FOR every cloud, a silver lining, and for every devastating flood there is also delight for at least one group: the farmers and rural communities who depend on groundwater.
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The aquifers, comprising water trapped in gravel 50 to 100 metres below the surface, are being replenished.
Dr Wendy Timms, the chief investigator for the national centre for groundwater research at the University of NSW, said the aquifers were receiving a huge boost in the Murray-Darling system, which would absorb water from the floods in NSW and parts of southern Queensland.
The aquifers in the Murray-Darling had not been replenished for the past 10 years.
In aquifers in the Condamine, Gwydir, Lachlan, Namoi and Macquarie River regions, groundwater levels had fallen by up to 30 metres since the 1960s because of heavy pumping.
Normal rainfall did not recharge them because the water was trapped by tree roots and other ground cover.
''Many aquifers in the Murray-Darling system have been pumped quite heavily, and in some areas groundwater levels have fallen,'' Dr Timms said.
''If an aquifer falls too much it can damage the aquifer permanently. Saline groundwater can get into the system.
''We have seen a few sites in the Namoi catchment where the salinity has doubled or trebled, which means the groundwater is not really suitable for irrigating young crops.
''There are certainly areas where there is very high salinity. At the moment we are seeing the first indications, subject to confirmation, that the groundwater itself is becoming more saline. If we get a recharge along the river system, that is terrific and it can dilute any salts.''
Dr Timms said groundwater was neither understood nor managed as well as it needed to be, but it was common ground that the prime requirement for aquifers was the timely injection of new water.
The main problem for water flowing in rivers or being conveyed across the country in canals was evaporation.
She said the potential for groundwater - which was free from such problems, and which received a boost from relatively infrequent floods - had to be taken into account when lamenting the devastating losses caused by the recent flooding.
Dr Timms said her centre had researchers at Wellington and in the Namoi catchment in northern NSW. Bores were strategically placed throughout the state monitoring what was happening in aquifers, she said.
