The tributaries of the Nile.
9. =Lake Victoria Nyanza.=--Lake Victoria, the true source of the Nile,
lies on the Equator, and fed by abundant rains and numerous streams,
discharges its surplus waters over the Ripon Falls, and gives birth to
the Victoria Nile. Its most important feeder, the Kagera, whose
southernmost tributary rises in the Kangosi hills 2000 metres above sea
level in south latitude 4°, has a length of some 600 kilometres. The
direct line across the lake from the mouth of the Kagera to the Ripon
Falls is 220 kilometres, so that in academical language the length of
the Nile at the Ripon Falls is already 820 kilometres. Lake Victoria
lies 1129 metres above sea level, and has an area of 60,000 square
kilometres; though until the parallels of longitudes are definitely
settled, the lake may be credited with an area of between 60,000 and
65,000 square kilometres, constituting it the largest fresh water lake
in the old world. Its waters are beautifully clear and perfectly sweet.
The depth of the lake is not great and it is covered with many islands.
The greatest depth found by Commander Whitehouse in the northern half of
the lake has been 73 metres, while the bays are shallow. The northern,
southern and eastern shores of the lake, as described by Sir William
Garstin, are generally clear, while the western shore, especially at the
mouth of the Kagera, is flat, marshy and covered with papyrus. The
country surrounding the lake is undulating or hilly and rises to a
height of 700 metres above the lake at the south-east corner. The rocks
are generally granites, chrystalline schists and quartzites, etc. The
hills are covered with red clay and marl on the higher lands, while the
valleys consist of a rich black loam.
The catchment basin of the lake is 244,000 square kilometres of which
60,000 are water. Most of the important streams feeding the lake
traverse extensive marshes and swamps and must lose a great part of
their waters by evaporation. According to Capt Lyons (Appendix III of
Sir William Garstin’s report), the climate of the lake basin is
typically that which is known as equatorial; two rainy seasons and two
dry seasons make up the year, the rains coinciding more or less with the
equinoxes and the dry seasons with the solstices, except that the second
minor rains are delayed about 1 to 2 months after the autumn equinox. As
Capt. Lyons hopes soon to publish a monograph on the meteorology of the
Nile valley, I shall say little about the details of rainfall of the
different catchment basins, contenting myself with broad principles and
main features. March, April and May form the greater rainy season, and
October, November and December the lesser. The rainfall of the former
season may be considered twice as heavy as that of the latter, but it is
the latter which practically decides the height of the lake in the
following year. This, according to Capt. Lyons, is due to the fact that
in the summer months, when the rainbelt lies to the north of the lake,
the dry south winds must blow across the lake basin even though the
diurnal reversal of winds on the lake is not mastered by them. These dry
winds greatly increase the evaporation, and there is a marked diminution
of the water between July and November, which must be primarily due to
the increased evaporation.
[Illustration: PLATE III.
RIPON FALLS
PLAN AND SECTION
Scale 1 : 6.000
Lith. Sur. Dep. Cairo.
Victoria Nile upstream of Ripon Falls]
The rainfall in the catchment basin may be taken as 1250 millimetres per
annum on the average. As the evaporation off the lake is probably the
same, the area of the lake may be left out of the catchment altogether.
The balance of the catchment basin amounts to 184,000 square kilometres,
on which there is a mean annual rainfall of 230 cubic kilometres. The
mean discharge of the Victoria Nile over the Ripon Falls appears to the
approximately 580 cubic metres per second or 18 cubic kilometres per
annum. This represents about ¹⁄₁₂ the mean rainfall. The greatest
discharge of the lake seems to be about 850 cubic metres per second and
the lowest 450. As the lake has risen in a single year 80 centimetres,
which represents an increase of water of 48 cubic kilometres, and has
fallen 60 centimetres which represents a decrease of water of 36 cubic
kilometres, it will be seen that the discharges from the lake are
factors of less importance in determining the level of the lake than the
heavier rainfall and diminished evaporation in a year of good rain, and
the lighter rainfall and increased evaporation in a year of poor rain.
The great function of Lake Victoria in the economy of the Nile supply is
the insuring of a nearly constant discharge of water into the Victoria
Nile, and providing much of the evaporation which comes down in the
catchment basin itself in the shape of rain.
The principal feeders of Lake Victoria are the following streams:--
on the north (1) Lukos or Yala,
(2) the Nzoia 250 kilometres long,
(3) the Sio.
on the east (1) the Nyando,
(2) the Inyayo,
(3) the Gori,
(4) the Mara Dabash,
(5) the Rawana.
on the south (1) the Symiya,
(2) the Moame.
on the west (1) the Lohungati,
(2) the Kagera, with its branches the Nyavarongo, the
Akanyaru and the Ruvuvu, with a maximum length of 600
kilometres and a discharge varying between 140 and
some 600 cubic metres per second.
(3) the Ruizi with a length of 280 kilometres traversing
much marshy ground in its course.
and (4) the Katonga 250 kilometres long.
The northern and western feeders are generally perennial streams, while
many of the southern and eastern are torrents.
10. =The Victoria Nile.=--From the Ripon Falls to Lake Albert, the
Victoria Nile has a length of 400 kilometres. The first 64 kilometres
are down a steep slope, in a stream varying from 300 to 500 metres in
width. Any project for a regulator at the Ripon Falls should contemplate
development of electricity for working a railway along these 64
kilometres. The next 237 kilometres are through a flat marshy land,
partly lake, partly swamps, but with the water never more than 4 to 6
metres deep. In this reach the Nile is navigable. This many-armed swamp
is known as Lake Choga, whose western end is traversed for some 80
kilometres by the Nile with a perceptible current. These large sheets of
papyrus and water, which cover an area of over 2000 square kilometres,
must cause as much loss by evaporation as they receive by direct
rainfall. The Victoria Nile leaves the lake in a broad stream some 900
metres wide, past Mruli station, on to Fowera. In the longitudinal
section on Plate II, I have considered Fowera as 1060 metres above sea
level, and the slope upstream of it as ¹⁄₂₀₀₀₀. From Fowera to the foot
of the Murchison Falls, the Nile falls 377 metres on a length of 68
kilometres, and then in the next 30 kilometres reaches Lake Albert.
Considerable quantities of floating pistea weeds pass down the Victoria
Nile from Lake Choga. They are well churned up between Fowera and the
Murchison Falls, but finally enter Lake Albert. It would be easy to
develop electricity to work a railway along these 68 kilometres.
[Illustration: PLATE IV.
CROSS SECTIONS of the NILE & its TRIBUTARIES
_Horizontal Scale 1 : 2.000_
_Vertical Scale 1 : 600_
Lith. Sur. Dep. Cairo.
No. 1. _Victoria Nile upstream of Ripon falls_
No. 2. _Kagera River within 10 km. of mouth_
No. 3. _Semliki River about 50 km. upstream of Albert Lake_
No. 4. _Albert Nile at Wadelai._
No. 5. _Asua River about 2 km. above junction with Nile._
No. 6. _Albert Nile at Gondokoro._
No. 7. _Albert Nile at Mongalla_
No. 8. _Albert Nile above Lake Nô_
No. 9. _Bahr el Ghazal 51 km. from mouth_
No. 10. _Bahr el Zeraf 20 km. from mouth_
No. 11. _Albert Nile 4 km. above junction with Sobat_
No. 12. _Sobat River at Doleib Hills_
No. 13. _White Nile 14 km. below Taufikia_]
The principal tributaries of the Victoria Nile are the following:--
On the right bank, the Gogonia, the marshy Kwania and Lenga, and the
Duki. And on the left bank; the lake-like Sensiwa; the Kafu with its
numerous feeders, large catchment basin but generally insignificant
discharge; and the Titi. The Uganda rivers are more like sponges than
rivers, and in all probability the tail of the Victoria Nile has a
discharge only slightly in excess of that at the head.
