Watpac Hamilton Reach

Mobile Dewatering

Contractor: WATPAC

Project Value: $78 million

The Riverlight apartment building under construction by WATPAC in the prestigious Brisbane riverfront community Hamilton Reach will offer 240 apartments across two towers, and 283 parking spaces in a basement car park. 

For this major project, WATPAC engaged the MDW Group for dewatering and environmental management services. 

With an original scope of work requiring dewatering internally of sheet piling, the job changed due to sheet pile design. The scope of dewatering evolved to encompass a dropping of the water table to 5.5 metres outside of the sheet piling. 

Creating a need for extra monitoring, a survey of the sewer pipe lines near the site indicated a local geology comprised of clay with coarse sand layers.

Well-points were installed inside and outside sheet-piles, connected to a common header pipe. Internal to the sheet-piling the dewatering system used sumps with submersible pumps and a system for lift-shafts. Precast piles intersected a highly permeable hydrostatically charged layer, which required some additional horizontal dewatering so the lift shaft could be poured. 

Average flowrate for the total dewatering system was 15 litres per second.

Outgoing pH was raised to within allowable limits (6.5-8.5) and iron levels were reduced with a site-specific purpose-built water filtration system to consistently below the allowable trigger value of 0.3 mg/l. Other metals such as AL, Mn, As, Zn, were also monitored for and were well below ANZECC trigger values at the discharge point.

Dissolved Oxygen and Turbidity values were all within the acceptable limits which meant the conditions of the DMP and local authorities were all met. This task was made more complex with incoming water quality fluctuating frequently with rain water run-off.

All project licensing applications, approvals and coordination with the relevant authorities were managed internally by MDW Environmental Services, streamlining the dewatering process. 

WATPAC was highly impressed with the service provided by Mobile Dewatering on this project and have recommended the group as their preferred supplier for future works.