Engineering Wonders of the World
Volume I

THE NILE DAMS AND THE ASSOUAN RESERVOIR 391 foundations of the Delta Barrage, which had to be based on the settled silt of the river. Making Foundations. During low Nile a trench 111 feet wide and 10 feet deep was excavated as far as possible in the dry. Sheet piling was afterwards driven along each side of the trench, and the exca- vation carried down through the water to a uniform level of 16 feet above sea-level. On a bed so prepared the main floor of concrete, 10 feet thick, was deposited, also through the water. In the founding of the piers a wooden coffer-dam was employed. This, large enough to the Egyptian Government on this question, that the summer discharge of the Nile—which might fall as low as 16 million tons per day —would have to be supplemented as follows : To irrigate perennially all the cultivable land in Lower Egypt an additional amount of water, averaging 12| million tons per day for 120 days, would be required from the beginning of April to the end of July ; and to irrigate, perennially, all the cultivable land in Middle Egypt, additional water, averaging 14 million tons per day for 150 days, would be needed from the beginning of March to the end of Fig. 6.—PLAN OF THE SITE OF THE ASSOUAN DAM. Showing Channels, Sudds, and Islands at low Nile. to enclose five piers, was planted on the con- crete floor and emptied. A skin of masonry was laid over the concrete, and on this stone- work the five piers were raised above water level. Then the coffer-dam was moved on, and the same process was repeated in the building of five more piers. The task of rendering the Delta Barrage effective, so that the whole of th© summer supply could be used, having been accom- plished, the old problem, how to supplement the water supply in order to meet the agri- cultural necessities of both Upper and Lower Egypt, again forced itself on the attention of the irrigation engineer. It was estimated, in the reports presented July. Roundly, this meant the accumulation during flood time, and the storage, of 4,000 million tons. Of the many schemes put forward to meet the situation, none was quite equal to dealing with so vast a body of water. But eventually there issued Assouan that of the Assouan Reser- voir, capable of storing 2,500 million tons of water, and this received the approval of the chief authorities concerned. One grave objection against this project existed—it would submerge for five months in the year (January to Juno) the beautiful island temple at Philæ. After much serious consid- eration it was determined to lower th© water