Securing Mullumbimby’s water supply

Demand on an ageing system is increasing

Mullumbimby’s drinking water comes from Lavertys Gap weir on Wilsons Creek. 

Water flows from the weir through an open channel and tunnel to the Mullumbimby water treatment plant (WTP), which was built in 1940. 

The weir and channel were constructed in the 1920s to supply water to Mullumbimby and the former Mullumbimby hydro-electric scheme. 

Lavertys Gap weir and the channel are listed on the NSW State Heritage Register and the WTP has local heritage significance.

Regional water supplier

Rous County Council is the regional water supplier for the Byron Shire, excluding Mullumbimby. 

Rous is also the supplier for:

• Lismore
• Ballina
• Richmond Valley. 

Emergency connection during droughts and floods

An emergency connection to the Rous water supply can currently supply restricted water to parts of East Mullumbimby in extreme circumstances such as the 2019 drought and 2022 floods. 

The emergency connection will be extended to provide a restricted supply to the entire town by May 2025.  

New water source needed

Mullumbimby’s demand for water is increasing with development and population growth. 

Lavertys Gap weir cannot meet forecast demand without the potential for more frequent and severe water restrictions. 

A new water source is needed to provide water security for the town in the near future. 

If the raw water supply is not augmented, it is likely that restrictions will be more frequent, and the weir supply will be depleted if there is a prolonged drought. 

If the weir supply continues to be used, the open channel is in poor condition and the raw water transfer system must be upgraded. 

The ageing WTP will also require replacement to ensure continued supply of safe drinking water.  

Continuing to use Lavertys Gap weir will require:

• upgrades of the existing raw water transfer system
• a new water treatment plant (WTP)
• emergency connection to the Rous County Council regional supply.

Mullumbimby’s current supply is expected to be secure until 2027, assuming the emergency supply is available and water loss management measures are successful.

Beyond 2027, water restrictions may become more frequent and more severe.

If Lavertys Gap weir cannot meet the water demand, the emergency responses below are available as temporary measures only. Water restrictions would also be required.

Use the emergency connection to Rous County Council regional water supply

Water from the emergency connection has a much higher cost than normal supply from Lavertys Gap weir or the regional bulk supply. This pipeline can currently supply some water to lower elevation areas in East Mullumbimby. It will be extended to provide restricted supply to the entire town by May 2025. 

Water carting

Until the emergency supply can serve all of Mullumbimby, carting water may be needed if there is a drought or failure of the raw water channel or WTP.

The large volumes needed (267,000 litres/day) involve many truck movements (11-25 tanker loads per day) and high cost (estimated at $7,150-$14,300/day).

Accessing “dead storage” in Lavertys Gap Weir

There are small parts of the weir storage that are not currently accessible. The volume in this “dead storage” would only be sufficient to supply 20 days at emergency restriction level 7, provided it can be accessed and the water is of suitable quality.

Use a new groundwater bore as an emergency source

A suitable groundwater source has not been identified. Significant lead time would be required to investigate and develop a groundwater source.

The consultant's scenario assessment starts at page p145 of the Mullumbimby Water Supply Strategy document.  

This option involves building a new off-stream water reservoir between Lavertys Gap weir and the town.

This would be used to store high river flows that would normally overtop the weir.

This scenario will require improvements to:

• the existing raw water transfer system
• a new WTP
• full emergency connection to the regional supply.

This scenario could provide a secure water supply until about 2060, depending on the size of the storage.

A 200 ML storage is expected to be required. For comparison a 50m swimming pool holds 2.5 ML of water so the capacity of the off-stream storage would be similar to approximately 80 pools. 

This option is not recommended by the consultants and Byron Shire Council staff, mainly due to the high cost and the need for a replacement WTP.

The consultant's scenario assessment starts at page p145 of the Mullumbimby Water Supply Strategy document. 

Rous County Council is the regional water supply authority for the Byron Shire, with the exception of Mullumbimby. 

Rous also supplies:

• Ballina Shire
• Lismore Shire
• Richmond Valley Shire.

Permanent connection to the Rous regional water supply would mean that water is no longer sourced from Lavertys Gap weir and the Mullumbimby water treatment plant (WTP).

As a result, there would be no need to build a new WTP at Mullumbimby. 

Permanent, full connection to the regional water supply is the option recommended by the consultants and Byron Shire Council staff based on the environmental, economic and social assessment.

Benefits of full connection

Connecting to the regional supply has significant benefits over local supply scenarios.

Full connection offers:

• minimal environmental impact
• lower energy consumption
• reduced infrastructure modifications.

There are significant capital cost savings in avoiding the need to replace the WTP and upgrade the weir supply in addition to constructing new infrastructure. However, the ongoing costs of a regional supply are higher than local scenarios. 

Permanent connection to the regional supply means Mullumbimby’s long-term water security is determined by Rous County Council's bulk supply system, as is the case for the rest of Byron Shire. 

Rous Future Water Project

Rous has outlined a three-stage approach to regional water security in its Future Water Project 2060, covering:

• conservation measures
• groundwater sources
• desalination.

For 2030 to 2060 potential options include:

• direct and indirect potable reuse
• new groundwater sources
• new surface water storages.

Some people are concerned about the potential construction of Dunoon Dam, for which Rous has commissioned cultural heritage and biodiversity assessments

Mullumbimby’s water demand would account for less than five percent of total demand in the regional water supply area at 2030. Rous County Council has informed Byron Shire Council that full connection at Mullumbimby has no effect on its future water security plans.

The consultant's scenario assessment starts at page p145 of the Mullumbimby Water Supply Strategy document. 

This option involves supplementing Mullumbimby’s existing water supply from Lavertys Gap weir with a new groundwater source.

The groundwater could be pumped directly to the Water Treatment Plant (WTP) for treatment or to the weir storage, depending on the location of the bore supply and future location of the new WTP.

The North Coast Volcanics fractured rock source bounded by Lismore to the south, Mullumbimby to the east, Kyogle to the west and extending north to the Queensland border may be a viable groundwater source.

A groundwater yield of 1.1 ML/day is expected to be needed to provide a secure supply.

Risk to ecosystems

Drawing water from the ground can potentially impact on groundwater-dependent ecosystems (GDEs). A 2016 NSW Department of Primary Industries study determined that changes in groundwater levels posed a high risk to GDEs such as:

• springs
• rainforests
• dependant soils
• seasonal drys.

Further assessment is needed to determine any GDEs which may be affected by extracting groundwater from this source.

Further investigation

If groundwater is pursued, further investigation of potential bore locations will need to consider:

• land ownership and acquisition
• heritage constraints
• local geology
• environmental constraints.

Once potential bore locations have been identified, test bores need to be established and samples taken to determine the yield, salinity and other parameters of concern for drinking water supply.

The infrastructure required to utilise groundwater includes transfer and treatment systems will depend on the location of the source and quality of the groundwater and may require significant investment. 

This scenario ranked second in the environmental, economic and social assessment but would require significant additional investigation and lead-time as discussed above.

The consultant's scenario assessment starts at page p145 of the Mullumbimby Water Supply Strategy document.