The $51.8 million replacement of the Mandurah Bridge was part of a broader project scope, which included decommissioning the existing structure and designing and constructing a new bridge over the Mandurah Estuary, along with associated roadworks, public amenities, and infrastructure.

Initiated in January 2016 and completed in March 2018, the new Mandurah Bridge increases traffic capacity and serves as a prominent landmark, improving amenities for the Mandurah community.

The previous bridge was deteriorating, and the upgrade was essential to accommodate two traffic lanes in each direction while improving safety for pedestrians and cyclists with more comprehensive, separate facilities across the bridge.

BG&E provided structural and civil engineering design, flood modelling, and hydrology services for the bridge replacement, which spans the Mandurah Estuary and extends into the surrounding marina precinct.

Our design incorporated a unique curved soffit cross-section that runs the entire length of the 243 metre bridge, creating a cost-effective yet visually striking structure. The bridge comprises six spans, with 42 metre internal spans and 37.6 metre end spans. The post-tensioned superstructure is supported by elegant columns on piled foundations.

The new bridge also includes wider, lower level shared paths that offer greatly enhanced pedestrian experiences, such as fishing platforms, public art, and landscaping.

Water Engineering Scope

The Mandurah Estuary Bridge Duplication project involved replacing the existing timber bridge structure on Pinjarra Road, near Mandurah’s CBD in WA. As part of the project, BG&E was engaged specifically for the water engineering scope to relocate the water distribution main that ran over the existing timber bridge.

This work was divided into two key stages to accommodate the new bridge structure and ensure continued water supply during construction.

Stage 1: Relocation of Water Mains

Stage 1 involved relocating 200 metres of DN450 PE water distribution main, including installing valves and a magnetic flow meter within a permanent underground concrete enclosure. This stage was essential to maintain the water supply while the new bridge was constructed.

Stage 2: Seabed Crossing and Redundancy Measures

Stage 2 required installing 250 metres of twin DN630 PE water distribution mains horizontally drilled beneath the Mandurah Estuary seabed. This stage involved complex valving and bypass arrangements on both sides of the estuary crossing, allowing the Water Corporation to switch between the pipelines if needed, ensuring redundancy in future pipe failure beneath the seabed.