The lake catchment of 3300sq km covers many streams and rivers with the largest inflows coming from the Tongariro River and from the Tongariro Power Development, both of which drain the peaks in the Kaimanawa Ranges and Tongariro National Park.

This is the clean and renewable source of energy used by Mighty River Power in the company's nine hydro stations. Water passes, as it has for centuries, from the mountains of the central North Island into Lake Taupo and down the Waikato River to the Tasman Sea.

Resource management requirements mean the lake must be kept above a minimum set level with only one percent of its volume available for electricity generation. This means that the frequency and volume of inflows to the lake determine the amount of available stored energy in Lake Taupo. Even when full, the lake provides only 4-6 weeks or 800 million cubic metres of storage for the Waikato hydro scheme. There is little effective storage in the eight hydro dams on the river. The Taupo Gates, located just north of Taupo under the State Highway 1 bridge, provide some ability to control the amount of water flowing down the Waikato River.

Mighty River Power operates the lake within a narrow 1.4 metre range, using the gates to ensure that the water is used efficiently and managed in response to inflows to Lake Taupo and energy demand patterns. Once released from the gates, water for generation takes more than 18 hours to move from Taupo to Karapiro - the last station in the Waikato hydro system.

In times of extreme rainfall, the Taupo Gates can be used to help reduce the severity of flooding in the lower Waikato. In dry conditions, the gates are used to conserve water in Lake Taupo while meeting generation and minimum flow requirements for the Waikato River. This requires a careful balancing act in which Mighty River Power takes into account the needs of its customers and their requirements, environmental factors and the interests of each of the communities along the river.

History

Following an electricity supply crisis that had been steadily worsening since the late 1930s, the construction of the flow gates at Taupo spearheaded a 10-year plan to develop the Waikato hydro system. At that time, only the Arapuni and Horahora power stations existed. Control of Lake Taupo's water level was crucial to the plan. Seasonal flows down the river were uncontrolled and water could not be stored in the lake for use in times of high electricity demand.

Construction of the gates began in 1940 and was completed in 1941. Since then the structure has been strengthened to withstand the increased traffic on State Highway 1.