Engineering Wonders of the World
Volume III

2.38 ENGINEERING WONDERS OF THE WORLD. HEAD-WORKS OF THE SIRHIND CANAL ON THE SUTLEJ RIVER. back into rivers at the points where they are needed is, in most cases, impossible. As an alternative, several depressions in the ground have been surrounded with earthen banks to form reservoirs, into which a portion of the discharge can be turned, in an emergency. The water in them soon dries up, and leaves them free for further use. They are planted with trees, and form little forests as well as escape reservoirs. At the head-works of the Chenab Canal the river is about 3| miles broad—broader than is necessary for the discharge of the floods. In the bed of the river has been The Chenab a weir hold Up Weir. x water as much as 12 feet above low-water level. The weir itself is only 4,000 feet long, but over it the whole discharge is compelled to pass by a system of training walls. Measured in the direction of the stream it is 250 feet wide. The crest is of masonry 8 feet high and broad, with its base generally but 4 feet below the original summer level of the river. Forty feet up-stream of this wall a masonry curtain wall has been sunk 20 feet into the bed, to prevent under- mining. The weir is divided by masonry piers into eight bays, each 500 feet wide. Between the piers, on the crest of the wall, are rows of vertical iron shutters, the con- struction and action of which may be taken as typical of all those now generally employed on Indian weirs. The shutters, 6 feet high, 3 feet broad, and made of A-inch steel plat- ing stiffened with angle iron, stand side by side in a continuous row between the piers. Heavy double hinge blocks placed between two adjacent gates are bolted down to the masonry. Three feet up-stream of each shutter a tie rod is hinged to the crest Weir of the weir ; its other end slides _ Shutters. in a groove on the nearer face of the gate, and is fitted with a hook which falls automatically into a slot when the gate is erect and is caught by a trigger on the down- stream face of the gate. To let the shutter fall, this trigger is knocked to one side by hand or mechanically, and the shutter is laid flat by the pressure of the water behind. For raising the shutter, a crane, running along the crest of the weir behind the shutters, is pro- vided. It is not often needed, however, as three men can easily lift a shutter in three ONE BAY OF THE HEAD REGULATOR (TO LEFT) AND ONE BAY OF THE HEAD SLUICES (TO RIGHT) OF THE SIRHIND CANAL. The regulator has a masonry sill to keep out of the canal the heavy silt which is carried at the bottom of the stream, and formerly caused a great deal of trouble. Each sluice has three iron gates—an upper, a middle, and a lower—working in separate contiguous grooves, so that the water may be let through at any level required.