Science is revealing how the Ord River will cope if it becomes the "food bowl" of Western Australia.
CSIRO scientists who have been studying the northern WA river say the impact of plans to intensify farming and power generation in the region are crying out for further research to make sure development is managed in a way that preserves the river's water quality and prevents salinity.
Research scientist with CSIRO's Land and Water Division Dr Barbara Robson, who has just finished a two-year field study of the Ord River, made an important new finding about what drives ecological production in the river.
Her research, due out in a written report in June 2008, found that the river is a very varied environment during the dry season, ranging from clear, fresh water just below the dam to very muddy, relatively nutrient-rich, salt water in the estuary.
"What this may mean is that because growth of algae in the upstream section is controlled by phosphorus concentrations, water quality in this part of the river is likely to be sensitive to changes to run-off from farmland," she said.
The CSIRO team studied the river from Kununurra Diversion Dam to the Cambridge Gulf to predict how it would be affected by proposed water allocation and land use changes if more farmland was opened up in the region and if more power was generated from the hydroelectric dam.
"Currently, water quality in the Ord River is pretty good, and the purpose of our study was to see whether this is likely to change as a result of the sorts of changes currently being planned," Dr Robson said.
"Our simulations suggest that the currently planned increase in irrigation area, which will involve taking more water out of the dam, is not likely to have a big impact on water quality in the river, and nor is the plan to increase dry-season flows to increase power production from the hydroelectric dam."
On the other hand, she said modelling showed changes to the river caused by irrigation - that is, taking more water out of the river to irrigate crops - did not look like having a big effect on the river's water quality.
"Any changes that affect the amount of water flowing back into the river after it has passed through irrigated land are more likely to have an effect, as irrigation return flow tends to carry more nutrients and can carry other pollutants," she said.
Dr Robson said more algae in the water was generally bad for the health of a river for a number of reasons, including that it could reduce the amount produced by algae and plants growing on the bottom, which are usually more important to the food web.
With her study complete, Dr Robson said more research was now needed to determine how the proposed changes would impact on fish, bird and insect life in the river - a project being undertaken by scientists at the University of Western Australia.
Her finding builds on other research conducted by the CSIRO research scientist and groundwater hydrologist Dr Tony Smith into the risk of salinity on land near the Ord River due to the rising watertable.
His research was concerned with how to manage the watertable on land near the river, which had risen half a metre a year for the past 40 years due to the building of the Kununurra Dam, land clearing to make way for crops and other changes to the area known as Ord River Stage I.
This was problematic because once the watertable rose to within a metre or two of the surface, the area was at risk of salinity, he said.
But irrigation drains were found to have stopped the rising watertable problem, giving scientists the idea that groundwater drains could be used to prevent the problem from occurring throughout the next area to be opened up for irrigation, known as Ord River Stage II.
"What needs to be recognised is that groundwater drainage is an integral part of the design of any irrigation area in the Ord River region," he said.
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