After the floods
After the floods
27 Jan 2011
A decade of drought has taken salinity – one of agriculture’s most pressing problems during the 1990s – off the agenda.
La Trobe University groundwater expert, Dr John Webb, warns that once the drought-breaking floods pass, it will be critical to refocus on this issue – and to take remedial action as rapidly as possible.
Initially the floods will perform a useful service, washing salt from our rivers.
At the same time they also replenish our supplies of underground water. In salinity-prone areas, especially near creeks and low-lying farmland, this is a very mixed blessing.
‘One effect of the long drought was to lower the water table,’ says Dr Webb. ‘Salinity is strongly related to how close the ground water is to the surface. Ground water levels in much of Victoria dropped to a depth of four metres or more during the drought.’
Dr Webb expects the current floods to increase the level of the ground water table, thus bringing it very close to the surface in many parts of Victoria.
He says this makes it imperative that action to lower water tables – such as planting trees near creek beds and low-lying farmland – starts as soon as possible after the floods pass,
Once ground water rises again to within two metres of the surface, possibly within a few years, evaporation will concentrate the water, making it more saline.
‘It’s difficult to predict exactly how long this will take. A lot depends on how much rain we get between now and then. But the floods provide an ideal opportunity for trees to strike roots and help lower the water table.
‘The longer we leave this the more difficult it will get, and the more damage there will be to farm land.’
The La Trobe University Environmental Geoscience group headed by Dr Webb has been studying dryland salinisation in western and central Victoria for more than eight years.
It conducts studies into floods, the impact of commercial forestry plantations on ground water, and aspects of climate change.
Researchers measure ground water levels through a network of data loggers installed in bores. These provide scientists with readings at intervals which vary from 30 minutes to monthly.
‘With climate change, one theory is that overall rainfall might decrease but individual rainfall events might become larger and more intense, and we might see more and bigger floods.
‘So how much impact does a large flood have on ground water? Could it balance out the effect of less rainfall?’ says Dr Webb.
‘Initial results show that in some places a big rainfall event will put a lot of ground water into the ground quite quickly. In other places it makes almost no difference.’
Contact: Dr John Webb T: 03 9479 1273 E: firstname.lastname@example.org