11. =The Semliki River.=--The Semliki river has its sources in Lake
Edward just south of the Equator and flows into the southern end of Lake
Albert, just as the Victoria Nile flows into the northern end. Lake
Edward with the addition of Lake Dueru has an area of some 2500 square
kilometres and lies about 965 metres above sea level. Its waters as
described by Sir William Garstin, are green in colour and brackish. The
Semliki river discharges the surplus waters of the lake, and may be
considered as having a discharge of 100 cubic metres per second as a
minimum and 400 cubic metres per second as a maximum. In some 120
kilometres of its length this river traverses the eastern end of the
Congo forest, and the day may not be far distant when this timber will
be floated down the Semliki, towed across Lake Albert and sent down the
Albert Nile to Gondokoro and Khartoum. The fall of the Semliki,
according to accepted levels is 285 metres in 260 kilometres. The
feeders of Lake Edward are the following:--
On the west, none.
On the south, the Rutshuru and Ruendu.
On the east, the Msalala, the Wampuna, the Chambura, and the Mpanga
which has its sources on the slopes of Ruenzori.
On the north, numerous glacier-fed torrents from the slopes of
Ruenzori, the Nyamgasha and the Dibirra. The dry season discharges of
all these rivers are small. The largest is under 10 cubic metres per
second. The flood discharges are considerable.
12. =Lake Albert Nyanza.=--Lake Albert has an area of 4500 square
kilometres and lies about 680 metres above sea level. We have left the
high lands of Uganda and are in the stifling heat of tropical Africa.
There are considerable deposits of salt along the east shore of Lake
Albert, as there are also around Lake Edward. According to Sir William
Garstin, the waters of Lake Albert are brackish near the shores, but
perfectly sweet and clear in the middle of the lake. It is due to the
waters of Lake Victoria that those of Lake Albert are sweet. The
catchment basin of the Albert Nile at its head where it leaves Lake
Albert is about 379,000 square kilometres of which 244,000 square
kilometres discharge into Lake Victoria. The rainfall over the
additional 135,000 square kilometres may be considered as 1250
millimetres per annum, with seasons similar to those on Lake Victoria.
The evaporation from Lake Albert must be greater than that from Lake
Victoria, but if we exclude the joint areas of Lakes Victoria, Albert,
Edward and Choga, and taking them as 70,000 square kilometres, consider
that their rainfall is equalized by their evaporation, there remains
from the 379,000 square kilometres of catchment basin about 309,000
square kilometres. An annual rainfall of 1250 millimetres means for
309,000 square kilometres a total rainfall of 380 cubic kilometres. The
discharges of Lake Albert may be taken as varying from 500 cubic metres
per second to 1100, with a mean of 800 cubic metres per second. This
latter figure represents in one year 26 cubic kilometres or ¹⁄₁₅th the
annual rainfall. We may compare with this the mean discharge of Lake
Victoria of about 580 cubic metres per second and ¹⁄₁₂th of the annual
rainfall of its catchment basin excluding the lake area.
A reference to Plate V will show how great is the regulating effect of
Lake Albert on the Nile. Owing to the fact that an increase in the
discharge of the Victoria Nile cannot pass down the Albert Nile before
the whole area of Lake Albert has risen, the floods of the Victoria Nile
are delayed nearly 5 months in their passage down the Albert Nile; a
rise of 1 metre on Lake Albert meaning an increased cube of
4,500,000,000 cubic metres. If this takes place in one year, it
represents an increased discharge of 150 cubic metres per second
irrespective of what passes down the channel of Lake Albert.
If it were considered necessary to insure 1200 cubic metres per second
as the discharge of the Albert Nile from the 15th January to the 15th
May, it would mean adding 400 cubic metres per second to the mean
discharge for 4 months, and deducting 200 cubic metres per second from
the mean discharge for the remaining 8 months. By storing the surplus
waters of good years by means of a weir capable of holding up 3 or 4
metres of water at the outlet of the lake, it would be possible to
insure this discharge every year during the four months which decide the
summer contingent of the White Nile to the Nile in Egypt during the
months of April, May, June and July.
[Illustration: PLATE V.
GAUGE & DISCHARGE DIAGRAM of LAKES VICTORIA & ALBERT
_Luba (subsequently Jinja) gauge, near the Ripon Falls, represents Lake
Victoria._
_Wadelai gauge (60 km. below Lake Albert) represents Lake Albert._
Lith. Sur. Dep. Cairo.]
The shores of Lake Albert are generally steep and barren, though in
places they are shelving and covered with papyrus, notably at the inlets
of the Semliki river and the Victoria Nile. The Lake is fairly deep and
admirably suited for a reservoir. At the outlet of the lake enormous
quantities of pistea weeds, especially in high floods, enter the Albert
Nile. The passage of these weeds through the future regulator of Lake
Albert will be an exceedingly interesting engineering problem.
The principal feeders of the lake are:--
On the north, the Victoria Nile.
On the east, the Waiga, the Wakki, the Hoima, the Wahamba, the Horo,
the Ngusi and Msisi, discharging between them under 20 cubic metres
per second in the dry season, though good streams in flood.
On the south, the Semliki; and no streams worth mentioning on the
west.
13. =The Albert Nile.=--The Albert Nile, or the Bahr-el-Gebel, has a
length of 1280 kilometres from Lake Albert to the mouth of the Sobat
river. For 218 kilometres, past Wadelai to Dufile, it has a broad stream
with a sluggish current as a rule, and covered with islands and papyrus
marshes. This reach of the Nile is navigable. The fall here must be very
little, and it may be considered as 8 metres. In high floods enormous
quantities of pistea weeds float down this reach of the Nile. Papyrus
and ambatch are very common along the shores and on the islands.
At Dufile begin the Fola rapids followed by numerous cataracts up to
Fort Berkeley. In this reach of 155 kilometres the river falls 223
metres. Sir William Garstin states that some of the falls have a width
of only 12 metres. The depth must be extraordinary, while the velocity
is terrific. The green water of the upper reaches is purified in its
passage through these cataracts. The rock is granite. If the regulator
for Lake Albert were constructed near Dufile, it should contemplate
development of electricity for working a railway along these 155
kilometres.
South of Dufile the principal tributaries of the Albert Nile are on the
right bank viz: the Achua and Umi. In the dry season they are dry, but
after rains they may add some 50 cubic metres per second to the river.
Between Dufile and Fort Berkeley many rivers flow into the Albert Nile.
The Asua, the Atappi, the Umi, the Karpetu, the Kweh and many others
from the right bank bring down water in flood well laden with sand. In
the dry season all but the Asua are dry. The left bank tributaries are
numerous but insignificant. The volume discharged by these streams in
the rainy season is very considerable, as will be seen if the discharges
at Gondokoro north of Fort Berkeley are compared with those at Wadelai.
They are between them capable of increasing the discharge of the Albert
Nile for short intervals of time by 1500 cubic metres per second. All
these streams are torrential. They rise and fall quickly.
From Fort Berkeley to Khartoum, the Albert and White Niles are
navigable.
From Fort Berkeley to Bor past Gondokoro on a length of 206 kilometres
the Albert Nile falls some 18 metres and has a good velocity and slope,
and though the river is divided into two and more channels, it is within
its banks and may be considered an ordinary river. The maximum discharge
is about 2600 cubic metres per second and the minimum 550. In high
floods the river scours out its bed and sides very considerably. The
real flat lands begin at Gondokoro a little to the north of Fort
Berkeley. The soil is light and sandy and capable of offering little
resistance to the stream. Between Gondokoro and Bor the Albert Nile can
lose some 30 per cent of its discharge when the river is high and
capable of overflowing most of the islands and a great part of the
valley. The main channel has a width of about 230 metres and depth of 3
or 4 metres when the discharge is below 600 cubic metres per second and
well within banks. The main tributaries of the Albert Nile in this reach
are on the east bank, the Kit, second only to the Asua, and the
Lokadero; and on the west bank a number of unimportant torrents which
however help to swell the river in flood.
