The binding of the Nile and the new Soudan

by Sidney Cornwallis Peel

There was much literature on the subject. During the last sixteen years nothing had been done, but much had been written, and more said. Commissions, expert and inexpert, had issued voluminous and condemnatory reports, and had even prepared expensive schemes of repair. Mr. Willcocks (now Sir William) is an indefatigable reader, and could hardly have been encouraged thereby, till an examination of the structure itself showed that all the later reports had been drawn up without reference to facts. It had been observed that whenever the gates were let down there was very severe action of the water on the downstream side. The authors of the reports concluded that the foundations were honeycombed. It is characteristic of the Looking-glass days of Ismail that no one ever thought of trying to find out by actual observation whether there might not be some other cause. But Mr. Willcocks, looking for himself, found that this action of the water was caused, not by honeycombed foundations, but by open gratings which intervened between the bottom of the sluice-gates and the platform. They had been put down originally to keep the silt away from the bottom of the gates. Someone had fixed them so as to prevent the gates from being lowered to their full extent and then they had actually been forgotten. Measures were at once taken to close these gratings, and eventually to remove them altogether. 20,000 cubic metres of rubble pitching were added to the talus. The Damietta Barrage was likewise strengthened with various ingenious expedients, improvised to meet the demands of the moment. Sluice-gates were put in for the first time and gradually closed. Part of it was closed by a temporary stone dam. Eventually in the summer of 1884 2·2 metres of water were held up on the Rosetta branch, and 1 metre on the Damietta. Next year the same nursing process was continued. The coffer-dam round the weak arches was strengthened, the talus of rubble pitching below each Barrage was completed, and this year 3 metres were held up on the Rosetta branch and 1·6 on the Damietta. The effect was extraordinary. The acreage under summer cultivation was doubled, rising from 600,000 to 1,200,000 acres. Not only was the supply of water in the Delta canals greatly increased throughout the summer, but, as it was delivered at a higher level, there was a great saving of expense in lifting it on to the land. For the first time the Egyptians thoroughly realized that a new power had come amongst them.

The experiment had been successful, but temporary expedients could not last for ever. The more water held up, and the greater the area of the summer cultivation, the more necessary it became to insure the stability of the structure. A thorough repair would cost money. Fortunately, this was now forthcoming. Mr. Willcocks’ success had settled the claim of the Barrage to a share in the famous Irrigation Million borrowed in 1885.

At the end of 1886 the work was begun, under the charge of Colonel Western and Mr. Reid, sent specially from India for the purpose. The operations were spread over four years. In the first year the left half of the Rosetta Barrage was taken in hand and finished before the flood, next year the right half. In 1889 and 1890 the Damietta Barrage was similarly taken in hand and finished. Each year the part to be repaired was enclosed by earthen dams, and the water pumped out so as to lay the foundations dry. The whole of the existing floor was raised, both on the upstream and downstream side, and it was also considerably lengthened. It was, in fact, enclosed in a new and reliable suit of armour. The dangers and anxieties of the work were incessant. The protecting dams were always liable to be breached. Spring after spring burst out through the treacherous bed of the river, and threatened the destruction of the year’s work; and again and again each of them was successively stopped by a number of ingenious devices. There is no enemy so persistent and so insidious in its attacks as running water. It is always feeling for and finding out the weak spots. It never sleeps or slackens by day or by night. It can only be met successfully by a corresponding activity. While work was possible, it was carried on unceasingly by night as well as by day. Sometimes as many as 1,600 men worked through the night. The upper brickwork was generally sound, but new iron sluice-gates moving in special grooves were fitted throughout. The whole of the repairs cost £465,000. It was money well laid out. Not only was the safety of the Barrage assured, but it was found possible to hold up yet another metre of water. The area of summer crops matured rose once more from 1,200,000 to 1,520,000.

It might have been thought that the work was now complete. Both in 1891 and 1892 (a year of specially low summer supply) all the water in the Nile was held up, and diverted into the canals. Not a drop reached the sea during the summer without having done duty. But the engineers were now looking forward to a time when the supply would be greatly increased. The idea of a reservoir had become an affair of practical politics. It was necessary to make assurance doubly sure. Accordingly, in 1896 a new experiment was tried—namely, stock-ramming with clay.

