The utilisation of the Nile.
24. =The Nile in flood.=--We are now in a position to apply our
knowledge of the Nile and its tributaries to an examination of the
behaviour of the rivers in flood and in time of low supply. Lake
Victoria, the Victoria Nile, and Lake Albert may all be considered as
the great equatorial regulators of the Nile. The river, as a river,
begins at the outlet of Lake Albert, i.e., at the head of the Albert
Nile. Generally at its lowest in April, it rises gradually and reaches
its maximum in November. The mean minimum of 600 cubic metres per second
is gradually increased to its mean maximum of 900 cubic metres. The
regulating effect of the lakes is very evident.
Between Lake Albert and Gondokoro the heavier rains begin late in April
and with a break in June and July continue to November. The mean minimum
discharge of 600 cubic metres per second in April is increased by
alternating rises and falls to the mean maximum of 1600 cubic metres per
second in September, which has disappeared by the end of November, when
the water of Lake Albert alone remains in the river.
The Gazelle river in no way affects the flood or the low supply. Its
great function is to maintain the levels of the great swamps between
latitudes 7° and 9°, saturate the soil, and prevent the complete
disappearance of the waters of the Albert Nile between January and May.
The functions this river performs are humble ones, but deprived of its
aid, the Nile north of Khartoum would frequently be dry in April and
May.
The Albert Nile at its tail just upstream of the mouth of the Sobat is
at its lowest in April and May with a mean low discharge of 375 cubic
metres per second, when it is joined by the Sobat river with an
approximate mean low discharge of 125 cubic metres per second; making a
joint discharge for the head of the White Nile of 500 cubic metres per
second as a mean minimum. Now begins one of the most interesting
operations of any in the whole valley of the Nile, exceeded only in
interest by what happens at Khartoum lower down. The Albert Nile and the
Sobat river both rise together, the Albert Nile on a very gentle slope
freely overflowing its banks in the Sudd region, and the Sobat river
confined within its channel during its highest floods. The White Nile
has a very gentle slope, little carrying capacity and is quite incapable
of taking on both floods. The water rises at the junction and the Sudd
region becomes a reservoir flooded to a depth of 3 metres. As the Sobat
river increases its discharge gradually from 75 cubic metres per second
in April to 1000 cubic metres per second in October and November (for it
is confined to its channel), the Albert Nile decreases the actual
discharge it sends down the White Nile and increases what it spreads
over the Sudd region. The Albert Nile, having increased its quota for
the White Nile from 375 in April to 450 cubic metres per second in
September, gives less in October and November and gradually passes on
its waters in December, January and February when the Sobat has fallen.
The White Nile at its head near Tewfikieh has its mean minimum of 500
cubic metres per second in April, and increases slowly to its mean
maximum of 1500 cubic metres per second in December. During this
interval its water surface is raised by 3·50 metres. This water travels
very slowly on to Khartoum, where the mean minimum is 450 cubic metres
per second in May, the slope is very insignificant, and the trough of
the river is 1500 metres wide.
At Khartoum the White Nile meets the Blue Nile. No greater contrast
exists in the world. If maximum discharges are alone considered, the
little finger of the Blue Nile is thicker than the loins of the White
Nile.
The Blue Nile is at its lowest on the 1st May with a mean minimum supply
of 200 cubic metres per second rising to a mean maximum flood of 10,000
cubic metres per second on the 1st September. The flood has fallen to
2000 cubic metres per second by the middle of November.
Up to the middle of July the Blue and White Niles keep increasing their
discharges steadily at Khartoum, but after that date the Blue Nile gauge
and discharge rise rapidly together, and the Blue Nile not only feeds
the Main Nile, but flows up the White Nile and arrests its discharge, so
that at Duem, 200 kilometres above Khartoum, the White Nile discharge
decreases in July and August while the Blue Nile is steadily flowing up
the White Nile valley and converting it into a reservoir for the Nile in
winter. It is only after the 15th September, when the Blue Nile has
begun to fall steadily and continuously that the White Nile discharge
really commences and reaches its mean maximum of some 2000 cubic metres
per second in October.
The mean minimum discharge of the Nile of 650 cubic metres per second at
Khartoum is obtained on the 1st May and the mean maximum of 9000 cubic
metres per second on the 1st September. Fed by the White Nile reservoir
the river falls comparatively slowly. Whether this peculiar relation of
the two rivers to each other could not be taken advantage of to increase
the supply in December, January and February, and decrease it in October
and November by means of a regulating dam built across the White Nile at
Khartoum is worthy of study.
