Impact of logging in the Gellibrand catchment.

Greater Arkins creek catchment

Research by Sinclair Knight Merz (SKM) released last year investigated three scenarios regarding forest management within the Greater Arkins Catchment area (1100 ha) which is an important high rainfall component of the Gellibrand water supply catchment.
(Note: The SKM study did not include the high rainfall headwaters of the catchment which is managed by SWW and not logged).

	Scenario	*Scenario Result*
*Scenario One*	End of Otways clearfell logging in Greater Arkins Creek catchments	Water run off would increase by 23% in about 60 years and 28% in 100 years.
*Scenario Two*	Fire burnt 50% of the Arkins creek catchment area	Water run off would decrease by 20% within 20 years. Separate scientific research has shown clearfell logging is making wet forests drier and increases the risk of a big wildfire fire. (Age 13/5/02)
*Scenario Three*	Clearfell logging continues at current levels	Water run off in the Greater Arkins Catchment would increase between 6% and 14% due the forest still recovering from past fire disturbance which is greater than proposed logging disturbance.

The net loss in water yield attributed to logging in the Greater Arkins Catchment is about 17% or 650 ML a year.

There is an estimated 17,000 ha of high rainfall forest on public land available for clearfell logging on the southern side of the Gellibrand catchment. If it was assumed that this entire area behaved similar to the Greater Arkins Catchment and ignore logging in lower rainfall areas, there would be at least an annual 10,000 ML of extra water running off into the Gellibrand river within 60 years if clearfell logging on public land was stopped now.

Fire and logging implications for the Gellibrand

If a large fire burnt out a significant component of the native forest in the high rainfall areas of the Gellibrand catchment, considerable social and economic stress will occur as water yield began to decrease in the summer months. There could be considerable political pressure to construct more dams in the Gellibrand catchment as a means of improving water supply reliability at a cost of hundreds of millions. Proposals to build new dams could result in the flooding of agricultural land in the Gellibrand and disrupt environmental flows.

See Clearfell logging is making the wet forests of the Otways drier and more fire prone.

No logging and no fire will increase summer flows

Research done in the Maroondah catchment area (Melbourne Water Supply) demonstrated that extra water run-off would occur in summer months if forest is allowed to mature and not be clearfell logged or burnt.
(See Crotty Creek catchment experiment and Picaninny catchment experiment. SKM2 page 30,31 )

For the Gellibrand catchment, increased water runoff in summer months would improve water security when demand is highest. See Gellibrand river summer flow vulnerability.

Also see Clearfell logging is making the wet forests of the Otways drier and more fire prone.