What: The Bowraville Off-River Storage dam and Water Security Supply Strategy
Who: Nambucca Shire Council
Why: To secure the Nambucca Shire Council local government area against drought
How much: $53 million
After taking the plunge and investing millions in a literally groundbreaking dam project, Nambucca Shire Council says it has successfully secured its community against drought until at least 2046.
The Bowraville Off-River Storage (BORS) dam, completed in October 2014, represented the final stage of the built elements of the $53 million Nambucca Shire Council Water Security Supply Strategy.
BORS and associated projects were proposed as part of an Integrated Water Cycle Management (IWCM) Strategy.
Nambucca Shire Council Assistant General Manager Engineering Services Paul Gallagher says the devastating drought of 2002 and 2003 demonstrated how vulnerable the existing Nambucca and District Water Supply Scheme was. During that period, it was estimated only 60 days supply of water remained in the system.
“They were very worrying times for the council and the community,” Gallagher says. “It was certainly the catalyst for the project to move forward, and it gained top priority as part of the NSW State Government Country Towns Water Supply and Sewerage Program.”
Gallagher says the council went to the community to determine the preferred option for securing the water supply against drought.
“The dam option was the preferred option against which a Project Development Plan was then documented,” Gallagher says. “The council engaged the NSW Public Works Department to act as their project managers, and consultants were subsequently engaged.”
Funding for the project came from three tiers of government, with the Federal Government contributing $10 million, the State Government $14.8 million, and the council contributing the remaining $30 million.
Gallagher says the decision to commit such a huge amount of funds to the project was one of the most difficult councillors have had to make. “It was a massive undertaking for the council, with significant risks and costs,” he says.
The BORS has a remarkable design, Gallagher says. “The dam was a ‘soft’ foundation dam designed to be able to be raised in the future to increase capacity from 5500 ML to 14,000 ML,” he says.
Steps taken to facilitate future rising include:
● The core trench has been constructed to a depth required for the raised embankment;
● The valves have been constructed well downstream of the existing embankment toe to provide space for the extended toe in the future; and
● The intake tower and access bridge have been constructed in a way that enables the tower deck and bridge pier caps to be raised.
Gallagher says the construction teams came up against a number of challenges during the
project’s design and construction, including:
● Ensuring that sufficient suitable material could be excavated from on site sources for the embankment construction.
● Availability of rock and filter materials for the construction works
● Competition with major roadworks in the area around the Pacific Highway
● Encountering groundwater in the foundations
● Encountering unexpected rock in the foundations
● Wet weather
The BORS will now provide drought security for predicted demands up to the year 2046, and maintain higher environmental flows in the Nambucca River. The project encompassed an earth filled dam wall, the expansion of the existing bore field, the upgrading to the headwork and access roads and installation of pipelines for transferring water to storage.
Its success was recognised at the IPWEA NSW 2015 Excellence Awards, where the project won the Innovation in Water Supply and Wastewater category.
“The project demonstrated an effective partnership of government agencies, local government, contractors through the leadership and commitment of the council,” Gallagher says. “It means recognition of our very diverse team consisting of our councillors, staff, the public works consultants, contractors and most importantly our community to deliver a very valuable asset that will now serve the current and future generations of the Nambucca valley.”