four times in modern history: in 1877, when it caused widespread famine and death throughout Upper Egypt, 947,000 acres remained barren, and the land revenue lost £1,112,000; in 1899 and again in 1902 and 1907, when by the thorough remodelling of the whole system of canals since 1883 all famine and disaster were avoided and the loss of revenue was comparatively slight. In 1907, for instance, when the flood was nearly as low as in 1877, the area left unwatered was little more than 10% of the area affected in 1877.
This regularity of flow is the first exceptional excellence of the river Nile. The second is hardly less valuable, and consists in the remarkable richness of the alluvium brought down the river year after year during the flood. The object of the engineer is so to utilize this flood-water that as little as possible of the alluvium may escape into the sea, and as much as possible may be deposited on the fields. It is the possession of these two properties that imparts to the Nile a value quite unique among rivers, and gives to the farmers of the Nile Valley advantages over those of any rain-watered land in the world.
Until the 19th century irrigation in Egypt on a large scale
was practised merely during the Nile flood. Along each edge
of the river and following its course has been erected
an earthen embankment high enough not to be
Irrigation during
high Nile.
topped by the highest floods. In Upper Egypt,
the valley of which rarely exceeds 6 m. in width,
a series of cross embankments have been constructed, abutting
at the inner ends on those along the Nile, and at the
outer ends on the ascending sides of the valley. The whole
country has thus been divided into a series of oblongs,
surrounded by embankments on three sides and by the
desert slopes on the fourth. These oblong areas vary from
60,000 to 1500 or 2000 acres in extent. Throughout all
Egypt the Nile is deltaic in character; that is, the slope
of the country in the valley is away from the river and not
towards it. It is easy, then, when the Nile is low, to cut
short, deep canals in the river banks, which fill as the flood
rises, and carry the precious mud-charged water into these
great flats. There the water remains for a month or more,
some 3 ft. deep, depositing its mud, and thence at the
end of the flood the almost clear water may either be run
off directly into the receding river, or cuts may be made
in the cross embankments, and it may be allowed to
flow from one flat to another and ultimately into the river.
In November the waters have passed off; and whenever
a man can walk over the mud with a pair of bullocks,
it is roughly turned over with a wooden plough, or merely the
branch of a tree, and the wheat or barley crop is immediately
sown. So soaked is the soil after the flood, that the grain
germinates, sprouts, and ripens in April, without a shower of
rain or any other watering.
In Lower Egypt this system was somewhat modified, but it was the same in principle. No other was known in the Nile Valley until the country fell, early in the 19th century, under the vigorous rule of Mehemet Ali Pasha. He soon recognized that with such a climate and soil, with a teeming population, and with the markets of Europe so near they might produce in Egypt something more profitable than wheat and maize. Cotton and sugar-cane would fetch far higher prices, but they could only be grown while the Nile was low, and they required water at all seasons.
It has already been said that the rise of the Nile is about
2512 ft., so that a canal constructed to draw water out of the
river while at its lowest must be 2512 ft. deeper than
if it is intended to draw off only during the highest
Irrigation during
low Nile.
floods. Mehemet Ali began by deepening the canals
of Lower Egypt by this amount, a gigantic and futile
task; for as they had been laid out on no scientific principles,
the deep channels became filled with mud during the first flood,
and all the excavation had to be done over again, year after
year. With a serf population even this was not impossible;
but as the beds of the canals were graded to no even slope, it
did not follow that if water entered the head it would flow
evenly on. As the river daily fell, of course the water in the
canals fell too, and since they were never dug deep enough to
draw water from the very bottom of the river, they occasionally
ran dry altogether in the month of June, when the river was at
its lowest, and when, being the month of greatest heat, water
was more than ever necessary for the cotton crop. Thus large
tracts which had been sown, irrigated, weeded and nurtured for
perhaps three months perished in the fourth, while all the time
the precious Nile water was flowing useless to the sea. The
obvious remedy was to throw a weir across each branch of the
river to control the water and force it into canals taken from
above it. The task of constructing this great work was committed
to Mougel Bey, a French engineer of ability, who designed and
The Nile Barrage.
constructed the great barrage across the two branches
of the Nile at the apex of the delta, about 12 m. north
of Cairo (fig. 2). It was built to consist of two bridges—one
over the eastern or Damietta branch of the river having
71 arches, the other, over the Rosetta branch, having 61 arches,
each arch being of 5 metres or 16.4 ft. span. The building was
all of stone, the floors of the arches were inverts. The height of
pier from edge of flooring to spring of arch was 28.7 ft., the
spring of the arch being about the surface-level of maximum flood.
The arches were designed to be fitted with
self-acting drop gates; but they were not
a success, and were only put into place on
the Rosetta branch. The gates were intended
to hold up the water 4.5 metres,
or 14.76 ft., and to divert it into three main
canals—the Behera on the west, the Menufia
in the centre and the Tewfikia on the east.
The river was thus to be emptied, and to
flow through a whole network of canals,
watering all Lower Egypt. Each barrage was provided with
locks to pass Nile boats 160 by 28 ft. in area.
 |
| Fig. 2.—Map showing the Damietta and Rosetta dams on the Nile. |
Mougel’s barrage, as it may now be seen, is a very imposing and stately work. Considering his want of experience of such rivers as the Nile, and the great difficulties he had to contend with under a succession of ignorant Turkish rulers, it would be unfair to blame him because, until it fell into the hands of British engineers in 1884, the work was condemned as a hopeless failure. It took long years to complete, at a cost which can never be estimated, since much of it was done by serf labour. In 1861 it was at length said to be finished; but it was not until 1863 that the gates of the Rosetta branch were closed, and they were reopened again immediately, as a settlement of the masonry took place. The experiment was repeated year after year till 1867, when the barrage cracked right across from foundation to top. A massive coffer-dam was then erected, covering the eleven arches nearest the crack; but the work was never trusted again, nor the water-surface raised more than about 3 ft.
An essential part of the barrage project was the three canals, taking their water from just above it, as shown in fig. 2. The heads of the existing old canals, taken out of the river at intervals throughout the delta, were to be closed, and the canals themselves all put into connexion with the three high-level trunk lines taken from above the barrage. The central canal, or Menufia, was more or less finished, and, although full of defects, has done good service. The eastern canal was never dug at all until
