Alice Springs town basin, review 2003
Read, R. E.
E-Publications; E-Books; PublicationNT; Report ; no. 42/2003
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Department of Infrastructure, Planning and Environment
Report ; no. 42/2003
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5.11 Volume of water in storage 5.11.1 Extractable volumes by quality and zone Estimated extractable volumes are listed in Table 8 . Figure 29 shows the relation between TDS and extractable volume for the Southern Zone. These were derived using Surfer to estimate volumes of saturated aquifer, and assuming a specific yield of 0.07, and porosity of 0.2. It is essential to distinguish between the meaning of these numbers. The specific yield is the volume released by draining a unit volume of aquifer. Most of the water in the aquifer is held by capillary tension and is not released by gravity drainage. However for calculating the volume of water of low salinity that may be displaced by lateral flow of more saline water the total porosity of about 0.2 may be applicable. For the Northern Zone the estimate is quite straightforward, as the volume of water of under 1000 mg/L in storage exceeds the volume that could be released by gravity drainage. Table 8 Extractable volumes in zones Salinity Northern Zone Southern Zone, >5L/s (1) Area km2 Volu me ML <5 L/s >5 L/s Area km2 Volume ML Total working storage (2) 1.9 440 120 320(3) 5.8 2100 All <500 mg/L 0(4) 0 0 0 0 0 All<800 mg/L 0.26 260440 120 320 0.04 70 All<1000 mg/L 0.72 440 (5) 0.16 200 All<1500 mg/L (5) 0.69 1000 All<2000 mg/L (5) 1.1 1700 > 2000 mg/L (5) 4.7 400(6) (1) There are areas of aquifer with yields under 5 L/s, but all the available resource could be extracted from areas where bore yields are > 5L/s. (2) This has been determined by estimating the difference in stored volume between the 08/2002 potentiometric surface and the 10/1964 potentiometric surface. (3) The only known area where bores yielding above 5L/s can be constructed is around RN 6823 in Colacag Park. (4) There is some water in this zone under 500 mg/L, but experience is that it could not be extracted in significant quantities. (5) There is water of these salinities in the Northern Zone, but all the available storage could be extracted by pumping only the better quality water. (6) This is based on the total storage less what could be extracted at better quality. The volume of stored saline water is far larger than this, and it could be beneficial to remove some of it to induce recharge of better water. 45