The Orongorongo-Karori Pipeline:
A Vital Water Supply for Wellington
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 was designed to meet 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 the Orongorongo Tunnel, also known as Semple’s Tunnel, a 3.2-kilometre tunnel that connected the Orongorongo Valley to the Wainuiomata Valley. Once the water reached Wainuiomata, it merged with existing water supplies and was transported via pipelines to Wellington.
The steel pipeline, spanning approximately 5.6 kilometres, was built to withstand high pressures of up to 346 pounds per square inch. Unlike older pipelines that used riveted joints, this one featured steel and rubber joint systems, where pipes were connected with rubber rings and heavy cast iron collars, bolted tightly to ensure a secure seal.
Building the pipeline was a major engineering feat, as materials had to be transported through rugged terrain. Lighter materials were carried along a 6.5-kilometre pack track, rising 300 metres in elevation, while heavier components were hauled by horse teams through riverbeds to the tunnel entrance.
The pipeline was rigorously tested under extreme pressure, sometimes exceeding five times its expected working load. In one test, a joint remained intact even when the pressure gauge failed at 2000 pounds per square inch. After exiting the Orongorongo Tunnel, the water continued through pipelines to the Lower Karori Reservoir in Wellington, where it was distributed to the city.
For decades, this system provided untreated but filtered water to Wellington, undergoing basic filtration and chlorination before delivery. It wasn’t until the Wainuiomata Water Treatment Plant began operations in 1993 that more advanced water treatment, including coagulation and fine filtration, was introduced.
The Orongorongo-Karori Pipeline remains an essential part of Wellington’s water infrastructure, demonstrating both the engineering ingenuity of its time and its role in securing a reliable water supply for the city.
