The determination of geomorphologically effective flows for selected eastern sea-Board Rivers in South Africa
- Authors: Dollar, Evan S J
- Date: 2001
- Subjects: Rivers--South Africa River channels Geomorphology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4824 , http://hdl.handle.net/10962/d1005499
- Description: In South Africa the need to protect and manage the national water resource has led to the development of the Reserve as a basic right under the National Water Act (1998). The Ecological Reserve relates to the quality and quantity of water necessary to protect the sustainable functioning of aquatic ecosystems. The geomorphological contribution to setting the Reserve has focussed on three groups of information requirements: the spatial and temporal availability of habitat, the maintenance of substratum characteristics, and the maintenance of channel form. This thesis focusses on the second and third information requirements. The thesis has attempted to achieve this by adding value to the theoretical and applied understanding of the magnitude and frequency of channel forming discharge for selected southern African rivers. Many of the eastern sea-board rivers are strongly influenced by bed rock in the channel perimeter, and by a highly variable hydrological regime. This has resulted in characteristic channel forms, with an active channel incised into a larger macro-channel being a common feature of eastern seaboard rivers. Within the active channel inset channel benches commonly occur. This alluvial architecture is used to provide clues as to the types of flows necessary to meet the Reserve. Three river basins are considered : the Mkomazi, Mhlathuze and Olifants. The Mkomazi is a relatively un-impacted perennial eastern-sea board river and forms the research component of the study. The Mhlathuze and Olifants rivers are highly regulated systems and form the application component of the study. Utilising synthesised daily hydrological data, bed material data, cross-sectional surveys, hydraulic data and relevant bed material transport equations, channel form was related to dominant discharge and effective discharge in an attempt to identify the magnitude and frequency offlows that can be considered to be ' effective'. Results from the Mkomazi River indicate that no single effective discharge exists, but rather that there is a range of effective discharges in the 5-0.1% range on the 1-day daily flow duration curves that are responsible for the bulk (>80%) of the bed material transport. Only large floods (termed 'reset'discharges) with average return periods of around 20 years generate sufficient stream power and shear stress to mobilise the entire bed. The macro-channel is thus maintained by the large ' reset' flood events, and the active channel is maintained both by the range of effective discharges and the ' reset 'discharges. These are the geomorphologically 'effective' flows. Results from the Mhlathuze River have indicated that the Goedertrouw Dam has had a considerable impact on the downstream channel morphology and bed material transport capacity and consequently the effective and dominant discharges. It has been suggested that the Mhlathuze River is now adjusting its channel geometry in sympathy with the regulated flow environment. Under present-day conditions it has been demonstrated that the total bed material load has been reduced by up to three times, but there has also been a clear change in the way in which the load has been distributed around the duration curve. Under present-day conditions, over 90% of the total bed material load is transported by the top 5% of the flows, whereas under virgin flow conditions 90% of the total bed material load was transported by the top 20% of the flows. For the Olifants River there appears to be no relationship between the estimated bankfull discharge and any hydrological statistic. The effective discharge flow class is in the 5-0.01% range on the 1-day daily flow duration curve. It has also been pointed out that even the highest flows simulated for the Olifants River do not generate sufficient energy to mobilise the entire bed. It is useful to consider the Olifants River as being adapted to a highly variable flow regime. It is erroneous to think of one ' effective' discharge, but rather a range of effective discharges are of significance. It has been argued that strong bed rock control and a highly variable flow regime in many southern African rivers accounts for the channel architecture, and that there is a need to develop an ' indigenous knowledge' in the management of southern African fluvial systems
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The historical development of geography as a subject in the schools of the Cape Province (1772-1951)
- Authors: Knox, John Charles
- Date: 1959
- Subjects: Geography -- Study and teaching -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1974 , http://hdl.handle.net/10962/d1012702 , Geography -- Study and teaching -- South Africa -- Cape of Good Hope
- Description: As the title indicates, this is a study of the historical emergence of geography as a subject in Cape schools, and covers the period 1772-1951. The account is not merely descriptive and factual, for wherever possible an attempt is made to assess the nature and scope of the geography which was taught at different periods in relation to modern, authoritative ideas concerning the pedagogic application of the subject in the school. The work as a whole is predominantly concerned with the historical development of geography in the secondary school. However, in the initial four chapters the slight and insubstantial nature of the available data precludes the possibility of differentiating between geoeraphy of primary standard and that of secondary standard, and in these early chapters all references to the subject are consequently generalized. In Chapter 5, which deals with the period during which Langham Dale was Superintendent-Genera l of Education, geography of secondary standard becomes distinguishable from that of primary standard for the first time, and from this point onwards the two are differentiated to the fullest extent possible, and the former is chiefly emphasized. The entire study is presented against a broad background of relevant, educational developments of a general nature.
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