SW rivers at risk of bloom

The health of South West rivers continues to suffer with latest figures showing declining rainfall has caused low water flow in several major waterways.

Recent Department of Water figures have categorised the volume of several waterways during 2012 as “very low’’ and well below historical averages.

Despite major rainfall at the end of 2012, annual flow figures for last year put both the Collie and Capel Rivers into the “very low’’ category – although the flow had improved considerably compared with 2010 figures.

In the Blackwood River last year, all three recording sites registered their second lowest flows, with the lowest taking place in 2010.

Long-time Collie River campaigner Ed Riley said the waterway was at “disturbingly low levels’’, despite not being at its lowest.

“Despite the 180mm of rain last December, water levels in the Collie River are very low,’’ he said.

He said many of the river’s tributaries, such as Bingham River and Collie River South, had not flowed in a number of months.

Department of Water spokesman Paul Brown said the low levels were the result of reduced rainfall.

Mr Brown said the low rainfall and seasonal low flows in the South West during the summer months could lead to less dilution of nutrients which could increase the likelihood of algal growth and blooms.

The 2012 flow for the Collie River was 39,065 megalitres, less than half of the historical average flow of more than 91,000ML, but significantly higher than the record low of 7176ML in 2010.

The Capel River recorded a flow of 8945ML in 2012, well below the historical average of 34,377ML.

In 2010, the Capel River recorded a record low annual flow of 3611ML.

“Work by the department looking at the impact of reduced rainfall on rivers and dams has shown that a 10 per cent reduction in rainfall can cause up to, and in some cases more than, a 30 per cent drop in runoff,’’ he said.

Despite heavy falls and a flood in Collie in December, the Department of Water classified the rainfall in the area for 2012 as “dry’’.