Less salt, but a lot less groundwater, too

The Murray-Darling Basin Commission (MDBC) recently awarded its National Salinity Prize to the Pyramid Creek salt interception and harvesting scheme, which evaporates groundwater and sells the remaining salt.

There have been quite a few salt interception schemes built along the Murray River over the last 20 years to reduce river salinity levels and they appear to have been very successful.

At the key site of Morgan, just upstream from the offshoots for Adelaide's water supply, salt levels have halved.

There is also a special federal Budget allocation of $500 million for more salt interception schemes.

But hang-on!  How much lower do we want to push Murray River salt levels and what's the trade-off in terms of lost groundwater?  There is concern that irrigators are over-pumping groundwater and must give up some of their allocation, yet the MDBC is worrying about rising groundwater.  No sense there.

A recent CSIRO report on "risks to the shared water resources" published by the MDBC included a section entitled "groundwater extraction" which stated that "groundwater stores are declining at alarming rates".  Read on, it refers to high levels of groundwater extraction in the Shepparton-Katunga region (where the Pyramid Hill Scheme was built) contributing to salinity mitigation.

The report concluded that clearing of native vegetation and irrigation had raised water levels in many parts of the basin, forcing saline groundwater into the streams.  That might have been the case 20 years ago, but not now when we have salt interception schemes and across most of the Basin the problem is declining, not rising, groundwater levels.

Indeed, since the late 1990s groundwater levels have been falling in the Murray, Murrumbidgee and Coleambally irrigation areas -- regions once considered most at risk from rising groundwater.

In 2004, the CSIRO said the falling water levels were due to improved land and water management practices, a drier climate, deeper groundwater pumping and more leakage from shallow to deeper aquifers.

So when will it be realised the real issue is disappearing groundwater and it is likely to be exacerbated by the next salt interception scheme?  The MDBC's next national salinity prize should perhaps look to schemes that work out how to get rid of the salt, while saving the water.

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