Gellibrand river summer flow vulnerability
The Gellibrand water supply system is particularly vulnerable to logging because there is no major dam or reservoir to store water. If there was any major drop in water flow in the river, particularly in summer months when water consumption is high, communities and industries dependant on water could face a crisis.
There are three take off pipes in the Gellibrand system: Arkins Creek, North Gellibrand and South Gellibrand. Bulk water entitlements were introduced in 1998 to restrict water extraction from the river during low flow periods.
According to research by Sinclair Knight Merz (SKM), water extracted at the north pipeline drops below 22.5 ML/day for 55 days a year, and is less than or equal to 12 ML/day for 22 days or three weeks on average.
The South Pipeline is similar, with extraction dropping to less than or equal to 12ML/day for 22 days or three weeks on average.
However variability on the average flows occurs. For example in 1974 flow pass the South take-off pipe dropped below 12ML/day for 66 days. This highlights the limitations to the Gellibrand catchment if there is too much demand in summer periods.
Bore fields at Carlisle have been installed as a back up for low flow rates in the Gellibrand river. However only 6ML/day is allowed to be pumped. The environmental impact of pumping larger quantities of water from bores if the Gellibrand river stopped flowing have not been tested .
Additionally it is estimated
private diversion of water for uses that include irrigation, consume at
least 7ML/day during peak demand in summer.