dune, leaving a small isolated residual dune fragment, cut off by a mobile arc of sand. The paper concluded that such blowouts are characteristically formed under highly negative beach budgets, and that blowout formation along this coast is more likely at sites in the proximity of rocky headlands.

The paper traces the major themes in southern African geomorphology from its early roots in both geography and geology at the start of the twentieth century through to the present. The development ...

Hazelmere Dam, located on the Mdloti river 12 km from the KwaZulu Natal coast, was completed in 1975. Since then it has lost more than 25% of its original design capacity through siltation, a fact which could threaten its economic life. This has occurred partly because of high annual average sediment accumulation rates under normal climatic conditions, and partly as a result of the 1987 floods, an extreme event with a return period of between 50 and 200 years. The objective of this work was to indicate why sediment production rates per km- of catchment area as indicated by dam siltation were higher than in most other KwaZuku Natal dam catchments. Basic rainfall, soil and slope conditions cause the Mdloti catchment to have a high erosion potential, which has been exacerbated in recent years by large scale population increases, vegetal degradation and road construction activities. These together created conditions for massive sediment transport during the 1987 floods. In terms of the theories of fl...

A 3.55 km2 catchment in Orangekloof Nature Reserve, Hout Bay, here conceptualised as an assemblage of landforms, is valued with respect to its ability to attenuate flood discharges derived from pre...

Stereoscopic air photos from 1944/5 and 1976–81 were used to conduct a temporal comparison of area affected by erosion in the Tugela catchment. The results show that the amount of eroded terrain had decreased with time. There was no significant difference in eroded area between KwaZulu and Natal in either time period, and both administrative regions showed a decline in eroded area from 1944/5 to 1976–81. This and other relevant studies indicate a decline in erosional activity in the area. This may be due to land use changes or improved conservation techniques, but could also result from medium or long term changes in variables in trinsic to the erosion system.

Despite frequent occurrences of slope failure in Berea red sand, it is commonly used as fill or embankment material in the Durban area. An investigation of a small rotational slip in this material showed that it could be explained in terms of rainfall, soil moisture content and soil properties.

Although Land Systems mapping is one of the most important aspects of applied geomorphology, its value to civil engineering projects is questionable at scales greater than 1 : 10000. This paper describes two examples of reconnaissance engineering geomorphological maps suitable for larger scales. The need to adapt cartographic representation to the -requirements of the project and the physical nature of the terrain is stressed, and it is concluded that photo-interpretation is a particularly useful tool in this kind of work, since it reduces time spent in the field.

Recent reviews and textbooks show that South Africa has contributed very little to the field of soil erosion research. Strongest areas of research are the study and estimation of sediment yield. and the evaluation of rainfall erosivity. whilst major weaknesses include the lack of knowledge of the nature and extent of erosion. and a poor understanding of the mechanics of erosional processes. General co-ordination of research policy is required if research is to make a significant contribution to the solution of problems caused by soil erosion.