An erosion and sediment delivery model for semi-arid catchments
- Authors: Bryson, Louise Kay
- Date: 2016
- Subjects: Sedimentation and deposition , Erosion , Watershed management -- South Africa , Water-supply -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:6056 , http://hdl.handle.net/10962/d1020331
- Description: Sedimentation has become a significant environmental threat in South Africa as it intensifies water management problems in the water-scarce semi-arid regions of the country. As South Africa already allocates 98% of available water, the loss of storage capacity in reservoirs and degraded water quality has meant that a reliable water supply is compromised. The overall aim of this thesis was to develop a catchment scale model that represents the sediment dynamics of semi-arid regions of South Africa as a simple and practically applicable tool for water resource managers. Development of a conceptual framework for the model relied on an understanding of both the sediment dynamics of South African catchments and applicable modelling techniques. Scale was an issue in both cases as most of our understanding of the physical processes of runoff generation and sediment transport has been derived from plot scale studies. By identifying defining properties of semi-arid catchments it was possible to consider how temporal and spatial properties at higher levels emerged from properties at lower levels. These properties were effectively represented by using the Pitman rainfall-runoff model disaggregated to a daily timescale, the Modified Universal Soil Loss Equation (MUSLE) model incorporating probability function theory and through the representation of sediment storages across a semi-distributed catchment. The model was tested on two small and one large study catchment in the Karoo, South Africa, with limited observed data. Limitations to the model were found to be the large parameter data set and the dominance of structural constraints with an increase in catchment size. The next steps in model development will require a reduction of the parameter data set and an inclusion of an in-stream component for sub-catchments at a larger spatial scale. The model is applicable in areas such as South Africa where water resource managers need a simple model at the catchment scale in order to make decisions. This type of model provides a simple representation of the stochastic nature of erosion and sediment delivery over large spatial and temporal scales.
- Full Text:
- Authors: Bryson, Louise Kay
- Date: 2016
- Subjects: Sedimentation and deposition , Erosion , Watershed management -- South Africa , Water-supply -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:6056 , http://hdl.handle.net/10962/d1020331
- Description: Sedimentation has become a significant environmental threat in South Africa as it intensifies water management problems in the water-scarce semi-arid regions of the country. As South Africa already allocates 98% of available water, the loss of storage capacity in reservoirs and degraded water quality has meant that a reliable water supply is compromised. The overall aim of this thesis was to develop a catchment scale model that represents the sediment dynamics of semi-arid regions of South Africa as a simple and practically applicable tool for water resource managers. Development of a conceptual framework for the model relied on an understanding of both the sediment dynamics of South African catchments and applicable modelling techniques. Scale was an issue in both cases as most of our understanding of the physical processes of runoff generation and sediment transport has been derived from plot scale studies. By identifying defining properties of semi-arid catchments it was possible to consider how temporal and spatial properties at higher levels emerged from properties at lower levels. These properties were effectively represented by using the Pitman rainfall-runoff model disaggregated to a daily timescale, the Modified Universal Soil Loss Equation (MUSLE) model incorporating probability function theory and through the representation of sediment storages across a semi-distributed catchment. The model was tested on two small and one large study catchment in the Karoo, South Africa, with limited observed data. Limitations to the model were found to be the large parameter data set and the dominance of structural constraints with an increase in catchment size. The next steps in model development will require a reduction of the parameter data set and an inclusion of an in-stream component for sub-catchments at a larger spatial scale. The model is applicable in areas such as South Africa where water resource managers need a simple model at the catchment scale in order to make decisions. This type of model provides a simple representation of the stochastic nature of erosion and sediment delivery over large spatial and temporal scales.
- Full Text:
A review of sediment-hosted gold deposits of the world with special emphasis on recent discoveries outside the U.S.A
- Authors: Daglioglu, Yasar Mehmet
- Date: 1996
- Subjects: Gold ores , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4997 , http://hdl.handle.net/10962/d1005609 , Gold ores , Sedimentation and deposition
- Description: Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).
- Full Text:
- Authors: Daglioglu, Yasar Mehmet
- Date: 1996
- Subjects: Gold ores , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4997 , http://hdl.handle.net/10962/d1005609 , Gold ores , Sedimentation and deposition
- Description: Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).
