Bulletin

Issue: November/December 2007

News

Water Below The art of divining is still alive

Who says that Australia is geologically boring? The green basalt plains around Clunes in Central Victoria have seen their share of exciting geological events.

Twenty million years ago earthquakes disrupted the sediments of sand and gravel along the riverbed of the ancient Loddon River, and two million years ago about fifty volcanoes were erupting and punching holes in the earth’s crust.

These geological events are not just part of the colourful history of the area – although they did result in the goldbearing sediments going missing in the Creswick area. They are of vital importance when it comes to locating groundwater in our drought-stricken times.

La Trobe geologist Dr John Webb has the first detailed map of a 30 by 40 kilometre region around Clunes that shows the contours of the water-bearing sands to 100 metres below the surface.

The map, built on the toil of Honours student Sarah Hagerty, will be used by local water authorities to pinpoint the best places for drilling for water to supplement the region’s dwindling supplies. These are generally the thickest sections of the aquifer where water has been accumulating for up to 20,000 years.

Dr Webb said that the reserves are a third less than would be expected by the lay of the land. ‘When we looked at this area in detail we found that the sediments along the buried riverbed are not continuous. There is actually a lot less sediment and groundwater than people first thought.’

Ms Hagerty used data from hundreds of bores drilled in the area. Many contained no evidence of sand. She used this data to draw up the map which also shows the cause of the disruption – earthquakes along a series of faults that cut across the area.

The La Trobe research will be fed into the calculation of the permissible annual volumes (PAV s) of water that are drawn from the reserves. The good news for farmers is that the reserves are being topped up, continuously but slowly, by rainwater entering through the volcano craters.

The geologists are working in other areas of the State, filling in the gaps in our knowledge by using this new art of water divining.