Study looks at feasibility of drainage systems to fight salinity in Blackwood
Released 31 Jul 2008
Findings released from the most recent study into the use of drainage to counter salinity in the Blackwood River region have provided good news for farmers, but have dispelled notions that massive drainage will be the silver bullet for ending salinity problems.
Department of Water's Director Water Resource Management John Ruprecht said the study showed that use of deep drains to counter salinity in the Blackwood River region appeared to be feasible at the farm scale, but he warned the study also revealed deep drains at larger scales could be problematic and costly.
"The study found that large scale drains may involve considerable cost to stop environmental problems as a result of discharging salty and acidic waters into natural stream and lake systems," Mr Ruprecht said.
The Blackwood River Regional Drainage Evaluation is a study that looked at the effects of salinity and water management options for the Blackwood over the period 1965 to 2100.
The evaluation was undertaken by researchers at the Department of Water and CSIRO as part of the State Government's Engineering Evaluation Initiative (EEI) and the CSIRO Healthy Country Flagship, which has been investigating the use of engineering methods such as drains and groundwater pumping to counter Wheatbelt salinity.
"The Blackwood River is the largest river system in the south-west of Western Australia, with 14 major lakes and was divided into 111 sub-catchments covering some 22,000 square kilometres," Mr Ruprecht said.
"It currently carries about a million tonnes of salt a year to the ocean, with salinities in the lower Blackwood predicted to double in the next 50 years if no action is taken to better manage dryland salinity."
Mr Ruprecht said the Blackwood evaluation utilised the LASCAM (Large Scale Catchment Model) computer model. It looked at a complex mix of variables such as stream flows, water quality, environmental impacts, salinity spread, drain design, climate change, and the associated economic benefits.
The model predicted stream flows and salt loads for 111 sub-catchments over a 135-year period from 1965–2100 resulting from the above scenarios. It also included a 'do nothing' scenario which involved no change to current land and water management practices.
It looked at several scenarios including leveed and open drains discharging into local lakes or bypassing them; re-planting woody perennials at various parts of the catchment; and the effects of climate change and rainfall on stream flows and salt loads.
"The evaluation found that it is possible that over the next 100 years – if appropriate water management strategies are not implemented – that salinity will cause the extinction of large numbers of native plants and animal species, and a significant loss of remnant vegetation along the Blackwood Valley system," Mr Ruprecht said.
In one drainage scenario that included no management of drain discharge, predicted changes to river salinity would mean that upper tributaries that once discharged low volumes of brackish water would discharge higher volumes of saline water. This would mean the main channel of the Blackwood River above Boyup Brook could become saline quicker.
Mr Ruprecht said the Blackwood evaluation, and an earlier one which looked at regional drainage in the Avon River basin, would be used to help evaluate any proposals for a regional drainage scheme in the Wheatbelt.
"The reason we undertook the Blackwood evaluation is that there is considerable concern at the potential environmental consequences of constructing any large-scale drainage schemes in the Wheatbelt," Mr Ruprecht said.
"We know that deep drains can help counter salinity at the farm level, which might involve one or two properties.
"But there are proposals for far bigger regional schemes involving river systems such as the Blackwood and the Avon which might involve large areas of the countryside having an extensive drain system – almost like canals – leading into waterways and rivers and ultimately the ocean.
"Up until now the Government and the community had no way of understanding the pros and cons of such regional drainage schemes.
"Just as engineers and scientists need to evaluate the effects of proposed regional roads or highways before deciding to build them, much the same process should apply to arterial or regional drainage proposals.
"We need to make sure such schemes would benefit the wider community, particularly in view of the high cost of undertaking such infrastructure."
Mr Ruprecht said the Blackwood and Avon evaluations have provided tools that could now be used to evaluate proposed Wheatbelt regional drainage schemes.
"With these tools, we will be able to make a good job of evaluating regional drainage schemes and informing proponents how to better plan their schemes. Better planning may be the difference between schemes being successful or not," he said.
The preliminary findings of the Blackwood regional drainage and evaluation are being presented at three, free public meetings in Wagin, Moodiarrup and Bridgetown.
Contact: Peter Collins
Phone: (08) 6364 6848 / 0434 603 441