As the supply of water raised by the sageer is received in a reservoir, from which the irrigating channels radiate through the plantations, so should great reservoirs be formed throughout the varying levels of Egypt, from Khartoum to the Mediterranean, comprising a distance of sixteen degrees of latitude, with a fall of fifteen hundred feet. The advantage of this great difference in altitude between the Nile in latitude 15 degrees 30 minutes and the sea, would enable any amount of irrigation, by the establishment of a series of dams or weirs across the Nile, that would raise its level to the required degree, at certain points, from which the water would be led by canals into natural depressions; these would form reservoirs, from which the water might be led upon a vast scale, in a similar manner to the insignificant mud basins that at the present day form the reservoirs for the feeble water-wheels. The increase of the river's level would depend upon the height of the dams; but, as stone is plentiful throughout the Nile, the engineering difficulties would be trifling.
Mehemet Ali Pasha acknowledged the principle, by the erection of the barrage between Cairo and Alexandria, which, by simply raising the level of the river, enabled the people to extend their channels for irrigation; but this was the crude idea, that has not been carried out upon a scale commensurate with the requirements of Egypt. The ancient Egyptians made use of the lake Mareotis as a reservoir for the Nile waters for the irrigation of a large extent of Lower Egypt, by taking advantage of a high Nile to secure a supply for the remainder of the year; but, great as were the works of those industrious people, they appear to have ignored the first principle of irrigation, by neglecting to raise the level of the river.
Egypt remains in the same position that Nature originally allotted to her; the life-giving stream that flows through a thousand miles of burning sands suddenly rises in July, and floods the Delta which it has formed by a deposit, during perhaps hundreds of thousands of inundations; and it wastes a superabundance of fertilizing mud in the waters of the Mediterranean. As Nature has thus formed, and is still forming a delta, why should not Science create a delta, with the powerful means at our disposal? Why should not the mud of the Nile that now silts up the Mediterranean be directed to the barren but vast area of deserts, that by such a deposit would become a fertile portion of Egypt? This work might be accomplished by simple means: the waters of the Nile, that now rush impetuously at certain seasons with overwhelming violence, while at other seasons they are exhausted, might be so controlled that they should never be in excess, neither would they be reduced to a minimum in the dry season; but the enormous volume of water heavily charged with soil, that now rushes uselessly into the sea, might be led throughout the deserts of Nubia and Libya, to transform them into cotton fields that would render England independent of America. There is no fiction in this idea; it is merely the simple and commonplace fact, that with a fall of fifteen hundred feet in a thousand miles, with a river that supplies an unlimited quantity of water and mud at a particular season, a supply could be afforded to a prodigious area, that would be fertilized not only by irrigation, but by the annual deposit of soil from the water, allowed to remain upon the surface. This suggestion might be carried out by gradations; the great work might be commenced by a single dam above the first cataract at Assouan, at a spot where the river is walled in by granite hills; at that place, the water could be raised to an exceedingly high level, that would command an immense tract of country. As the system became developed, similar dams might be constructed at convenient intervals that would not only bring into cultivation the neighbouring deserts, but would facilitate the navigation of the river, that is now impeded, and frequently closed, by the numerous cataracts. By raising the level of the Nile sixty feet at every dam, the cataracts would no longer exist, as the rocks which at present form the obstructions would be buried in the depths of the river. At the positions of the several dams, sluice gates and canals would conduct the shipping either up or down the stream. Were this principle carried out as far as the last cataracts, near Khartoum, the Soudan would no longer remain a desert; the Nile would become not only the cultivator of those immense tracts that are now utterly worthless, but it would be the navigable channel of Egypt for the extraordinary distance of twenty-seven degrees of latitude--direct from the Mediterranean to Gondokoro, N. lat. 4degrees 54 minutes.
The benefits, not only to Egypt, but to civilization, would be incalculable; those remote countries in the interior of Africa are so difficult of access, that, although we cling to the hope that at some future time the inhabitants may become enlightened, it will be simply impossible to alter their present condition, unless we change the natural conditions under which they exist.
From a combination of adverse circumstances, they are excluded from the civilized world: the geographical position of those desert-locked and remote countries shuts them out from personal communication with strangers: the hardy explorer and the missionary creep through the difficulties of distance in their onward paths, but seldom return: the European merchant is rarely seen, and trade resolves itself into robbery and piracy upon the White Nile, and other countries, where distance and difficulty of access have excluded all laws and political surveillance.
