The dam's spillway is located south of the dam. Because of the dam's location in a narrow gorge, there was insufficient space to construct an orthodox spillway, so the diversion tunnel used in construction was reconfigured to become the dam's spillway. The spillway tunnel is long, and in diameter, and is blocked by three spillway gates, each high and wide. Generation Maraetai I Water for Maraetai I is taken from Lake Maraetai at the dam, and is conveyed to the powerhouse by five steel penstocks, each long and in diameter. The water is used to turn five Vertical Francis turbine, each revolving at 167 rpm. Water is then deposited back into the Waikato River. Each of the five turbines turns a generator, each generating 36 MW of electricity at 11,000 volts. For one megawatt of electricity to be generated, of water must pass through the turbines every second. Electricity from each generator is then conveyed to a 40 MVA transformer, where the electricity is stepped-up to 220 kV for transmission. A sixth penstock is fitted to Maraetai I, which takes water to two auxiliary turbines and generators. These generators are used to generate electricity for the requirements in both Maraetai I and Maraetai II. Maraetai II Water for Maraetai II is diverted down a canal south of the dam to the powerhouse. The canal to Maraetai II is long, wide, and deep. Water is taken from the canal to the powerhouse via five steel penstocks, slightly different from Maraetai I's. The penstocks are long and in diameter. The water is used to turn five Vertical Francis turbines, revolving at a higher speed of 187 rpm. The generators at Maraetai II produce 36 MW each at 11,000 volts. This is stepped-up by 40 MVA transformers to 220 kV for transmission. Transmission Electricity from both stations is sent to the Maraetai switchyard, between the two powerhouses. Electricity from the downstream Waipapa Power Station links into Maraetai via a single-circuit 220 kV line (MRI-WPA-A), and electricity from Maraetai and Waipapa is then transmitted to Whakamaru via two single-circuit 220 kV lines (MRI-WKM-A and MRI-WKM-B). From Whakamaru, electricity generated at Maraetai is distributed via Transpower's 220 kV grid to Hamilton, Taupo, Palmerston North, and Auckland. References External links Maraetai - Mighty River Power Generation Ministry of Works 1950 progress report (pages 21–22) Buildings and structures in Waikato