Delivering on our plan

In developing the Infrastructure Strategy 2025-55, trade-offs have been made due to affordability pressures and market capacity. Renewals investment prioritises the most critical and high-risk areas. Our strategic system planning project has informed the prioritisation of the capital expenditure programme. Over the 30 years to 2055, most three waters-related buildings and structures will require replacement or significant upgrades to maintain service levels. Climate change impacts in South Dunedin and SDF adaptation planning will continue to shape the three waters capital expenditure programme in the medium  to long term.

The first five years of Dunedin’s 9 year plan 2025-34 prioritises areas of highest risk and activities most in need of investment, with a continued focus on pipework renewals and large-scale plant renewals, such as the renewal of the city’s main central interceptor sewer and terminal wastewater pump station. New capital investment in the 10 years to 2039 aims to improve water supply resilience by investigating and developing new groundwater supplies, improving water use efficiency, and upgrading wastewater and stormwater networks. This includes improvements in wet weather flow management and projects to reduce carbon emissions from biosolids and create bioresources. Rationalisation of wastewater treatment plants in the north of the city and Mosgiel will reduce ongoing maintenance costs, enhance plant efficiency, and streamline operational processes.

Further improvements to the resilience of the water supply are programmed from 2034 onwards, including the construction of an additional raw water storage dam, and building new treated water reservoirs. The replacement of the Deep Creek and Deep Stream raw water pipelines (including replacing the Taieri River pipe bridge) is planned for the medium term, with condition assessment underway in early 2025 to inform timing. The replacement of these two pipelines is particularly significant as both carry significant risk in terms of the DCC’s ability to supply water. Failure to address these assets in this timeframe would expose the assets to an increasing risk of failure, denying the city of its two primary water sources. Resilience to natural hazards and climate change will be supported by raising critical wastewater assets, sealing manholes against infiltration, and improving stormwater network resilience and efficiency with green infrastructure and catchment upgrades. Ongoing renewals and minor upgrades to larger treatment plants will continue over the medium term. Significant investment is required to support city growth, mainly within the networks. While most treatment plants can handle forecast population changes, some smaller plants will need upsizing.

Over the longer term, efforts will continue to reduce network water losses, reducing the volume of raw water required from sources and the volume of water requiring treatment. Additional protection for the Tahuna and Green Island WWTPs from sea level rise impacts will be required, as well as protection or relocation of other critical wastewater network assets such as pump stations in coastal hazard zones. These facilities will also need ongoing upgrades to align with changing legislation and standards. Stormwater systems will be upgraded over the longer term using a ‘green infrastructure’ approach, using place-based solutions such as daylighting streams (uncovering buried waterways) and retrofitting of treatment devices such as wetlands and detention ponds. These approaches support resilience in the face of a changing climate, providing more space for water as heavy rainfall events become more common.

We will continue to monitor key variables such as population forecasts, sea level rise, legislative changes, and asset performance to ensure the strategy adapts to meet current and future challenges. Our Dynamic Adaptive Planning Pathway (DAPP) approach will guide our investments, allowing us to adjust plans based on emerging signals and changing conditions, ensuring our infrastructure remains resilient and effective.

5.1 Three waters budget 2025-2034

Figure 12: Three waters capital expenditure by type 2025-34

Three waters capital expenditure by type 2025-34 - enlarge to full image

Table 11: Three waters capital and operating expenditure budget

5.2 Three waters 30 year budget

Figure 13: Projected three waters capital renewal and operating expenditure in 5 year bands for the 11 to 30 year period.

Figure 13: Projected three waters capital renewal and operating expenditure in 5 year bands for the 11 to 30 year period.

Table 12: Three waters capital renewal and operating expenditure budget, five year bands for the 11 to 30 year period

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