From Bor to Ghaba Shambe on a length of 196 kilometres, the main stream
of the Albert Nile flows between banks lower than those further south
and more heavily inundated in flood, with a width of some 60 metres and
depth of water of 5 metres. According to Sir William Garstin, the grass
swamps end half way down this reach and the papyrus swamps begin. About
10 kilometres to the east of the main stream is another branch known as
the Atem river fed by artificially maintained and natural spills from
the main stream itself. These spills are kept open by the Dinkas living
along the Atem river. They were noted by Werne in 1842. The Atem river
at its tail apparently divides into two branches, of which one feeds the
Zeraf river and the other returns to the Nile at Ghaba Shambe.
Capt. Lyons has pointed out to me that all this course of the river is
extraordinarily like the course of the Mississippi south of Vicksburg,
with its severe curves and oxrings which correspond to the mayahs of the
Albert Nile. Such mayahs or lagoons can be seen in the last 20
kilometres of the Rosetta branch of the Nile. Placed as they are between
Bor and Ghaba Shambe, they mean that while south of Bor, the Albert Nile
has more or less formed its delta; north of Bor, the delta is in a more
embryonic stage, with probably the Atem river the more ancient of the
two streams. North of Ghaba Shambe, the Zeraf river leaves the Albert
Nile, and fed by the Atem Nile, takes off its water eastwards through
marsh and swamp to again tail into the Albert Nile below Lake No. About
30 kilometres further north is the cut made by Sir Samuel Baker to
enable him to enter the Albert Nile from the Zeraf river.
The real Sudd region lies between Ghaba Shambe and Lake No, on a length
of 380 kilometres. Between Fort Berkeley and Gondokoro, the flood as
well as the summer supplies are within banks. Between Gondokoro and Bor,
the summer supply is well within banks, but the floods overflow the
valley. Between Bor and Ghaba Shambe the summer supply is just within
banks, but the floods overflow freely. Between Ghaba Shambe and Lake No
the summer supply overflows the banks, and hence there result the
periodical barrings or sudds of the Nile by the floating vegetation so
common in this region. While the summer supply is within banks it can
insure a clear waterway; but when not only the floods but the summer
supplies ordinarily overflow the banks, the stream must be aided
artificially if it is to keep its waterway clear.
The ordinary width of the river south of Hillet-el-Nuer is between 50
and 60 metres, but in the reach of the old sudd blocks numbers 16 to 19
it diminishes in places to 25 metres, and in the reach blocked by sudd
block number 15 increases to 200. North of Hillet-el-Nuer, the width
varies from 60 to 150 metres, but the mean width may be taken as from 75
to 80 metres. The velocity is about 75 centimetres per second, which is
a good velocity for clear water; and Sir William Garstin remarks at one
place that since the sudds were cleared the channel of the Albert Nile
seems to be deepening and widening itself, and he states in another
place that the extent of overflow over the mayahs or side depressions is
decreasing.
With proper training works and dredging it should be possible to reduce
the length of the main channel of the Albert Nile between Gondokoro and
Bor from 175 kilometres to 160; between Bor and Ghaba Shambe from 206
kilometres to 145; and between Ghaba Shambe and Lake No from 380
kilometres to 305. Or the length of channel from Gondokoro to Lake No
might be reduced from 761 kilometres to 610. Some of the curves are
nearly complete circles, needing but little work to cut off extensive
lengths.
Between Ghaba Shambe and Lake No there were 19 sudd blocks of which all
but one were removed by Major Peake, R. A., and Lieut. Drury, R. N., in
1900 and 1901. Their positions are indicated on Plate VI. South of
Hillet-el-Nuer is sudd block No. 15, the only one remaining to be
removed. Owing to this block, the Albert Nile leaves its true channel,
which is from 5 to 6 metres deep, and, on a length of 43 kilometres,
follows a series of mayahs, pools and marshes with a depth of from 1¹⁄₄
to 2 metres. The original channel was closed by a boat laden with ivory
sinking in the true channel during the Dervish domination. The boat has
been found, the ivory recovered and the work of sudd clearing commenced,
but the work has not yet been completed.
The maximum discharge of the Albert Nile at Hillet-el-Nuer may be taken
as 450 cubic metres per second, and into Lake No as 320 cubic metres per
second. The water of the river is dark-coloured and contains no
sediment. Very little ambatch is met with north of Ghaba Shambe.
Between Ghaba Shambe and Lake No on the left bank, in the first 120
kilometres, three channels carrying very appreciable quantities of water
flow into the Albert Nile. These are considered to be the tails of the
river Yei. At Hillet-el-Nuer, about 170 kilometres north of Ghaba
Shambe, a branch takes off from the west side of the Albert Nile, known
as Gage’s channel, with 35 metres of clear waterway, 1 metre depth and
0·60 metre per second velocity, discharging 20 cubic metres per second.
This stream flows westwards and is lost in the swamps. On the right
bank, downstream of Ghaba Shambe, are the two heads of the Bahr Zeraf,
one natural and the other artificial made by Sir Samuel Baker. About 90
kilometres north of Ghaba Shambe a few spills take water towards the
Zeraf river.
[Illustration: PLATE VI.
THE ALBERT NILE.
FROM GONDOKORO TO THE SOBAT JUNCTION
Scale 1 : 2,000,000
Lith. Sur. Dep. Cairo.
Part of Albert Nile
_South of Sudd No. 15_]
From Lake No to the Sobat mouth, on a length of 134 kilometres is the
tail reach of the Albert Nile. The Albert Nile flows into Lake No in its
south-eastern corner and leaves it on its east side. On the west side
the Gazelle river flows into the lake. Lake No has an area of some 20
square kilometres in times of low supply and 100 square kilometres in
flood. In low supply the depth is between 1·50 and 2·50 metres. In the
reach between Lake No and the Sobat mouth, the river is very fairly
straight; the summer channel is about 170 metres wide and as a rule
about 5 metres deep upstream of the mouth of the Lolle, though in one
place about 8 kilometres from Lake No it becomes only 50 metres wide for
a short distance. Between the tail of the Lolle river and the mouth of
the Sobat river, the summer width widens out to about 400 metres with 3
metres depth of water. However extensive the marshes may be, the high
land forming the limit of the inundation is everywhere in this reach
visible from the main stream. The Gazelle river, which flows into Lake
No, has a discharge varying from 0 to 40 cubic metres per second. The
Lolle river which flows in on the left bank upstream of the Sobat mouth
is probably an arm of the Albert Nile or an overflow of the Gazelle and
has a discharge varying from 0 to 40 cubic metres per second. On the
right bank, the Zeraf river flows into the Albert Nile, with a discharge
varying from 30 to 160 cubic metres per second. The Megahid river flows
in 30 kilometres below the tail of the Zeraf river and adds an
undetermined quota of water.
At its junction with the Sobat river, the Albert Nile discharges from
300 to 450 cubic metres in summer; it does not discharge much more in
flood as the waters of the Sobat river in flood hold up the Albert River
and make it overflow the low lands up to Lake No and beyond for a depth
of 3 metres in high floods. This reach of the Nile is a flood reservoir,
which empties itself ordinarily by the end of winter.