I greatly prefer the idea of storing the flood waters of the White Nile
at Khartoum to any storage of the Albert Nile water above the junction
of the Sobat river. A regulator above the Sobat junction would store up
a very considerable quantity of water, but the quality would be very
doubtful and possibly dangerous to health.
At El Damer, south of Berber, the Atbara flows into the Nile. Dry from
January to May, the flood begins in June and is at its maximum as a rule
in the last week of August; with a mean high flood discharge of 3500
cubic metres per second. This water cannot come on to Assuân without
filling up the 200 kilometres downstream of the 6th cataract where the
slope of the Nile is gentle and the river lends itself to being used as
a reservoir. It is owing to the fact that none of the main feeders of
the Nile flow in immediately below cataracts that the rise and fall of
the Nile in Egypt, is so regular and constant. If the Sobat, Blue Nile
and Atbara all flowed into the White or Main Niles below cataracts we
should have floods in Egypt whose sudden changes of level and
fluctuations would be an unending source of danger to the country.
It is owing to the earliness of the Atbara high flood and the
comparative lateness of the Nile high flood, that the ordinary maximum
discharge of the Nile at Assuân is only 10,000 cubic metres per second.
This is generally on the 5th September. When the monsoon is early the
maximum at Assuân is reached before or on the 5th September; when the
monsoon is late the maximum is reached about the 20th September. An
early maximum at Assuân is generally followed by a low summer, while a
late maximum is generally followed by a high summer supply. Only once
has this rule been broken and that was in 1891 when there were two
maxima, one on the 4th September and another on the 27th. In this year
there must have been an extraordinary fall of rain in Abyssinia in
September, for the flood of the 27th September was very muddy, while as
a rule the river at Assuân is very muddy in August, less so in
September, still less so in October and much less in November when the
White Nile is the ruling factor in the supply of the river.
If the September rains in Abyssinia are very heavy, an ordinary flood
passes Assuân at the end of September and is disastrous for Egypt. This
happened in 1878. Table 26 contains details of this flood, of the
minimum flood year 1877 and the mean of the 20 years from 1873 to 1892.
At Assuân the Nile enters Egypt, and it now remains to consider it in
its last 1,200 kilometres. The mean minimum discharge at Assuân is 590
cubic metres per second and is reached about the end of May. The river
rises slowly till about the 20th July and then rapidly through August,
reaching its maximum about the 5th September, and then falling very
slowly through October and November. The deep perennial irrigation
canals take water all the year round, but the flood irrigation canals
are closed with earthen banks till the 15th August, and are then all
opened. These flood canals, of which there are some 45, are capable of
discharging 2,000 cubic metres per second at the beginning of an
ordinary year, 3,600 cubic metres per second in a maximum year, and have
an immediate effect on the discharge of the Nile. The channel of the
Nile itself and its numerous branches and arms consume a considerable
quantity of water (the cubic contents of the trough of the Nile between
Assuân and Cairo are 7,000,000,000 cubic metres), the direct irrigation
from the Nile between Assuân and Cairo takes 50 cubic metres per second,
130 cubic metres per second are lost by evaporation off the Nile, and
400 cubic metres per second by absorption. Owing to all these different
causes, there is the net result that, from August 15th to October 1st,
the Nile is discharging 2,400 cubic metres per second less at Cairo than
Assuân. During October and November the flood canals are closed, and the
basins which have been filled in August and September discharge back
into the Nile, and in October the Nile at Cairo is discharging 900 cubic
metres per second in excess of the discharge at Assuân and 500 cubic
metres per second in excess in November.
The mean minimum discharge at Cairo is 500 cubic metres per second and
is attained on the 15th of June; the river rises slowly through July and
fairly quickly in August, and reaches its ordinary maximum on the 1st
October when the basins are full and the discharge from the basins is
just beginning. The ordinary maximum discharge at Cairo is about 7,600
cubic metres per second. Through October the Nile at Cairo is
practically stationary, and falls rapidly in November.
North of Cairo are the heads of the perennial canals which irrigate the
Delta proper. The canals, with their feeders lower down, discharge 1,200
cubic metres per second, and the ordinary maximum flood at Cairo of
7,600 cubic metres per second is reduced by this amount between Cairo
and the sea. Of the 6,400 cubic metres per second which remain, 4,100
cubic metres per second find their way to the sea down the Rosetta
branch, and 2,300 cubic metres per second down the Damietta branch.
