Project goal:

Secure long term water supplies for the region.

Status:

In planning and construction

Delivery Date:

Ongoing

What's happening?

The Warren Blackwood regional water supply scheme supplies the towns of Manjimup, Bridgetown, Nannup, Greenbushes, Boyup Brook, Balingup and Hester. In early 2022 it was expanded to also supply Mullalyup and Kirup with the completion of the Greenbushes to Kirup pipeline.

Historically relying on independent local dams for its water source, the now integrated scheme relies on groundwater supplementing dams due to the impact of climate change. 

As climate change continues to impact the yield and quality of surface water due to increasing evaporation and decreased rainfall, it is necessary for us to plan diligently to ensure local communities can continue to have access to secure drinking water supplies for generations to come.

As a result, we are currently undertaking a water supply planning review for the Warren Blackwood scheme which will involve preparing a Source Development Plan. 

Since 2009 we have been working to create the now integrated scheme that provides secure, high quality water to Warren Blackwood communities. As such, there are some projects in planning or have been completed that are already focussed on this. Infrastructure will be extended and upgraded in accordance with future demand growth in the area.

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Why is this happening?

The south west’s water supply has traditionally relied on dams - a single dam supplying a single town.  The south west of Western Australia has been increasingly affected by climate change through declining rainfall. The dam sources are now becoming unreliable due to decreased streamflow, increased evaporation and human activity within the catchment, which in turn creates water quality risks. 

Water Corporation is responding to this new reality in a number ways including developing more robust, integrated drinking water schemes.

Why are we reviewing our water source planning for the Warren Blackwood scheme?

Climate change and declining water quality

Rainfall and streamflow to dams has declined significantly over the last two decades due to impacts of climate change. This has also affected the quality of water within the dams.

Modelling forecasts Millstream and Manjimup Dams will, at some point in the future, produce less water than is lost to evaporation. This will result in a net loss in total water supply as groundwater is currently transferred to dams for storage, which is then subject to evaporation and seepage loss.

Conflicting land use within water source catchments areas

Conflicting land use within the catchment areas of the sources are not supported, and where possible it should be avoided. Otherwise, additional treatment is required to minimise water quality risks from such sources.

Increasing demand

Water Corporation is currently licensed by the Department of Water and Environmental Regulation (DWER) to abstract groundwater from the Nannup Bore, consistent with the South West Groundwater Allocation Plan. Our current license is for 1,500 million litres per year. Forecast scheme demand indicates 1,800 million litres per year will be required by approximately 2025, and 2,100 million litres per year by 2050. Current demand is approximately 1,400 million litres per year.

The public water supply reserve set by DWER for groundwater from the Yarragadee aquifer is 3,000 million litres per year. Our current license allocation is will within this limit.

Reviewing our water source development plan for the Warren Blackwood scheme

As a result of all these factors, we are currently updating the Source Development Plan for the Warren Blackwood area. This will consider updated demand projections, dam water yield estimates and potential expansion of the scheme to include Pemberton, Northcliffe and Quinninup. This is being done in consultation with DWER.

What work is planned?

  • Warren Blackwood groundwater treatment plant and transfer upgrade - We are planning to construct a new groundwater treatment plant near Nannup to treat groundwater from the bore, as well as upgrade the bore and pump stations. The new treatment plant will remove the iron and manganese from this source rather than relying on settlement in the dams. Storing groundwater in the dams leads to the loss of water from the system due to evaporation. Consequently, treatment of the groundwater allows the dams to be bypassed as required in the future, reducing the amount lost to evaporation and needing to be extracted. More information about this project can be found here. 

What work has been completed?

