Our performance – how we are doing

Our service provision is generally strong, but there are significant areas needing improvement. Some assets are in poor condition, and in certain cases, we lack sufficient information about their status. Additionally, we face several performance challenges that must be addressed to ensure reliable and efficient services.

For instance, our water supply network, despite delivering high-quality drinking water, struggles with capacity issues due to ageing infrastructure, leading to water supply losses and difficulties in meeting demand during peak summer periods. Our wastewater systems, although functioning well in dry weather, perform poorly during wet weather, resulting in overflows and a large carbon footprint. Similarly, our stormwater systems often fail to meet capacity levels of service, with limited treatment and contaminant removal capabilities. These issues highlight the need for targeted interventions to enhance our infrastructure and service delivery, ensuring we meet both current and future demands effectively.

It is important to note that the funding allocated in Dunedin’s 9 year plan 2025-34 does not aim to renew all assets before they fail. Such an approach would be neither economically feasible nor practical. Instead, renewals are prioritised based on asset criticality, and failure rates. Allowing non-critical assets to fail before replacement is an approach that can improve affordability while adequately managing risk. Funding over the 30-year infrastructure strategy period is calibrated to meet these renewals and address historically deferred renewals, ensuring the DCC can maintain service levels in the future.

3.1 Water supply

The DCC provides high-quality drinking water that complies with Water Services (Drinking Water Standards for New Zealand) Regulations. However, ageing infrastructure in some areas reduces network capacity and fails to meet current requirements, such as minimum flows for firefighting, particularly in cast iron mains where tuberculation reduces flows. Urban growth and development, as planned in the FDS and enabled under District Plan provisions, are constrained by network capacity in some areas. Dunedin’s 9 year plan 2025-34 includes expenditure to address these constraints. Some smaller, rural plants require improvements to ensure resilience and reliable compliance with more rigorous regulatory standards. Most non-compliances with recently strengthened standards have been technical non-conformances, related to missed manual samples or outages in automated data collection systems. The DCC remains confident that the water supplied to consumers is safe to drink but recognises that further work required to consistently meet all compliance requirements.

3.1.1 Condition of Water Plant and Civil (Built) Assets)

Figure 1: Age-based condition of water supply plant and civil assets

Figure 2: Assessed condition of critical water assets, grouped by criticality rating (Minor/Moderate/Major/Extreme) and site

The charts above show the condition of water supply plant and civil (built) assets. The chart on the left (Figure 1) shows the assumed condition of these assets based on how far through their useful lives they are. For example, if an asset is 85% or more through its expected useful life, it is considered to be in poor or very poor condition. Currently 34% of water supply plant and civil assets, by replacement value, fall into this category.

The chart on the right (Figure 2) represents the condition assessed through direct observation, focusing on critical assets at critical sites only (critical assets being those assessed as being ‘moderately critical’ or above). The assessment indicates approximately 90% of these assets across the six water treatment sites are in fair to very good condition. Works are underway to replace the remaining 10% of critical assets in poor condition. Six highly critical raw water pump station assets are in poor or very poor condition, with half located at the Puddle Alley pump station, where works are programmed for 2025/26. Among treated water pump stations, several highly critical assets are in poor or very poor condition. Additionally, 75% of the critical pump station assets identified as being in poor condition have reached or exceeded their lifespan. Replacement works are either underway or planned, with budgets allocated for these projects in the 9 Year Plan 2025-34.

3.1.1 Condition of Water Network Assets

The average age of Dunedin’s water pipelines is 49 years, with an average total expected useful life of around 80 years depending on the pipe material and diameter. Older pipes are more prone to leakage, loss of fire flow capacity, and aesthetic water quality issues, such as discolouration, sedimentation, and odour complaints due to higher chlorination levels needed to address biological build-ups, particularly in cast iron mains.

Water pipe conditions are assessed by removing small sections of pipe for inspection. CCTV filming is not commonly used because it requires taking the assets out of service. Data on material, age, condition, performance, location, capacity, criticality and remaining useful life is collected for three waters assets. DCC staff routinely inspect treatment plant assets to ensure proper maintenance, with specialist engineering advice used as needed. The following map (Figure 3) indicates the current state of water supply reticulation infrastructure.

Figure 3: Water Supply network condition by age

Figure 3 shows water supply network (reticulation) assets by age. Red indicates our oldest water main assets which are beyond 85% of their expected lifespan. These are generally in the older parts of our city that received reticulated services first. 29% of our water mains are classified as being in poor to very poor condition. Much of our work programme focuses on renewing these older pipes to ensure continued reliable service. Work programmes prioritise assets in poorest condition, with renewal priority based on age and break history.