- Full Text:
Review of carbonate hosted lead-zinc (copper) deposits and the geological factors affecting their shape, size and grade
- Authors: McDonald, B
- Date: 1981
- Subjects: Lead ores , Zinc ores , Copper ores , Sedimentology , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5028 , http://hdl.handle.net/10962/d1006903
- Description: From Introduction: For at least two centuries and a corresponding number of generations of geologists and miners there has been active argument concerning the origin of certain types of carbonate hosted mineral deposit. The characterization of the type itself was and still is debatable. Objections have been raised to grouping several examples under one heading because each has its individually distinctive features. ·This is especially applicable to the carbonate hosted lead-zinc "sedimentary" deposits. The type that will be discussed in the text to follow is composed chiefly of galena, sphalerite, barite and fluorite, with pyrite , marcasite and chalcopyrite as conspicuous accessory ore minerals. Exceptions to this general copper deficient characteristic displayed by the sedimentary carbonate-hosted lead-zinc deposits are the deposits at Tsumeb and Kombat, Namibia. These deposits are hosted by the carbonate sequence of the Otavi Shelf sediments, and copper, in the form of tennantite, chalcopyrite and bornite, is the major ore constituent. Calcite, aragonite, dolomite and quartz are the commonest nonmetallic gangue minerals but siderite and silica may also be present. In contrast with other lead and zinc sulphide (volcanogenic) deposits, those to be considered here seldom carry noteworthy amounts of silver or any other precious metals. Commonly the country rock is a carbonate; limestone or dolomite, but deposits in. sandstone, shale and conglomerate are not unknown. Characteristic features are ore bodies that extend parallel or nearly so with the bedding although many such deposits are partly, or completely developed along crosscutting fissures and breccias. Some observers regard these fissure fillings as evidence for a magmatic source of the metals, whereas others regard them as an indication of remobilization of ions, metals or minerals orginally present in low-grade stratiform deposits elsewhere in the stratigraphic succession.
- Full Text:
- Authors: McDonald, B
- Date: 1981
- Subjects: Lead ores , Zinc ores , Copper ores , Sedimentology , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5028 , http://hdl.handle.net/10962/d1006903
- Description: From Introduction: For at least two centuries and a corresponding number of generations of geologists and miners there has been active argument concerning the origin of certain types of carbonate hosted mineral deposit. The characterization of the type itself was and still is debatable. Objections have been raised to grouping several examples under one heading because each has its individually distinctive features. ·This is especially applicable to the carbonate hosted lead-zinc "sedimentary" deposits. The type that will be discussed in the text to follow is composed chiefly of galena, sphalerite, barite and fluorite, with pyrite , marcasite and chalcopyrite as conspicuous accessory ore minerals. Exceptions to this general copper deficient characteristic displayed by the sedimentary carbonate-hosted lead-zinc deposits are the deposits at Tsumeb and Kombat, Namibia. These deposits are hosted by the carbonate sequence of the Otavi Shelf sediments, and copper, in the form of tennantite, chalcopyrite and bornite, is the major ore constituent. Calcite, aragonite, dolomite and quartz are the commonest nonmetallic gangue minerals but siderite and silica may also be present. In contrast with other lead and zinc sulphide (volcanogenic) deposits, those to be considered here seldom carry noteworthy amounts of silver or any other precious metals. Commonly the country rock is a carbonate; limestone or dolomite, but deposits in. sandstone, shale and conglomerate are not unknown. Characteristic features are ore bodies that extend parallel or nearly so with the bedding although many such deposits are partly, or completely developed along crosscutting fissures and breccias. Some observers regard these fissure fillings as evidence for a magmatic source of the metals, whereas others regard them as an indication of remobilization of ions, metals or minerals orginally present in low-grade stratiform deposits elsewhere in the stratigraphic succession.
- Full Text:
An examination of the spatial variation of surficial sediment characteristics in the Howison's Poort Reservoir
- Authors: Weaver, Alex van Breda
- Date: 1979
- Subjects: Howison's Poort Reservoir , South Africa , Sedimentation and deposition
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:4790 , http://hdl.handle.net/10962/d1001890
- Description: From Introduction: Lakes, estuaries and man-made water impoundments can be considered as intervening basins which provide for the temporary storage both of sediment and of water. Because of the potential energy of soil in elevated positions and because of the kinetic energy of water flowing under the influence of gravity, eroded material is eventually transported to the lowest possible level, i.e. the ocean deeps, or some intervening basin. This denudation process may be compared with Newton’s second law of thermodynamics which states that each system tends to move in the direction of lowest energy. Sedimentation in intervening basins may be seen as part of the natural process of landscape evolution. The rates at which sedimentation occurs may be strongly influenced by the activities of man.
- Full Text:
- Authors: Weaver, Alex van Breda
- Date: 1979
- Subjects: Howison's Poort Reservoir , South Africa , Sedimentation and deposition
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:4790 , http://hdl.handle.net/10962/d1001890
- Description: From Introduction: Lakes, estuaries and man-made water impoundments can be considered as intervening basins which provide for the temporary storage both of sediment and of water. Because of the potential energy of soil in elevated positions and because of the kinetic energy of water flowing under the influence of gravity, eroded material is eventually transported to the lowest possible level, i.e. the ocean deeps, or some intervening basin. This denudation process may be compared with Newton’s second law of thermodynamics which states that each system tends to move in the direction of lowest energy. Sedimentation in intervening basins may be seen as part of the natural process of landscape evolution. The rates at which sedimentation occurs may be strongly influenced by the activities of man.
- Full Text:
- «
- ‹
- 1
- ›
- »