Schemes must be investigated well ahead of construction, for extensive geological surveys are required to ascertain whether the rock formation at the proposed site can withstand the weight of the dam and powerhouse structures as well as the pressure of water from behind the dam. Investigational and design work takes a long time, and machinery has to be ordered well ahead. The transmission system must be expanded at the same time so that power may become available when needed. In 1957 a combined committee, consisting of members of the Electricity Department and the Ministry of Works (who are responsible for carrying out hydrology investigations and civil engineering work for the Electricity Department) and representatives of the electrical supply authorities, made recommendations on how to meet future power demands. In June 1957 the Government approved the Committee's report in principle as a basic plan for the comprehensive and orderly development of the electric power system. The report is therefore a blueprint for the future.

Committees have become a permanent feature of planning. This is the procedure used. The Power and Finance Utilisation Committee of the Electrical Supply Authorities Association (on which the Electricity Department is represented) collates detailed estimates of unit consumption and peak demand for five years ahead. These figures, revised and extended each year, show for all parts of New Zealand when and where power will be needed. The estimates are made by those with a personal knowledge of the needs and the economics of each area. This Committee's estimates are considered by a Committee to Review Power Requirements under the chairmanship of the General Manager of the New Zealand Electricity Department, with his Chief Engineer, representatives of the supply authorities, Treasury, and the Government Statistician as members. This Committee combines and projects the supply authority estimates for a further five years for the North and South Island needs and for New Zealand as a whole, also comparing them with statistically adduced national needs. The findings of the Review Committee are then considered by a “Planning Committee on Electric Power Development in New Zealand” which consists of members of the Electricity Department, the Ministry of Works, and the Treasury, and the supply authority representatives, also chaired by the General Manager. This Planning Committee then recommends the works it considers should be constructed, and when they should be constructed if the estimated needs are to be met. The review and planning reports are submitted to the Minister of Electricity, who tables them in the House of Representatives.