  • Aquifer Pumping Test of the Warren Blackwood bore in Nannup - Between the 25 November  to 3 December 2023, we conducted an continuous 8-day pumping test on the Yarragadee aquifer from the existing bore in Nannup. The purpose of this activity was to help assess the hydrogeological impacts that increased groundwater abstraction may have on the Yarragadee aquifer, shallower groundwater and the surrounding environment. The data obtained from over 30 monitoring bores using during the test are currently being analysed, and will help determine if an increase in groundwater abstraction at this bore is a feasible option. The results will also assist the Department of Water and Environmental regulation with ongoing management of the South West Yarragadee Aquifer and the future water and licencing allocation decisions. Further updates about the results of the pumping test and hydrogeological assessment are expected to be provided in later 2024. 
  • Millstream Dam Bypass - to manage water quality concerns, this work will allow the bypass of Millstream Dam. Installation of a new water tank and and dosing unit was completed in 2023. Only minor remedial works remain. More information is available here
  • Greenbushes to Kirup Link – a 16km pipeline between Greenbushes and Kirup was completed by April 2022. This secured the supply to Balingup, Kirup and Mullalyup and removed the need of water carting from Donnybrook.
  • Millstream to Greenbushes pipeline – a new 16.2km pipeline between Millstream Dam and the town of Greenbushes commenced in November 2013. Construction on this project was completed at the end of January 2017. Commissioning of this new pipeline, with water being supplied into Greenbushes was completed on 1 March 2017. Two new pump stations and two one million litre storage tanks were also constructed as part of this work. 
  • Hester Dam remedial works – an upgrade to Hester Dam was completed in April 2011, ensuring the reservoir can continue to operate at full capacity. This project involved modifications to the dam embankment and new outlet works.
  • Hester to Boyup Brook pipeline upgrade – works to duplicate the existing 9km pipeline between the Hallett tanks and Boyup Brook were completed in October 2015.
  • Doubling the capacity of Millstream Dam – works to upgrade the Millstream Dam from 0.45 billion litres to 1 billion litres capacity were completed in January 2013. The upgrade to the Scheme’s central storage component enables capture of more water during wet years, ensuring adequate surface water storage capacity.
  • Manjimup supply from Nannup Bore – in June 2013, Manjimup joined the Scheme following the construction of a pipeline to link the Nannup bore to Manjimup Dam. Whilst the town’s two dams will remain the principal supply source for Manjimup, the new pipeline is now supplementing Manjimup Dam with groundwater as required, securing water supply for the town even in the driest of years.
  • Yarragadee Bore – a bore near Nannup was completed in 2009 and has since been used to boost supply to Bridgetown, Boyup Brook and Hester via Millstream Dam when needed. Approximately 75% of the water supplied to the Warren Blackwood scheme comes from this bore. 

Water conservation

While this infrastructure will guarantee a safe, reliable and sustainable drinking water supply in an increasingly dry climate, demand management remains a vital aspect of our strategy to deliver long-term climate resilience.

To support achievement of this objective, water efficiency and other compliance measures will continue to be complemented by educational initiatives and partnerships as required. Information on the current Waterwise Towns program can be found here.

Communities in the Warren–Blackwood are commended for embracing water conservation efforts to date.

The scheme currently relies mostly on groundwater from the region’s deepest aquifer, the Yarragadee aquifer, via a bore near Nannup. Some of the water supply (approximately 25%) comes from the larger local dams - Millstream Dam, Manjimup Dam and Tanjannerup Dam. The contribution from dams varies with rainfall. Originally, the bore was only used for backup supply, but now it is the main source. />

We all take responsibility of environmental management seriously. Water is a precious resource and should be carefully managed and used. DWER is responsible for the allocation of water resources for the state, including the Yarragadee aquifer and the entire groundwater system in the South West. As part of our planning, we are carefully considering the environmental impact of any changes to groundwater abstraction. We rely on expert advice provided from hydrogeological assessments to ensure we do not negatively impact the environment and groundwater system. We coordinate this work in collaboration with DWER.

Future source options being considered within the Warren Blackwood Source Development Plan include:

  • More water from existing Yarragadee bore (near Nannup). We are working with DWER to assess potential impact of this through comprehensive hydrogeological investigations.
  • A small filtration water treatment plant for Manjimup Dam and/or Millstream Dam to treat water stored there for as long as the sources are viable.
  • A small borefield (two to three bores) drawing from the superficial aquifer near Manjimup. Investigative drilling was completed in early 2021.
  • A new Yarragadee bore at an alternative location where environmental impacts can be demonstrated to be acceptable if an increase in capacity is not able to be achieved from the existing Yarragadee bore.

The final solution may be a combination of these options. The adoption and timing of this will depend on approval outcomes and the pace of climate change impact on dam inflow.

We have been investigating shallow groundwater sources around Manjimup through investigative drilling. We will also undertake aquifer tests and hydrogeological assessments to determine any environmental risk and better inform our decision making. The decision on which source expansion option (or a combination of options) is preferred will depend on the outcomes of environmental risk assessments, cost, consultation with regulators and community feedback.

Dumpling Gully, Boyup Brook, Balingup and Kirup dams are no longer used as drinking water sources. We are partnering with a number of Warren Blackwood Shires to support community-benefit water projects through the provision of water and access arrangements to facilitate recreation at these dams or supply water from the dams to town recreational facilities.

Tanjannerup Dam will continue to supply most of Nannup’s water, supplemented by the Nannup bore when required. The water treatment system currently used for Tanjannerup Dam continues to provide adequate treatment levels.

Millstream Dam and Manjimup Dam may be taken offline in the coming years due to the continuing decline of streamflow, increasing water quality concerns and evaporation losses. As the water levels in these dams decrease, the water becomes increasingly difficult to treat to an adequate level and becomes more costly. This will be considered in our evaluation of the options outlined above.

If taken offline, Millstream and Manjimup dams may remain as emergency source options to ensure supply to the northern Warren Blackwood towns and Manjimup. Potential alternative use of these dams will be investigated if they are taken offline and not used as emergency potable water sources.

Alyce Nehme - Community Engagement Senior Advisor

Phone icon (08) 6330 6523

Email icon alyce.nehme@watercorporation.com.au

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