TO REBUILD THE BANKS OF THE RIVER TORRENS, THE CONTRACTORS FIRST NEEDED TO DEWATER THEIR CONSTRUCTION SITES.

The Project

Severe storms that hit South Australia in 2016 damaged the banks of the River Torrens and SA Water received funding from the state government to remediate five sections of damaged riverbank.

Construction and engineering company, SEM Utilities, was contracted to complete the remediation works at Lockleys, Gilberton and Hardies Road, using Gabion Baskets, which are wire mesh cages filled with rocks.

The Problem

The remediation project required an excavation and rebuilding of the damaged riverbanks, which meant sections of the river needed to be dewatered to allow machinery and workers to operate safely and effectively.

SEM Utilities constructed weirs – which are cofferdam walls made of steel and clay – to wall-off the remediation work sites, but the sites had to be dewatered to keep them dry.

If the remediation sites became inundated the works would have to be stopped, causing delays to the project. The project started in July 2018 and was complicated by heavy spring rains that raised the level of the River Torrens and increased the volume of water flowing around the sites.

The Solution

SEM Utilities contracted Coates Hire to dewater the bypassed work sites and ensure the works could proceed safely and with no delays. Coates Hire is a specialist provider in shoring, propping and dewatering services, supplying not only the equipment but design engineering, engineering and installation.

Coates Hire’s Scott Stanley, Product Specialist - Pumps, Traffic, Shoring and Lift and Shift, says the three remediation sections varied in size between 20 metres and 140 metres.

At the first site – Lockleys – the works area was 53 metres long and required five 8-inch diesel pumps installed upstream of the works. The pumped water was piped around the works area and released back into the River Torrens. But when the river started rising, and an area of the work zone was taking on water, Coates Hire added three electric submersible pumps driven by a 350kva generator. Together the pumps and pipes were clearing 1200 litres per second from the river.

“A river is a dynamic environment and you have to be ready to adjust your response to the actual flows,” says Stanley.

In the other two remediation sites – at Hardy’s Road, Torrensville and Murray street, Thebarton – Coates Hire used a combination of diesel and electric pumps to shift the water and keep the worksite dry. Project Manager for SEM Utilities, Dhayanand Manoharan (Mano), says the rebuilding of the riverbank sections was only possible if they were successfully dewatered.

“We are excavating the riverbank and rebuilding it with Gabion walls,” says Dhayanand. “We can’t have water in the works area. Even when the river was rising, we had to have a solution.”

He says SEM Utilities built the weirs but the sites had to be mechanically cleared of water on a constant basis or workers could be injured and expensive construction washed-out. He says the Coates Hire pump designs operated at around 1200 litres per second but they had available capacity to increase to 1800 litres per second if required.

“Coates Hire engineers work with our engineers to come up with the best solutions. And then they support us with managers, electricians and mechanics,” says Dhayanand.

“We use Coates Hire because they’re reliable and they can adapt to dynamic situations. Once a site is dewatered, it has to stay dewatered.”