unrest and the nature of the site, the target completion date of 1951 became less achievable. Work on the diversion tunnel - in diameter and in length - began in late 1946 on the southern side of the site. However, work was slowed by large amounts of water that poured into the tunnel until it was extensively grouted with cement and bitumen and lined with concrete. Because of the constant water seepage, it was not uncommon for the workers to work in knee-high or even waist-high water. By 1948, some 800 workers were working on the site. The tunnel was completed in March 1949, when the northern portal was opened and the first water flowed through the tunnel. Work then started by building cofferdams to block the natural channel of the river and allow dam construction to begin. The Taupo control gates were shut to lower the water level in the Waikato, and 11 bulldozers frantically pushed spoil into the river to stop the natural flow. The process was hampered by unexpected heavy rain which caused the river to rapidly rise, with it taking 27 hours to finally dam the river's natural course. The spillway tunnel was then constructed, which dropped at a 45-degree angle to intersect with the diversion tunnel. In late 1949, work finally started on the dam foundations. Extensive and careful grouting of the rock took place, reaching below the river bed, and along the sides for a length of . The grouting involved drilling thousands of holes in the rock face, and of cement was used in the process. Construction of the dam began in September 1950, and soon the work force had reached its peak of 1200. A large mechanised batching plant had been bought on site to produce in excess of of concrete that was required for the dam, which was reinforced with of steel. For the first time in New Zealand, a system of cooling mass concrete was used. This involved embedded pipes through which refrigerated water was passed. The powerhouse was constructed rapidly to have the machines operating as soon as possible. The foundations were started in early 1950, and the powerhouse was completed within a year. It consisted of a steel structural frame with a pre-cast concrete sectional roof. The transformer station was placed at the back and on top of the powerhouse itself due to the confines of the gorge.