Certain arches in the Damietta Barrage were selected, and in them five-inch holes were bored right down through pier and platform alike. When the bore-holes were complete, they were lined with iron tubes. Clay was then forced through the tube by means of an iron rammer, and as much as could be made to spread out at the bottom of the hole was put in and rammed. As far as the clay went, the experiment was not an entire success; but the boring brought to light a condition of things in the very vitals of the Barrage which demanded drastic treatment, for the bore-holes proved the existence of large cavities in the original platform, and in some places there was free water communication between one bore-hole and another. Some piers in the Rosetta Barrage were therefore chosen for a similar experiment, but this time liquid Portland cement was used instead of clay, and the results were entirely satisfactory. Few discoveries have been of more signal service than the invention of Portland cement. It is not too much to say that it has revolutionized hydraulic engineering by the facilities it affords for constructing solid works in water. Its strength and resisting power is enormous, but its greatest quality is that it hardens and solidifies under the action of water, and, so far as is known, only goes on getting harder and harder with time. The borings in the Rosetta Barrage having revealed similar deficiencies to those in the Damietta, it was decided to apply to both a thorough dose of this invaluable and invigorating medicine.

In 1897 five holes were bored in each pier of the Rosetta Barrage (their united length amounted to very nearly 6 kilometres), and into each was poured a quantity of liquid cement. The necessity for the treatment was proved by the fact that in some cases the cement travelled right through from the bore-hole in one pier and rose through the bore-hole in an adjoining pier till it reached the top. One pier actually swallowed 439 barrels of cement, while its neighbour took a lesser but still gigantic draught of 327 barrels. There was no doubt that the cement thoroughly explored and filled all the cavities existing in the foundations under the bridge. In all, 3,254 barrels were used in the Rosetta Barrage alone. In 1898 the grouting process, as it is called, was applied with equal success to the Damietta Barrage.

To use Sir Hanbury Brown’s homely but expressive image, the process applied to the Barrage was exactly that followed by a cook who wishes to finish off a cold pie with its proper complement of jelly. The jelly is introduced into the pie in the form of warm gravy, which penetrates into and fills every recess of the succulent interior, and then solidifies as it cools.

And still the engineers were not satisfied. So treacherous is the river’s bed that no possible safeguards seemed superfluous. It speaks volumes for the courage and skill of those who in 1885 held up 3 metres of water with the old unreformed Barrage, that in 1897, after the successful execution of such great and costly repairs, it was still thought advisable to undertake completely new works to assist in the task of holding up 4, or at the most 5, metres.

It is a principle in hydraulics, not easily understood at first by the layman, that the pressure upon a weir or barrage in a river depends entirely upon the difference in level between the water on the upstream and on the downstream side, and not on the mere volume of water in the river behind it. In December, 1897, the Caisse de la Dette voted £530,000 for the construction of two subsidiary downstream weirs, with the object of relieving the pressure on the Barrage by raising the level of the water on the downstream side, thus dividing the head of water to be held up into two—in other words, by making two steps instead of one. Each weir was to consist of a core of rubble masonry set in cement, sunk well below the bed of the river, and protected up and down stream by a long slope of rough stone blocks or pitching. To make the masonry core thoroughly watertight, a mass of clay puddle was to be put on either side of it. The weirs were thus to be a solid dam, blocking the course of the stream up to such a height that the head of water on the Barrage, at that time amounting to 4 metres, would be reduced to 2·5 metres. The flood would pass freely over the top of the weirs. At the same time the sluice-gates of the existing Barrage were to be heightened, so as to permit the upstream level to be raised 1 metre more in June and July, so as to take full advantage of the rising flood and facilitate the early sowing of maize, a great point with the Egyptian cultivator.

By the summer of 1900 this programme had been completed. The building of the weir on the Rosetta branch was an especially fine performance, for which great credit was due to Sir Hanbury Brown and Mr. Brooke, who were in charge of it. Five hundred metres in length, it was begun at the end of December, 1899, and actually finished before the flood began to come down in July. The same Portland cement played a great part in its construction. It may now fairly be said that the Barrage is complete at last, and fully equal to every strain that it can be called upon to bear.