Guest post written by Gail Hamilton. Views expressed are the author’s and not the official opinion of NQCC.

This is the first part in a four-part series that discusses issues about water security in our region. Part two explores dam infrastructure options, and part three is a summary report of information shared by Townsville Enterprise Ltd. about the Hell’s Gate Dam feasibility study at our AGM and forum. Part four asks how climate change will affect our region’s water security.

Townsville has an excellent water supply system, with highly treated and very safe water sourced from the Ross, Paluma and Burdekin dams.

While the Ross is our main supply dam, it is highly variable, with a limited catchment and low rainfall.  The Paluma Dam is situated in the wet tropics and is much more reliable, but can only supply 30 ML per day.  The Burdekin Dam is a huge system, with over 1 000 000 ML per year of water allocations, some of which is not committed. Townsville has 120 000 ML of allocation from the Burdekin.[1]

CURRENT SITUATION

In 2014, the Department of Energy and Water Supply undertook an assessment of Townsville’s water security.  

It found that at current consumption levels of 60 000 ML per year, we would have to be on Level 4 water restriction on average once every 160 years.[2]  It’s almost certain that we will have Level 4 water restrictions this year.  And maybe next year too. (Ed’s note: Level 4 restrictions are triggered when the dam reaches 10%. Check the current dam capacity here). But will we have a serious water supply shortage? The DEWS report predicts that at current consumption there is a 1 in 900 years likelihood of the existing system failing to be able to meet Townville’s water supply demand.[3]

The report generally shows that the current water consumption level of Townsville has reached a point where the level of water supply security is reducing over the next 12–15 years from a current, to a less acceptable more frequent likelihood of failure of around 1 in 100 years. Whilst additional improvements to water supply security aren’t required immediately, Council will continue to work collaboratively with relevant Queensland Government agencies to address these issues with the following work proposed to be undertaken in the short term:

1. Determine what is an appropriate level of service for water supply security for Townsville.
2. Undertake further water supply security planning to identify what measures are required
3. Commence the detailed design of the second Haughton pipeline and pumping station from the Haughton Main Channel to Ross River Dam.
4. Investigate opportunities associated with water demand management.

Under Townsville’s current water strategy, if Ross Dam falls below 10%, then even if it doesn’t rain in the near future, we have the opportunity to pump 130 ML per day from the Burdekin and 30 ML from Paluma, which is sufficient to meet our current demand under water restrictions. In theory this could happen for years, as The Burdekin and Ross Dams are unlikely to be low at the same time, and modelling shows the Burdekin Dam is unlikely to fall below 20% , even in drought conditions with Townsville drawing its full allocation.

As the DEWS report shows, there is no immediate threat to our water security, provided we manage our total water consumption within 60 000 ML/year.  Once we increase, say to 75,000 ML/year, the risks to our water security significantly increase, with our water supply failure likely to occur on average every 150 years, rather than every 625.[4]

It should be noted that the DEWS report used historical data in its modelling and did not consider the impacts of climate change on rainfall and catchment flows.

FUTURE POSSIBILITIES

To meet an increased demand up to 75,000 ML/year by 2026, there are several options:

• Duplicate the Haughton pipeline to allow increased pumping from the Burdekin dam system.
• Construct a new dam. Hells Gate is mooted as an option
• Construct a desalination plant
• Use recycled water

Haughton pipeline

The Haughton pipeline duplication has been costed at $250 million, with only minimal environmental impact.  However, the benefit of the additional pipeline is dependant on Townsville securing more high priority allocation from the Burdekin dam, which may not be available in the long term as irrigated agriculture and mining develop in the region. Relying on pumping from the Burdekin has high operating costs, around $75,000 per day of pumping for just the one pipeline.

Hell’s Gate Dam

A dam at Hells Gate will have significant economic and environmental costs.  The construction costs of a 100m dam plus 100km pipeline to Townsville would be in the order of $2-3 billion.  Environmentally, the dam is likely to result in:

• reduced downstream water clarity and oxygen levels
• changed flow pattern
• restrictions to fish migration
• changes to sediment and nutrient transport

All of which will cause significant impacts to riverine and coastal ecology. In addition, there will be destruction of potentially sensitive habitat from the impoundment itself.

The operating costs of the dam and pumping to Townsville would be significantly more than for the Haughton pipeline due to its much greater distance.  Despite Hells Gate being more elevated than Townsville, there will still be a need for pumped transport due to head losses in the system.

Desalination

Desalinisation of seawater has also been mooted as a source of potable water supply in Townsville.  Desalinisation plants are not only very expensive to construct (potentially $5 billion) but are hugely energy intensive to operate and create potentially toxic brine waste streams.

Recycled water

Townsville discharges 40 ML per day of treated water into the sea.  There is an opportunity for reuse of this water, either in a third pipe system for irrigation or returned to the Ross Dam for additional treatment as part of the potable water supply.  Reuse of treated wastewater directly into the water supply dam is not only safe, but common in many parts of the world, including Europe.  For example in England, it is  reported that water in London’s water supply has already been in and out of 6 bodies upstream.  However direct potable reuse of wastewater effluent is difficult for Australian consumers to accept, despite the high levels of treatment and the very low risk of contamination.

It is considered that reuse of treated wastewater for irrigation would be more palatable.  Townsville City Council has undertaken studies regarding the viability of water reuse, however these studies were not undertaken in the context of high future consumption and the comparison with alternative expensive water sources such as desalination and dams.

Maintain current water demand

Alternatively, we can maintain our water demand to 60 000 ML/year and these works wills not be required.  To reduce our total city demand means we either reduce our per capita consumption by 20%, or reduce our population growth.

The average Townsville household uses 1,700 litres of water per day, while in Brisbane, Sydney and Melbourne households use around 210 to 285 litres per day. More than 70% of Townsville’s water supply is currently being used on residential lawns and gardens.[5]

Townsville is well and truly within the Dry Tropics.  That is, it's dry here.  Mostly. Townsville’s average annual rainfall is 1143 mm, which is much lower than our tropical neighbours, with Cairns having 2000mm, Innisfail 3550mm and Proserpine 1800mm.

This means that we are severely constrained by our availability of water. It is time to have a healthy discussion about Townville’s appropriate population, in the context of our water supply limitations.  Further, Townsville residents need to adapt our water use habits to better manage our water use.

[1] Townsville has 10 000 ML per year of high priority allocation from the Burdekin and 110 000 ML of medium priority.

[2] The DEWS report was based on Level 4 water restrictions being introduced when Ross Dam is below 3.5%. The current water strategy is for Level 4 restrictions to be introduced at 10%.

[3] Department of Water and Energy Supply, ‘Regional Water Supply Security Assessment’, October 2014, p. 15.

[4] Department of Water and Energy Supply, ‘Regional Water Supply Security Assessment’, October 2014, p. 13.

[5] Townsville Water, ‘Water Restrictions Frequently Asked Questions’, p. 1.