A certain
steady volume of water is required, from which the arteries shall
flow throughout a large area of dry ground; thus, the reservoir
insures a regular supply to each separate channel.
In any civilized country, the existence of which depended upon
the artificial supply of water in the absence of rain, the first
engineering principle would suggest a saving of labour in
irrigation: that, instead of raising the water in small
quantities into reservoirs, the river should raise its own waters
to the required level.
Having visited every tributary of the Nile during the
explorations of nearly five years, I have been struck with the
extraordinary fact that, although an enormous amount of wealth is
conveyed to Egypt by the annual inundations of the river, the
force of the stream is entirely uncontrolled. From time
immemorial, the rise of the Nile has been watched with intense
interest at the usual season, but no attempt has been made to
insure a supply of water to Egypt during all seasons.
The mystery of the Nile has been dispelled; we have proved that
the equatorial lakes supply the main stream, but that the
inundations are caused by the sudden rush of waters from the
torrents of Abyssinia in July, August, and September; and that
the soil washed down by the floods of the Atbara is at the
present moment silting up the mouths of the Nile, and thus
slowly, but steadily, forming a delta beneath the waters of the
Mediterranean, on the same principle that created the fertile
Delta of Egypt.
