The text below the diagram reads:
The comprehensive scheme whereby the capacity of the Mangahao River will be utilised to the full in the generation of electric power is shown clearly in the above plan, which was supplied by the Public Works Department. As has been already pointed out in The Post, the volume of water in the Mangahao is not great, and for that reason it will be necessary to construct the three big reservoirs which are marked, respectively, No.s, 1,2, and 3. These reservoirs, or dams, will be of enormous capacity. The No. 1 Reservoir will have a capacity of 84,402,000 cubic feet, or, roughly, 500,000,000 gallons. The height of the dam will be 85 feet above the level of the stream. The No. 1 Reservoir is on one side of a hill, and the water will be conveyed to No. 3 Reservoir through a tunnel (plainly indicated in the plan) 80 chains long. No. 3 Reservoir, the smallest of all, will have a capacity of 46,014,000 cubic feet, or, roughly, 300,000,000 gallons. These two dams will be completed first, and their completion is essential before further operations can commence. At present the river flows on towards Woodville, but its course will be diverted by means of the tunnel already referred to. As the Mangahao carries very little shingle—it does not erode itself at a very fast rate—it is anticipated that the treatment proposed will not prove difficult. From Reservoir No. 3 the water will be carried by means of a longer tunnel (107 chains in length) to the surge chamber, at which it will enter the pipe lines which will carry it to the power station, 2½ miles from Shannon. Reservoir No. 2 will not be proceeded with until the remainder of the scheme is completed. It will be, in every sense of the word, a storage reservoir, and will have a storage capacity of 106,143,000 cubic feet, or, roughly, 650,000,000 gallons. The height of the dam from the bed of the stream will be 90 feet. The height of the dam at No. 3 Reservoir will be 85 feet. The preliminary work, which is to be taken in hand at once, includes the improvement of the present road, which is shown in the plan as a double line running close to the Tokomaru Stream. This road is, in its present state, quite unsuitable for the conveyance of the necessary constructional material. In addition, the road will have to be extended from a point near where it crosses the Tokomaru to No. 3 Reservoir, thence by a circuitous route to No. 1 Reservoir, and, ultimately, on to No. 2 Reservoir. The tunnelling is, of course, regarded as the most important part of the undertaking, for it will necessitate the employment of experts. However, as far as the longer tunnel is concerned, it will be possible to work from several faces, and that will expedite the work. The inset is a longitudinal sectional plan, the understanding of which calls for a little imagination. Those examining the inset must try to imagine for themselves the three dams in a straight line. The nature of the hills to be tunnelled is plainly shown. But more than that, the inset shows the extent of the drop, which is 900 feet from the surge chamber to the powerhouse, or nearly 1,000 feet from No. 3 Reservoir. The whole scheme will provide for the generation of 24,000 horsepower all the year round, and the estimated cost of it is £438,654.