Water from rivers in Wainuiomata are directed into a water treatment plant, then distributed through a pipeline network through the valley and into Wellington.
The Wainuiomata pipeline system is part of the Wainuiomata/Orongorongo Water Collection system. On the Orongorongo side, weirs in the Orongorongo River, Big Huia, and Little Huia Streams are piped to the Wainuiomata treatment plant via a 5.6km pipeline and tunnel, with pressure release valves installed upstream of the plant intake. Next to the valves, the water passes through turbine generators housed in a small brick building before the water reaches the plant. On the Wainuiomata side, weirs along Wainuiomata River and George Creek are piped to the same treatment plant.
From the plant, water is then directed to various locations such as Wainuiomata, the Wellington City Business District, and the southern and eastern suburbs of Wellington City. This is achieved through a combination of gravity and pumping stations. The water supply for Wellington originates from two primary bulk water systems, which are interconnected at Nguaranga. This connection between the Kaitoke to Karori and Wainuiomata to Wellington pipelines ensures water security by enabling the transfer of water between them, thus allowing for multiple water sources.
Over the years, pipes have been replaced and even rerouted. The original pipeline has a number of smaller pipes in and around the old pipeline. At least one functioned as a scour pipe, while others were designed to divert water from creeks to protect the main pipeline.
Wainuiomata Water Race
The original water race in Wainuiomata was part of an early water supply system built in the late 19th century to transport fresh water from the Wainuiomata River to Wellington. The system was designed to channel water through a combination of a race, pipes, and tunnels, helping to secure a reliable supply for the growing city.
Construction of the race and Coleman’s Tunnel took place between 1881 and 1883. Over time, as new infrastructure was developed, the race was replaced by a pipeline that bypassed Coleman’s Tunnel. Remnants of the race, including sections of tunnels and old waterworks structures, can still be found in Wainuiomata Regional Park.
Replacement Pipeline
The replacement pipeline between the old dam and Coleman’s Tunnel was constructed between 1899 and 1901. Colemans Tunnel, built during 1881/82, was abandoned during this period due to functionality issues such as water leakage. This led to installation of a new pipe from the old dam to the existing pipeline at the Colemans Tunnel’s terminus, a 760 mm (30-inch) diameter cast-iron pipe extended for 5.6 km (three and a half miles), passing through a 1 km (50-chain) long tunnel.
While most of this section of pipeline is buried, some sections of the old pipeline can still be seen, with small sections visible in parts of the Wainuiomata Regional Park and surrounding areas.
Morton Dam Pipeline
The Morton Dam pipeline was an integral part of Wellington’s early 20th-century water supply system. Constructed between 1908 and 1911, Morton Dam, named after Wellington City Engineer William Hobbard Morton, was designed to augment the city’s water reserves. This dam, notable for its reinforced concrete flat slab buttress structure, spanned 128 metres in length and stood 17 metres tall.
To transport water from the dam to Wellington, a pipeline was laid, connecting the reservoir to the city’s distribution network. This infrastructure project included the construction of a duplicate water main from Gracefield to Wellington, completed in December 1912, enhancing the capacity and reliability of the water supply.
The pipeline’s route through Sinclair Valley (now Wainuiomata Regional Park) was lower down the valley hillside than both the raceway and its replacement pipeline. This newer pipeline follows Reservoir Road and passes under the pumping station on that road. It then follows this road around a corner to the head of Coleman’s Tunnel and connects with the pipeline across the Wainuiomata River.
Orongorongo Pipeline
Before the establishment of the Wainuiomata Water Treatment Plant in 1993, the Orongorongo Pipeline played a crucial role in supplying untreated water to Wellington. Constructed between 1921 and 1926, this engineering project aimed to address the city’s growing water demands.
The project involved building weirs on the Orongorongo River and its tributaries, Big Huia and Little Huia Creeks, to collect water. This water was then channeled through a 3.2-kilometre tunnel, known as the Orongorongo Tunnel or Semple’s Tunnel, which connected the Orongorongo Valley to the Wainuiomata Valley.
Once the water reached the Wainuiomata Valley, it merged with existing water supplies and was transported via pipelines to Wellington. During this period, the water underwent basic filtration and chlorination processes to remove larger particles and disinfect the supply. However, comprehensive treatment methods, such as coagulation and advanced filtration, were not implemented until the Wainuiomata Water Treatment Plant became operational in 1993.
The construction of the Orongorongo Pipeline was a significant engineering feat, especially considering the challenging terrain. Materials had to be transported over difficult landscapes, with light materials carried along a 6.5-kilometre pack track rising to 300 meters, and heavier materials hauled by horse teams through riverbeds to the tunnel entrance.
The pipeline spanned approximately 5.6 kilometers, including a 3.2-kilometer tunnel connecting the Orongorongo and Wainuiomata Valleys. After exiting the tunnel into the Wainuiomata Valley, the water continued through pipelines, eventually reaching the Lower Karori Reservoir in Wellington.
This pipeline was smaller in diameter and ran alongside the Morton Dam pipeline.
The Latest Pipeline
Following the decommissioning of the Morton Dam in 1988 due to earthquake risk , and the construction of the Wainuiomata Water Treatment Plant in 1993, Wellington’s water infrastructure underwent significant upgrades to enhance resilience and reliability.
In 1988, a new water pipeline was constructed through the Wainuiomata Waterworks area, running alongside the existing pipelines. This project aimed to enhance the water supply infrastructure for the Wellington region.
This pipeline, often referred to as the “green pipe” due to its distinctive colour, was installed alongside existing pipelines to improve the capacity and reliability of the water distribution system.
This pipeline plays a crucial role in transporting treated water from the Wainuiomata Water Treatment Plant to various parts of the Wellington region, ensuring a consistent and safe water supply for the community. Its construction marked a significant upgrade in the region’s water infrastructure, addressing the increasing demand and enhancing the resilience of the water supply network.
Recent projects have focused on renewing ageing water pipelines in the Wainuiomata area. For instance, in December 2023, work commenced on replacing water pipelines in Lees Grove and Holland Street. This initiative, undertaken on behalf of the Hutt City Council, aims to improve the resilience and reliability of the water service .
Additionally, in April 2024, efforts began to renew drinking water pipes in Wainuiomata and Stokes Valley. This project targets reducing leaks and increasing the network’s resilience, ensuring a more dependable water supply for the region
These upgrades are part of a broader strategy to modernise Wellington’s pipeline system, replacing outdated infrastructure with contemporary solutions to meet current and future demands.
