Toxic Algae Warning
Infrastructure provides an important base for our activities; the foundation for our economy to prosper, our people to be healthy, and our city to be safe. Water infrastructure in particular is critical to sustaining Te Awa Kairangi ki Tai Lower Hutt as a resilient and liveable city.
The following information about drinking water, wastewater and stormwater infrastructure shows the challenges we face under the current approach to managing water services.
Water supply
Council’s water supply network receives treated water from the Greater Wellington Regional Council’s bulk water network. The water is stored in local reservoirs and distributed via a pressurised pipe network to consumers at their boundary toby. The water supply network consists of reservoirs, water mains, pumping stations, area meters, and tobies. Critical water supply assets include large diameter pipes, together with all reservoirs and pumping stations. Most areas of the city meet expected water quality standards for water storage and water pressure, and careful management of this water supply and distribution infrastructure contributes to making sure good health outcomes are maintained.
Wastewater
The wastewater system collects, treats, and disposes of wastewater from residential and business properties, including industrial liquid wastes. The wastewater system consists of a network of pipes connecting to each property, which in turn discharge into a system of largerdiameter trunk sewer pipes. There are two main trunk sewer pipelines for the Hutt Valley. One follows the western Hutt River stop bank, and the second passes through the eastern suburbs of Taitā and Naenae, before following the rail corridor through to Moera.
The trunk sewers convey wastewater from Lower Hutt (including Wainuiomata) and Upper Hutt to the Seaview Wastewater Treatment Plant. Treated liquid effluent from the Seaview plant is dispersed via an outfall at Pencarrow Head, while the treated solid effluent is disposed of at the Silverstream landfill. Resource consents are in place for the discharge of treated wastewater and for overflows in the case of high flows.
Ongoing monitoring and environmental scanning ensures compliance with current and potential future resource consents. Critical wastewater assets include large diameter pipes, trunk pipes, the Seaview Wastewater Treatment Plant, and the Silverstream storage tank. Seven out of the 22 pumping stations in the city’s wastewater network are identified as critical assets and these are closely monitored to ensure maintenance and renewals are undertaken when an unacceptable risk of failure is observed or predicted.
Stormwater and flood protection
The stormwater system manages surface water run-off to minimise flooding and any adverse effects on the quality of the water it runs into. The primary stormwater system consists of pipes, open drains, retention dams, and pumping stations. Stormwater is directed through streams, rivers, channels, and pipes to the harbour.
Secondary flow-paths are provided in some areas to accommodate floodwaters when the primary system is overloaded. F
lood protection is important for city planning and development based on management of risk. Components of a robust flood protection system include stop banks to prevent the occurrence of flooding, stormwater management to drain water away effectively and efficiently, and land use controls to minimise exposure of property or infrastructure to flood risk.
To help manage storm events, resource consents are in place for when water levels cause discharges into rivers and streams, including intermittent discharges to the Waiwhetū Stream. This includes contaminants from the road such as oil and rubber.
Ongoing monitoring and environmental scanning ensures compliance with current and potential future resource consents.
Our water infrastructure challenges and risks
Water infrastructure in Te Awa Kairangi ki Tai Lower Hutt is ageing, resulting in reduced network resilience, water loss, leakage of wastewater into the environment, and reduced ability to support population growth.
Our infrastructure is old and very tired, especially sewer and stormwater pipe work and drinking water pipe work, designed, and installed with limited future proofing for the expanding city we now live in. It needs major upgrading now.
Determining when assets need renewing is a complex task requiring good information. Some water infrastructure assets are visible, and their condition can be easily observed, while others are underground, making it difficult to forecast when they may fail. Wellington Water Ltd (WWL) uses closed circuit television cameras to check on the condition of the pipe network as well as smoke testing to check whether wastewater infrastructure is operating effectively. The poor condition of our water infrastructure is evidenced by WWL estimates that throughout the wider region, over 40% of drinking water is being lost due to leaks resulting from ageing infrastructure, historic underinvestment, and a backlog of renewals and repairs. WWL has received record numbers of service requests for leak repairs and is working to address these.
