Merewether upgrade for merry weather with Interflow

In the beachside suburb of Merewether in Newcastle lies the Merewether Emergency Relief Structure (ERS). After years of environmental impact and weathering, Interflow came in to repair the pipe.

The Merewether Emergency Relief Structure (ERS) relieves major sewer networks during wet weather events or failure of the Burwood Waste Water Treatment Works (WWTW). The non-circular (ovoid) pipeline extends from an access hole adjacent to the baths all the way out past the beach to the nearby rock shelf.

In 2011, a failure of the WWTW activated the ERS, which was unable to perform as needed because of high tide and blockages. The result was uncontrolled discharge from access chambers along the foreshore. This resulted in the closure of Merewether Ocean Baths.

After this event, Interflow was engaged to reline a 90m section between two access holes. As part of their inspection, CCTV revealed that the downstream areas of the pipe were in poor condition. They also found cracks along the pipe wall, allowing sand in. This was exacerbated by the shape, slope, and lack of a non-return valve, meaning sand accumulation within the pipe was inevitable.

Allan Moran, Hunter Region Project Manager for Interflow, reflected on the project.

“This pipe was originally installed in the 1900s, and we were asked to reline a 90-metre section after 2011. This section extended past the ocean baths, and it turned out that the pipe had a lot of sand in it. It was about 50 per cent full of sand when we got there,” he said.

Initial goals and challenges

The project’s primary objective was to reduce sand infiltration into the overflow system by relining an additional 130m section of the pipeline. This concept seemed simple enough in theory, but the unique site conditions saw the project team take on the ocean itself to safely deliver relining works.

“When we went back in 2022, we found that the pipe had anywhere from 600 to 700 millimetres of sand along much of its length. That filled half the pipe, which meant we had to remove tons of sand,” said Moran.

At high tide, the pipe was about a metre below the surface. This meant Moran and the team needed to find a way to isolate the pipe from the tide. This was not just to reline the pipe but to clean and prepare the pipe for the lining.

“One of the biggest challenges was removing over 50 tons of sand from the pipe,” he said. “While that sounds easy enough to deal with, we found that much of that sand had been washed back into the pipes again over two large storm events. The storm had some huge swells.”

Safety is key

Another critical aspect for Moran was keeping the team safe. Being so close to the ocean, there were questions about how to keep the people inside the pipeline safe in the event of freak weather events or a WWTP failure.

“We had to cover many safety issues before we even started,” Moran said. “In most situations, we experience fluids coming downstream from further up the pipe. In this case, we were worried about fluids coming up from the end of the pipe (downstream) and fluids coming down the pipe. We had to spend a lot of time thinking about things like overtop waves.”

Keeping that water out required introducing a massive bulk bag sea wall made of over 100 tons of sand. Interflow also had two separate pumps for pumping seawater out of the system. Running these pumps non-stop meant that infiltration rates were brought down to nearly zero.

Interflow’s unique technology

Interflow used its ultraviolet cured-in-place pipe (UV CIPP) solution from its Interline range. It is a trenchless, structural lining method that uses ultraviolet light to cure the liner once it is inside the pipe. As part of the project, Moran and his team had to find a clear four to five-day window to insert the line.

“We had established earlier that we would spend a week sealing the pipe,” he said. “However, a massive storm came through that weekend and dumped between 20 and 30 tons of sand. We had to clean it all up and then put the seawall up. It took us two weeks to clean and seal the pipe.”

Just 48 hours before the liner was due to be installed, a second freak storm created more problems for Interflow and the team on Merewether Beach, with three to four-metre waves hitting Mereweather Beach.

“We had to go and clean the entire pipe again. We lost the Sunday and Monday to rebuild the seawall,” said Moran. “Extra crews had to come in to clean the pipe, which took a solid 24 hours. We started pulling the liner through the pipe on the Tuesday night. The team needed a perfect period of three to four days with really low tides, no wind, and not much else to impact the lining of the pipe.”

Weather played critical role

While this seemed like an easy enough task, the weather was not playing. A storm was due to hit Newcastle on Friday, so the entire job had to be completed before the storm came through.

“Because of the storm on the Sunday night, it pushed that whole process back,” Moran said. “It meant that we were cutting on Wednesday. On Thursday, we then had to pump concrete in and have everything packed up ahead of the Friday morning storm. Just having a liner in was the best thing ever.”

In the eyes of Moran, this was mostly a typical project, but in an exceptional environment.

“In the end, we were successful because our people were so resilient. They had the right skills, of course, but it was their ability to adapt and keep going in the face of so many setbacks that got us through.”

For more information, visit https://www.interflow.com.au/