During extraordinary floods the Damietta branch has discharged 4,300
cubic metres per second and the Rosetta branch 7,000 cubic metres per
second.
25. =The Nile in low supply.=--We have so far considered the Nile in
flood, it now remains to quickly dispose of the low supply. After
reaching its maximum, the Atbara, which is a torrential river, falls
more rapidly than others, and by the end of September has practically
disappeared; after the middle of September the Blue Nile falls quickly,
while the White Nile with its large basin, gentle flow and numerous
reservoirs, falls very deliberately. The mean minimum discharge of the
White Nile at Gondokoro in an ordinary year, at the time of low supply,
is 600 cubic metres per second. Of the Sobat river it is 100 cubic
metres per second. By the time the water reaches Khartoum it is reduced
to 450 cubic metres per second. The mean low supply of the Blue Nile is
200 cubic metres per second, giving a mean low supply to the Nile at
Khartoum of 650 cubic metres per second. The Atbara supplies nothing.
Between Khartoum and Assuân there is a further loss of 60 cubic metres
per second, and the mean low supply delivered at Assuân is 590 cubic
metres per second. In very bad years the discharge at Assuân has fallen
to 400 cubic metres per second.
Lombardini was no untrue prophet when he wrote that he was convinced
that the more carefully the discharges were taken and the results known,
the more would engineers be astonished at the extraordinary amount of
the subsoil water which filtered into the Nile from the head of the
White Nile to the sea, and which gave back to the Nile in the months of
deflux of the river, the water which had percolated into the soil during
the afflux. He predicted that heavy as the evaporation was in April, May
and June in the Nile valley, the influx of subsoil water would be found
to counterbalance it. When we calculate the extent of the water used in
irrigation along the course of the Nile, and compare the discharges at
Tewfikieh, Khartoum, Assuân, Cairo and at the tails of the Rosetta and
Damietta branches during the time of low supply we can only admire the
perspicacity of the greatest hydraulic engineer of the last century.
26. =Nile water.=--For the following information I am principally
indebted to M. J. Barois’ “Les irrigations en Egypte” just published,
and to an article by Mr G. P. Foaden in the Journal of the Khedivial
Agricultural Society for January 1903. The colour of Nile water is
generally a pale yellow, but in June, when the first indications of the
coming flood are given by a continuous gentle rise of the river from its
minimum gauge, the water changes to green and remains so for two or
three weeks. This green water has a very disagreeable taste and odour,
and is especially objectionable when the Nile has been very low and the
rise is a slow one. In June 1900 it was extraordinarily bad, and the
river water was so poor in oxygen that standing on Kasr-el-Nil bridge at
Cairo one could see the surface of the water covered with fish which
apparently could only live near the surface. In the deep reaches near
Kalabsha in Nubia, the fish died in myriads. This green water is
attributed by some to the immense amount of vegetable matter brought
down by the White Nile from the Sudd region. Some say that it comes
principally with the first rise of the Sobat river. But the generally
accepted theory to-day is that the green water is the result of
vegetable growths from germs is the water itself, and that wherever or
whenever the current becomes exceedingly slack they multiply greatly.
Upstream of the Assuân dam in June 1903 the water was extraordinarily
green and exceedingly objectionable. As it was shot out of the upper
sluices of the dam and broken up into spray on the downstream side of
the dam it became so purified that I found it difficult to understand
that the water flowing past Elephantine Island was what I had seen at
Shellal. The green water is followed by the red water of the Nile flood,
which has always thoroughly established itself at Cairo by the 1st of
August. This red water comes from the scourings of the volcanic plateau
of Abyssinia by the Blue Nile and the Atbara. Rich in mud and rich in
manures, this red water is the creator of Egypt. Egypt is nothing more
than the deposit left by the Nile in flood. The water is most heavily
charged with detritus in August, less in September, and still less in
October.
Many analyses have been made of Nile water. Following M. Barois, I place
side by side the analysis of Dr. Letheby of 1874⁄75 and Dr. Mackenzie
of 1896/97/98. The year 1874 was an extraordinarily high flood.
