Institute for Groundwater Studies (IGS)
Permanent URI for this community
Browse
Browsing Institute for Groundwater Studies (IGS) by Subject "Abstraction rate"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
Item Open Access Manual on pumping test analysis in fractured rock aquifers(University of the Free State, 2000-11) Van Bosch, Izak Jacobus; Van Tonder, G. J.English: With the depletion of surface water resources in South Africa the utilisation of groundwater as the only potable water resource for communities in some rural areas is quickly becoming a reality. Failure of this resource will cause serious problems and it may even lead to loss of life. To prevent failure and to ensure the sustainability of this new resource, pumping tests are performed to determine the long-term sustainable yield of bore hole. This is the main reason why pumping tests are performed in South Africa, but in some instances pumping tests are performed to determine parameter values for aquifers. This research focussed on presenting guidelines on the proper planning and execution of the different types of pumping tests. To perform a proper pumping test involves big financial costs and therefor it is important to ensure that the correct information is obtained during such a test. Recommendations regarding the lengths of pumping tests as well as the abstraction rates during pumping tests are also made in this research. Before the interpretation of pumping test data it is important to obtain a better understanding of the basic concepts and characteristics involved in groundwater hydraulics. These concepts, together with the interpretation of diagnostic and derivative data plots are discussed in detail and it will provide the reader with enough knowledge to identify and understand the different flow regimes present in an aquifer. This research looks at the different steps involved in the interpretation of pumping test data and these steps are illustrated by means of worked examples. The different analytical methods to determine parameter values for an aquifer are also discussed in this thesis and the assumptions made in developing these methods are pointed out to the reader. In most cases these assumptions result in incorrect parameter value estimates. Numerical models, developed for the unique aquifer systems of South Africa, yielding the correct parameter values, are also discussed. Well losses can be divided into linear and non-linear losses. Non-linear well losses are mainly caused by turbulent flow inside the aquifer and borehole. This research however shows a non-linear relationship between drawdown and abstraction rate while the flow inside the aquifer is still linear. The non-linearity between drawdown and abstraction rate is corroborated by means of several examples and this nonlinearity can only be the result of the unique composition of aquifers in this country. Different abstraction rates result in different fractures being dewatered and fracture extents that are reached, causing a smaller effective T-value. The consequence of this non-linearity is that it is very difficult to extrapolate the future water levels in an aquifer. To estimate a sustainable yield in the case of non-linearity this research recommends a revised step drawdown test. This l00-minute test, conducted without constant time intervals, will also point out the positions of the main water strikes. A method, developed in South Africa, with which the long-term sustainable yield can be determined, is also discussed in detail and it is explained by means of a step by step worked example. Included in this method is the effect of boundary conditions as well as a risk analysis.