No description available.

No description available.

This study is concerned with the physical and human causes of soil. erosion. Some quantitative information on the magnitude of soil erosion for different ecoregions in South Africa is available. However, such quantitative data is available only from a few sites. One objective of this thesis is to add to the existing data. Site specific data is provided for the two study areas in the Eastern Cape Province, namely, Chani area in Mt Frere and Brooks Nek area in Mt Ayliff. A comparison is made between the physical and chemical characteristics of the soils found in both study areas. The spatial and temporal extent of the erosion problem is also given. Another major objective is to evaluate the soil rehabilitation measures used at these two areas. An evaluation of the relevance and efficiency of the erosion control measures is made. (For gully erosion especially, the present study provides an evaluation of the suitability and effectiveness of the gully control mechanisms adopted.) Most importantly, a third objective of this study is to investigate the awareness and attitudes of the members of the communities affected by the erosion problem. Among the many different factors found to be important in the causal nexus that results >f in soil erosion, it has been found that many of the problems originate from social causes, like that of too large a population for the limited available resources. Added to this, factors like poor development programmes, bad agricultural practices, bad road management, have exacerbated the erosion problem. In other words, from research and interviews conducted in the study areas, erosion problems linked to recent political policies; to farming and to other practices were found to be associated, inter alia, with the shortage of land, unemployment, the lack of the necessary farming equipment, overgrazing and so on. To stress the point, the five important factors contributing to erosion were identified as an over exploitation of the land resource for basic needs, bad road management, floods, drought, and concentrated flow on furrows made by both on and off-road vehicles. We noted that another important feature of this thesis is to give an account of the psychological attitudes of individuals living near the areas affected by erosion, Respondents to interviews and to questionnaires generally agree that there has been a lot of change in their natural and man-made environments, especially in terms of gully development and vegetation reduction. However, there is a disturbing level of ignorance concerning the causes and consequences of erosion. When asked to estimate the date of gully initiation in Brooks Nek, for instance, none of the respondents could give even rough estimates or a specific incident leading to the current dominant erosion problem. The general attitude towards the problem in their midst was one of indifference. The general belief is that erosion is caused not by themselves but by natural phenomena. Further, most respondents thought it is someone else's (e.g. government's) responsibility to ameliorate the harmful consequences associated with land deterioration and soil loss. The data for this thesis have been obtained through surveying the landscape directly over a three-year period (1994-6), and by using aerial photographs for 1982 (Mt Frere site) and 1993 (Mt Ayliff site). Detailed analysis was undertaken of chemical and physical characteristics of soil at both sites. In addition, quantitative and qualitative surveys of people in the area were attempted; to ascertain their understanding and contribution to the problem. The implications, as shown from the results of this investigation, are that the soil erosion problem at both study areas are largely independent of soil characteristics. On the contrary, this study will show that human practices are the major initial causes for soil erosion in all the cases investigated. It was found that over the years, the land use practices in both sites have changed significantly. Factors accelerating the development of erosion forms at Brooks Nek, for instance, include the footpaths and stock trails. In contrast, artificial contouring and poor gabion layout are the major causes in Chani. However, it must be mentioned that it is not always easy to separate the effects of human from natural causes. Once the effects of human activities exceed the optimum limits of soil resistance and resilience, erosion starts. Then erosion acceleration will not necessarily be confined to the original cause(s). Natural storms and floods, or even drought will contribute in accelerating the erosion rates. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

Thesis (M.Eng. (Hons.)) -- University of Western Sydney, 2003. / "Thesis submitted for the degree of Masters of Engineering (Honours) Environmental Engineering" Includes bibliography.

Thesis Ph. D.)(Soil Sciece)--University of Pretoria, 2004. / Title from opening screen (viewed Oct. 09, 2004). Includes bibliographical references).

Thesis (doctoral)--Wageningen University, 2004. / Includes bibliographical references.

No description available.

published_or_final_version / Geography and Geology / Doctoral / Doctor of Philosophy

This dissertation represents a unique contribution to the Spanish literature of soil erosion. The author of this document has written and published "Procesos y control de la erosion", a textbook about the engineering of soil erosion processes and the design of the most up-to-date methods and products used for erosion control. The text has been presented in Appendix A.Besides the above, the author of this dissertation is an active committee member at the International Erosion Control Association (IECA), specifically the International Development and the SOIL Fund programs. IECA members are drawn from individuals and erosion control business of different sizes. However, there was a lack of knowledge within IECA members about the formation of post-fire water repellent layers. For instance, Appendix B is represented by an article written by the author of this document, published in Environmental Connection (Volume 2, Issue 3), on July of 2008. The article gives a general description of what post-fire water repellency is, how is it formed, what factors affect it, its consequences on soil erosion, and how to control soil erosion on an efficient way when such a layer has been formed as a consequence of fire.Finally, Appendix C is a research paper in process of submission to the International Journal of Wildland Fire, about the formation of post-fire water repellent layers on Chilean Monterrey pine plantations. Since water repellent layers following wildfires have never been documented on Chilean soils, the need for such a publication is urgent, because Chilean land managers have been ignorant of such phenomenon.

