Dartmoor

Key points for consideration

• Design consideration: The detailed design of the option will be undertaken considering constructability, temporary access, safety in design, and residual operational risk management.
• Longer spans and fewer columns: Whenever feasible, the bridges will incorporate longer spans and fewer columns in the water. This design approach aims to reduce the risk of flow blockage caused by debris and slash during flood events. However, earthquake resilience is still a major consideration.
• Project timeline: The goal is to begin construction on a permanent replacement structure to the community by mid-to late 2025. 

Background

A new permanent bridge at Dartmoor is being constructed due to the catastrophic damage incurred to the existing structure during the Cyclone Gabrielle floods.  

During the cyclone, the bridge suffered a complete loss of all five bridge piers and seven spans.  In the immediate aftermath, Council’s roading team and contractors focussed on reconnecting communities and restoring access as quickly as possible.   

The site of the old bridge following Cyclone Gabrielle

A pedestrian bridge was installed at the end of March 2023, followed on 5 April by the temporary single-lane bridge now in use.  Some of the abutments remain in place and have been repaired and reused to support the temporary structure. The weight restrictions that apply to this bridge are 40T MAX at 10km/hr.

Pedestrian bridge

Feasibility study

A feasibility option study has been conducted, where potential solutions for Dartmoors bridge rebuild have been assessed. The feasibility report covered the condition of the original structure, damage caused by the Cyclone, and a feasibility assessment of multiple bridge and alignment options. The feasibility report was based on the following:

• Geometrics 
• Hydrology and climate effects 
• Geotechnical/geology considerations 
• Environmental considerations 
• Constructability 
• Cost 
• Social impacts 
• Other factors 

The proposed bridge will be a like-for-like replacement of the original structure (i.e. single lane bridge) with no cycle/walking provisions. Using minimum widths this equates to a bridge width of 5.1m. An overall bridge length of 104m is anticipated, with the increased bridge length accommodating the anticipated increase in flood levels.