COLLAPSE OF DAM

Waikato Times, Volume 116, Issue 19430, 3 December 1934, Page 6

COLLAPSE OF DAM

temporary structure. LITTLE INCONVENIENCE CAUSt WORK AT ARAPUNI. (Times Special Reporter.) ARAPUNI, Sunday. The Arapuni hydro-electric work* are again a scene“Of activity with preparations for the extension of the power house and installation of two more generating turbines,- well in hand.■ Over 100 extra hands have been employed for several weeks blasting the cliff face south of the power house to make room for the extensions. Hundreds of thousands of yards of spoil have been removed from the cliff and the excavation work has reached an advanced stage. The cliff is being hewn out, to the depth of the face where the present power house stands and the extension will be attached to the end of the present building. The design of the building will be similar to the existing structure. Dam Swept Away.

Some anxiety was felt in Hamilton over the week-end when a rumour that a “ coffer ” dam at Arapuni had been swept away was circulated and many people anticipated some sensational news. Their forebodings were unwarranted, however, as, although there was a collapse of a dam it was of little consequence. With the excavations of the cliff well in hand preparations are now being made for the laying of the foundations of the new building. The water discharged from the present power house backs a considerable distance up the gorge and the site for the foundations would be under water if the excavations were carried to a greater depth than they are at present. , The water, therefore, has to he blocked from backing up past the power house to enable work on the foundations to proceed. A “ needle ’ ! dam across the river, from the southern end qf the present building is being constructed to block the water. Concrete piles were sunk years ago when the present power station was built, and it is proposed to bolt heavy iron railings on to these piles and dam the river ' by matai tongue and grooved timber. The railings had been affixed and several planks stretching about one quarter df the way across the river had also been bolted on. These planks were attached on the power house side of the river and had been constructed in such a way that the pressure of the water would help to hold them in place.

Great Rush of Water. This part of the dam had stood up well but' 1 on Friday evening when No. 4 turbine was put into operation the backwash created swept the sheathing away. The water from No. ,4 turbine is discharged at the southern end ’ of ,the power house adjacent to the “needle" dam and the fact-that only some of the planks had been affixed, allowing the rush of water still to hack up behind the construction, no doubt accounts for the collapse. The planks were recovered and some have been p'laced in position with No. 4 turbine turned off.. When the dam is completed and no water can get beliind it No. 4 turbine can again be used as the -structure Is so constructed that the pressure of water will hold it. together.. The blasting of the cliff face is still being carried out and the spoil taken away by a huge overhead crane and pulley arrangement. Heavy cablesaare,e e , stretched across the gorge just above' the suspension bridge and huge boxes, carrying two yards of spoil at a time, are hoisted up and carried across to the top of the cliff on the opposite site of the gorge to be taken away. Inorease In Capaolty. Three turbines are kept going daily ' at Arapuni at present to cope with the huge demand for electricity and the station, which now, under no pressure, can produce between 40,000 to 50,000' kilowatts will, with the new turbines, produce, easily, about 60,000 to 80,000 kilowatts. The penstock tunnels for the two ' units were constructed when the other four were built, and have been disclosed now so much of the cliff has been removed. The units will not arrive for some lime yet as it is not anticipated that the extensions will be completed for another 12 to 18 months.

The leakage that was reported in ■the headrace some time ago has been effectively blocked. The concrete on the falls shows very little signs of wear and the machines and equipment are in first-class order. The second gate in the diversion tunnel is tested regularly and everything at tile works is proceeding well to schedule.