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East Alligator district centre water supply assessment : Kakadu National Park



East Alligator district centre water supply assessment : Kakadu National Park

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D . Pidsley


Jamieson, M.; Pidsley, D.; Paiva, Jerome


E-Publications; E-Books; PublicationNT; Technical Report ; 26/1991




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






Water-supply -- Northern Territory -- Kakadu National Park; Groundwater -- Northern Territory -- Kakadu National Park; Kakadu National Park (N.T.)

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Power and Water Authority

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Technical Report ; 26/1991


1 v. : ill., maps ; 30 cm.

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Technical Report WRD91026 Viewed at 15:07:48 on 29/07/2010 Page 42 of 107. Using Darcy's flow equation with the long term parameters discussed in Section 4.5, and taking a single extraction point, the slope of the pumped water level in the aquifer is 1 in 50. For an aquifer width of 200 m, this gives a water level drop of 2 m at the edges of the strip aquifer. This is a small enough drop to allow the, following assumption. It is assumed that water level contours through the aquifer are perpendicular to the sides of the strip aquifer. Using this, and an extraction rate of 122 kL/day a drawdown of 14.5 m is determined. Drawdown due to well effeci:s at an extraction rate of 2.2 Ljs is 0.5 m (see Section 4.4), 60 the total calculated drawdown in the well is 15 m. SeasonEll variations in water levels are about 4 m (see Section 4.4). When drilled in the early dry season, the water level in these bores was 2 m below ground level (BGL). The maximum pump setting in RN 23449 is 22 m depth (BGL). The available drawdown in the bore is then 16 m. The calculated drawdown in the bore is quite close to this (15 m compared to 16 m). There have been reports of (mainly in the late dry bores not being able season of 1988). to produce water There wel:e no measurements taken of water levels in the bores at these times so it is not known if the bores forked. It could have been due to perforation of the galvanised steel pump column due to corrosion (see S,'wtion 2.4.4) which can stop a pump from producing water. However, the bores reportedly took 12-14 hours to recharge to a level where water could once again be pumped, and so it is inferred that drawdown in the bore when it stopped producing was significant. Based on the pre:::eding discussion the capacity of the main borefield at East Alligator has probably already been reached, and may be surpassed on some occasions of peak demand. The sustainable capacity of the bore field is therefore estimated to be between 120 and 130 kL per day. (Given that an extraction rate of 122 kLjday was used in the analysis). 005MJ