More on Salt: What is the 'Rising Ground Water' Theory?

Since last Sunday's feature story 'Australia's Salinity Crisis, What Crisis?', I've received comment that it is difficult to understand the different models and theories explaining dryland salinity. The dominant theory has been the rising ground water theory which Dr Brian Tunstall suggested was complete "bunkum" on Sunday.

In my opinion the model has some application, but lets start with a basic description of the theory:

If you dig a hole in the sand at the beach, or a bore in your backyard, chances are you will strike water at some depth. This water is often referred to as 'ground water'.

The 'rising ground water' theory is essentially based on the idea that if you remove lots of trees from an area or irrigate an area, then more water will percolate down than would occur naturally and the ground water will eventually rise. If there is a lot of salt in the landscape the rising groundwater will be salty.

The theory is applicable to many irrigation areas and I have previously written about how Murray Irrigation Ltd, in the NSW Riverina, has dramatically reduced the area at risk of salinity working from this model (click here for that blog post).

I have also acknowledged the value of salt interception schemes along the Murray River (click here for an article recently published by Online Opinion). These schemes are based on the idea that if the rising ground water is intercepted, and the water evaporated and salt collected, the amount of salt entering the Murray River will be reduced and salt levels will fall.

But a potential problem with salt interception schemes is that they can draw groundwater from a distance away, and in this way potentially suck the soil profile dry of water.

It really depends on whether the groundwater is confined or whether the ground water covers a much larger area and may be flowing underground along, for example, old river beds.

A fellow called Geoff emailed the following comment yesterday:

"As I see it and please correct me if I am wrong, there has been a blanket campaign to lower water tables to combat salinity. In reality, some areas need to lower their water tables while others have no water table problems. In fact these areas need to increase the water infiltration to leach the root zone salt down the profile.

Chisel plowing, stubble retention, avoiding excessive grazing are all well established and accepted ways of increasing this water infiltration by increasing the organic matter and bacterial activity in the soil. And, dare I say it; clearing trees followed by careful soil husbandry would be the preferred option in many areas."

It is worth remembering that many people in rural and regional Australian rely on groundwater for 'stock and domestic' as well as irrigation and that groundwater is not necessarily salty. Groundwater is mostly a very valuable resource and while the National Land and Water Audit gave the impression it is everywhere increasing in abundance, the reality is quite the opposite (click here for a Land column I wrote on this issue).

In summary the rising ground water model has some application, but I don't believe it has general application outside of irrigation areas in eastern Australia. I am less familiar with the situation in Western Australia. The model probably has limited application through most of Queensland and NSW and yet it has been applied inappropriately across this landscape including through the National Land and Water Audit, and specifically at places like Dick Creek (click here for BrianTunstall's explanation as to why Dick's Creek is a soil heath rather than rising ground water issue).

Professor Pannell, from Western Australia, has a different view. He has posted comment at his website defending the rising groundwater model and suggesting it has general application including in eastern Australia. He also supports Wendy Craik's view that the drought has lowered water tables. But hang on, which drought? Despite all the hype, the rainfall record for the Murray Darling Basin as recorded by the Australian Bureau of Meterology does not suggest the last few years have been partiucularly dry:

The last very dry year was 2002 and that wasn't unusually dry in the scheme of things.

Professor Pannell writes:

"Contrary to the claims expressed on the [Sunday] program, there is copious evidence in support of the rising groundwater model, including a catchment in WA [Western Australia] where groundwater and stream salinity levels have been monitored ever since the land was cleared. There are numerous areas where establishment of perennial vegetation has lowered watertables and thereby mitigated salinity (e.g. Burke’s Flat in Victoria, the Denmark River in WA).

Powerful recent evidence in the Murray-Darling Basin has been the decline in saline discharge in many areas, due to extended periods of below-average rainfall. For example, in a site at Kamarooka (northern Victoria), there was formerly a large area of saline discharge, but the recent dry period has lowered saline groundwaters to 2 metres or more below the surface for the first time in 50 years. This widely observed recent phenomenon is completely consistent with the groundwater model of salinity, and (unless I’ve misunderstood it) completely inconsistent with the soil-health model. The same is true of the fall in salinity in the Murray River, which was rightly emphasised in the program.

... I’d also be very interested to know how the alternative model explains the onset of salinity affecting roads and buildings in the middle of rural towns, or occurring within remnant native vegetation (where soil health is presumably pretty good). It seems to me that these things can only be explained by rising groundwater."

In fact a bit has been written about 'lateral flow' and 'soil health' to explain impacts on roads and other infrastructure from salt, click here for a piece by Ken Tretheway and Rob Gourlay.