Page:Municipal Handbook of Auckland 1922.djvu/141

 impounded by a reinforced concrete slab and buttress dam, 38 feet above stream level. Its construction was undertaken as an emergency measure, to augment the storage at Waitakere, pending the completion of the Main Dam at Nihotupu, but it will form a permanent portion of the storage system.

The Main Dam is situated over 1½ miles down the stream, at the top of the main falls, where the sides of the river contract, but on account of the comparative steepness of the sides of the valley above, it has had to be constructed to a height of 146 feet from river bed to weir level. The dam, which is designed as a gravitation dam, is curved on plan, the radius being 450 feet, and the maximum length will be, approximately, 540 feet, while the maximum thickness is 104 feet, diminishing at the top to 12 feet. The total quantity of water impounded will be 540 million gallons. The water area of the Reservoir, when full, will be 36 acres, while the total area of the gathering ground is 2,400 acres.

It is expected that the Dam will be completed in the first half of 1923.

It is being constructed of mass concrete, with blue stone plums or sinkers embedded, and will contain, when finished, upwards of 70,000 cubic yards of concrete.

The Nihotupu Stream, with the two reservoirs above described, is expected to yield a daily supply of 5 million gallons of water.