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Diagnostic derivative interpretation of drawdown data from pumping tests is discussed in this paper. An emphasis is placed on the conceptualization of derivative term of dlgs/dlgt. Use of a combined plot of dlgs/dlgt and ds/dlgt is made to identify various flow patterns from variable discharge tests with infinite conditions, constant rate tests in bounded aquifers, and tests involving double porosity, which can be used to further characterize the aquifer. Compared with the standard derivative method (ds/dlgt), the combined derivative analysis of dlgs/dlgt and ds/dlgt of drawdown behaviours possesses certain advantages identified as follows: (1) the plot of dlgs/dlgt is strikingly sensitive for use in unveiling differences between pumping and recovery periods in a variable discharge test; (2) storativity (S) of pumped aquifers can be accurately evaluated by the combined plot; and (3) a quantitative assessment of double porosity behaviour can also be achieved. Based on applied case studies, Lagrange Interpolation Regression (LIR) is recommended for numerical derivative calculation. Advantages and disadvantages of LIR and traditional methods are demonstrated via a selected case study. The result of the case study confirms that LIR is a preferred method for numerical derivative calculation as it can be used to effectively minimise noisy effect during derivative processes. The proposed derivative approach provides the hydrologists with an additional tool for characterizing pumped aquifers.

Although water resources managers speak of a water crisis in Africa, the management of ground water has to date not featured strongly in national and regional African water agendas. Examination of the physical environment of the continent and, in particular, the water resources in relation to the socioeconomic landscape and regional development challenges makes it clear that widely occurring, albeit largely low-yielding, ground water resources will be crucial in the achievement of water security and development. Ground water is important primarily in domestic water and sanitation services, but also for other local productive needs like community gardens, stock watering, and brick-making, all essential to secure a basic livelihood and thus to alleviate poverty. Despite the importance of small-scale farming in Africa, there is little information on the present and potential role of ground water in agriculture. In contrast to its socioeconomic and ecological importance, ground water has remained a poorly understood and managed resource. Widespread contamination of ground water resources is occurring, and the important environmental services of ground water are neglected. There appear to be critical shortcomings in the organizational framework and the building of institutional capacity for ground water. Addressing this challenge will require a much clearer understanding and articulation of ground water's role and contribution to national and regional development objectives and an integrated management framework, with top-down facilitation of local actions.