ARAPUNI SEEPAGE

Dominion, Volume 25, Issue 265, 4 August 1932, Page 10

ARAPUNI SEEPAGE

Concrete Work Examined WITHSTANDING STRAIN An Intriguing Happening ACACIA VALLEY FLOODING By Telegraph—Press Association. Hamilton, August 3. As the lowering of the water level ■ to below the lip of the spillway at Arapuni stopped the flow over the waterfall and through the buried forest, the engineers took the opportunity to examine the concrete work and the surrounding country from the base of the spillway to some distance below, including the waterfall. The whole bed was concreted to prevent further erosion. From to-day’s inspection it would appear- that these remedial measures withstood the strain satisfactorily. What may either be a peculiar coincidence or a significant connection with the trouble occurred when Acacia Gully flooded. The gully is on the Ara-puni-Te Awamutu road, in the vicinity of Pukeatua, and is some six miles from Arapuni Lake and four miles in a direct line from the spillway. Simultaneously with the appearance of serious cracks in the terrain between the spillway and the old river bed in 1930 the gully became flooded. It was thought at the time that the water from the lake came down an old drain and banked up there. A concrete wall was placed there to prevent a similar occurrence. However, when the present seepage was discovered it was found that the gully had agajn filled, thus disproving the drain theory. An explanation how,suggested is that water 1 from the lake has seeped six miles. What connection there is between the flooding of the gully and the trouble at the spillway is a matter of conjecture. 1 As soon as the increased flow of water down the old course was felt at Horahora, remedial measures In hand there had to be abandoned. Men were engaged in covering the bed at the spillway to take the force of water and prevent further erosion in similar manner as at Arapuni. A line of light railway was constructed to facilitate the work, but this morning the river had risen to such a height that it swept away the supports under about 50 feet of rail and the rails themselves, and a hydraulic pipe which runs along them is sagging dangerously and is liable to be torn adrift and hurled down stream.

OFFICIAL SURVEY Source of the Trouble SEARCH FOR LEAKAGE At the present time the volume of water coming from the seepage at Arapuni is filling a drainage pipe 2ft. in diameter, but it was stated yesterday by the Engineer-in-Ohlef to the Public Works Department,, Mr. F. W. Furkert, that the trouble was not regarded as ■•serious. ' Mr. Furkert has inspected the plant since the seepage was first reported some days ago, and he said on returning to Wellington that the engineers considered that once they* traced the source of the trouble there should be no difficulty in stemming the flow. • Within the past 24 hours there had been a decrease of 25 per cent in the amount of water flowing from the - ' seepage, Mr. Furkert said yesterday afternoon, and an important consideration was that the water coming through the drainage pipe was clear, •which showed that there was no erosion of the soil in the area where the seepage was occurring. It was admitted that if the amount of water percolating increased, the effect on the works might be serious, but it was hoped that the trouble'could be combated without it being necessary to cease generating operations. Work of Drainage System. As a result of the recommendations of Professor Hornell a drainage system had been provided to carry off any water that might find its way beneath the headrace, and it had been proved during the past few days that this system was fully justified and that it was performing 'its work admirably. The floor of the headrace had been lined with a secure layer of impervious material, and it had been proved that the present seepage was not occurring through this layer up to the cut-off wall at the top end of the headrace area, for a diver had reported that every part of this was functioning well, and that there was no leaking through the floor at all. A six-inch post hole had been sunk near the cut-off wall at the top of the headrace, and this showed that water was present, lending colour to the opinion that it was finding its way round the wall and under the impervious lining. The source of the leakage had been confined to a space about 12 feet square on the up-stream side of the cut-off wall on the gorge side of the headrace. If the seepage were definitely traced to that source the flow might be checked by the dumping of spoil and concrete grouting. - Drastic Steps Unnecessary’. It might prove necessary to de-water the headrace in order to rectify the fault, although it could not be said at the moment whether this would be necessary. As far as could be seen at the moment there would be no need to de-water the lake above the dam, , and it was not expected that the plant would have to be shut down in order to carry out the work necessary to stopping the seepage. Once the source of the seepage was found it was not anticipated there would be any trouble in stopping it. As the plant was generating 50.000 kilowatts it could be understood that it would not be closed down unless this course proved absolutely necessary. and there was no desire to stop the machinery in view of the fact that the undertaking was earning about £5OO a day. The surplus water in the headrace had already been lowered by about four feet, and this process would be continued meanwhile. It would be possible to lower the level by 15ft. without stopping the generators. as. even then, sufficient water would be flowing through the penstock Intakes to serve the power-house. Once the source of the seepage had been found, the leak would be plugged. and although the task would be the actual plugging could ho do-e without de-watering the headmice. '