O solo é um recurso natural e fundamental para toda a vida terrestre e a questão da degradação do solo assume importância não apenas ambiental, mas também de ordem social e econômica. A erosão pela água da chuva é o mais severo tipo de erosão, podendo ser encontradas diversas feições erosivas resultantes desse processo tais como erosão laminar, em sulcos ou em voçorocas. Ainda, são encontradas as feições erosivas subsuperficiais (pipes), que embora sejam menos estudadas e difíceis de quantificar, provocam perdas de solo que podem ultrapassar as quantias advindas dos processos erosivos mais tradicionalmente estudados. O objetivo deste trabalho foi o de entender a gênese das feições erosivas superficiais e subsuperficiais através da análise dos atributos físico-hídricos do solo e do relevo. Foi efetuado o mapeamento subsuperficial de pipes e a caracterização dos materiais de subsuperfície por meio da técnica geofísica da eletrorresistividade. Aliado a isso, utilizou-se a técnica da dendrogeomorfologia como ferramenta para datação, quantificação e reconstrução da dinâmica dos processos erosivos ocorrentes na área de estudo. Os resultados demonstraram que a gênese e desencadeamento dos pipes da área de estudo foi governada por fatores concorrentes, dada a complexidade da área de estudo, tais como gradiente de atributos físicos entre horizontes do solo (textura, estrutura, porosidade), estrutura e composição geológica, e gradientes topográficos. Fatores neotectônicos e morfoestruturais também poderiam estar afetando, entretanto devem ser melhor estudados. O método da eletrorresistividade foi eficiente na caracterização da geometria dos materiais em subsuperfície e na deteccção da presença de pipes, colapsados e ainda não colapsados, sendo importante para não subestimar os processos subsuperficiais. Os resultados obtidos também demonstraram o potencial da espécie Esenbeckia leiocarpa para estudos dendrogeomorfológicos, uma vez que as mudanças nos padrões de crescimento após a exposição das raízes possibilitaram datar o primeiro ano de exposição. A técnica da dendrogromorfologia se mostrou eficaz em entender a dinâmica do processo de sistemas complexos, tais como a abertura de voçorocas e voçorocas efêmeras e que a subsidência da superfície do solo causada pelos pipings é responsável pela formação e evolução das voçorocas efêmeras e pela ramificação da voçoroca principal. / Soil is a natural and fundamental resource for all terrestrial life and the question of soil degradation assumes not only environmental but also social and economic importance. Erosion by rainwater is the most severe type of erosion, and several erosive forms resulting from this process can be found such as sheet erosion, ephemeral gullies or gullies. Also, subsurface erosive forms (pipes) are found, although they are less studied and difficult to quantify, they cause soil losses that exceed the amounts coming from the more traditionally studied superficial erosive processes. The objective of this work was to understand the genesis of superficial and subsurface erosive forms from the perspective of soil and relief properties. Subsurface pipe mapping and the characterization of subsurface materials using the geophysical technique of electroresistivity, was performed. The dating, quantification and reconstruction of the dynamics of the erosive processes occurring in the study area were done using dendrogeomorphology as a tool. The results demonstrated that the genesis and the initiation of pipes in the study area was governed by competing factors, due to the complexity of the study area, such as the gradient of physical attributes between soil horizons (texture, structure, porosity), structure and geological composition, and topographic gradients. Neotectonic and morphostructural factors could also be affecting, however they should be better studied. The electroresistivity method was efficient in characterizing the geometry of the materials in subsurface and in detecting the presence of pipes, collapsed and not yet collapsed, aiding in avoiding the underestimation of the subsurface erosive processes. The results obtained demonstrated the potential of the species Esenbeckia leiocarpa for dendrogeomorphological studies, since the changes in the patterns of root growth after exposure allowed to date the first year of exposure. Dendrogromorphology also proved effective in understanding the process dynamics of complex systems, such as the opening of gullies and ephemeral gullies, and that the subsidence of the soil surface caused by pipings is responsible for the formation and evolution of ephemeral gullies and the branching of the main gully.