=========+==============================
Month. | PARTS IN 100,000 OF WATER
+----------+--------+----------
| Dr. | Dr. |The Mean
|Mackenzie.|Letheby.|of the two
---------+----------+--------+----------
January | 31·0 | 16·7 | 27·4
February | 25·3 | 12·6 | 22·1
March | 12·7 | 5·3 | 10·9
April | 15·8 | 6·6 | 13·5
May | 14·7 | 4·8 | 12·2
June | 14·1 | 6·9 | 12·3
July | 13·9 | 17·8 | 14·8
August | 159·0 | 149·2 | 156·6
September| 156·1 | 53·3 | 130·4
October | 110·0 | 37·8 | 92·8
November | 70·8 | 34·4 | 61·7
December | 47·0 | 28·9 | 42·4
---------+----------+--------+----------
Mean | 56·0 | 31·3 | 49·8
=========+==========+========+==========
From this last column M. Barois concludes that in high floods
100,000,000 tons of solid matter pass Assuân, and 88,000,000 in mean
floods. It is unfortunate that we have no analyses of low floods like
1877, 88, 99, 1902 and 1904 which were extraordinarily muddy. The water
had little sand but much mud. The sand is scoured out of the bed of the
river itself in high floods.
After Dr. Letheby the composition of Nile deposit is as follows:--
=========================+=========+==============
|In flood.|In low supply.
+---------+--------------
Organic matter | 15·02 | 10·37
Phosphoric acid | 1·78 | ·57
Lime | 2·06 | 3·18
Magnesia | 1·12 | ·99
Potash | 1·82 | 1·06
Soda | ·91 | ·62
Alumina and oxide of iron| 20·92 | 23·55
Silica | 55·09 | 58·22
Carbonic acid and loss | 1·28 | 1·44
-------------------------+---------+--------------
Total | 100·00 | 100·00
=========================+=========+==============
Comparative analyses of subsoil water in Egypt and Nile water in time of
low supply are given below.
=================================+========================
| PARTS IN 100,000
Dissolved matter. +-----------+------------
|Well water.|Summer water
| | in Nile.
---------------------------------+-----------+------------
Lime | 16·56 | 4·24
Magnesia | 4·53 | 1·00
Soda | 8·20 | 6·20
Potash | ·37 | 1·44
Chlorine | 13·60 | ·67
Sulphuric acid | 5·93 | 2·16
Nitric acid | ·17 | --Traces
Silica, alumina and oxide of iron| 1·80 | ·97
Organic Matters | ·60 | 1·75
Carbonic oxide and loss | 12·26 | 4·03
---------------------------------+-----------+------------
| 64·02 | 22·46
=================================+===========+============
It must be remembered that Nile water in the time of low supply consists
in a very appreciable part of subsoil water which has filtered into the
Nile.
Mr. Foaden states that, speaking in round numbers, we may say that Nile
deposit in flood contains
Nitrogen ·1 per cent
Phosphoric acid ·2 „
Potash ·6 „
He values the manure deposited by the Nile annually in a well irrigated
basin at £·75. He concludes that Nile water in flood is rich in potash,
fairly rich in phosphoric acid and poor in nitrogen.
27. =The soil of the Nile valley.=--According to numerous analyses made
of Egyptian soil in 1872 by MM. Payen, Champion and Gastinel, the soil
of Egypt consists of
Silica 45 per cent
Argile 53 „
Magnesia ·2 to 1·6 „
Lime 1·3 to 4·9 „
Nitrogen ·03 to ·10 „
Phosphoric acid ·03 to ·32 „
Some stiff soils contain 84 per cent argile and some light soils contain
68 per cent sand. As one approaches the Mediterranean the quantity of
chloride of soda increases and runs from a fraction to 4, 5, and even 10
per cent.
From the means of ten samples of soil from Kena Mudirieh analysed for me
in May by Mr. Frank Hughes of the Agricultural Society we gather that
the constituents of the soil are as follows:--
=====================================+======+======+=======
Ingredients. |Max %.|Min %.|Mean %.
-------------------------------------+------+------+-------
Silica etc., insoluble in strong acid|66 |53 |60
Total Lime | 3·80 | 2·50 | 3·34
Total Potash | 1·19 | ·46 | ·74
Total Potash available | ·072| ·020| ·042
Total Phosphoric Acid | ·49 | ·20 | ·35
Total Phosphoric available | ·090| ·029| ·066
Carbonic Acid = Chalk | 3·52 | 1·79 | 2·69
Nitrogen | ·106| ·056| ·084
=====================================+======+======+======
We have here a general sufficiency of phosphoric acid, plenty of potash
and lime, and a low proportion of nitrogen.
