SUCCESS AT ARAPUNI

Poverty Bay Herald, Volume LIX, Issue 17871, 30 August 1932, Page 5

SUCCESS AT ARAPUNI

LOCATING THE LEAKAGE

COFFER DAM PUMPED DRY

EXTENT OF DAMAGE SEEN

It would seem that the efforts of the .Public Works Department engineers to locate and isolate the leakage in tho headrace at the Arapuni electric-power works have been ’crowned with coin- , piete success. The result of tho 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 cut-off wall on the slope of the right bank of the headrace. It tfas not 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 detehhine 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 ;*on. Saituday the engineers completed their plan for making tho wall watertight* and f6ur electric pumps used oft tpe job quickly lowered the water in. the enclosure. ? ; C RESULT OF TESTS V | The result of tests made on Sunday proved verv satisfactory and highly gratifying to the engineering staff. It Wab found that when .the level of th : 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 tho outflow ’ at the power-house end returned to its normal sizo. • The,station is continuing under load and, according, to Mr T. Enbone, engineer in chargo,.it will continue so while the damage revealed in the coffer dam. is being repaired. Although four powerful pumps wore previously unable to cope with the inflow at the coffer dam, the final measures taken 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 tho spaces between the bags of sand which form the walls of the dam layers of canvas were spread ove-r the outer faces of the wall and the pressure of the water in the headrace forced this material into the 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 -■■ ■ • ■ V ■ ■ With the coffer dam free of water the extent of the. damage to the concrete lining was seen. The bulk of the subsidence was ou the sloping sid:> wall of the headrace, the small hexagonal concrete slabs having coiK, lapsed over an area about 30ft. long! and extending up <thc 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 on Sunday in cleaning out this hole, these activities being continued throughout the night. The area was brilliantly lighted with powerful lamps and a .temporary inclined railway with wooden rails laid down the slope of tho lining had been constructed to facilitate the removal of the ddbris. Compressed-air winches were being used to haul tlio trolleys to the surface. As a precaution the foftferete slabs surrounding the fracture were also being removed so that the engineers might assure themselves that the damage did not go beyond the fracture. . - , Mr Rabone said that he was satisfied on the evidence that the damage was eottfined to. the area enclosed by the eoffer dam, and expressed the Opinion that the job of pealing the leak and restoring the lining would take only a comparatively short time. Mr F. T. M. Kiasell, chief electrical engineer, iwho • was in Arapuni, shares these Vifewp. ’ ' The diversion tunnel was closed on Thursday at midnight, and was carefully examined. -It was found that the tunnel and the gates were standing up satisfactorily to the pressure caused by. the flow of part of the river through the tunnel.