PREPARING TO BUILD DAM

Taranaki Daily News, 12 October 1929, Page 11

PREPARING TO BUILD DAM

PROGRESS AT MANGAMAHOE DIVERSION TUNNEL NEARS 'FINISHRIVER TO BE TURNED IN A WEEK. I The construction of the diversion tunnel through which the waters of the Waiwakaiho River are to be turned to enable the Mangamahoe dam to be built should be completed in a little over a week. Immediately the tunnel is finished work will be begun both on the laying of the foundations for the concrete core of the dam and on the earth filling which is to be banked on both sides of the core. The concreting of the floor of the intake tunnel, which is 400 ft in length, has been- completed, except for a few feet which will have to be relaid, ami about 300 feet of the sides and roof has been concreted. The remaining 100 feet is expected to take about a week to finish but the work has been hindered for a few days through a bad shipment of cement which was used in the floor and,: though it has been laid . for four days, has not yet shown any signs of setting. As each section of the concrete roof is laid any gaps between the. concrete * and the earth roof of the tunnel must be filled, and though it probably is not, the work appears to be laborious- and slow, having to be done by hand in a space which does not allow of a good swing of a shovel. In places rocks had to be blasted in order to give the roof of the tunnel the true arch shape which alone makes it safe to work under-, and here there are biggeb gaps to fill.

Everything is in readiness for the diversion of the river through the tunnel the minute it is completed. A small sump in- the middle used for drainage purposes will have to be filled with concrete, and all that will remain ..to be done will be the. cutting through ,of the foot or two of the river-bank which separates the river from the tunnel. Sandbags ready filled are heaped up waiting to be placed in the river to turn the water into the tunnel, and piles of rock lie ready to form a toe across the river to back up the sandbags, which will be only a temporary dam, and make the deviation complete and secure. The toe will be built up beyond the highest flood level to avoid any possible risk of water reaching the old bed of the river.

Once the present channel is dry the foundations of the dam will be begun after the concrete mixer and chute .have been moved to a more convenient position. The cutting in the sides of the gully of the trenches into which the concrete core will extend has already been begun and the removal of the layer of black soil to prevent any seepage of water through the clay filling around the sides of the dam is proceeding fast. Tractor-drawn scoops to facilitate and expedite the work of removing clay from the higher ground nearby to compose the earth filling for the dam were tried out a few days ago and proved successful.

Progress is being made on the other part of the scheme, the south-west embankment. Part of the trench .Jo containd the concrete core has been dug and filled with concrete and the rest of the work is well in hand. The depth of the trench is 25 feet in one place. On the top of the concrete already laid has been placed a wall of galvanised iron sheeting which will strengthen the top of the embankment. Here, too, ‘the black soil has to be cleared off before the filling to be placed on both sides of the concrete core can be begun.