Galiwinku Groundwater Resource and Evaluation DLH-492
Yin Foo, Des
E-Publications; E-Books; PublicationNT; Report ; 6/1984
Made available via the Publications (Legal Deposit) Act 2004 (NT).
Dept. of Transport and Works
Report ; 6/1984
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Technical Report WRD84006 Viewed at 14:07:13 on 29/07/2010 Page 28 of 60. 4 . MODELLING BOREFIELD PERFORMANCE The performance of the aquifer was modelled under present and proposed extraction rates. A finite difference computer program developed by Prickett and Lonnquist (Ref 7) was used. 4.1 Borefield Modelling The following assumptions were made about the aquifer in developing the model: (i) (ii) (iii) (iv) (v) its extent is as shown in Figure 4.1 (b). Where it is confined, it has been modelled as partly extending beneath the sea, boundaries exist on all to no-flow conditions, sides and are subject it is horizontal and aroundwater throughflow has been neglected due to lack of data; the aquifer is isotropic. A value of transmissivity of 600 m2/day has been adopted througl.l<;jut. It has a storage coefficient of 2 x 10 when confined and a specific yield of 0.1 when unconfined; it is fully recharged each wet season. These assumptions were neglect of throughflow in conservative measure. based the on available data. The model is considered a The model was calibrated against test pumping results from bore RN 20921. Although the results of that test could not be analysed, the model was calibrated by considering the order of magnitude of drawdown. A maximum drawdown of 0.9 m in the test was attained at approximately 350 minutes. The model predicted a drawdown 15% greater at the corresponding time as shown in Figure 4.l(a). Water levels during the test can also be assumed to contain a component due to tidal effects. The results of simulated pumping in the unconfined aquifer region showed the model to be very conservative in this area. The specific yield value of 0.10 was adopted since a higher value could not be justified. The following pumping regimes were simulated for 300 days continuous pumping: (i) currently operating bore field i.e. - bores RlJ 20927, RN 6252, RN 8474 and RN 8475 being pumped at 13.3, 2.3, 3.2 and 5.0 Lis respectively; and (ii) borefield upgraded to produce a total of 30 Lis i.e. - bores RN 20927, RN 20921 and RN 6252 being pumped at 15 Lis, 10 Lis and 5 L!s respectively.
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