The salts of the soil, when in excess, are chlorides and sulphates of
soda: the carbonates are present in very small quantities indeed.
The following selection from a paper by Mr. Lang Anderson in the
December 1903 number of the Journal of the Khedivial Agricultural
Society is interesting.
“Voelcker’s analyses of the two samples of soil taken from the drained
bed of what was Lake Edku near Alexandria give the following results:--
============================+=======+=======
| No. 1.| No. 2.
----------------------------+-------+-------
Oxide of iron | 11·69 | 11·04
Iron pyrites | 0·08 | 0·11
Aluminium | 6·36 | 10·88
Lime | 2·08 | 7·73
Magnesia | 1·79 | 0·93
Soda | 0·79 | ..
Sodium chloride | 8·11 | 8·56
Potash | 0·65 | 1·23
Sulphuric acid | 2·23 | 2·56
Carbonic acid | 0·19 | 4·75
Phosphoric acid | 0·16 | 0·19
Insoluble silicates and sand| 62·23 | 45·81
Organic matter | 3·64 | 6·21
| |
Total |100·00 |100·00
----------------------------+-------+-------
Containing nitrogene | 0·035| 0·070
„ ammonia | 0·042| 0·079”
============================+=======+=======
28. =Basin irrigation.=--Considering the times of flood and low supply,
the climate of Egypt, the turbidity of the Nile flood, and the deltaic
formation of the Nile valley, no better system than basin irrigation as
practiced in Egypt could possibly have been devised. If the flood had
come in April and May and been followed by a burning summer, or if the
actual autumn floods had been followed by the frozen winters of Europe
or the warm winters of the Sudan, basin irrigation would have been a
failure or a very moderate success; but, given the Egyptian climate,
basin irrigation has stood without a rival for 7000 years.
Basin irrigation, as it has been practised in Egypt for thousands of
years, is the most efficacious method of utilising existing means of
irrigation which the world has witnessed. It can be started by the
sparsest of populations. It will support in wealth a multitude of
people. King Menes made his first dyke when the Egyptian nation was in
its infancy. Egypt, in Roman times, supported a population twice as
dense as that of to-day. The direct labour of cultivation is reduced to
an absolute minimum.
Shakespeare’s genius has crystallised the system for all time:--
“They take the flow o’ the Nile
By certain scales in the Pyramid; they know,
By the height, the lowness, or the mean, if dearth
Or foizon follow: the higher Nilus swells,
The more it promises: as it ebbs, the seedsman
Upon the slime and ooze scatters his grain,
And shortly comes to harvest.”
If we cast back our view to the dawn of Egyptian history, we can picture
the Nile Valley as consisting of arid plains, sand dunes, and marshy
jungles, with reclaimed enclosures on all the highest lands. Every eight
or ten years the valley was swept by a mighty inundation. The seeds of
future success lay in the resolve of King Menes’ engineers to confine
their attention to one bank of the river alone. It was the left bank of
the river which history tells us was first reclaimed. A longitudinal
dyke was run parallel to the stream, and cross dykes tied it to the
Lybian hills. Into these basins or compartments the turbid waters of the
flood were led by natural water-courses and artificial canals and
allowed to deposit their rich mud and thoroughly saturate the soil; and
meantime the whole of the right bank and the trough of the river itself
were allowed to be swept by the floods. It must have been on this wild
eastern bank that were conducted all the hippopotamus hunts which are
crowded on the wall pictures of buildings of the early dynasties. In all
probability, the first six dynasties contented themselves with
developing the left bank of the Nile. As, however, the population
increased, and with it the demand for new lands, it became necessary to
reclaim the right bank of the river as well. The task now was doubly
difficult, as the river had to be confined to its own trough. This
masterful feat was performed by the great Pharaohs of the XIIth Dynasty,
the Amenemhats and the Usartsens, who, under the name of Sesostris,
usurped the place of Menes in the imagination of the ancient world. They
were too well advised to content themselves with repeating on the right
bank what Menes had done on the left. By suddenly confining the river
they would have exposed the low-lying lands of Memphis and Lower Egypt
to disastrous inundations. To obviate this, they widened and deepened
the natural channel which led to the Fayoum depression in the Lybian
hills, and converted it into a powerful escape to carry off the excess
waters of high floods; and so successful were they in their undertakings
that the conversion of the Fayoum depression into Lake Mœris was long
considered by the ancient world as one of its greatest wonders. They led
the flood into the depression when it was dangerously high, and provided
for its return to the river when the inundation had come to an end. By
this means, they insured the lake against being at a high level during a
period of flood. The gigantic dykes of entry and exit were only cut in
times of emergency, and were reconstructed again at an expense of labour
which even an Egyptian Pharaoh considered excessive. To understand how
capable Lake Mœris was to control the floods, and turn a dangerous into
a beneficial inundation, I should recommend a study of Sir Hanbury
Brown’s “Fayoum and Lake Mœris.” As years rolled on the Nile widened and
deepened its own trough, to which it was now confined; and, eventually,
the time came when Lake Mœris could be dispensed with without danger. It
was gradually reclaimed and converted into the Fayoum with its 350,000
acres of cultivated land.
