TRANSACTIONS OF SECTION G. 497 
branch of the river, the two provinces between the branches, and the two to the 
right of the eastern, or Damietta branch. 
In Upper Egypt, with one very important exception (the Ibrahimieh Canal, which 
is a perennial one), the early flood system of irrigation, yielding one crop a year, 
prevailed until very recently, but it was immensely improved after the British 
occupation by the addition of a great number of masonry head sluices, aqueducts, 
escape weirs, &c., on which some 800,000/. was spent. With the completion of 
these works, and of a complete system of drainage, to be alluded to further on, 
it may be considered that the irrigation system of Egypt was put on a very satis- 
factory basis. There was not much more left to do, unless the volume of water at 
disposal could be increased. 
Probably no large river in the world is so regular as the Nile in its periods of 
low supply and of flood. It rises steadily in June, July, and August. Then it 
begins to go down, at first rapidly, then slowly, till the following June. It is 
never a month before its time, never a month behind. It is subject to no excep- 
tional floods from June to June. Where it enters Hgypt the difference between 
maximum and minimum Nile is about 26 feet. If it rises 34} feet higher the 
country is in danger of serious flooding. If its rise is 6 feet short of the average 
there existed in former days a great risk that the floods would never cover the 
great flats of Upper Egypt, and thus the ground would remain as hard as stone, 
and sowing in November would be impossible. Fortunately the good work of the 
last twenty years very much diminishes this danger, 
The Assuan Dam and Reservoir. 
In average years the volume of water flowing past Cairo in September is from 
thirty-five to forty times the volume in June. Far the greater part of this flood 
flows out to the sea useless. Hlow to catch and store this supply for use the 
following May and June was a problem early pressed on the Inglish engineers in 
Egypt. 
During the time of the highest flood the Nile carries along with it an im- 
mense amount cf alluvial matter, and when it was first proposed to store the 
flood-water the danger seemed to be that the reservoir would in a few years be 
filled with deposit, as those I have described in India. Fortunately it was found 
that after November the water was fairly clear, and that if acommencement were 
made even as late as that there would still be water enough capable of being stored 
to do enormous benefit to the irrigation. 
A site for a great dam was discovered at Assuan, 600 miles south of Cairo, 
where a dyke of granite rock crosses the valley of the river, occasioning what is 
known as the First Cataract. On this ridge of granite a stupendous work has now 
been created. A great wall of granite 6,400 feet long has been thrown across the 
valley, 23 feet thick at the crest, 82 feet at the base. Its height above the rock- 
bed of the river is 180 feet. This great wall or dam holds up a depth of 66 feet 
of water, which forms a lake of more than 100 miles in length up the Nile Valley, 
containing 38,000 million cubic feet of water. 
The dam is pierced with 180 sluices, or openings, through which the whole 
Nile flood, about 360,000 cubic feet per second, is discharged. A flight of four 
locks, each 260 x 30 feet, allows of free navigation past the dam. The foundation- 
stone of this great work was laid in February 1899, and it was completed in less 
than four years. At the same time a very important dam of the pattern of the 
barrage north of Cairo was built across the Nile at Assiut, just below the head of 
the Ibrahimieh Canal, not with the object of storing water, but to enable a requi- 
site supply at all times to be sent down that canal. 
The chief use of the great, Assuan reservoir is to enable perennial irrigation, such 
as exists in Lower Egypt, to be substituted in Upper Egypt for the basin system 
of watering the land only through the Nile flood; that is, to enable two crops to 
be grown instead of one every year, and to enable cotton and sugar-cane to take 
the place of wheat and barley. But a great deal more had to be done in order to 
obtain the full beneficial result of the work. About 450,000 acres of basin irriga- 
1905. K K 
