Bores to rescue dry Sydney


The NSW Government has released a new report, ‘Groundwater: Investigations for Drought Water Supply,’ detailing the results of an 18-month search for aquifers in the Sydney region, reported The Sydney Morning Herald (1/7/2006, p.11).

400GL under Sydney: Scientists with the Sydney Catchment Authority (SCA) estimated that there are around 400 billion litres of water in the rock under the Upper Nepean Catchment and possibly larger volumes in the area from Wallacia to Richmond. The overwhelming bulk of the groundwater found under the Upper Nepean and at Leonay appears to come from the 1950s and 1970s – two of the wettest decades in modem times.

11,000 yr-old water: A range of ages was also recorded, using carbon dating, across the last 10,000 years and in one of the test bores, water was found to be 11,000 years old. For the past fortnight drilling has been under way near Warragamba and Wallacia, with two test sites already completed.

Three possibilities: One hole was sunk to 290 metres – deep enough to swallow all but the tip of Centrepoint Tower’s needle – and a second to 246. According to the Sydney Catchment Authority’s groundwater project manager, John Ross, the early data suggests there may be a third usable aquifer in that area.

37.9pc of capacity a year ago: With the Government desperate to guarantee Sydney’s water supply it was only a matter of time before the political cycle caught up with the geological one. At the height of the recent drought between 2002 and 2004, Sydney’s water supply seemed to be in free fall, reaching an historic low of 37.9 per cent on Thursday 23 June last year. At its worst point there were warnings that without rain the city could run out of water within two years.

Dire conditions push govt to bore-domThe Carr government came under attack for not doing enough and began looking around for a quick fix. A dam on the Shoalhaven was ruled out, a desalination plant was mooted and politicians began to listen to the scientists who had been telling them for years part of the solution may lie beneath their feet.

New SCA report states: “The 2006 [Metropolitan Water] Plan confirmed groundwater remains a critical line of defence for the greater Sydney water supply in the event of severe drought. The Government has stated that bore fields to tap into groundwater reserves will be constructed if dam levels drop to around 40 per cent of the system’s capacity. Pumping is unlikely to occur unless supply levels fall to around 35 per cent.”

First site under consideration: The first bore field that would be built would be east of Bowral and north of Robertson, near the SCA lands along Tourist Road. “The area occupied by any bore field is likely to be a thin corridor about 50 metres wide over a length of around 30 kilometres although the area influenced by any bore field is likely to be around 200 square kilometres,” the report said.

Up to 1800 L/second: There would be as many as 60 cased and screened production bores more than 500 metres apart, each producing between five and 30 litres per second. The water brought up by these bores would be discharged into flowing creeks or pipelines, all located within the Upper Nepean Catchment. The groundwater would then make its way downstream into one of the Nepean dams. According to the study, a pipeline option to Avon Dam is also being considered.

13b litres a year: The SCA expects volumes extracted would be around 15 billion litres per annum, diminishing the longer the borefield is pumped continuously. “An operational period of two, possibly three years is considered reasonable. If bores are cycled within the borefield then supplies around 13 billion litres per annurn are likely. Actual capacity will depend on bore location, spacing, operational patterns, recovery cycles and rainfall recharge. The installed capacity of all production bores will be around 18 billion litres per annum.”

The Sydney Morning Herald, 1/7/2006, p. 11

Source: Erisk Net  

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