Tararua District Council is progressing upgrades to the Dannevirke Water Treatment Plant to improve the quality, resilience and reliability of the town’s drinking water supply, particularly during periods of heavy rainfall and high river flows.

Dannevirke’s water supply is sourced from the Tamaki River and stored within the Dannevirke impounded water supply and reservoirs. During heavy rainfall, the river can become highly turbid (murky), resulting in elevated Nephelometric Turbidity Unit (NTU) levels in the raw water.

At present, the Dannevirke Water Treatment Plant is only able to treat water with turbidity levels of 10 NTU or lower. When river turbidity exceeds this threshold, the plant cannot process raw water adequately and the town must instead rely on stored water reserves.

This creates a vulnerability during adverse weather events when river conditions are most challenging.

To address this, Council is upgrading the treatment process through the installation of coagulation, flocculation, as part of the clarification pre-treatment systems. These improvements will allow the plant to better manage higher turbidity levels in raw river water before it enters the main treatment process.

Once completed, the upgrades are expected to significantly improve the plant’s ability to operate during periods of poor river water quality, reducing reliance on stored water alone and strengthening the security of supply for the Dannevirke community.

These works form part of a wider programme of resilience initiatives connected to the Dannevirke Impounded Water Supply project. This broader programme includes investigations into alternative or enhanced raw water sources, additional treated water storage reservoirs, improved access to stored water within the impounded supply, and ongoing monitoring and maintenance of existing infrastructure.

The impounded supply is stable and has remained stable following the repair work. While some seepage remains present, it is at a significantly reduced rate. This is expected as the design allows for some discharge from the system for naturally occurring groundwater; however, Council does not have the historical baseline data needed to definitively distinguish groundwater flows from any residual leakage.

What we can say with confidence is that the repair work substantially reduced flows, the reservoir remains stable, and ongoing monitoring indicates the supply is operating as intended. The focus is now on continued monitoring and management, rather than further repair works, while Council progresses additional resilience improvements to support the long-term security of Dannevirke’s water supply.

Together, these projects are intended to strengthen the long-term security, resilience, and operational flexibility of Dannevirke’s water supply network.

Tararua District Council remains committed to keeping the community informed as the project progresses, including providing updates on key milestones and any potential impacts during delivery.

For more information, head to Dannevirke Water Resilience Projects | Tararua District Council