Water is a valuable commodity to all councils, so maintaining the assets that deliver this precious resource to communities is critical. Central Coast Council, in New South Wales, has the third largest urban water supply system in the state with a lot of assets – some dangerous to access following extreme weather – to keep a close eye on. For this reason, Council chose a futuristic solution for asset management and is sending robots to do the inspecting for them.

Water is a valuable resource to the Central Coast community, with a large network that has hundreds of thousands of Australians relying on it.

Ensuring Council’s assets are working to the best of their ability is important, which means an essential part of Council’s asset management planning is the inspections of its major water infrastructure.

The Central Coast has the third largest urban water supply system in New South Wales, serving the region’s population of more than 342,000 people and delivering water to more than 135,000 homes and businesses.

The system has three water storage dams, three weirs, three water treatment plants and over 50 reservoirs – with 2,200km of pipelines.

Maintaining the infrastructure to ensure a reliable, clean water supply is an enormous and often complicated job, made even more difficult in 2022 with unprecedented weather and subsequent flooding events.

Futuristic solutions to today’s issues

When Central Coast Council was faced with logistics and safety issues, following extreme rainfall, to maintain its Mangrove Creek Dam, it chose an innovative solution – robot technology. Council used the technology to facilitate inspection of a 2.3m diameter, 415m long diversion tunnel in Council’s largest dam, Mangrove Creek.

Mangrove Creek Dam is 30km north-west of Gosford in a narrow valley on Mangrove Creek. Built between 1978 and 1982, the Dam provides approximately 98 percent of the region’s water storage.

Mangrove Creek Dam is a large storage dam, not primarily a collection dam. Water can be pumped into the dam from Wyong River via a pipeline between Mangrove Creek Dam and the smaller Mardi Dam.

The inspection was necessary as the diversion tunnel is a critical piece of infrastructure which crosses under the dam wall and directs flow from Central Coast’s storage dam into Mangrove Creek to Lower Mangrove Weir, for subsequent pumping to Somersby Water Treatment Plant. The tunnel also provides the emergency drawdown facility for the Dam.

The inspection was required in order to carry out a condition assessment, however, before the inspection could take place, the diversion tunnel had to be isolated and drained.

Central Coast Council’s Director, Water and Sewer, Jamie Loader, said the isolation planning required enormous stakeholder involvement from many of Council’s Water and Sewer business units over many months.

The planning was needed to develop clear roles and responsibilities, isolation steps and timeframes, manage resourcing, coordinate with associated contract works, assess water supply system risks and implement measures to ensure the four week isolation would not adversely impact water treatment and system operations.

“The isolation commenced on 6 June 2022, with the teams’ very conscious of particular risks, challenges and responses. Particularly because Council’s current team had little experience for this high risk isolation work. The last person to enter the tunnel was in 1989, five years after its first inspection in 1984!” Mr Loader said.

Limited information was available on previous isolations and an adequate isolation and flow management plan did not exist.

Due to the design of the intake tower, it is only possible to achieve a single isolation of the tunnel, making it very high risk with high level approvals required for entry.

Robot to the rescue

Mr Loader said a significant, and unexpected, complication was that between the contractor’s engagement, planning and development of the project requirements, and the start of the tunnel isolation, the dam level rose from 53 per cent to a record 91 per cent.

By the time the tunnel was recommissioned, the Dam had reached 100 per cent and the spillway was overtopping for the first time since its construction in 1982.

“The increased dam level required a change of methodology, switching from use of a diver to operate an isolation valve on the tunnel filler pipeline in the intake shaft, to the only other option (other than Navy Seal Divers), the lowering of a Remote Operating Vehicle (ROV) to a depth of 70m to undertake the work,” Mr Loader said.

The ROV about to enter the Dam. Image: Central Coast Council.

The engagement of a ROV entailed a number of key steps to ensure the process would work and assist in the tunnel isolation and inspection, including:

  1. Off-site trial: underwater field testing off-site – this proved to be the key to the success of the project as the test showed equipment modifications were needed to be made prior to a trial run onsite
  2. Site trial: complete trial run within the Intake Tower – this proved that the ROV could reach and open and close the valve prior to any works proceeding and also identified site constraints, allowing further improvements to be made to the methodology
  3. Inspection: inspection of the tunnel bulkhead frame prior to insertion of the bulkhead, to ensure it would seal and allow draining of the tunnel for subsequent inspection
  4. Completion: after completion of the works, including physical inspection by a team of professionals entering the tunnel, the ROV returned to site, was lowered into the intake tower and driven to the intake shaft to open the valve – allowing the dam water to fill the tunnel via the filler pipeline

In addition, a second downstream filler valve was installed in the outlet works so that next time, double isolation of the filler pipeline will be achievable without having to enter the intake tower to isolate the flow.

Mr Loader said the entire project was completed, with the Dam returned to service by 6 July 2022.

“After 40 years of service, only two 10mm defects were identified in the Steelshield coating under the dam wall, as well as a leak through a small crack in the concrete-lined section, so a decision was made to repair the defects while small to avoid a larger repair at the next tunnel inspection. This is quite a remarkable result for a piece of infrastructure over 40 years old,” Mr Loader said.

“Not only have we now introduced a precedent to use robot technology, the team involved say they have learnt so much about this important infrastructure and how to isolate it safely and effectively, despite the increasing challenges such as record water level.”

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