Geotechnical investigations begin for The Bight Bridge replacement

Geotechnical investigations have started for the planned replacement of The Bight Bridge at Wingham, marking an important step in restoring and future-proofing the Manning River crossing. The works involve a barge-mounted core drilling rig collecting core samples from four locations across the river.

The investigation is being carried out to support the design of the new bridge, which will replace the existing flood-damaged structure. Information from the boreholes will help engineers understand the ground and rock conditions beneath the riverbed and determine the most suitable foundation system for the replacement bridge.

The project is being progressed by MidCoast Council, with early design and scoping funding approved by the NSW Reconstruction Authority. The current project timeline aims to complete the bridge design later this year, have the project ready for tender in early 2027 and open the new bridge to traffic in 2028.

For bridge replacement projects, geotechnical investigation is one of the most important early design activities. The bridge deck and superstructure may be the most visible parts of the project, but the performance of the bridge depends heavily on the behaviour of its foundations.

The core samples collected from the Manning River will provide information on soil layers, rock depth, material strength and possible variability across the river channel. This data will help engineers determine how the bridge piers and abutments should be founded and anchored into the riverbed.

This is particularly important for a river crossing exposed to flooding. During flood events, bridges are subjected not only to vertical traffic loads, but also to hydraulic forces, debris impact, scour and erosion around foundations. If foundations are not designed to account for these effects, bridge stability and long-term serviceability can be compromised.

The replacement of The Bight Bridge is therefore more than a reconstruction task; it also presents an opportunity to improve resilience against future flood events and changing loading conditions. Reliable geotechnical data will allow designers to assess foundation depth, bearing capacity, lateral resistance and scour protection requirements.

Investigations from a barge-mounted rig are technically challenging, as drilling must be carried out safely over water while maintaining accurate borehole locations and recovering representative core samples. However, this work is essential before detailed structural design can be finalised.

According to MidCoast Council, the investigations form part of a strategy to progress multiple elements of the design process at the same time. By collecting ground data now, alongside other design activities, the design team can reduce uncertainty, avoid later redesign and move the bridge replacement toward procurement more efficiently.

For the Wingham community, the start of the geotechnical investigations represents visible progress on a long-awaited project. From an engineering perspective, it provides the essential groundwork: the new bridge must be designed not only to restore connectivity, but also to perform reliably under future river, traffic and flood conditions.