Vickerman subcontracting the electrical design to Brown and Forsdick of Auckland. All of the designs were to be approved by the Public Works Department. Hay and Vickerman's fee was 2% to undertake the design with an additional 1% to be paid for supervising the construction. The approved design called for building an earth dam with control gates to raise the lake level. The outflow would follow the river bed until at a weir it would be diverted into wooden pipelines to convey it to an 8,000 hp capacity powerhouse located by the confluence of the Monowai and Waiau Rivers. Construction commences It was estimated that 5,000 tons of material would need to be transported to Monowai. from the nearest railhead which was at Tuatapere on the Tuatapere branch railway. Investigations were undertaken into how best to do this, with consideration given to trucks, horse-pulled carts, traction engine as well as transporting it up the Waiau River which would require some blasting to remove hazards. The decision was made to employ a traction engine and two trucks which required SEPB to upgrade the existing roads and also extend them to the construction site. Until the road was completed material was brought in by horses pulling wagons. In 1920 Alfred Pryde Walker (1891–1953) was appointed the resident engineer in charge of construction. Walker had experience as an engineer in Canada, South Africa, Ceylon, Fiji and Australia (where he had worked with Hay). By the end of 1920 a total of 80 men and 40 horses were working in the project, building the road and preparing the sites for the construction camp and powerhouse. A Boving water wheel was established on site to provide power to the construction camp, but it was switched off at 10:00 pm. A timber mill was established on Diggers Hill on the Western side of the Waiau River to provided timber for the project. By early 1921 not only was the access road to Lake Monowai completed but also the construction camp as well as a new suspension bridge across the Waiau River at Sunnyside. Up until the completion of the bridge material and men had been conveyed across the river by a ferry. After the Wallace Country complained about the impact of the increased vehicle traffic on its roads over the winter SEPB began using teams of horses pulling wagons instead of the traction engine and trucks