Figure 4 shows the number of water main breaks per month as a 12-month rolling average. The trend indicates an increase in breaks over time (as shown by the dotted line) which is expected where renewals have lagged behind depreciation over time.

Figure 4: Number of water main breaks (12 month rolling average)

3.2 Wastewater

The performance of Dunedin’s wastewater systems varies with age. Our wastewater systems generally operate as designed during dry weather, safely transporting, treating and discharging treated wastewater. However issues arise during wet weather, with severity increasing with rainfall. While most of the city’s wastewater treatment plants are in reasonable condition, many mechanical and electrical components are reaching the end of their useful life, affecting operational performance and staff safety. Some plants face challenges meeting current consent conditions, resulting in non-compliance or abatement notices. Several areas of the wastewater network are in poor condition due to ageing pipes, leading to stormwater and groundwater infiltration. During heavy rainfall, this can cause wastewater overflows and insufficient treatment before discharge as treatment processes are overwhelmed. These issues constrain urban development in some parts of the city, with improvements needed to support development.

Wastewater treatment, including energy-intensive processes, biosolids production and biogenic methane, is the DCC’s largest carbon emitter. Significant work, including developing a dedicated bioresources handling facility is planned (see section 4 ‘Our Plan’).

Currently, CCTV inspections are completed in response to reported issues or when an asset is due for renewal. This approach skews the data toward assets in poor condition, making it an unreliable indicator of overall network condition. Network performance is a more reliable indicator.

With an average age 62 years, ageing wastewater pipes are causing varying issues for residents, particularly in older areas like Kaikorai Valley, North East Valley and South Dunedin. Renewals are underway in North East Valley and Kaikorai Valley. Renewals in South Dunedin have not commenced due to the complex interactions between groundwater, stormwater and wastewater. There is some evidence to suggest that South Dunedin’s ageing wastewater infrastructure acts as a series of field drains, artificially lowering groundwater levels. The South Dunedin Futures project has examined these interactions and will guide renewals in both wastewater and stormwater networks to improve services without adversely impacting properties.

Inflow occurs when stormwater enters the wastewater network through direct connections like manhole covers, while infiltration refers to groundwater seeping in through cracks or joints in the pipes. Excessive inflow and infiltration can overwhelm the system during heavy rainfall, leading to overflows and increased treatment costs. Larger issues arise from inflow and infiltration of ground and surface water into older pipes, leading to surcharges, where network flows exceed capacity, creating pressure at access holes and flooding treatment plants.

Renewal programmes focus on reducing inflow and infiltration to minimise wet weather overflows and treatment plant washouts, which reduce treatment capacity and can lead to consent breaches. At pump stations, the aim is to increase reliability to maintain network performance, while renewals at treatment plant focus on compliance with resource consents and reducing health and safety risks.

3.2.1 Condition of Wastewater Plant and Civil (Built) Assets

Figure 5: Age-based condition of wastewater plant and civil assets

Figure 6: Assessed condition of metropolitan wastewater treatment plant assets, grouped by criticality rating (Minor/Moderate/Major/Extreme) and site

The charts above show the condition of wastewater plant and civil (built) assets. The chart on the left (Figure 5) shows the assumed condition of these assets based on age. Currently, 29% of wastewater plant and civil assets, by replacement value, are considered to be in poor or very poor condition due to their age.

The chart on the right (Figure 6) represents the condition of metropolitan treatment plant assets, as assessed through direct observation. The assessment indicates that approximately 82% of assets across the treatment sites are in fair to very good condition. Treatment assets at rural plants (not shown here) are generally in reasonable operating condition, with the exception of the Middlemarch WWTP which is programmed for upgrade in the short term, and Seacliff which has recently been refurbished. Wastewater pump station assets are routinely inspected as part of normal operations. The condition of pumps is assessed during programmed plant maintenance inspections, however formal condition grades are not assigned during this inspection. Works are underway or planned to replace assets in poor condition.

3.2.2 Condition of Wastewater Network Assets

Figure 7 Wastewater network condition by age

Figure 7 above shows wastewater network (reticulation) assets by age. Assets marked in red are the oldest, having exceeded 85% of their expected lifespan. As with water, these older assets are typically located in the older parts of our city. 30%of our wastewater mains are classified as being in poor to very poor condition. Our work programme primarily targets the renewal of these ageing pipes to maintain reliable service. We prioritize assets in the poorest condition, with renewal decisions based on age and break history.

