A study of the airflow on the windward slope of a transverse dune in the Alexandria coastal dunefield
- Authors: Burkinshaw, Jennifer Ruth
- Date: 2021-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52734 , vital:43883
- Description: Our understanding of the evolution of dune morphology has been hampered by a lack of empirical observations of airflow behaviour over dune forms. Sand dunes intrude into the atmospheric boundary layer and convergence of streamlines results in an acceleration of airflow up the windward slopes of dunes. This study examines the airflow structure and corresponding bedform development on the windward slope of a 7 m high transverse dune on the edge of the Alexandria coastal dunefield, Algoa Bay, South Africa. The Alexandria dunefield is subjected to a trimodal wind regime, consisting of the dominant south-westerly which blows all year round, summer easterlies and winter northwesterlies. The morphology of the study dune, Dune13, is controlled by the easterlies and north-westerlies, and reverses seasonally with respect to these two winds. Seven section lines 30 m apart and normal to the dune crest were surveyed regularly over the period of a year to monitor the reversal process. Three detailed topographic surveys were also done during this period. Airflow behaviour was monitored during the year. Wind speed profiles on the windward slope of the dune were measured using 4 to 5 vertical arrays of anemometers positioned from the base of the dune to the crest on a 1 selected section line. Usually 4 to 5 anemometers were deployed in each vertical array, from a height of 6 to 10 cm above the surface, up to a height of 150 cm above the surface. Initially 8 microanemometers were available; ultimately 28 anemometers were run simultaneously. An independent weather station at an elevation of 6 m recorded the unaccelerated flow. Local gradient measurements and erosion and deposition rates were recorded along selected section lines. Strong summer easterly winds (14 m/sec at 1.4 m above the dune crest) were measured on a dune slope in the process of being transformed from a slipface to a stoss slope. The following winter, light north-westerly winds (typically B m/sec at 1.6 m above the dune crest) were measured on the new windward slope already reversed by the prevailing winter wind. Airflow data confirm the compression of airflow against the windward slope resulting in a non-logarithmic wind speed profile. Compression results in an increased shear velocity within 30 cm of the dune surface, and the dune slope is eroded. Higher up in the wind speed profile, shear velocity decreases to 0.1 m/sec. It is not known at what height the wind speed profile recovers from the intrusion of the dune into the boundary layer. High values of shear velocity (1.6 m/sec) above the rounded crestal area of the dune record the recovery of the wind speed profile from flow divergence, which is a response to the rapid reduction of dune gradient and is accompanied by deposition of sand in this region. 2 The erosion pin data act as a simple and sensitive test for changes in gradient, reflecting the dune's response to changes in the airflow regime. The shape of the dune plays a major role in determining the extent of the compression and the distribution of shear velocity up the slope. Increased shear velocity is experienced on that part of the slope which is nonaerodynamic with respect to the prevailing wind. Under unidirectional conditions, feedback between flow and form results ultimately in a slope with a curvature such that shear velocity increases systematically upslope. The survey data and erosion pin data record the reversal process as the dune achieves a new steady state during each wind season. The existence of a non-logarithmic wind speed profile makes it difficult to know what relevant measure of shear velocity is to be used in sand transport equations. Future work should include wind speed measurements within 10 cm of the surface. An ideal study modelling aeolian bedform development would utilise wind tunnel measurements, combined with field measurements such as obtained in this study, for comparison with numerical modelling. The study needs to be extended to 3-dimensional airflow measurements. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Burkinshaw, Jennifer Ruth
- Date: 2021-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52734 , vital:43883
- Description: Our understanding of the evolution of dune morphology has been hampered by a lack of empirical observations of airflow behaviour over dune forms. Sand dunes intrude into the atmospheric boundary layer and convergence of streamlines results in an acceleration of airflow up the windward slopes of dunes. This study examines the airflow structure and corresponding bedform development on the windward slope of a 7 m high transverse dune on the edge of the Alexandria coastal dunefield, Algoa Bay, South Africa. The Alexandria dunefield is subjected to a trimodal wind regime, consisting of the dominant south-westerly which blows all year round, summer easterlies and winter northwesterlies. The morphology of the study dune, Dune13, is controlled by the easterlies and north-westerlies, and reverses seasonally with respect to these two winds. Seven section lines 30 m apart and normal to the dune crest were surveyed regularly over the period of a year to monitor the reversal process. Three detailed topographic surveys were also done during this period. Airflow behaviour was monitored during the year. Wind speed profiles on the windward slope of the dune were measured using 4 to 5 vertical arrays of anemometers positioned from the base of the dune to the crest on a 1 selected section line. Usually 4 to 5 anemometers were deployed in each vertical array, from a height of 6 to 10 cm above the surface, up to a height of 150 cm above the surface. Initially 8 microanemometers were available; ultimately 28 anemometers were run simultaneously. An independent weather station at an elevation of 6 m recorded the unaccelerated flow. Local gradient measurements and erosion and deposition rates were recorded along selected section lines. Strong summer easterly winds (14 m/sec at 1.4 m above the dune crest) were measured on a dune slope in the process of being transformed from a slipface to a stoss slope. The following winter, light north-westerly winds (typically B m/sec at 1.6 m above the dune crest) were measured on the new windward slope already reversed by the prevailing winter wind. Airflow data confirm the compression of airflow against the windward slope resulting in a non-logarithmic wind speed profile. Compression results in an increased shear velocity within 30 cm of the dune surface, and the dune slope is eroded. Higher up in the wind speed profile, shear velocity decreases to 0.1 m/sec. It is not known at what height the wind speed profile recovers from the intrusion of the dune into the boundary layer. High values of shear velocity (1.6 m/sec) above the rounded crestal area of the dune record the recovery of the wind speed profile from flow divergence, which is a response to the rapid reduction of dune gradient and is accompanied by deposition of sand in this region. 