These rubble dams were well tested when the high Nile ran over them; and on work being resumed in November, after the fall of the river, water-tight sandbag dams, or were made around the site of the darn foundation in the still waters above the rubble dams, and pumps were fixed to lay dry the bed of the river. This was the most ex citing time in this stage of the operations, for no one could predict whether it would be possible to dry the bed, or whether the water would not pour through the fissured rock in overwhelming volume. Twenty-four 12-inch centrifugal ?tulips were provided to deal, if necessary, with one small channel; but happily the sandbags and gravel and sand embank ments stanched the fissures in the rock and interstices between the great boulders cover ing the bottom of this channel, and a couple of 12-inch pumps sufficed. The masonry of the dam is of local granite, set in British Portland cement mortar. The interior is of rubble set by hand, with about 40 per cent of the bulk in cement mortar, four of sand to one of cement. All the face work is of coursed rock-faced ashlar, except the sluice linings, which are finely dressed. This was steam crane and Italian masons' work. There was a great pressure at times to get a section completed before the inevitable rise of the Nile, and as much as 3600 tons of masonry was executed per day, chiefly at one point in the dam. A triple line of railway and numer ous cars and locomotives were provided to convey the materials from quarries and stores to every part of the work. The maximum number of men employed was 11,000, of whom 1,000 were European masons and other skilled men. Mr. Wilfred Stokes, chief en gineer and managing director of Messrs. Ransomes and Rapier, was responsible for the detailed designing and manufacture of the sluices and lock gates; 140 of the sluices are 23 feet high by 6 feet 6 inches wide, and 40 of them half that height; 130 of the sluices are on the °Stoney° principle with rollers, and the remainder move on sliding surfaces. The larger of the Stoney sluices weigh 14 tons, and are capable of being moved by hand under a head of water producing a pres sure, after the heightening of the dam, of 325 tons against the gate. There are five lock gates, 32 feet wide and varying in height up to 62 feet. They are of an entirely different type from ordinary folding lock gates, being hung from the top on rollers and moving like a sliding coach-house door. This ar rangement was adopted for safety, as over 1,000,000,000 tons of water are stored up above the lock gates, and each of the two upper gates is made strong enough to hold up the water, assuming that the four other gates were destroyed. After the heightening of the dam
a fifth lock and gate were added. When the river is rising the sluices are open and the red water passes freely through, without de positing the fertilizing silt. After the flood when the water has become clear and the discharge of the Nile has fallen to about 2,000 tons per second, the gates without rollers are closed, and then some of those with roll ers; so • that between December and March the reservoir is gradually filled. The reopen ing of the sluices takes place between May and July, according to the state of the Nile and the requirements of the crops. On 10 Dec. 1902 the dam was formally declared com plete, the total cost having been about $11, 900,000. In 1907-12, in accordance with a plan prepared by Sir Benjamin Baker, it was raised about 16% feet and its thickness in creased about an equal amount. The capacity of the original dam was thus increased from about 1,000,000,000 cubic metres to 2,423,000, 000 cubic metres, its depth from about 65 feet to 88 feet, and the extent of river affected from 140 miles to 185 miles. The total cost of raising the dam was about $7,500,000. It has been estimated that each milliard of cubic metres of water suffices for the irrigation of 225,000 acres of summer crop and has a value to the treasury of about $2,500,000 per year. In 1905-06 a talus was constructed down stream at a cost of $1,413,500. Since the rais ing of the dam the Island of Philw is flooded between December and May, when the res ervoir is full, and is only entirely above wa ter between August and December. Elaborate operations have taken place to preserve the ruins as far as possible from the injury which is bound to ensue from their annual submer gence. It is impossible to estimate the far reaching beneficial influence these irrigation works will bestow upon Egypt; but the recla mation of so many thousands of acres of desert for agricultural development cannot fail to improve the agricultural possibilities of the land and assist t to regain the pros perity it enjoyed in tFEpFphMe era of the Pharaohs, with a greater cultivable area than it had even then. See ImanATioN; NILE. Consult Willcocks, The Nile Reservoir Dam at As suan) (London 1903); Willcocks and Craig, Irrigation) (London 1913) and Fowler, (Heightening of the Assuan (in Engineering News, 30 Sept. 1909).