The Mangahao scheme, built between 1920 and 1924, provided electricity to Wellington, the Hutt Valley, Manawatū, Whanganui and Wairarapa. Mangahao, Arapuni and Waikaremoana power stations were the beginning of the North Island transmission grid.

Building the Mangahao scheme was hard work. All three construction sites – Mangahao and Arapeti for the dams and Mangaore for the powerhouse – were in narrow gorges. The Mangahao site was the worst – all accommodation was in floorless tents, it rained 200 days a year, mud was everywhere, and clothes were often damp and mildewed.