SUCCESS AT ARAPUNI

New Zealand Herald, Volume LXIX, Issue 21273, 29 August 1932, Page 8

SUCCESS AT ARAPUNI

LOCATING THE LEAKAGE COFFER DAM PUMPED DRY OUTFLOW NOW NORMAL EXTENT OF DAMAGE SEEN GRATIFYING TESTS MADE [BY TELEGRAPH —SPECIAL REPORTER] ARAPUNI, Sunday It. would seem that" the efforts of the Public Works Department engineers to locate and isolate the leakage in the headrace at the Arapuni electric-power works have been crowned with complete success. The result of the initial exploratory work, carried out with the aid of divers, convinced the engineers that the water was finding its way beneath the concrete lining of the headrace just below the cutoff wall on the, slope of the right bank of the headrace. It was not so certain, however, that the water was actually entering the lining at that point, so, in addition to building a coffer dam round the portion of the lined race where there were evidences of subsidence, a series of vertical and horizontal bores were made to determine whether any water was getting through the unlined bed of the headrace above the cut-off wall. Considerable difficulty was experienced in pumping the coffer dam dry, but yesterday the engineers completed their plan for making the wall watertight, and four electric pumps used on the job quickly lowered the water in the enclosure. Result of Tests The result of tests made to day proved very satisfactory and highly gratifying to the engineering staff. It was found that when the level of the water in the coffer dam fell the leakage near the power-house site in the gorge below eased off considerably, and when the last of the water was pumped from the hole in the concrete lining caused by the subsidence the outflow at the power-house end returned to its normal size. The station is continuing under load and, according to Mr. T. Rabone, engineer in charge, it will continue so while the damage revealed in the coffer dam is being repaired. Although [our powerful pumps were previously unable to cope with the inflow at the coffer dam, the final measures taken yesterday to seal the wall have proved so satisfactory that one pump is easily coping with the small amount of water that is finding its way through the wall of the dam. When the utmost had been done to caulk the spaces between the bags of sand which form the walls of the dam layers of canvas were spread over the outer faces of the wall and the pressure of the water in the headrace forced this material into tlie crevices responsible for the leakage, and arrested the flow of water in much the same way.as a sail or tarpaulin is used to save a sinking ship. Area of the Collapse With the coffer dam free of water the extent of the damage to the concrete lining was seen. The bulk of the subsidence was on the sloping side wall of the headrace, the small hexagonal concrete slabs having collapsed over an area about 30ft. long and extending up the slope for about 20ft. from the level concrete bottom of the race. The water had eaten into the earth below the level of the concrete lining, leaving a concave depression about Bft. deep at its lowest point. Gangs were working to-day in cleaning out this hole, and these activities are being continued throughout the night. The area is brilliantly lighted with powerful lamps and a temporary inclined railway with wooden rails laid down the slope the lining has been constructed to facilitate the removal of the debris. Compressed-air winches are being used to haul the trolleys to the surface. As a precaution the concrete slabs surrounding the fracture are also being removed so that the engineers may assure themselves that the damage does not go beyond the fracture. Mr. Rabone said to-night that he was satisfied on the evidence that the damage was confined to the area enclosed by the coffer dam, and expressed the opinion that the job of sealing the leak and restoring the lining would take only a comparatively short time. Mr. F. T. M. Kissell, chief electrical engineer, who was in Arapuni to-day, shares these views. Tlie diversion tunnel was closed on Thursday at midnight, and was carefully examined. It was found that Hie tunnel and the gates were standing up satisfactorily to the pressure caused by the flow of part of the river through the tunnel.