Department keeping watch on Gascoyne salinity
Released 18 Jun 2012
The Department of Water is continuing to monitor and assess the salinity of the lower Gascoyne River to assist growers and protect local aquifers.
Mid West Gascoyne Regional Manager Adam Maskew said a reduction in both rainfall and river flow is contributing to the higher than normal salinity levels in the Gascoyne River for this time of year.
"The pattern of rainfall and river flows starting with the 2010-11 flood events has led to increased soil salt mobilisation in the catchment and evaporative salt concentration in the Gascoyne River.
"The salt levels of the river flows have been higher than typical with above 1,800mg/L TDS (milligrams per litre total dissolved solids) at the end of the flow last year and into this year.
"It is important to acknowledge that the river flow salinity is not due to over abstraction. We are protecting the aquifers from salinisation by stopping pumping while the salt content is so high.
"Our regulation of pumping to protect water quality has benefits at other times of the year when the flows are low in salt and we allow unrestricted pumping from the riverbed sands aquifer to assist it fill up with good quality water.
"In 2011 this allowed unrestricted pumping for four months which was not counted against the licensed entitlement but this year it was only for one month.
Mr Maskew said without significant rainfall in the Gascoyne River catchment and subsequent river flow, the salt can't be flushed out from the river system.
He said recent rains in the catchment were not significant enough to flush out the system. It was unlikely there will be flows sufficient to do this before the start of 2013.
"As our management decisions are based on aquifer science, we cannot control this but we can manage it for the benefit of the water source using the best available information.
Monitoring work by the Department of Water is important in guiding management decisions to protect the local groundwater supplies for the benefit of users.
"The department has been undertaking monitoring of the Gascoyne River alluvial aquifer and water use in lower Gascoyne River catchment for a very long time," Mr Maskew said.
"This includes sampling private draw points and quarterly aquifer monitoring to measure depth to water table and salinity.
Mr Maskew said the next aquifer status report is due out next month. The department will use this information to lead discussions with stakeholders and other agencies about the health of the aquifer system and any associated management decisions.
The 2011 Lower Gascoyne Water Allocation Plan sets out how to manage water abstraction while supporting horticultural development and protecting its ecological and social values in the plan area.
In the case of water shortfalls in Subarea A, the plan allows for 2 GL of water to be drawn from alternate subareas further inland, as was done in the dry period of 2009-10.
For more information on the 2011 Lower Gascoyne water allocation plan go to www.water.wa.gov.au
Contact: Peter Collins