PLAINS WATER

Hauraki Plains Gazette, Volume 55, Issue 32667, 23 January 1946, Page 5

PLAINS WATER

IMPROVEMENTS TO DAM TO COVER LARGE AREA ALTERATIONS SUGGESTED Suggestions for an improvement in the Hauraki Plains West water supply were embodied in .a report by Mr E. F. Adams to the county council at its January meeting. The improvements involved alterations’ to the existing dam. The headworks were designed! to conform to the surroundings, said the report, and the height would be limited by the quality of the rock foundation and profile. . To. build 1 .the dam four feet higher than at present would entail nearly double the length of the dam in place. The present condition of the foundations within the water cushion should be investigated, as the rock is liable to have been undercut by the overfall of flood water passing, over the spillway.. ’ Catchment Of Dam The spillway is at present 24 feet wide, except on top, where the width is 34 feet and depth five feet. This was inadequate in the storm in February, 19136, when the whole structure was overtopped for a length of 125 feet.

There is an extensive catchment above the dam, being double the area of the Apakura, but giving a propor-

tionately poor run off in a dry summer. ■ The minimum catchment is about 400,900 gallons per day, sufficient to provide for about 20,000 acres. The present storage conserves night water, which would 1 otherwise be lost. To augment the value of the minimum run off, and to provide a good water supply over a large area, it yrould be necessary to enlarge the storage to a degree equivalent to two months’ supply. The present site would allow such excavation without raising the dam, but would limit the capacity to about 22,000 acres. Sludge in Mains It was possible that, a sludge deposit in the main pool would in time reach the supply main and tunnel. A temporary sluice valve on the downstream end of the sludge pipe would act as a safeguard. Work would have to be done when the weather breaks, concluded the report, and a temporary connection could be made the stream above to the delivery' main.. This would enable the surplus flow to be used in sluicing to get rid of the sludge. The county engineer will investigate the work to be done.