The sheer scale of Upper Mangatawhiri Dam takes your breath away. Its imposing presence dominates the Moumoukai Valley. This isn’t just any dam. It’s a testament to engineering ingenuity. A vital part of Auckland’s water supply system.
Completed in 1965 Upper Mangatawhiri Dam is one of a series of rolled earth dams. These dams represent a significant advancement in New Zealand’s dam-building techniques. They were constructed between 1950 and 1977 in the Hunua Ranges. The valley itself holds a fascinating history. It’s an intermontane valley formed millions of years ago by fault-tilting. An ancient lake once filled this space. Today the valley floor contains gravels and silt remnants of that long-gone lake.
The dam’s construction was a marvel of its time. The ideal materials for the dam’s core were readily available. Fine-grained greywacke and argillite were found nearby. These materials were perfectly suited to create the robust clay and clay-rubble core. Spurs of country rock on either side of the valley provided ideal locations for the spillway and other essential structures. The spillway itself is a curved side weir an impressive 117 meters long capable of discharging a huge volume of water.
Construction was remarkably fast. Earthworks were completed in a mere 276 days. This was due to advanced earth-moving equipment and favourable weather. The project also marked a significant step in education. Students from Ardmore Engineering School participated in the project. They started as laborers later becoming technicians conducting important compaction tests.
Upper Mangatawhiri Dam is more than just a structure. It’s a crucial part of Auckland’s water infrastructure. Upon completion the dam fulfilled 50 percent of the Hunua catchments’ potential storage. It also marked the transition of Auckland’s water supply responsibilities. From the Auckland City Council to the Auckland Regional Authority in 1965. Its reservoir holds an impressive 16 550 000 cubic meters of water. Providing a safe yield of 66 700 cubic meters daily.
Take a moment to appreciate the Upper Mangatawhiri Dam. It stands as a symbol of human ingenuity and a vital resource for the city of Auckland. Its story is one of progress innovation and a vital contribution to the region’s water security. Its construction was a significant engineering achievement a testament to the skill and dedication of those involved. Its ongoing importance to Auckland’s water supply is undeniable. The dam stands as a silent sentinel a guardian of Auckland’s precious water resources.