The figure below shows the number of blockages per month as a rolling 12-month average. The dotted line indicates a decreasing trend in monthly blockages and breaks, reflecting the DCC’s efforts to reduce wastewater overflows by focusing on areas with older infrastructure susceptible to inflow and infiltration.

Figure 8: Number of wastewater blockages (12 month rolling average)

3.3 Stormwater

Stormwater services in the city are provided by the DCC, Otago Regional Council (ORC) and private landowners through open and piped watercourses and infrastructure. During heavy or prolonged rainfall, the drainage network in some areas underperforms, causing surface flooding and property damage. Peak stormwater flows are increasing due to climate change, which makes rainfall more intense and raising ground water levels in some areas.

Many areas experiencing capacity issues have seen significant change in use or density, or upstream development since the networks were first installed. Differing service levels design parameters for neighbouring borough councils prior to 1980s amalgamations also contribute to the issues. As a result, and acknowledging that development increases impervious surfaces and affects flow paths, the DCC now requires properties with significant development impacts on stormwater to undertake an assessment. This may require a stormwater management plan to ensure that post-development flows do not exceed pre-development levels. This approach allows for growth while ensuring it does not negatively affect the existing stormwater service level. Unreported development on private property, such as additional decking, paths, or sheds increases impervious surfaces and can cumulatively reduce the network’s ability to meet service levels.

Issues also arise when private watercourses are not maintained or when private pipes are too small to safely convey flows. The integrated system plan includes an assessment of the quantity and criticality of private stormwater assets (e.g., watercourses) interacting with the DCC’s network.

The average age of stormwater pipes owned by the DCC is 65 years. With little to no information on the nature of privately owned infrastructure it is impossible to determine how old these assets are, but they are likely to be similar, or older than surrounding structures.

The current provision of stormwater services is below target levels in some areas of the city. Climate change is intensifying rainfall, further exacerbating this issue, and in some areas, shallow groundwater limits soil storage capacity. These factors will make it more difficult to meet desired stormwater service levels in the future, requiring additional investment stormwater infrastructure to maintain existing service levels. To support this, DCC is focusing on renewing assets and initiating new projects to address current service level issues. Following previous floods, improvements are planned for the most heavily affected areas such as South Dunedin and Mosgiel. Work programmes to support planning are in place, such as the development of flood hazard assessment models for urban areas of Dunedin, new stormwater models for North East Valley and Kaikorai Valley, and improvement to the accuracy of stormwater hydraulic models in South Dunedin for planning and operational purposes.

Current service provision includes little infrastructure to improve stormwater quality before discharge or prevent contaminants from entering the stormwater system. Future regulatory changes are expected to require increased levels of stormwater treatment to protect receiving environments. Contaminants can enter stormwater from multiple sources including roadways and footpaths, roofs, and cross-connections. Most sources of contamination are outside the control of the DCC and will require treatment, but some sources, such as cross connections, can be identified and addressed either through capital works, or enforcement actions.

3.3.1 Condition of Stormwater Plant and Civil (Built) Assets

Figure 9: Age-based condition of stormwater plant and civil assets

Figure 9 shows the assumed condition of stormwater plant and civil (built) assets based on age. Currently, 78% of our stormwater assets, measured by replacement cost, are in very poor condition. Three-quarters of these assets by value are concentrated at the main Portobello Road pump station. Modifications and upgrades to this pump station will be considered as part of the South Dunedin flood alleviation programme, pending the outcomes of the South Dunedin Futures (SDF) project. A further 12% of the remaining assets in very poor condition are located at the Reid Avenue stormwater pump station, which is programmed for upgrade in the early years of the programme. Stormwater pump station assets are routinely inspected as part of normal operations. The condition of pumps is assessed during programmed plant maintenance inspections, however formal condition grades are not assigned during this inspection.

3.2.2 Condition of Stormwater Network Assets

Figure 10: Stormwater network condition by age

Figure 10 shows stormwater network (reticulation) assets by age. Assets marked in red are the oldest, having exceeded 85% of their expected lifespan. As for water and wastewater, these older assets are typically located in the older parts of our city. 61% of our stormwater mains are classified as being in excellent to average condition (less than 85% through their lifespan). Our work programme primarily targets the renewal of these ageing pipes to maintain reliable service.

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