Landowner Jeff Ryan (right) and NSW DPI technical officer, Chris Lee, checking stream water collection devices on Jeff's property at Duri where salinity research is underway.

Salinity research by NSW Department of Primary Industries scientists at Duri, near Tamworth, has thrown up some contradictions.

It found that the Timbumburi Creek, one of eight key sites being monitored across NSW, is recharging groundwater, rather than being a point of groundwater discharge as expected.

In flood, the creek water transports salt away from the creek edge to adjoining land, adding to the existing salt levels.

While the Timbumburi Creek situation may be a phenomenon of the extended drought, and results may be quite different during a prolonged wet period when the creek may discharge groundwater, the Duri discovery could have implications for the entire Namoi catchment.

"This is not a typical situation with groundwater systems and it makes us rethink our management strategies for this location," NSW DPI hydrologist agronomist, Dr Peta Derham, Tamworth, said.

"What we thought we should be managing may not be the total picture and we might need to manage salt in the creek as well as in our soils."

Results from groundwater monnitoring and stream flow do not correlate with the initial conceptual models for the Duri site.

They indicate that there is a groundwater mound under the creek bed and a subsequent groundwater sink up to 750 metres away from the creek base, which means groundwater is moving away from the creek bed.

During a flow in July 2005, an increase of 4000 litres in flow volume was measured over a distance of 2.5 kilometres between two stream gauging stations (a low figure from a catchment of around 650 hectares).

Also, there was a net loss of 1.5 tonnes of salt, which indicates that the creek is losing salt to groundwater, which has also been confirmed with electrical conductivity testing.

Dr Derham said the hydrological study had identified that the lighter textured soils (chromosols) have high run off and are running onto the heavier soils, which can be managed.

"We have a range of management systems that can handle additional water, such as companion crops, pastures, lucerne and native pastures," she said.

"Now we have to consider the flow back into the profile during a flood event and the challenge is to come up with effective ways to do that.

"It probably means we have to reduce the run off because the creek is not a natural pathway and would have been a series of billabongs in pre-European times.

"So what we have done over time is generated an ephemeral creek that flows after heavy rainfall, which is when the creek moves salts, so it’s a conundrum."

The research has confirmed that maintaining ground cover brings benefits for water management.

The hydrology of the catchment is still being investigated, and further research is being conducted to better understand the processes involved and how this system can be managed.

Funded by the National Action Plan for Salinity and Water Quality, the research is also comparing Queensland native blue grass with lucerne on heavier soils; companion crops versus pastures; and the use of groundcover to manage degraded sites.

Contact David Mitchell, Orange, 02 6391 3852.