Since the 1940s Mullumbimby’s water supply has come from a concrete weir on Wilsons Creek, at Lavertys Gap, piped by gravity through a treatment plant perched beside Wilsons Creek Road, to two concrete balancing reservoirs above the old Mullumbimby hospital on Azalea Street.
The future viability and reliability of this supply has been under review for about 20 years, since the drought of 2002-03 caused water shortages. However, in 2005, consultation with the Mullum community demonstrated a strong desire to maintain the local supply.
Several problems with supply
A recent consultant’s report (Hydrosphere 2022) has highlighted several problems with the present supply: the treatment plant is aged and needs quite urgent replacement in order to maintain water quality; projected population growth will result in a 67 per cent increase in total demand for water by 2050; and climate change is expected to increase the frequency of drought conditions and hence reduce flow in the upper reaches of Wilsons Creek, affecting reliability of the supply to Mullum.
Council staff, councillors and community representatives on the Water and Sewer Advisory Committee agree that action is necessary to ensure a reliable water supply.
Two basic approaches are under discussion.
The local approach includes building an ‘offstream’ storage reservoir in the valley between Lavertys Gap and the Azalea Street reservoirs, to provide backup storage during drought conditions.
Such reservoirs are being built to help to drought-proof water supplies to several regional areas in NSW, including in Walcha Shire and the MidCoast Council area.
Also, constructing a new water treatment plant between this offstream reservoir and the Azalea Street reservoirs.
The regional approach comprises abandoning the Wilsons Creek supply and attaching Mullum’s network to the Rous County Council supply.
Rous currently supplies three neighbouring Council areas as well as the other towns in Byron Shire, but the future reliability of this supply, chiefly from Rocky Creek Dam, is under review, with various options to increase supply.
The possibility of constructing the Dunoon Dam is still under consideration, as is the contentious use of groundwater from the Tyagarah coastal aquifer in our shire.
In the meantime, the pipeline that connects the Rous CC supply mains at Uncle Toms to the eastern end of Mullumbimby (built in 2003) is to be extended to the Azalea Street reservoirs, for use throughout the town, but only in emergencies.
Future drought conditions
Given that future drought conditions will affect all water supplies in the region, water supplied during an emergency comes at a financial cost. When supply from Wilsons Creek was greatly reduced by drought conditions, in December 2019, the emergency supplementary supply was used for the eastern part of Mullum at a cost of $62,000 for a month.
Rous were asked recently to enumerate the potential environmental and social costs of adding Mullum to their supply network. They replied that this addition ‘will have a minimal overall increase in the total demand for water for the RCC bulk water supply’.
They say that they would not have to update their current strategy regarding future water security plans to provide for Mullumbimby’s future water needs. Nevertheless, if Mullum’s water is to be supplied by Rous CC this will add about 12.5 per cent to the projected extra demand on the Rous network by 2060.
Rous CC’s future augmentation options all have environmental, social and economic impacts. Mullum’s needs would add to those impacts.
Further investigation
At their meeting on 23 April 2023 councillors agreed to carry out further investigations into potential offstream storage sites, the hydrology and impact of climate change on Wilsons Creek, and infrastructure needs and environmental impacts for offtake, storage, treatment and delivery to the town’s reservoirs.
However, no decision has yet been taken as to whether to hand over Mullum’s water supply to Rous, adding to the burden on that network, and at unknown cost, or to maintain a viable, independent supply from Wilsons Creek, albeit one which would require capital investment to achieve reliability for at least the next half century. Community consultation should be the next step.
Ben Fawcett is a water and sanitation engineer with worldwide experience and has been a community member of the Water and Sewer Advisory Committee since 2018.
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