REPAIRS AT ARAPUNI

New Zealand Herald, Volume LXIX, Issue 21279, 5 September 1932, Page 10

REPAIRS AT ARAPUNI

CAUSE OF LEAK LOCATED COLLAPSE OF A CULVERT RENEWING HEADRACE LINING WORK WELL ADVANCED [FROSI orn OWN correspondent] HAMILTON. Sunday Tho repairing of the damaged lining in tho headrace at Arapuni is now well advanced, and is expected to be completed by Wednesday. A visit was paid to Arapuni by the Hon. J. A. Young, Minister of Health, during tho week-end, nnd the work that bar been done in the headrace daring the last few weeks was explained to the Minister by Mr. T. Rabone, the engineer in charge. Mr. Rabono said that a theoretical possibility of an underground passage of water near the cut-off wall bad existed, and in order to establish certainty in this direction a well 50ft deep was sunk within 60ft. of the eastern wall of tho headrace, and near tho cut-off walL Horizontal bores were made from the bottom of tho shaft, and theso radiated in all directions. The explorations carried out showed that no underground channel existed. Moreover, the level of the water in the well was 25ft. lower than the level of the water in the headrace, and this level was rising by only three-quarters of an inch every 24 hours. Mr. Rabone said the investigations established the fact that the water in tho headrace was not connected with tho water in the well. Advantage was taken of the bores to grout the country, but the cement remained in tho bores and showed that the country was impervious and tight.

Mr. Rabono informed Mr. Young that the cause of the subsidence in the beadrace lining had been due to the overcharging of a Gin. pipe culvert in the underground drainage system. This culvert was within a few feet of the headrace lining, and evidently heavy pressure of storm water had overtaxed the pipe culvert and caused it to collapse. The porous mat between the culvert and the lining gave way and a Superficial leak under the cut-off wall was thus caused. Erosion beneath the porous mat then developed, and the increasing flow of water led to the subsidence of the wall.

To repair the damage the coffer dam was built, and in the past week the area in the dam had been made bone-dry. The lining of the wall had been stripped back over an area 25ft. by 20ft., and the background had been filled in with substantial material and well tamped. The culvert which led to the development of the leak had been eliminated. A strip of concrete block had been laid at the foot of the wall, and everything was in preparation to bitumeniso the lining and replace the steel sheets and concrete flags. The work would be fcompleted by Wednesday. The engineer stated that from observations made twice daily he was certain that the source of the leakage was at the wall within the coffer dam, and that the repair work in hand would remedy it. In order to make absolutely sure the present coffer dam would be removed and an island coffer dam would be made to enable a section of the headrace floor to be examined. The diversion tunnel would bo closed and'the water level in the headrace would be raised in order to reduce the current.