Basin irrigation holds the flood waters for some 45 days per annum over
the whole of the valley. The water is in places 3 metres deep, and in
others only 30 centimetres deep, while the average depth is about 1
metre. Now the retention of this water over the land for a period of six
weeks permits of the thorough saturation of the subsoil in places where
the subsoil is of proper consistency; and this water can be drawn on, in
winter and summer, for maturing certain crops and growing others. It was
where the subsoil gave a plentiful supply of water, and permitted of
intense cultivation throughout the year, that we find all the ancient
capitals of Egypt. Abydos has the finest subsoil water in the Nile
Valley; Memphis has an excellent supply; while Thebes has the only good
subsoil water on the whole of the right bank. Good subsoil water was to
the ancient Egyptian world what the presence of a rich gold mine is to
one of our new colonies.
[Illustration: PLAN XIV
THE NORTH SOHAG SYSTEM OF BASINS
_Scale 1 : 200,000_
Lith. Sur. Dep. Cairo.]
Subsoil water supplies the link between basin and perennial irrigation.
It explains the reason why modern Egypt is not satisfied with the
irrigation which has come down from the remotest antiquity, but is
desirous of conferring on the length and breadth of the Nile Valley
those advantages which gave Abydos, Memphis, and Thebes their
pre-eminence in the past. Any country which possesses rivers and streams
whose waters are in flood for six weeks per annum at a suitable season
of the year can betake itself to basin irrigation with more or less
profit. The science of dams, weirs, and regulators has received such
development during recent years that there can be no problem so
difficult that it cannot be solved by experience and originality. Basin
irrigation allows of the thorough development of countries whose streams
have short and turbid floods which precede a fairly cool season; whether
such irrigation be the stately irrigation of the Nile Valley, perfected
by the science and experience of 7,000 years; or the less perfect, but
still highly developed and river-fed tank systems of Madras; or the
primitive, but effective basins of Bundelkund, where the impounded water
irrigates the crops on the down-stream sides of the basins for one
season, and then allows of the basins themselves being dried and
cultivated in the next.
The Nile in high flood rises 10 metres above its bed, in a mean flood 9
metres and in a poor flood 7¹⁄₂ metres. The beds of the main basin
canals are about 4¹⁄₂ metres, and the cultivated land at the river’s
edge about 9 metres above the river-bed. The basins have an average area
of 7,000 acres. Where the valley is narrow, they average 2,000 acres
each, and where it is wide 20,000 acres; while some of the tail basins
are 40,000 acres in extent. Each canal has about seven or eight basins
depending on it, of which the last is always the largest. There are
masonry regulators at the canal heads, at each crossing of the cross
banks, and at the tail escapes into the river. In the more perfect
basins the canals and escapes syphon under one another and overlap and
supply each other’s deficiencies, so as to meet the requirements of
every kind of flood which Egypt can experience. Colonel Ross’s work on
the basin irrigation of Egypt is a monument of patient observation and a
storehouse of information. Some of the canals like the Sohagia on Plate
XIV are veritable rivers, discharging 450 cubic metres per second; but a
good average canal discharges 30 cubic metres per second. The largest
canal has a width of 75 metres, while the average width is 9 metres.
Good basin canals discharge in an average year one cubic metre per
second per 700 acres. Forty-five days suffice for a perfect irrigation.
The cost of providing basin irrigation in Egypt for basins of 10,000
acres may be taken at £3 per acre thus made up:--Banks, £1·50.; canals,
£·75.; masonry works, £·50.; and bank protection, £·25. If the basins
are under 5,000 acres, the cost will be nearly double this. The annual
cost of maintenance is £·10 per acre; while the lands themselves are
rented at £3 per acre. In well irrigated basins no manures are needed,
and alternate crops of cereals and legumins have been reaped for
centuries without the land having been exhausted in any way whatever.