Stormwater risks
Most of the existing stormwater infrastructure was originally designed to accommodate a five-year average recurrence interval rainfall event. Much of this stormwater infrastructure can be overloaded when more severe rainfall is experienced. Service level expectations are now higher than when the system was designed, and general replacement or renewals are now built to a 10-year average recurrence interval standard.
During wet weather both stormwater and groundwater can infiltrate the wastewater system, leading to possible overloading of the system and overflows which create health, water recreation, and water quality issues. Infiltration reduction strategies include pipeline inspection and renewal programmes and are aimed at minimising the entry of stormwater or groundwater to the wastewater system.
We are now experiencing more intense rainfall events that put pressure on our stormwater networks. Planning for the effects of rainfall intensity because of the changing climate is being incorporated into design standards and stormwater mitigation solutions.
It is not always practical, however, to build our way out of stormwater flooding issues, and case-by-case solutions such as plan changes or overland flow path options must be considered. The graph below shows WWL’s assessment of the condition of the water supply, storm water and wastewater infrastructure in Te Awa Kairangi ki Tai Lower Hutt, including the length of pipe infrastructure in each condition category. Condition four (poor) means that the infrastructure has between 5% and 20% of its life remaining, while at condition five (very poor) the infrastructure has less than 5% of its life remaining, which is around three years.
The pressure of growth on water infrastructure
As the population of Te Awa Kairangi ki Tai Lower Hutt grows, more fresh water is needed per day, with a corresponding demand on the capacity of the wastewater network. WWL estimates that an additional 150,000 people (more than the population of Te Awa Kairangi ki Tai Lower Hutt) could be living in the wider Wellington region within the next 30 years. It warns that water use in the Wellington region is at an all-time high, primarily due to water loss, population growth, and water usage patterns.
As more houses are built there will be increased pressure on stormwater networks, including intensive housing creating more solid surface areas with reducing pathways for water to run off, although Council’s draft District Plan will require new builds to incorporate rainwater and greywater capture and use systems.
Council’s Three Waters Growth Study 2022 found that a significant programme of investigative, design, and physical works was needed to meet the demands of future growth and bring existing networks up to target levels of service capacity. The study signalled that the possible costs of the interventions proposed in the study had an associated cost estimate of approximately $1.27 billion. There is increasing pressure on the water storage capacity in the Wellington region as well as on the capacity of its water service networks. Water use restrictions have become a regular occurrence across the Wellington region.
In Te Awa Kairangi ki Tai Lower Hutt the demand for water will be exacerbated by proposed District Plan changes which will allow for greater housing intensification in parts of the city.
WWL provides the region’s councils with advice on the interventions needed to address leaks and the increasing risk of water shortages. They provided the following recommendations at a regional water shortage summit in September 2023:
- Keep the water in the pipes – invest in finding and fixing leaks, managing water loss and replacing old infrastructure
- Reduce water demand through water metering – invest in universal smart meters across the metropolitan Wellington region
- Add more supply – build another pair of storage lakes to increase supply and complete the existing project to optimise Te Marua capacity.
The challenge facing Te Awa Kairangi ki Tai Lower Hutt is further illustrated by WWL’s assessment that the length of water infrastructure pipe renewals achieved in 2022-23 and 2023–24 is about half of what is needed on an annual basis to maintain our water network assets on a lifecycle basis.
They note that even if substantive additional funding was made available for water infrastructure renewal, the rate of renewal would be severely limited by the current capacity of the skilled workforce needed to carry out this work.
In summary, despite the increasing investment Council has and will make in water network renewal, current water storage constraints as well as capacity constraints in the regional water infrastructure workforce will impact the level of increased system and network capacity that can be achieved in the short to medium term.
In combination with the need for Council to operate with fiscal prudence, this means there are two potentially unavoidable future risks:
- The likelihood of ongoing and potentially increasing water shortages across the Wellington region
- That Council will be unable to provide infrastructure support in all areas of housing development or renew ageing water infrastructure on a lifecycle basis in Te Awa Kairangi ki Tai.