14. =The Gazelle River.=--The Gazelle river, which flows into Lake No,
has a catchment basin of 240,000 square kilometres, with an annual
rainfall of 75 millimetres; and an additional catchment basin of 230
square kilometres with an annual rainfall of 30 millimetres; and yet the
river discharges nothing in summer and about 40 cubic metres per second
in flood. It is the most extraordinary river in the world, often blocked
by sudd and invisible. It has practically no banks in flood or in times
of low supply, while the waterway varies in width from 6 metres to 90
and in depth from 2 metres to 6 metres. It makes its way between
interminable marshes of papyrus and water grasses. The Gazelle river is
a deltaic river in a still more embryonic stage than the Albert Nile
north of Ghaba Shambe. It, however, performs one good function. It keeps
the swamps of the Sudd region full of water, year in and year out; and
without it, the water of the Albert Nile would doubtless be lost by
percolation in the Sudd region and the White Nile be left high and dry
for 3 months every year.
Schweinfurth was the first to ascend and describe this river and its
tributaries. Beginning from the east, its principal tributaries
are:--the Rohl, the Dyow, the Tondy, the Kit, the Dyûr, the Dembo, the
Humr and the Bahr el Arab. With courses of between 450 and 750
kilometres in length, the tributaries fall from 500 to 700 metres in
their upper courses of from 300 to 500 kilometres, and in their
remaining courses they traverse swamps. Certain of the tributaries may
be discharging 10 cubic metres per second in summer and 250 cubic metres
per second in flood, but the main stream of the Gazelle seems never to
add more than 40 cubic metres per second to the Albert Nile. The whole
of the water is evaporated from the weeds, papyrus, watergrasses and
open sheets of water which cover a desolate area of 70,000 square
kilometres. Evaporation and rainfall balance each other. If the
«Singhara» or Indian water nut could be induced to grow in this waste of
waters, some profit might be got out of them.
15. =The Bahr Zeraf.=--The Bahr Zeraf is the right hand branch of the
Albert Nile which leaves the latter river north of Ghaba Shambe and
joins it again midway between Lake No and the Sobat river. It is fed
largely by the escape water of the Atem river brought down in a
traceable channel and in flood by torrents from the hilly region east of
Gondokoro. Beginning with a series of marshes and swamps, it gradually
establishes its right to be called a river and finally after a tortuous
and meandering course of about 270 kilometres tails into the Albert
Nile. In its lower reaches it is about 50 metres wide and from 2 to 4
metres deep in summer and 6 to 8 metres deep in flood. Its discharges
vary from 30 cubic metres per second in summer to 160 cubic metres per
second in flood. In its lower reaches the banks consist of solid earth,
proving that at one time it carried water other than that brought down
by the Albert Nile.
16. =The Sobat River.=--This river drains 156,000 square kilometres
lying between the catchment basins of Lake Rudolf and the Blue Nile. The
rainfall in the mountainous region of Gallaland is plentiful and
especially heavy in autumn, and were it not for the extensive lakes and
marshes in its middle course, it would be a torrent in flood. Regulated
and restrained by the lakes and marshes, this river has an
extraordinarily even rise and fall, as a reference to Table 24 will
certify. It is unfortunate that the Nasser gauge has been read so
interruptedly. The Doleb Hilla gauge is in the back water of the Albert
Nile and not very reliable. The discharges of the last four years have
varied from 40 cubic metres per second in low supply to 1000 cubic
metres in flood, though there have been years when the discharges have
fallen to zero in summer and when the flood must have exceeded 1500
cubic metres per second. April is the month of low supply and November
of maximum flood.
In its last 50 kilometres, the river has a deep, well defined channel
between high banks, which are never topped in the highest floods. The
width of waterway is about 110 metres and the depth 7 metres in summer
and about 10 to 11 metres in flood.
The principal tributaries of the Sobat are the Baro from the north-east
and east, and the Akobo and Pibor from the south-east and south. All the
tributaries meet and form extensive swamps from which the Sobat has its
origin. The village of Nasser is situated on the Sobat near its origin.
A gauge has been erected here.
17. =The Sudd region.=--The Sudd region of the Albert Nile lies north of
Ghaba Shambe and corresponds to that part of the river where not only do
the floods overflow the banks, but the summer supplies can do so in many
places. It is the delta of the river in a very embryonic stage. There
are two main branches to the river, the Albert Nile proper and the
Zeraf, which have both been already described. Both these rivers are
liable to be blocked by sudd or blocks of living vegetation. These
blocks are sometimes as much as 5 metres thick and capable of turning
nearly the whole supply of the river out of its course. They are formed
of papyrus, weeds and watergrasses, which grow on the half sandy half
peaty banks of the lagoons and marshes traversed by the river, and
which, under the double action of a rising flood and strong winds, are
torn up and driven into the channels wherever they are confined in
width, and there jammed into solid masses of floating weeds, filling the
whole width of the river, very nearly the whole depth, and sometimes
over a kilometre in length. In addition to the local weeds and grasses,
there are always at hand in high floods dense masses of pistea weeds
which have come from the upper waters of the Albert Nile south of
Dufile. While the sudd floats it is not so bad as when it sinks, as it
has done at block No. 15 north of Gaba Shambe, where the Nile has left
its course for 37 kilometres owing to sunken sudd. When the sudd sinks,
its becomes putrid and especially loathsome.
The Sudd region is unmistakably, as Lombardini pointed out years ago, an
old lake which has silted up and become full of peat and sand deposits.
At one time the lake must have had an extreme length of 400 kilometres
and width of 400 kilometres and been a larger sheet of water than lake
Victoria. The Sobat river flowed into it, and the Blue Nile may have
flowed backwards up the bed of the present White Nile for tens of
thousands of years. The north-east corner has been better filled with
deposit than any other part.
The dense masses of papyrus and water-grasses which shut out the horizon
in every direction intimidated the expedition sent up the Nile by Nero,
and it returned northwards without having accomplished anything. From
Nero’s time to that of Mehemet Ali little was known of these regions.
Mehemet Ali made a determined effort to discover what lay beyond these
inhospitable regions, and sent up a well-equipped expedition under
D’Arnaud.
One of the earliest descriptions of the Nile between the fifth and tenth
parallels of latitude is by Werne, who accompanied D’Arnaud’s expedition
sent by Mehemet Ali in 1840-1841. The expedition found the channel of
the White Nile and Albert Nile easily navigable between December and
March. The Albert Nile between 7° and 9° N. lat. had apparently a mean
width of 120 metres, depth of 5 metres, and velocity of about 60
centimetres per second, giving a discharge of some 400 cubic metres per
second. In this first description of the river the fact that strikes one
most forcibly is the omission of the Bahr Zeraf. Neither the inlet nor
the outlet are mentioned, though the Sobat, the Gazelle, and numerous
insignificant streams are minutely recorded. Practically the whole of
the water was confined to one stream, and that a good one. The water
level in winter was found to be some 50 centimetres below the general
level of the berm, and about 60 centimetres above this level in flood.
The swamps contained offensive and fetid water, which mixed with the
waters of the rising flood and helped to pollute the stream on the first
rise of the river. Between the river and the swamps in its southern
reaches were numerous cuts and openings, some natural and some
artificial, made by the aborigines for fishing purposes. While
traversing the swamps, the waters of the river in flood lost their silt
and became quite clear. On page 100 of Vol. II of Werne’s work there is
this significant sentence: “The report that the natives below (i.e. in
latitude 5° to 7°) had blocked the river to cut off our retreat, turned
out to be unfounded.” From the above it will be noticed that the
aborigines in 1840-1841 spoke of their ability to block the course of
the river, while the training works in the side channels and spills for
fishing purposes were described as solid works regulated by rows of
strong stakes driven into the ground.
Between 1841 and 1863 the expeditions up the Nile considerably
increased, while the aborigines were being brutally treated by the slave
traders. What could be more natural than that, as a measure of
protection, the aborigines should have widened and deepened the side
channels and spills which took off from the river between latitudes
5¹⁄₂° and 7¹⁄₂°, so that they might escape from the traders.