Where the subsoil water is good and double cropping resorted to, then
manures have to be applied.
29. =Perennial Irrigation.=--The foundation-stone of the conversion of
the whole of Egypt from basin to perennial irrigation was laid by
Mehemet Ali in 1833, when he began the construction of the Barrages
across the Nile branches north of Cairo. These weirs were intended to
raise the summer level of the Nile by 3 metres. As the ordinary summer
level of the Nile was 1.50 metres above its bed, the weirs were expected
to raise it 4.50 metres above the Nile bed. The old basin canals had to
be considerably deepened to take in the summer supplies; while in other
parts new perennial canals were dug. Perennial irrigation requires
canals capable of discharging 1 cubic metre per second per 3500 acres,
as against 700 acres for basin irrigation. Some of the perennial canals
are very capacious. The two largest discharge 700 and 450 cubic metres
per second respectively. There are no artificial canals in the world
like them. All the canals are liberally provided with regulators and
locks. The energies of the Irrigation Department during the last ten
years have been chiefly directed to the provision of sufficient drains
to meet that over-saturation of the soil, which all but the best
regulated perennial irrigation invariably entails. After many years’
experience in India and Egypt, we are convinced that the construction of
drains and escapes should precede, and not follow the canals. It seems
fatuous for engineers to be always over-saturating and half-ruining tens
of thousands of acres of low-lying lands, during the improvement of
hundreds of thousands of acres of high-lying lands, when it would be
perfectly easy, with a little foresight, to secure all the advantages
without piling up disadvantages. The drains have generally one-third the
capacity of the canals. Dry crops require 1 cubic metre per second per
3500 acres; and rice requires the same per 2000 acres. The drains in
dry-cropped lands provide for 1 cubic metre per second per 10,000 acres,
and in rice lands 1 cubic metre per second per 6000 acres.
[Illustration: PLATE XIX.
PERENNIAL CANAL SYSTEM OF LOWER EGYPT
Lith. Sur. Dep. Cairo.]
While basin irrigation is followed by the winter crops of wheat, beans,
clover, barley, flax, lentils, vetches and onions, perennial irrigation
allows of all the above winter crops and in addition the summer crops of
cotton, sugar-cane, oilseeds, gardens and orchards. It will readily be
understood that all this double cropping necessitates a very free use of
manures.
It would be a healthy innovation indeed, if the provision of suitable
manures were to be considered as an essential part of a project for
providing perennial irrigation. The day is not far distant, I believe,
when governments which provide irrigation works will also provide
manures, and sell the water and the manures together, one being as
essential as the other; I know well, from observation, that a
well-manured field needs only half the water that a poorly manured field
does; and in years of drought and scarcity manures almost take the place
of irrigation. Why should there not be a manure-rate as well as a
water-rate? Here in Egypt, the numerous ruins of old-world cities have
hitherto provided manure for a great part of the perennially irrigated
lands; but these are being fast worked out, and other sources must be
sought for. Farm-yard manure will never suffice for the intense
cultivation in this country. In connection with this subject, I can
recommend the study of a remarkably able paper on “Nile Cultivation and
Nitrates,” read by Mr. J. B. Fuller, C.I.E., before the Agricultural
Society of England, and embodied in the 3rd Series, Vol. VII., Part 4,
1896. Egypt possesses, in the vicinity of Luxor, natural beds of
nitrates of unlimited extent, which come down to the river’s edge. These
nitrate beds have been used from time immemorial, but were brought to
the notice of the general public by Mr. Floyer. They contain only about
6 per cent. of pure nitrates, but as they are on the edge of the Nile,
in a perfectly cloudless and very dry country, it might be possible,
with the aid of the plentiful supply of water always at hand to
profitably extract pure nitrates. The demand for nitrates is without
limit in the Nile Valley, as Nile water, though rich in everything else,
is exceedingly poor in nitrates.
The perennial canals and collateral works have cost £4.50 per acre, and
the maintenance charges are £·10 per acre. The perennially irrigated
lands are let at £5 to £8 per acre per annum as against £3 to £5 for the
basins lands.
30. =Flood protection in Egypt.=--The Nile during high floods is
considerably above the level of the country, which is protected by
embankments stretching from Assouân to the sea. In Upper Egypt, a very
high flood is one metre above the country; in Middle Egypt it is 2
metres, and the same on the Rosetta branch of the Nile. On the Damietta
branch it is 3·50 metres in places.
