An investigation into the nature of gully erosion at Golden Gate Highlands National Park.

Abstract

The general aim of this study was to gain an insight into the nature of gully erosion at Golden Gate Highlands National Park. In order to achieve this the spatial and temporal characteristics of six gullies were investigated by examining their typological and morphological characteristics, the relationship between their morphometric properties and their increase in extent over a 39 year period (1952-1991). Where possible these findings and observed gully forms were related to initiating factors. Extensive field surveys and measurements were carried out to ascertain the typological and morphological characteristics of each gully. The results of the field measurements were then statistically analyzed using linear regression analysis, principal component analysis and canonical variate analysis. These methods of analysis were used to get an indication of the relationships taht exist between the morphometric properties of the gullies as well as to highlight the similarities and differences that exist between them. These results showed that the morphometric varaibles of the gullies are strongly interrelated. Furthermore they revealed that the six gullies could be divided into three broad groups on the basis of their morphometric and sediment properties. The gullies within two of the three groups were found to be similar not only in terms of the above mentioned but they also occur on same facing slopes of similar gradients and appear to have been initiated by similar processes. Differences occurring within and between the gully groups were attributed to varying combinations of initiating factors. Aerial photographs from 1952 and 1984 were used together with surverys to map the extent and development of five of the six gullies - teh remainign gully was only initiated in 1988. The 1952 and 1984 photographs were selected as they represented the earleist and most recent photographs to be taken of the area. The maps show the gullies to have experienced a greater amount of growth during the 1984 - 1991 period than during the 1952 - 1984 period. This finding was attributed to the sporadic nature of gully growth. The spatial location of the gullies in relation to one another appears to have had little influence on their typological and morphological characteristics. However, their spatial location within the landscape has undoubtedly influenced these properties. In general the research described has shown that the spatial and temporal differences of the gullies occurring in the park are the result of various combinations of endogenous and exogenous factors that governed the initiation and development of each gully.