Water management solution keeps Muddy Creek canal dry for restoration

Restoring this NSW stormwater canal required a reliable water management solution to keep people safe and construction work on track – here’s how Coates delivered.

The project

In November 2022, revitalisation work commenced on a stretch of stormwater canal that feeds into Muddy Creek at Brighton-Le-Sands in NSW. This work is being led by D4C – the consortium engaged by Sydney Water to deliver, construct and maintain vital water infrastructure across south Sydney.

“This project will restore a section of the Muddy Creek canal as it nears the end of its design life and ensure the stability of its banks,” explains D4C Project Manager, Conor Harten. “It also provides an opportunity to naturalise and improve the appearance of the waterway for the community and to boost local ecology by attracting new fauna to the area.”

Coates was engaged by D4C to design and implement a comprehensive water management solution to keep the canal safe and dry for workers, and to minimise the environmental impact of construction.

The challenge

Keeping surface water out of the canal

The project requires a 1km section of the existing concrete canal to be demolished, removed and re-poured. For this work to be performed safely and allow time for the new concrete to cure, the stormwater that typically flows through this section of canal must be redirected.

Managing tidal flows is another challenge. “The stormwater line cannot be entirely closed off because rain events can still happen, and this would cause surface water to accumulate when it needs to be able to flow out,” explains Sobin Joseph, Water Treatment Solutions Specialist for Coates. “But because this canal is situated in an area with significant tidal variation, without completely blocking off the canal, tidal water can still move back into the construction area, adding to the complexity.”

A 1km surface water bypass keeps the canal safe and dry during restoration

Managing groundwater during construction

“To safely excavate to depths of 1-2m in an area where the water table sits less than 1m from the surface, a robust dewatering solution is required,” says Sobin. “On-site water treatment is also important for maintaining and improving the quality of groundwater, which contains varying levels of sediment and other contamination from nearby soils.”

In line with EPA and Department of Fisheries requirements, before any groundwater can be discharged it must be filtered, tested and treated to meet strict quality criteria for the required PH levels and total suspended solids (TSS). Groundwater must also be visually inspected for turbidity (or clarity), colour and the presence of oil and grease, with all of these levels closely and independently monitored throughout dewatering.

The solution

Coates is working closely with D4C to maintain water quality at Muddy Creek and to keep the canal safe and dry for construction. This comprehensive and reliable water management solution includes:

• A 1km surface water bypass to re-direct water away from the construction area. Designed to accommodate a flow rate of 90L/s, this system uses a combination of 150MM trailer pumps and 6” and 4” submersible pumps operating continuously, plus a flow meter and the necessary fittings.

• A tidal barrier is used to manage the tidal water that moves back into the canal. To achieve a flow rate of 60L/s, this system incorporates 2 electrical vacuum pumps to manage high flow (one operational, the other on stand-by), plus submersible pumps for managing low level flow.

• The backup pumps remain on site throughout excavation and construction, to safeguard the bypass system in the event of a breakdown.

• A submersible pump dewatering system is used to extract groundwater and keep the excavation sites dry. An on-site water treatment plant then uses a sediment tank to filter this water, and a chemical treatment process to neutralise contamination and reintroduce fluoride.

On-site water treatment ensured discharged groundwater was in line with EPA and Department of Fisheries requirements

The impact

Coates’ water management solution is helping to keep the canal dry and the workers in this environment safe. It’s also improving water quality and positively impacting the project schedule.

“If the bypass pumps break down or the treatment plant doesn't work and water quality is affected, we will have to stop work. But with stakeholders like local residents and Transport for NSW waiting to get on site, it’s important that construction work stays on track,” says Conor. “So far, it has been a positive experience working with Coates to deliver this project. Their water management solution is working well, and we are receiving good support from the Coates Engineering Solutions team.”

Sobin has also enjoyed contributing to this project and is pleased with the results Coates has been able to achieve – particularly for dewatering and water treatment.

“During the past 10 months, our water treatment system has allowed all water quality criteria to be comfortably met, despite the challenges this project presents,” says Sobin. “The improvement that Coates has been able to achieve has kept water quality within the required range and is visibly obvious in the samples taken from this site.”

Construction is due for completion by September 2024.

Connect with Coates Engineering Solutions if you need a reliable and cost effective water management solution for your next project