Subsequently, when the main river was patrolled by Government boats, the
slave-traders themselves used these side channels for prosecuting their
traffic. All the channels and spills tailed into the Bahr Zeraf, which
now began to form an appreciable stream, and which was navigated over
the lower part of its course by Petherick between 1853 and 1862. The
Bahr Zeraf was however always described as sudded, while the Albert Nile
was open to navigation. This action of dissipating the waters of the
river went on increasing till 1863, when there occurred a very high
flood indeed; the floating weeds brought down from the south were
excessive, the waters escaped everywhere from the main stream, while the
floating masses of creepers were confined by the grasses and papyrus to
the main channel, and sudded it downstream of Lake No.
On ascending the White Nile and Albert Nile in January 1863, Sir Samuel
Baker found the passage clear to the south. On returning in April 1865,
he found the sudd of the flood of 1863 still in the Albert Nile
downstream of Lake No. The sudd was 1000 metres long and had a passage 3
metres wide cut through the middle of it, down which the river ran like
a mill race.
In February 1869, Dr. Schweinfurth and his party, on their way to the
Gazelle, took six days to get through this sudd, though the main
obstruction was now only 200 metres long. In July 1872, Dr. Schweinfurth
on his way back found the sudd to the downstream of Lake No as before,
and described the opening through it as “a narrow stream of water which
rushed along as a wild brook. The depth of the fairway varied from 2 to
3 metres, and the boat nowhere touched the bottom.”
In February 1870 Sir Samuel Baker found the sudd in the Albert Nile
impossible for his expedition of heavily laden boats and steamers. He
found the Zeraf sudded in its southern 100 kilometres, and tried to cut
his way through but failed. And yet the slave traders had means of
getting slave boats down the Bahr Zeraf (“Ismailia” pages 61, 62 and
29). Baker returned in January 1871 to the Zeriba Kutchuk Ali on the
Bahr Zeraf and had before him the 100 kilometres of sudded channel. With
the aid of 1200 men he completed the work by March 13. The final
operation was a canal through stiff clay 600 metres long (known to-day
as Baker’s cut). The fall from the Albert Nile into the Bahr Zeraf was
so great that, in order to get the boats and steamers across the final
distance, Baker made a dam 120 metres long across the Zeraf by means of
a double row of piles, sand bags and fascines of the tall grasses. He
thus secured the necessary depth of water, and the flotilla sailed into
the Albert Nile. On his way back in June 1873, he thus describes the
appearance of the head of the Ziraf river where he had made the cut in
March 1871:--
“On arrival at the Bahr Zeraf cut, we found that the canals which we had
formerly cut were much improved by the force of the stream. Although
these passages were narrow, they had become deep and we progressed with
comparatively little trouble.” The rest of the journey down the Bahr
Zeraf was easily performed.
In January 1874, when the river was low, the sudd in the Albert Nile was
removed by Ismail Pacha Ayoub, Governor General of the Soudan.
From 1874 to 1878, while Gordon was Governor General, the Albert Nile
was clear of sudd, but the wide stream of 1840 had dwindled down to a
clear waterway free of weeds on a width of 6 metres over long reaches.
The escape of water down numerous spills had deprived the Albert Nile of
the power of keeping its channel clear and when the heavy flood of 1878
came down, the river was sudded.
In 1880 Gessi was blocked in the Bahr Gazelle. The sudd in this Bahr was
cut by Marno, who also cut the sudd in the Albert Nile in April 1880.
Emin Pasha mentions the fact that the Albert Nile was free of sudd and
navigated from 1880 to 1883. In 1884 he states that no steamers reached
Lado, but he attributed that to the Mahdi’s rebellion.
During the early years of the Mahdi’s and Khalifa’s rule there was no
sudd. In the Khalifa’s time a boat laden with ivory sank in the stream
where sudd block No. 15 is, south of Hillet-el-Nuer, and caused the
block to form.
In 1898 Lord Kitchener found the Albert Nile sudded south of Lake No,
and in March 1899 Sparkes bey, of the Egyptian Army, steamed up the Bahr
Zeraf to within 30 kilometres of its head.
At the same time Sir William Garstin thought the Bahr Zeraf a stronger
stream than the Albert Nile.
Descending the Albert Nile from Uganda, Colonel Martyr found the Albert
Nile sudded 30 kilometres north of Ghaba Shambe.
In 1900 and 1901 Major Peake, C. M. G., R. A., and Lieut. Drury, R. N.,
removed sudd blocks Nos. 1 to 14, and 16 to 19, between Lake No and
Ghaba Shambe. There now remains only block No. 15 south of
Hillet-el-Nuer.
The condition of the channel to-day has been described under the heading
of the Albert Nile. It is a very fair channel except at the diversion
round block No. 15, which Sir William Garstin is very eager to see
removed.
18. =The White Nile.=--The White Nile stretches from the Sobat mouth to
Khartoum and has a length of 838 kilometres and very little fall. It
everywhere bears traces of having been the channel of the Blue Nile when
in ancient times the Gebel-Royan hill had not been cut through by the
Nile, and the Blue Nile itself flowed south into the great lake which is
to-day the sudd region of the Albert Nile. If the Blue Nile discharged,
as it does to-day, about 2500 cubic metres per second throughout the
year, the Sobat 600 cubic metres, the Albert Nile 1000, the Gazelle
tributaries 700, and the rainfall on the lake itself was 1 metre per
annum, while the evaporation was 2¹⁄₂ metres, (all reasonable figures),
the water entering the lake was 300 cubic kilometres per annum and the
evaporation was the same, provided the lake had an area of 120,000
square kilometres, which is, moreover, reasonable when we examine the
plan. During the whole of this period, the valley of the Nile in Egypt
received its water from the Atbara alone.
The waters of the Sobat river in flood give its name to the White Nile.
At Tewfikieh, near the head of the White Nile, is a gauge. For the first
500 kilometres the river is described by Sir William Garstin as having a
waterway of from 300 to 500 metres in width with numerous islands. The
depth of water in summer is 5 metres and 7 metres in flood. On either
side of the waterway is a low ridge swamped in flood, and beyond that on
either side is a deep depression, deep in the centre and rising to the
ridge on one side and to the high land and forest on the other. Each
depression may be 3 kilometres in width where it is wide and a few
hundred metres where it is narrow, so that the flooded valley may have a
width of 6 kilometres in places. The ridges are about 3 metres wide, and
broken by openings through which the water passes in and out of the side
marshy depressions. The depressions are covered by a dense growth of
reeds and papyrus. When the reeds are burnt one can traverse the marshes
on foot. South of Kaka (200 kilometres north of the Sobat mouth) the
depressions are lower than they are further north, which, to me, goes to
prove that the channel of to-day is formed within the channel of old
days when the Blue Nile was flowing south into the Sudd region. At
Gebelain (250 kilometres north of Kaka) the side depressions contract
and the forests come nearer the river. At the Abu Zeid ford, 50
kilometres further to the north, is a serious obstacle to navigation
when the river is low, in the shape of a very broad sheet of shingle
studded thick with fresh-water oysters. This bar is 6 kilometres long,
as hard as stone, and has in very low summer supplies a depth of water
over it of only 50 centimetres. It is a wonder that a channel has not
been blasted through it. The swamping now visibly decreases and the
width of the river varies from 700 to 900 metres. Some 25 kilometres
north of Abu Zeid the papyrus and sudd grasses disappear, and though
there is flooding there are no swamps. We have now some well cultivated
islands in the river for the negroes have come to an end and the Arabs
inhabit the country. The summer channel may be now considered as 700
metres wide and the flood channel as 1300 metres. The summer depth of
water is 4 metres. At Duem, 220 kilometres south of Khartoum, the width
of the channel widens from 900 to 1000 and further north to 1500 metres,
and finally to 3000 metres. We are in a lake rather than in a river, and
in flood when the waters of the Blue Nile travel 300 kilometres up the
White Nile, and wait for a fall in the Blue Nile to discharge themselves
into the Nile, we are indeed in a pulsating lake and not in a river. It
must have been in September, when the discharge of the Blue Nile had
fallen from some 11,000 to 6,000 cubic metres per second, and the
stored-up waters in the valley of the White Nile were forcing themselves
down to take the place of those cut off from the Blue Nile, that Linant
Pasha took his discharges of the Blue and White Niles and found them
some 6000 and 5000 cubic metres per second respectively. The same remark
may be made about M. Chélu’s discharge of the White Nile at Khartoum of
4000 cubic metres per second in September 1876 and mentioned in his book
“_Le Nil, le Soudan, l’Égypte_,” page 17.
