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Dunedin City Council – Kaunihera-a-rohe o Otepoti

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Background to the Security of Supply project.

Three Waters Strategic Direction

The principles and priorities underpinning decisions about our water supply and infrastructure are set out in the Three Waters Strategic Direction Statement (2010–2060). A priority is to use existing sources to supply the city’s water for the next 50 years.

The most critical of Dunedin’s existing water sources are the Deep Creek (1936) and Deep Stream (1977) systems, which supply over 40% of the city’s water. The pipes travel a long way through unstable land and cross the Taieri River on a steel arch pipe bridge spanning 70m in a steep-sided gorge. This infrastructure works well, but would leave the city’s water supply vulnerable if it failed.

The Taieri River Bridge Bypass Project started in 2009. The proposal was to build a crossing under the Taieri River 1.5km upstream of the bridge, with 4.3km of detour pipeline to reach the new crossing.

An evolving project

In 2010, the scope was expanded to include other risks along these pipelines, such as landslides, rock falls and earthquakes.

In 2011, geotechnical investigations increased the estimate for construction of another crossing of the Taieri River from around $6m to at least $12.7m. This was a considerable setback for the project and we took a fresh look at the problem.

Ross Creek Reservoir

At the same time, monitoring of the Ross Creek Reservoir and associated infrastructure, which had been out of active service for nearly 20 years, showed that the infrastructure was nearing the end of its life. The dam embankment was unsafe, so an emergency irrigation system was built and the reservoir lowered. The cost to either decommission or stabilise the historic structure was estimated at $2.5– $5.5m.

It became clear that it might be more efficient and cost-effective to reduce the risks to Dunedin’s water supply by repairing the Ross Creek Reservoir and bringing it back into service, instead of building the crossing under the Taieri River.

Analysis led to the Security of Supply Strategy, which outlines a sequence of projects and investment that progressively makes Dunedin’s water supply more secure. The projects in the strategy are listed below:

Project Timing
Short / medium term projects
Minor renewal on Deep Creek pipe Completed
Renewal at Deep Creek intake Completed
Southern Water Treatment Plant to Mount Grand Water Treatment Plant — treated water pumping station Completed
Ross Creek Reservoir refurbishment 2017–19
Ross Creek Reservoir to Mount Grand Water Treatment Plant – raw water pumping station and pipeline 2018/19
Algal control – Ross Creek / Sullivan’s Dam 2019/20
Sullivan’s Dam to Ross Creek pipeline 2020
Dalziel Road pipeline 2022
Long term projects
Renew Deep Creek /Deep Stream pipelines as one pipeline 2036
Renewal at Deep Stream intake 2057
Renew Taieri River pipe bridge 2084

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