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Alice Springs town basin, review 2003



Alice Springs town basin, review 2003


Read, R. E.


E-Publications; E-Books; PublicationNT; Report ; no. 42/2003




Made available via the Publications (Legal Deposit) Act 2004 (NT).





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Department of Infrastructure, Planning and Environment

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Alice Springs


Report ; no. 42/2003

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I- 1 1 INTRODUCTION There is a great deal of pumping test data available for the Town Basin, and it was not possible to analyse all of them for this report. Table I-1 lists all the tests in the Alice Springs pump test register. 2 DISCUSSION Drawdown in a production bore at a given time can be described by the Jacob Equation. s=BQ +CQ2 Where s is drawdown at a given time Q is pumping rate B is a constant that contains both aquifer losses and bore construction effects C is a constant that describes the turbulent flow losses, usually in the bore screen and the immediately adjacent aquifer. The constants were determined for all production bores for which suitable step tests could be found, and are shown in Table I-2 . Figures I-1 to 7 show the relationships between the B and C parameters and screen length and aperture, to each other, and to transmissivity. The following conclusions can be drawn: Neither parameter shows a correlation with screen length. Both parameters show a correlation with screen aperture. The parameters are strongly correlated to each other. Both parameters are strongly correlated with transmissivity. Hence screens of sufficient length have been used. The relationship with aperture is probably an indirect effect of the correlation between transmissivity and grain size. Figure I-7 shows that the turbulent flow losses occur in the aquifer and not just in the slots. The relationships with transmissivity provide a means of assessing the efficiency of bore completions. There are only four bores completed with 150 mm screens, and the plot of their performance is scattered. Based on this limited data set there is no evidence to show that the large diameter bores are more efficient than 150 mm bores. 3 FRINGE AREAS 4 Introduction An attempt was made to estimate hydraulic parameters in the fringes of the Town Basin where few or no systematic pump tests have been conducted. Bores with yields were selected. In general it has been necessary to make assumptions as to storage coefficient and pumping times. In some cases qualitative descriptions such as small have been given a possible range of numerical values. Many bores have no logs. Of those with drillers logs it is not possible to distinguish between alluvium and weathered bedrock. For most of the bores there is no record of where the water was cut, and it is not clear whether the aquifers are in alluvium, weathered bedrock or fresh fractured bedrock. To estimate hydraulic conductivity it was generally assumed that the saturated thickness was the total depth of the bore below water table.