Page:History of the Periyár project. (IA historyofperiyar00mack).pdf/36

16 debatable shape, while the conviction that the substitution of masonry or concrete was a necessity deepened in the minds of all the officers who considered the subject. Finally the whole of the papers were handed May 1882, to be relieved of other duty with a view to his undertaking the revision of the plans and estimates for the entire project; and this officer submitted in the same year a report, with detailed estimates which were eventually sanctioned. Such of the proposals as relate to the head works are here reproduced in extenso, in order to mark the departures which took place during actual construction. "The height of the dam proper is to be 155 feet from the bed of the river, with a parapet 5 feet in height and 4 feet in thickness. The thickness of the dam proper is to be 12 feet at the top and 115 feet at the lowest part. It is to be constructed throughout of concrete, composed of 25 parts by measure of hydraulic lime (ground but not slaked), 30 of sand, and 100 of broken stone.

"The front face is to be plastered with plaster composed of equal parts of lime and sand.

"The lime will be ground, the stone broken and the concrete mixed by machinery driven by a turbine, the power for working which will be obtained from the river itself.

"The concrete will be conveyed from the machines to the point where it is required for use by a wire tramway, and rammed by machine.

"A temporary dam, 30 feet in maximum height, will be constructed above the site of the main dam, and a similar dan 10 feet in height below the site to enable it to be completely cleared and the foundation trenches blasted out before the main dam is begun. These dams will be constructed of material similar to that of the main dam.

"In order to provide for the passage of river water during construction, two culverts with an area of 96 square feet each will be cut through the rock on the left bank of the river; they will be closed by an equilibrium shutter with gearing so designed that the velocity through the culvert can never exceed 20 feet per second, but that subject to this limit the gate shall open or close 3 feet for every foot of rise or fall in the level of the water above the dam.

"On the right bank will be a similar culvert with one-fourth of the area for supplying the turbine which drives the manufacturing machinery. The gearing of the shutters of this culvert will be so arranged that, under ordinary circumstances, it will pass only the amount of water required for the turbine, but that on emergency it may be made to pass any quantity