Consider this: Wellington’s water supply relies heavily on these very lakes before us. The Macaskill Lakes at Te Marua. They stand as a crucial backup to the Hutt River supply.
These lakes weren’t always here. They were constructed on abandoned river terraces of the Hutt River. This area sits right next to the Wellington Fault. That’s a detail that adds a certain edge to their story.
Their main job? To provide clean water when the Hutt River is too murky. Heavy rain can make the river too dirty for the water treatment plant. The lakes ensure we still get water.
These aren’t just small ponds. The Macaskill Lakes are about 17 meters deep. Together, they can hold roughly 3350 million litres of water. In a bad drought, they could keep us going for two to three months. That depends on how much water everyone uses and what other sources are available.
Interestingly, during construction, workers dug a 10-meter-deep trench across the Wellington Fault. They found the bedrock was crushed and sheared. This damage stretched across a zone about 70 meters wide. The fault line itself had clay as thick as 40 cm running through the river gravels.
The lakes have been renamed. Originally called Te Marua Lakes. Then named after Stuart Macaskill. He was a long-serving chairman of the Wellington Regional Council. Later the first name was dropped. Two names contravened Geographic Board rules.
Water supply lines cross the Wellington Fault near the Macaskill Lakes. This poses a challenge. A fault rupture could easily break those lines. That would lead to water supply failures.
To deal with this risk, automatic shut-off valves have been installed. Smaller bypass pipes are ready for quick repairs. This should help restore at least some water supply quickly. But even with these precautions, a major earthquake would create significant water supply problems.
These lakes are filled from the Hutt River. This happens when the water is clean and plentiful. The stored water is then pumped back to the water treatment plant. This ensures a steady supply for the Wellington region.
The Hutt Water Collection Area is vast. It covers almost 9000 hectares of bush-clad mountains and valleys. It provides about 40 percent of the region’s water each year. Rainwater gathers in streams that feed the Hutt River. From there, it flows to a weir at Kaitoke. The water then travels through tunnels to the Te Marua Water Treatment Plant. Up to 150 million litres can be taken from the river daily.
So next time you turn on the tap. Remember the Macaskill Lakes. Remember their role in providing clean water. Remember too, the geological forces at play beneath them.