In parts of Upper Egypt, but nearly everywhere in Lower Egypt, the Nile
on curves is protected by stone spurs. These spurs contain each from
4,000 to 250 cubic metres. They are very effective where the Nile bank
has been well thrown back below them to a distance of some 50 metres on
a length of at least 100 metres. This allows the waters of the flood to
swirl harmlessly in whirlpools below the spurs while the banks are far
removed from their action.
When we first came to Egypt, we found that the policy was to spread the
flood into as many channels as possible and protect the whole of them
with tens of thousands of corvée, in addition to the corvée on the Nile
banks. We changed that and concentrated our energies on the Rosetta and
Damietta branches.
In 1861, 1863, 1866, 1869, 1874, and 1878 the Damietta branch was badly
breached, There has been only one serious breach on the Rosetta branch,
and that was in 1863. The great breach of 1878 on the Damietta branch
was attended with serious loss of life; but far more serious was the
breach of 1863 on the Rosetta branch not far from its head. The whole
western half of the Delta proper was swept by the river, and as the
canals there have not got good high banks, the people had no place of
shelter to flee to and were drowned in very great numbers. The same
thing would happen again if a breach were to occur now, only the damage
would be far more serious. The country is covered with villas and rich
plantations and the low lands to the very edges of Lake Borrilos are
being reclaimed and inhabited. The loss of life which would occur
nowadays would be truly appalling. A breach anywhere within 100
kilometres of the Barrage on the east bank of the Rosetta branch or the
west bank of the Damietta branch during a very high flood would be a
national disaster.
The terror reigning over the whole country during a very high flood is
very striking. The Nile banks are covered with booths at intervals of 50
metres. Each booth has two watchmen, and lamps are kept burning all
night. Every dangerous spot has a gang of 50 or 100 special men. The
Nile is covered with steamers and boats carrying sacks, stakes, and
stone; while the banks along nearly their entire length are protected by
stakes supporting cotton and Indian corn stalks, keeping the waves off
the loose earth of the banks. In a settlement of a culvert in the Nile
bank north of Mansourah in 1887 I witnessed a scene which must have once
been more common than it is to-day. The news that the bank had breached
spread fast through the village. The villagers rushed out on to the
banks with their children, their cattle, and everything they possessed.
The confusion was indescribable. A narrow bank covered with buffaloes,
children, poultry, and household furniture. The women assembled round
the local saint’s tomb, beating their breasts, kissing the tomb, and
uttering loud cries, and every five minutes a gang of men running into
the crowd and carrying off the first thing they could lay hands on
wherewith to close the breach. The fellaheen meanwhile, in a steady,
business-like manner, plunged into the breach, stood shoulder to
shoulder across the escaping water, and with the aid of torn-off doors
and windows and Indian corn stalks, closed the breach. They were only
just in time. This is the way the fellaheen faced a breach. And this is
how the old Governors of Egypt faced them. During the flood of 1887 I
complimented an official on the Nile bank, whose activity was quite
disproportionate to his apparent age. He told me that he was a
comparatively young man, but he had had charge of the Nile bank at Mit
Badr when the great breach occurred in 1878, and that Ismail Pasha had
telegraphed orders to throw him and the engineer into the breach. He was
given 12 hours’ grace by the local chief, and during that interval his
hair had become white; subsequently he was pardoned. These were the
senseless orders which used to petrify officials into stupidity.
The following estimate was made by me of the cost of protecting the
Delta proper between the two branches of the Nile during the high flood
of 1887:--
Cost of protection for 432 kilometres of bank or 1,200,000 acres of
cultivation:--
{Sand bags 60,000 @ £ ·03 = £ 1,800
_Materials_ {Stone 5,000 @ „ ·50 = „ 2,500
_paid for_ {Stakes 55,000 @ „ ·06 = „ 3,300
--------
£ 7,600
========
{Camel loads of stalk for 42 kilometres,
_Materials_ { 14,000 @ £ ·15 = £ 2,100
_not paid for_ { --------
Total materials £ 9,700
========
15 engineers @ £80 = £ 1,200
Unpaid corvee, 1,374,079 men @ £ ·03 = „ 41,222
========
Total labour £ 42,422
========
Total materials and labour £ 52,122
This works out to £120 per kilometre of bank, or £·045 per acre of land
protected. It is a very cheap insurance.