Published Article / A stream flow at an outlet of a catchment can be entirely a base flow or direct flow or a combination of both. The base flow component of a stream is mainly contributed from the ground water storage which often is an open aquifer whereas the direct flow component is mainly the result of a direct response of a rainfall event. The Upper Modder river basin catchment is considered to be the origin of the Modder River which supplies water to Rustfontein Dam, situated at the outlet of the C52A with an area of 928 km2. Nine years of daily stream flow showed a continuous none zero discharge throughout the year. During the rainy season the discharge of the stream increases significantly. Thus, it is necessary to separate the direct and base flow of the stream in order to understand the important component that is more likely to be affected by different land use changes in a catchment. The Modder river daily mean flow at the inlet of Rustfontein dam (in Central South Africa) was analysed using four base flow separation methods, the Nathan & McMahon (N&M), the Chapman, Smakhtin & Watkins (S&W) method and the frequency duration analysis. All the methods gave higher percentage of the low flow component, except for the S&W method which underestimated it. The N&M filtering equation gave base flow components greater than 66% in 1999 and increased to 84% in 2007 while the Chapman equation revealed 65% and 74% in 1999 and 2007, respectively. Similarly, the frequency duration analysis gave 62% in 1999 and increased to 79% in 2007. The frequency duration analysis gave up to 13% lower percentage than the N&M (1990) filtering equation. The nine year base flow averages are 69%, 69% and 75% for frequency duration analysis, Chapman (1999) and N&M (1990) filtering equations, respectively. The result revealed that the Modder River is largely supplied by the ground water discharge. The result seemed to concur with the fact that for a semi-arid catchment such as the Modder river basin, with an average annual runoff coefficient of approximately 6%, the contribution of annual rainfall to direct runoff is very minimal.

published_or_final_version / Applied Geosciences / Master / Master of Science

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Advances in manufacturing techniques over the last decade have made it possible to make electrical devices with dimensions as small as 90 nanometers [I]. Using similar techniques, devices that perform moving mechanical tasks less than 100 pm are being manufactured in quantity [2] [3], e.g., pumps, turbines, valves and nozzles. These devices are incorporated into microelectromechanical systems (MEMS) that can be potentially used in devices such as medical and chemical sensors, and fuel cells. The gas and fluid flows in devices of this size exhibit behavior that can not be described by the classical Navier-Stokes and Fourier equations of continuum mechanics. This happens when flows become rarefied such that the mean free path (distance between two subsequent particle collisions) is not negligible compared to the characteristic length scale. The rarefaction of a fluid flow is also seen in the upper atmosphere for larger length scales, e.g., for re-entry for space craft and some supersonic jet aircraft. Currently, when one looks to model fluid flow and heat transfer in a rarefied flow there are two predominantly accepted choices. Either one uses jump and slip boundary conditions with the Navier-Stokes and Fourier (NSF) equations, or a statistical particle model such as direct simulation Monte-Carlo (DSMC) [4] and the Boltzmann equation. DSMC is computationally intensive for complex flows and the NSF solutions are only valid for low degrees of rarefaction. As an alternative to these methods we have used Grad's 13 moment expansion of the Boltzmann equation [5]. For its implementation, a set of boundary conditions and three numerical methods for the solution have been devised. The model is applied to the solution of 2-D micro Couette flow with heat transfer. Results are compared to those obtained from the Navier-Stokes-Fourier equations, reduced Burnett equations, Regularized 13 moment equations and DSMC simulations.

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Graduation date: 1983 / Figures in original document are black and white photocopies. Best scan available.

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