[Illustration: PLATE IX.
CROSS SECTIONS OF THE NILE & ITS TRIBUTARIES
_Horizontal Scale 1 : 2.000_
_Vertical Scale 1 : 500_
Lith. Sur. Dep. Cairo.
No. 14. _White Nile at Duem._
No. 15. _Blue Nile at Lake Tsana_
No. 16. _Blue Nile at the Bridge 30 km. from Lake Tsana_
No. 17. _Blue Nile at Wad Medani_
No. 18. _Blue Nile at Khartoum_]
In 1903 the minimum discharge of the White Nile at its head was 380
cubic metres per second in April and the maximum discharge was 1470
cubic metres per second in December. Table 24 gives the behaviour of the
river. The minimum discharge of the White Nile at Khartoum may be taken
as 300 cubic metres per second. The preceding paragraph will explain how
difficult it will be to know its maximum discharge until a gauge and
discharge table are established for the Blue Nile 100 kilometres above
Khartoum well above back water, and a gauge and discharge table in the
Main Nile north of Omdurman. The difference between these two discharges
will be the true discharge of the White Nile which, with its slope of
¹⁄₁₀₀₀₀₀ in flood, is not a river but a flood reservoir. The discharges
taken at Duem on the White Nile and at Khartoum on the Blue Nile in 1902
and 1903 are interesting, but of little value for anything except the
very date on which they were taken. They were all in backwaters.
19. =The Blue Nile.=--Compared to any river we have yet described, the
Blue Nile is a true mountain stream. Draining the southern and more
rainy half of Abyssinia, it is the principal source of the Nile in
flood. Whatever waters it receives, it carries to the Nile and it is the
true parent of the land of Egypt, for the deposit from its muddy waters
is that Nile mud which has made Egypt. The Atbara carries waters which
are probably more muddy than those of the Blue Nile, but compared to the
Blue Nile the Atbara is a small river, and its quota is insignificant by
the side of that of the larger stream. The principal tributary of the
Blue Nile, the Abai, rises at a height of about 2,700 metres above sea
level and after a course of 110 kilometres falls into Lake Tsana. Lake
Tsana lies at a level of about 1,760 metres above sea level, and has an
area of about 3,000 square kilometres and catchment basin of about
14,000 square kilometres irrespective of the lake area. On the 31st of
January 1903, after a very poor rainfall, Mr. C. Dupuis found the
discharge 42 cubic metres per second. Calculating from his cross
section, it seems that the maximum discharge may be 200 cubic metres per
second. As at Lake Victoria, possibly not more than ¹⁄₁₂th the rainfall
finds its way into the lake; and, once there, the greater part is
evaporated. Little seems to leave the lake, which would consequently
make a very poor reservoir. The land rises from the lake in gently
undulating downs as a rule. Wherever observed by Mr. Dupuis, the lake
was shallow. There are many islands and some of them considerable ones.
The rivers feeding the lake are the following:--the Abai discharging 9
cubic metres per second in January 1903, the Reb 2 cubic metres, the
Gumara 2, the Magetch 0·3, the Arno Garno 0·3, the Gelda 0·5, the Unfraz
1·2, and many smaller streams say 1·7, or 17 cubic metres per second in
all. This of course was in the dry season. Mr. Dupuis considers the
evaporation as 4 millimetres per day.
Between Lake Tsana and Rosaires, on a length of about 750 kilometres the
Blue Nile falls some 1260 metres; between Rosaires and Sennar, on a
length of 270 kilometres, it falls about 60 metres, and between Sennar
and Khartoum on a length of 345 kilometres it falls about 50 metres. The
cross sections of the river at Wad Medani, 200 kilometres above
Khartoum, and at Khartoum are given on Plate IX.
In flood and early winter the river is navigable up to the Rosaires
cataract. The width of channel may be considered as varying between 350
and 700 metres with an average width of 500 metres. The river rises from
9 to 12 metres in flood and has a velocity in high floods of 3 metres
per second. Rivers with such velocities scour out their beds very
severely in high floods and deposit silt in low floods, and for the
discharges below 5 metres, cross sections should be annually established
and discharge tables made depending on the sections. The summer
discharge varies from 100 to 300 cubic metres per second and the flood
from 7,500 to 12,500 cubic metres per second. The behaviour of the river
is shown in Tables 24 and 25. The beginning of May is generally low
water and the beginning of September high water. The winter discharge
may be taken as 500 cubic metres per second.
The tributaries south of Rosaires are the following:--on the right bank,
the Folassa, the Durra, the Fatsam, the Bir and the Temsha, veritable
torrents; and on the left bank, numerous streams from north and
north-west of Addis Ababa, the Anjur, and the Didessa, the latter from
100 to 150 metres wide. North of the last is the Tumat. The Didessa is
about 350 kilometres long and the Tumat 200. It is not at all improbable
that in the valley of the Didessa far better reservoir sites could be
found than at Lake Tsana. Capt. Lyons tells me that there are important
reaches here with very little slope. North of Rosaires there are two
important tributaries on the right bank, the Dinder, north of Sennar,
and the Rahad, just north of Wad Medani. Both these streams run only in
flood and are dry in winter and summer. The Dinder has a bed width of
about 120 metres, depth 4 metres in good flood and a velocity of 2
metres per second, which gives a discharge of about 1000 cubic metres
per second in a high flood. The Rahad has a bed width of 60 metres,
depth of 3 metres in a good flood and a velocity of 2 metres per second,
which gives a discharge of 400 cubic metres per second in a good flood.
The deltas of the Blue Nile, the Dinder and the Rahad are formed of the
richest Nile mud. Such soil is rich in lime, potash and phosphates, but
is poor in nitrates.
[Illustration: PLATE VII
Lith. Sup. Dep. Cairo.
THE OUTLET OF LAKE TSANA
_From a rough Survey_
Scale 1 : 30.000]
The velocity of the Blue Nile may be taken as 75 centimetres per second
in low supply and 3 metres per second in high flood.
20. =The Atbara.=--The Atbara river flows into the Nile at El-Damer,
south of Berber. It is essentially a torrent fed by the rains of
north-eastern Abyssinia. The rains here begin early and end early, so
that the Atbara is in high flood in August and falls quickly through
September. Its floods last from June to October and the river is dry for
the remaining months of the year. By dry it is meant that there is no
running water, for the bed of the river contains numerous pools of
water, which are nearly always deep and often very extensive.
Mr. Dupuis has given a rough longitudinal section of the Atbara river.
Rising within 16 kilometres of Lake Tsana, at a height of about 2000
metres above sea level, in its first 300 kilometres it falls 1500 metres
to 530 metres above sea level, where it is met by the Salaam river. In
the next hundred kilometres it falls 40 metres and is joined by the
Settit river, a larger and more permanent stream than the Atbara itself.
Sixty kilometres lower down is the Khasm-el-Girba gauge, just upstream
of Fasher and about 420 kilometres from the Nile. Two hundred kilometres
below the Settit junction and about 280 kilometres from the Nile is
Gosrejeb, and 150 kilometres lower down Adarma. Finally, after a total
length of about 880 kilometres, the Atbara flows into the Nile.
