—Egypt already possesses the germ of all the storage works she needs. Six years ago a few far-seeing men saw clearly what all of us understand to-day; but among the few, no man had greater faith in the future of the country than Sir Ernest Cassel. The Assouân Reservoir project had been lying buried for four years in official pigeon holes, when in 1898 Sir Ernest came forward with the funds, and with Sir John Aird & Co., as contractors, and Sir Benjamin Baker as Consulting Engineer, undertook to complete the Assouân dam and the Assiout weir by December 1903. The Egyptian Government, advised by Sir William Garstin, accepted his offer, and received the completed works by December 1902.

The Assouân dam is a granite structure 2,000 metres long which crosses the head of the Assouân cataract of the Nile in one continuous straight line. The dam is pierced by 140 under sluices of 7 metres by 2 metres for passing floods, and by 40 upper sluices of 31⁄2 metres by 2 metres for passing the high level water of the reservoir. The sluices are regulated by “Stoney” gates worked by winches at the roadway level.

While the red, muddy waters of the Nile flood are pouring down the river, the whole of the sluices are open and the river discharges itself through them without parting with its silt. This is the real object of the sluices, for if the dam were solid and the river forced to flow over the top, the reservoir would soon be filled with deposit and obliterated, while Egypt, deprived of this rich mud, would be considerably the poorer. This is the great feature of the dam. While the dam holds together, the reservoir will be free of silt.

When the turbid flood has passed and the comparatively clear winter supply of the river has begun to arrive, the sluices are gradually closed and the reservoir filled. Beginning about the 1st December, the reservoir is filled in 100 days. It will ordinarily be full on the 1st March. No additional water is needed for irrigation between March 1st and May 1st as the river naturally has enough for the requirements of the area at present under crop at this season. As the area under perennial irrigation will be gradually increased, the demand for water for the new lands will begin about the 1st of April. The demand increases through May and June, and the reservoir will then be aiding the river with its supplement. If the flood is very late, water may be required from the reservoir till the 10th July; if the flood is early no water will be needed after the 20th of June, as in 1903, the first year of the reservoir. The earlier the flood the more effective the reservoir. By the time the flood has begun to get turbid, the under and upper sluices will all be open and the muddy waters of the Nile will sweep through the dam without impediment.

The dam has worked for two years and given satisfaction. When the Nile was at its lowest in May 1903, the natural discharge of the river, supplemented by all the subsoil infiltration water which enters the river between Assouân and the sea, was 400 cubic metres per second. The reservoir was adding 200 cubic metres per second to the supply, raising the total supply available for irrigation to 600 cubic metres per second. The reservoir was supplying one-third of the water which was being utilized in Egypt. This water will suffice for an increase to the perennially irrigated area of 1⁄2 million acres.

At the time of designing the dam it was intended that it should be of such a section that it could be raised 6 metres in height and hold up another milliard of cubic metres of water. Such an operation, if performed to-day, would mean: the whole length of dam being raised 6 metres, the winches working the sluice gates being raised 6 metres and provided with new wire ropes; and new copings being given to the parapets. It would necessitate two more locks and three more lock gates, and nothing else. The expenditure incurred would be about £500,000.

33. The Wady Rayan Reservoir Project.

—When the Assouân dam will have been raised, we shall be standing on the threshold of what it will be able to do. The projected Wady Rayan reservoir, or the modern Lake Mœris, will be well able to supply the two remaining milliards of cubic metres of water when working in conjunction with the Assuân Reservoir. The great weakness of this projected lake has lain in the fact that by itself it could give a plentiful discharge in April and May, less in June, and very little in July, and it was for this reason that in my report of 1894 to the Egyptian Government I had reluctantly to recommend that it be not carried out. But when the Assouân reservoir is capable of supplying two milliards of cubic metres of water it will be possible to utilise the Mœris Lake to its utmost capacity. The Assouan Reservoir, being high above the level of the Nile can give its supply at the beginning or end of the summer; it can give it slowly or with a rush; while the projected Lake Mœris, being directly in communication with the Nile, and only slightly above low Nile level, its discharge would depend entirely on the difference of level between it and the Nile, and consequently as the summer advanced its level would gradually fall and the lake would not be able to give at the end of the summer a quarter of the discharge it could give at the beginning.

PLATE XV

PROPOSED WADI RAYAN RESERVOIR
SHOWING THE FAYOUM
All R. L.s in metres, above (+) or below (-) mean sea.