2 The erosion pin data act as a simple and sensitive test for changes in gradient, reflecting the dune's response to changes in the airflow regime. The shape of the dune plays a major role in determining the extent of the compression and the distribution of shear velocity up the slope. Increased shear velocity is experienced on that part of the slope which is nonaerodynamic with respect to the prevailing wind. Under unidirectional conditions, feedback between flow and form results ultimately in a slope with a curvature such that shear velocity increases systematically upslope. The survey data and erosion pin data record the reversal process as the dune achieves a new steady state during each wind season. The existence of a non-logarithmic wind speed profile makes it difficult to know what relevant measure of shear velocity is to be used in sand transport equations. Future work should include wind speed measurements within 10 cm of the surface. An ideal study modelling aeolian bedform development would utilise wind tunnel measurements, combined with field measurements such as obtained in this study, for comparison with numerical modelling. The study needs to be extended to 3-dimensional airflow measurements. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text:
- Date Issued: 2021-04
Main thesis title: Onderwysers se belewing van multikulturele onderwys
- Authors: Strydom, Louise
- Date: 1999-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: Afrikaans
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/60003 , vital:62732
- Description: The South African Schools’ Act of 1996 terminated segregated education in South Africa. Multi-cultural education has become a reality in the new democratic South Africa. As a result of this major shift in policy, the researcher probed for an answer to the following question: “How does the teacher, especially the teacher already in service, experience this new situation regarding multi-cultural education?” To find an answer to this question, a literature study and empirical research, making use of a representative sample of respondents in the Southern Cape, were undertaken. The researcher has personally experienced the challenges of having to adapt from a mono-cultural teaching environment to a multi-cultural teaching environment at school level, hence a further interest in this research problem. Relevant terminology was highlighted and a brief historical synopsis of the course that multi-cultural education took in Western societies such as the USA, Canada, Australia and Britain was studied. These sources were utilised to draw a comparison with the South African situation. A concise synopsis of the history of multi-cultural education in South Africa was also undertaken to highlight the complexity of the educational situation presently being experienced in South Africa. The empirical research, with a target group representing teachers in the Southern Cape, was undertaken by means of a self-compiled questionnaire to make an analysis of teachers’ attitudes, expectations and perceptions of multi-cultural education as experienced in the classroom. The information obtained from the respondents indicated a generally positive attitude towards multi-cultural education amongst teachers. A great need for in-service training also became evident. xvi The researcher has thus made recommendations regarding in-service training that she thinks is of utmost importance. The practical problems that were highlighted during the research, make a vital contribution towards the successful implementation of multi-cultural education in South Africa. , Thesis (DEd) -- Faculty of Education, 1999
- Full Text:
- Date Issued: 1999-04
- Authors: Strydom, Louise
- Date: 1999-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: Afrikaans
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/60003 , vital:62732
- Description: The South African Schools’ Act of 1996 terminated segregated education in South Africa. Multi-cultural education has become a reality in the new democratic South Africa. As a result of this major shift in policy, the researcher probed for an answer to the following question: “How does the teacher, especially the teacher already in service, experience this new situation regarding multi-cultural education?” To find an answer to this question, a literature study and empirical research, making use of a representative sample of respondents in the Southern Cape, were undertaken. The researcher has personally experienced the challenges of having to adapt from a mono-cultural teaching environment to a multi-cultural teaching environment at school level, hence a further interest in this research problem. Relevant terminology was highlighted and a brief historical synopsis of the course that multi-cultural education took in Western societies such as the USA, Canada, Australia and Britain was studied. These sources were utilised to draw a comparison with the South African situation. A concise synopsis of the history of multi-cultural education in South Africa was also undertaken to highlight the complexity of the educational situation presently being experienced in South Africa. The empirical research, with a target group representing teachers in the Southern Cape, was undertaken by means of a self-compiled questionnaire to make an analysis of teachers’ attitudes, expectations and perceptions of multi-cultural education as experienced in the classroom. The information obtained from the respondents indicated a generally positive attitude towards multi-cultural education amongst teachers. A great need for in-service training also became evident. xvi The researcher has thus made recommendations regarding in-service training that she thinks is of utmost importance. The practical problems that were highlighted during the research, make a vital contribution towards the successful implementation of multi-cultural education in South Africa. , Thesis (DEd) -- Faculty of Education, 1999
- Full Text:
- Date Issued: 1999-04
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