TWICE SIZE OF KARAPIRO

Bay of Plenty Beacon, Volume 11, Issue 80, 15 September 1947, Page 6

TWICE SIZE OF KARAPIRO

MARAETAI POWER STATION A TREMENDOUS UNDERTAKING “How long will it be before the dam is completed,” was the obvious question asked by a representative of a Waikato paper when he visited Maraetai and Mangakino recently.

The answer was not so obvious. The engineer to whom he was speaking just smiled and talked of other things. However, when summing up the position, the following facts seemed to stand out:— 1. Work on the dam cannot be commenced until the coffer dams to cut off the water are constructed.

2. Nothing can be done to the coffer dams until the diversion tunnel is completed. 3. While work is being speeded up in the diversion tunnel, as a result of the arrival of new machinery, the time required for its completion is still expressed in years.

Maraetai is a tremendous undertaking, designed to produce just double the amount of electricity of Karapiro, yet it is but one of several hydro development schemes for which Mangakino is the headquarters. Because of this, the major undertaking at the moment is in connection with housing and general town planning. At Whakamaru and Waipapa, where power stations are to be erected in order, little has been done apart from survey work and rock testing, but all of the employees on these undertakings will continue tolive at Mangakino. It can be seen that with acdvity continuing over a long period of years the township of Mangakino has had to be built with some degree of permanence. Streets are well laid out and sections well defined, and although the houses would be tenned “sub-standard” according to borough requirements, they are a great improvement on the married quarters provided at Karapiro. Already 200 homes have been completed, and 70 more are in various stages of erection. It is accommodation which is the bottle-neck at the works just at present. With the exception of carpenters there are plenty of workers available, but housing is the problem even with single men. At the present time there are 720 men employed at Mangakino. The married men are housed as far as possible in the main village and there are two single men’s camps. Tunnellers and fitters form the bulk of one camp, which is situated near the dam site, while the other is close to Mangakino. Each camp has its own cookhouse and Y.M.C.A.

Covering an'extensive area is the Mangakino sawmill which provides much of the timber for housing.

Logs for milling are taken from the pine forests which will eventually be part of the flooded area. The mill has now be/en in operation for two months.

/ Of the 700 odd men employed, the majority are on contract work. In this category are the tunnellers, who still have a big task in front of them. The diversion tunnel will be 2,000 feet long compared with 850 at Karapiro. It will be 25 feet in-dia-meter and circular, whereas the Karapiro tunnel is horse-shoe shaped, with a flat floor. Excavation of the tunnel is being carried out from both ends, but so far the work has been delayed through excessive seepage. A modern concreting shield has now arrived and been erected to assist in speeding up work. This machine, which was manufactured by Messrs. Cable and Co., and was delayed as a result of disputes in Wellington, enables the tunnel to be concreted as the work proceeds, this minimising seepage.

Another labour saver in the tunnel, which was not used at Karapiro, is .a Conway Mucker, which cleans up all the loose rubble after a shot has been fired. It is in the form of a mechanical loader which picks up the rock and shovels it back to a conveyor belt and out to the waiting trucks. There is no convenient bend in the river at Maraetai like at Karapiro to enable the diversion tunnel to cut straight through the rock. The river is straight each side of the dam site and so the diversion tunnel has to be constructed with a bend where it will pass the abutment of the dam.

The radial cableway installed at Karapiro after the dam was well on the way proved one of the greatest labour savers in conveying concrete to all parts of the structure. At Maraetai, a cableway, which will travel at both ends will be erected before the dam is commenced. As well as being used for filling it will also play a big part in the excava-

lions. Preparations for the installation of the cableway are now being carried out. The lay-out for mixing concrete will be different to that, at Karapiro. Newer and bigger mixers will be used and as the material will be fed in on the horizontal, no silo will be necessary. The conformation of the country at Maraetai will enable a? much simpler set-up to be used in harnessing the river. The dam will be one big arch 1500 feet long, standing 100 feet higher than Karapiro. The pow-er-house will be in the centre of the river behind the arch. There will be no spillway and no syphon sections, all excess water flowing through the diversion tunnel. 'One of the early tasks will be the erection of a reinforced concrete bridge over the river on the road between Whakamaru and Maraetai. This bridge will be 250 feet long, and 100 feet high. Two quarries have been opened, and these are producing road metal and concrete aggregate. Mang'akino is 55 miles from Cambridge and an excellent road is provided the whole way. It is an interesting trip through Tirau, Putaruru and Tokoroa, and past many hundreds of acres of pine forests. The sealing of the last portion of the road after turning off from the Taupo main highway is to be undertaken when the weather becomes more favourable.