35. Flood protection for Egypt.
—In paragraph 30 it was stated that the floods in the Delta or in Lower Egypt can rise to a height of from 2 to 31⁄2 metres above the level of the country. Such floods are really dangerous and means should be found for moderating them.
The Wady Rayan reservoir, when converted into the modern Lake Mœris and acting as a reservoir, will have one great advantage, it will be able to lower a high flood 30 centimetres for 50 days. This will give relief to the Nile, a relief which will be much appreciated by the whole country from Beni Suef to the sea, and especially by Cairo.
I have already stated that the Damietta branch is especially dangerous and unfit to act as an escape under existing conditions. That branch could be regulated on at its head and treated like a canal. Thanks to Sir Hanbury Brown’s initiative the Barrages can be regulated on in flood as well as in summer, and by lowering the supply in the Damietta branch and turning the surplus down the Rosetta branch, the latter would become the flood escape of the Nile. It might be trained as Mr. Eads suggested that rivers should be treated.
Mr. Eads’ argument is very clear. He insists that rivers eat away their banks in places, not owing to the direct action of the water but by the alterations in the velocity of the current. When the river water is charged with sediment to its full carrying capacity it cannot take up more unless the rate of current be increased. If the channel be nearly uniform the river water cannot eat away any of its banks. If, however, the channel is varying, the silt deposits in the wide sections, and the water, free of some of its sediment, is ready to eat more. It is this alternate dropping silt and eating away of earth which does the harm. To treat the Rosetta branch according to Mr. Eads it would be necessary to fix the top width to be worked to, at say 550 metres. The river could be brought to this uniform top width by building light inexpensive permeable spurs on the sandy shoals. The land between the spurs would become cultivated and such river training would pay the Government, which taxes all cultivated land; it would even pay handsomely for any company to undertake the work once the rule about foreshores was understood. The Government would, however, always succeed; when it could not sell, it could always tax. Such training would permanently lower the flood.
In addition to the above it would be necessary to complete the system of spurs begun in 1884, and to throw back the banks as already recommended. It has been estimated that the completion of this work would cost £900,000 for spurs and banks, while the training works would pay for themselves in addition to greatly improving the channel and lowering the level of the flood.
It may be humiliating to make the confession, but from B.C. 2,200 to the Arab invasion of Egypt in A.D. 640, while Lake Mœris performed its allotted task and the Nile possessed training works such as those we can see to-day in Nubia, Egypt was better protected from inundation, and the Nile better trained, than it is to-day. And yet we have many advantages which no Pharaoh possessed. By the aid of telegraphy we have knowledge of a coming flood a full fifteen days before it arrives in the Delta; the Khartoum gauge allows us to anticipate its very height. Meteorology is aiding us still further. In a paper I read at the Chicago International Exhibition I stated that years of heavy rainfall in India are years of high flood in Egypt, while years of poor rainfall in India are years of low flood in Egypt. Sir John Eliot, the Director General of the Meteorological Department of India, corrected this statement. He said that though this was not true of the Bengal monsoon, it was true of the Bombay monsoon. Years of heavy rainfall in Gujerat and Bombay are years of high flood on the Nile, and vice versà. As the rain falls in Bombay a month earlier than the Nile flood reaches Cairo, we have information of a high flood a month before it arrives, if we receive telegraphic information from Bombay.
36. Complete project for water storage and flood protection for Egypt.
—The complete project for water storage and flood protection for Egypt as proposed by me, contemplates the following works:—
| Raising the Assuân reservoir (2 years) | £ | 500,000 |
| Wady Rayan reservoir (4 years) | „ | 2,600,000 |
| Training the Rosetta branch | „ | 900,000 |
| Total | £ | 4,000,000 |