The Settit junction is about 490 metres above sea level, Fasher 470
metres, Gosrejeb 410, Adarma 380, and El-Damer about 365 metres above
sea level. In the last 280 kilometres there is therefore a fall of 45
metres or about ¹⁄₆₀₀₀. In this reach the river has a width of about 330
metres and depth in flood of 6 metres.
Tables 24 and 25 give the behaviour of the river. In 1902 and 1904, two
very low years, the maximum discharge was about 2000 cubic metres per
second, and in 1903 about 3000 cubic metres. In high floods the Atbara
can discharge 5000 cubic metres per second.
The principal tributaries of the Atbara are the Salaam and Settit
already mentioned. On its right bank between Gosrejeb and Adarma it is
joined by the Gaash river, which flows past Kassala and loses itself in
the deserts. In years of extraordinary rainfall the Gaash reaches the
Atbara. The Gaash at Kassala has a width of 150 metres, depth of 1 metre
and approximate discharge of 300 cubic metres per second in an ordinary
flood. It has a course of about 160 kilometres before it disappears in
the desert.
21. =The Nile from Khartoum to Assuân.=--The Nile begins its course
without any gauge to record its varying height. A gauge north of
Omdurman, another upstream of the 6th cataract and a third downstream of
the cataract are badly needed. Until these three gauges are erected and
recorded, and another erected and recorded on the Blue Nile at Kamlin,
about 100 kilometres above Khartoum, the behaviour of the Nile and its
tributaries at their junction will never be exactly understood. Making
use of the information which is obtainable, we may say that the Blue
Nile is generally at its lowest between the 15th April and 15th May with
a mean low-water discharge of about 200 cubic metres per second, falling
to nearly zero in certain years; it is at its highest between the 15th
August and 15th September with a mean maximum discharge of some 10,000
cubic metres per second, rising to 13,000 and falling to 6,500 in
maximum and minimum years. If the larger figure is correct, the Blue
Nile bank at Khartoum is over a metre too low, and the town is liable to
be flooded out. If reference is made to Plate VIII it will be seen that
the flood of the Blue Nile in July, August and September travels up the
White Nile, holds back its waters and converts the valley of the White
Nile into a flood reservoir. When the Blue Nile falls rapidly in October
and November, the discharge of the Nile is maintained by the stored-up
waters in the White Nile and by the White Nile flood which has slowly
travelled down its almost level bed. Table 24 shows this more clearly
than any description could. I do not think that the maximum discharge of
the Main Nile on any given day is ever equal to the maximum discharge of
the Blue Nile.
The Nile between Khartoum and Berber has a channel wider and deeper than
that between Wady Halfa and Assuân and a gentler current. I have not
taken, or seen any discharges which have been taken in this reach, but
judging from what I saw I should say the channel was 800 metres wide on
the average. At a distance of 86 kilometres from Khartoum is the
Shabluka or 6th cataract. Here the Nile descends 6 metres on a length of
18 kilometres. Two hundred and twenty kilometres below the cataract the
Atbara flows into the Nile and repeats on a very small scale what the
Blue Nile does at Khartoum. The Atbara is a flood torrent and is dry
from October to May. In flood it discharges from a low maximum of 1,700
to a high maximum of 5,000 cubic metres per second, with a mean maximum
of 3,500 cubic metres.
[Illustration: PLATE VIII.
BLUE & WHITE NILE GAUGES
FLOOD OF 1903.
BLUE & WHITE NILE GAUGES
FLOOD OF 1904.
Lith. Sur. Dep. Cairo.]
In this reach the Nile has a maximum range of 8¹⁄₂ metres and an
ordinary range of 7 metres.
Twenty-four kilometres downstream of the Atbara junction is Berber, and
45 kilometres downstream of Berber is the beginning of the 5th cataract,
which has a length of 160 kilometres and a drop of 55 metres with three
principal rapids, the Solimania, Baggâra and Mograt. The village of Abu
Hamed is situated at the foot of this Cataract. Between Abu Hamed and
Dongola is the 4th Cataract, which begins at a point 97 kilometres
downstream of Abu Hamed, and has a length of 110 kilometres with a drop
of 49 metres. In this series of rapids are the Um Dâras and Guerendid.
Between the 4th and 3rd Cataracts is a reach of 313 kilometres on a
slope ¹⁄₁₂₀₀₀. On this reach is the town of Dongola. The 3rd Cataract
has a length of 72 kilometres and a drop of 11 metres with the Hannek
and Kaibâr rapids, surveyed and levelled by De Gottberg in 1857.
Upstream of the Hannek rapid, on the left bank of the Nile, is the
termination of the long depression in the deserts which goes by the name
of the Wady-el-Kab and is considered by many as lower than the Nile
valley. Between the 3rd and 2nd Cataracts is an ordinary reach of 118
kilometres. West of this part of the Nile are the Selima Wells and
according to some travellers an old abandoned course of the Nile
slightly above the present high level of the river. This waterless river
is said to terminate in the Oasis of Berys which is separated from the
Khargeh Oasis by a limestone ridge.
The 2nd Cataract, known as the “Batn-el-Haggar” or “Belly of Stone,” has
a length of 200 kilometres and a drop of 66 metres with the rapids of
Amâra, Dal, Semna and Abka. At Semna are the rocks where Lepsius
discovered the Nile gauges cut by one of the Pharaohs some 4,000 years
ago. The Nile flood recorded there is 8 metres higher than any flood of
to-day. As the Nile at Semna could be very easily barred by a dam, it
struck me when I was there in 1892 that probably King Amenemhat (of Lake
Mœris fame) had tried to bar the river with a dam in the hope of
creating a reservoir. At Wady Halfa, near the foot of the 2nd Cataract,
a masonry gauge divided into metres has been erected and read since
1877. Its accidental zero is R. L. 116.69 and the mean low-water level,
or true zero, is R. L. 117.89. Between the 1st and 2nd Cataracts, the
Nile has a length of 345 kilometres and a slope of ¹⁄₁₂₅₀₀. The mean
width of the river is 500 metres, and the mean depths in flood and
summer are 9 and 2 metres. The velocity in summer falls to 50
centimetres per second and rises to 2 metres per second in flood. The
river in this reach is generally within sandstone, and the greater part
is provided with gigantic spurs on both banks. These spurs perform the
double work of collecting soil on the sides in flood and training the
river in summer. They were probably put up by the great Rameses 3,000
years ago, as some of the most massive of them have evidently been
constructed to turn the river on a curve out of its natural channel on
to the opposite side in order to secure deep water in front of Rameses’
temple of Jerf Husain (“Jerf” means steep, scoured bank). The spurs have
been constructed with care, and as the courses of roughly-dressed stone
can be examined at fairly low water (I have never seen them at
absolutely low water) it is evident that there has been no great
degradation of the bed during the last 2,000 or 3,000 years. The first,
or Assuân Cataract, has a drop of 5 metres on a length of 5 kilometres.
From Khartoum to Assuân, on a total length of 1809 kilometres, there are
565 kilometres of so-called cataracts with a total drop of 192 metres,
and 1,244 kilometres of ordinary channel with a total drop of 103
metres.
At the head of the 1st Cataract is the Assuân dam, regulated on for the
first time in October 1902. It has 140 openings of 2 metres × 7 metres
and 40 openings of 2 metres × 3¹⁄₂ metres.
At the foot of the 1st Cataract, opposite the town of Assuân, on the
Island of Elephantine, has stood a Nile gauge from very ancient times.
An officer belonging to the Roman garrison in the time of the Emperor
Severus marked an extraordinarily high flood on the gauge. The maximum
flood-mark at the time of the visit of Napoleon’s French savants was
however 2.11 metres higher than the above. As the middle of Severus’
reign was A.D. 200, and the visit of French savants A. D. 1800, they
concluded that the bed and banks of the Nile had risen 2.11 metres in
1600 years or 0.132 metres per 100 years. The new gauge divided into
cubits and twenty-fourths was erected in 1869 and has been recorded
daily since then (a cubit = 54 centimetres). The accidental zero of the
gauge is R. L. 84.16. The mean low-water level or true zero is R. L.
