Australian Capital Territory Implementation Report 2005–2006
Performance of de-stratification system for Cotter Reservoir
Following the 2003 Canberra bushfires, monitoring of water quality in Cotter Reservoir revealed significant problems with low dissolved oxygen (DO) levels over the majority of the reservoir at certain times of the year (see NFS Annual Implementation Report 2004–2005).
The solar-powered de-stratification system installed following the bushfires has been operational since December 2004 and it has improved the water quality to the extent that the reservoir has been used as an integral part of Canberra’s water supply since February 2005.
Photo: Dean Ansell
The increase in the dissolved oxygen levels through the water column has decreased the iron and manganese levels and the associated turbidity. Although the dissolved oxygen levels continue to decrease in the lower depths of the reservoir in the summer months, the amount of oxygen in the upper levels remains relatively high. This not only provides a source of good quality water for supply but also increases the available habitat for the threatened Macquarie perch population residing within the reservoir.
The de-stratification system considerably reduces the seasonal pattern of oxygen depletion at the 6 m and 9 m depths in the period from January to May. Operational issues affected the system in March 2006. Nonetheless, when the system was restored to the normal operating regime, there was a rapid increase in DO levels and improvement in water quality.