WONDERFUL EFFECT OF WATERPOWER AT THE ASSOUAN DAM.
When large masses of water have to be controled, it is found that the discharge of that water through a limited space is likely to be the cause of erosion. Much depends upon what sort of surface it is on which the water so released pours forth with great swiftness and enormous pressure. If it is rugged and broken, and if there is any crevice, the effect of the checking of the water thereby is to produce an extraordinary violence almost equal to that of an explosion. One very remarkable and extraordinary exampleof this is shown in the accompanying illustration (reproduced through the courtesy of the Scientific American). “In this instance (says that journal) the rush of water through the sluices of the Assouan dam has dislodged a huge boulder from the rocky bed of the river. As is well known, this barrage extends right across the Nile just above the first cataract, and the flow of the river below Assouan is completely controled by this dam, the water passing through a series of sluices At times a huge volume of water is banked up behind the barrage to a height of sixty feet above the level of the down stream. The sluices, however, are built at different levels in the barrage, so that it is possible to control the velocity of the discharge. The maximum head of water allowed is 29.5 feet, and this enables the velocity of the released water to be controled within thirty-six feet per second. The bed of the river is solid rock; yet the rush of the water has dislodged this huge piece of rock measuring seventeen feet long, twelve feet wide, and seven feet thick, and has thrown it against the masonry face of the dam. The weight of the boulder Sir Benjamin Baker estimates to approximate sixty tons, yet it has been torn from the rocky bed and hurled backwards by the water with the greatest ease.”
Geographically the Susquehanna watershed lies in three physiographic divisions: The Allegheny, the Appalachian valley, and the Piedmont plateau. T he total area of the basin is 27,400 square miles, comprising 21,060 miles in Pennsylvania, or about forty-seven per cent, of the area of the State; 6.080 square miles in New York, or thirteen per cent, of the area of the State; and 260 square miles, or about two per cent, of the State of Maryland.