85.00.
[Illustration: PLATE X.
LONGITUDINAL SECTION OF THE NILE FROM WADY HALFA TO GEBEL SILSILAH
Lith. Sur. Dep. Cairo.
CROSS SECTION OF THE NILE VALLEY NEAR IBRÎM
CROSS SECTION OF THE NILE VALLEY NEAR ASSUÂN
TYPICAL CROSS SECTION UPSTREAM OF ASSUÂN DAM]
22. =The Nile from Assuân to the Barrage.=--From Assuân to the Barrage,
the length of the river is 973 kilometres in summer and 923 in flood.
The slope in summer is ¹⁄₁₃₀₀₀ and in flood ¹⁄₁₂₂₀₀ The mean fall of the
valley is ¹⁄₁₀₈₀₀. The slopes vary in the different mean reaches, the
least being ¹⁄₁₄₈₀₀ in the Kena Mudiria and the greatest ¹⁄₁₁₄₀₀ in Beni
Suef. In a high flood with a rise of 9 metres at Assuân, the rise in
Kena will be 9.5 metres and only 8.2 in Beni Suef. Table 42 gives the
mean areas of cross sections of the Nile, while table 44 gives the mean
widths. Neglecting spill channels, we may state that in a high flood the
mean area of the section of the Nile is 7,500 square metres and the mean
width 900 metres. In the Kena Mudiria, the area is 7,000 square metres
and the width 800 metres, while in Beni Suef the mean area is 8,000
square metres and the mean width 1,000 metres. Speaking generally it may
be stated that where the Nile valley is narrow the slope of the river is
small, its depth great and width contracted; while where the valley is
broad the slope is great, the depth small and the width enlarged. The
mean velocity in flood ranges between 2.0 metres and 1.0 metre per
second, while the velocity in summer varies from 0.5 to 0.9 metre per
second. We may say that the Nile in soil has a natural section whose
width in flood is 110 times its depth, while its mean velocity is 1.50
metres per second.
The natural canals, which take off the river and which never silt, have
a mean velocity of some 65 centimetres per second, while the proportion
of width to depth is about 12 to 1. Artificial canals of this section do
not silt if their velocities are 80 centimetres per second, while
silting takes place as readily when the velocity is greater as when it
is less than the above. In muddy streams, like the Nile in flood,
certain velocities demand certain proportions of width to depth, and if
these are not given to it, they will make it for themselves by eating
away the sides if they can, or, if they cannot eat away the sides, by
silting up and raising the bed.
To the north of Assiout is situated the Assiout weir or barrage across
the Nile with 111 openings of 5 metres and 10 metres depth of water in
high flood. It was regulated on for the first time in August 1902.
On Roda island, opposite Cairo, has stood a gauge from the earliest
times. It has been frequently reconstructed. The present gauge is
reputed to have been erected in A.D. 861 with its zero at the same level
as a more ancient one whose readings have been preserved since A.D. 641.
When the gauge was constructed, a reading of 16 cubits meant the lowest
level at which flood irrigation could be insured everywhere. The level
to-day is 20¹⁄₂ cubits on the gauge and the difference between them is
1.22 metres. As 1,026 years have elapsed since the construction of the
gauge it means a rise of 12 centimetres per 100 years. This is slightly
under the rise calculated at Assuân by the French savants.
The following table gives the means of the maximum flood and low water
levels per century:--
7th century 17.5 R. L. flood 11.0 R. L. low water 6.5 Difference.
8th „ 17.4 „ 11.1 „ 6.3 „
9th „ 17.5 „ 11.2 „ 6.3 „
10th „ 17.5 „ 11.3 „ 6.2 „
11th „ 17.5 „ 11.4 „ 6.1 „
12th „ 17.7 „ 11.5 „ 6.2 „
13th „ 17.7 „ 11.6 „ 6.1 „
14th „ 17.9 „ 11.7 „ 6.2 „
15th „ 18.2 „ 11.8 „ 6.4 „
16th „ 18.4 „ 11.9 „ 6.5 „
17th „ 18.8 „ 12.0 „ 6.8 „
18th „ 19.1 „ 12.1 „ 7.1 „
19th „ 19.5 „ 12.2 „ 7.3 „
It is evident from the above that the head of the Delta, or the
bifurcation of the Nile, was much nearer to Cairo in early days than
just now, and the last three centuries have seen great changes. The fall
of watersurface is very considerable at every bifurcation, and the
difference between mean high and low supply at the Barrage to-day is 6.0
metres against 7.2 metres at Cairo. Judging from the above figures, I
should say that from the 7th to the 13th century the bifurcation was
gradually approaching Cairo, while since the 13th it has been
receding.
[Illustration: PLATE XII.
LONGITUDINAL SECTION OF THE NILE FROM ASSUAN TO CAIRO
ALONG CENTRE LINE OF FLOOD
Lith. Sur. Dep. Cairo.
CROSS SECTIONS OF THE NILE VALLEY IN EGYPT]
The following table gives the highest and lowest floods at Cairo in
intervals of 25 years from A.D. 639 to A.D. 1904.
The gauges are in pics and kirats and are referred to mean low water or
R. L. 12·25 metres above mean sea.
=========+=============================+=============================+
Years | HIGHEST MAXIMUM | LOWEST MAXIMUM |
A. D. +-----+-------+------+--------+-----+-------+------+--------+
|Pics.|Kirats.|Metres| Metres |Pics.|Kirats.|Metres| Metres |
| | |R. L. |referred| | |R. L. |referred|
| | | |to zero | | | |to zero |
| | | |at R. L.| | | |at R. L.|
| | | | 12·25 | | | | 12·25 |
---------+-----+-------+--- --+--------+-----+-------+------+--------+
639- 650| 19 | .. | 18·16| 5·91 | 14 | 21 | 16·74| 4·49 |
651- 675| 19 | 23 | 18·42| 6·17 | 15 | 12 | 17·07| 4·82 |
676- 700| 18 | 17 | 18·08| 5·83 | 13 | 6 | 15·87| 3·62 |
701- 725| 18 | 22 | 18·14| 5·89 | 13 | 18 | 16·13| 3·88 |
726- 750| 18 | 13 | 18·04| 5·79 | 14 | ¹⁄₂ | 16·28| 4·03 |
751- 775| 18 | 10 | 18·00| 5·75 | 14 | 19 | 16·70| 4·45 |
776- 800| 18 | 4 | 17·93| 5·68 | 14 | 1 | 16·29| 4·04 |
801- 825| 17 | 18 | 17·82| 5·57 | 14 | 2 | 16·31| 4·06 |
826- 850| 17 | 12 | 17·76| 5·51 | 13 | 5 | 15·85| 3·60 |
851- 875| 18 | 8 | 17·98| 5·73 | 15 | 15 | 17·15| 4·90 |
876- 900| 17 | 22 | 17·86| 5·61 | 14 | 22 | 16·76| 4·51 |
901- 925| 18 | 1 | 17·90| 5·65 | 13 | 4 | 15·83| 3·58 |
926- 950| 19 | .. | 18·16| 5·91 | 14 | 17 | 16·65| 4·40 |
951- 975| 18 | 5 | 17·94| 5·69 | 14 | 19 | 16·60| 4·45 |
976-1000| 26 | 23 | 21·65| 9·40 | 15 | 2 | 16·85| 4·60 |
+-----+-------+------+--------+ | | | |
1001-1025| 19 | 8 | 18·25| 6·00 | 14 | 9 | 16·47| 4·22 |
1026-1050| 18 | 6 | 17·95| 5·70 | 15 | 9 | 17·01| 4·76 |
1051-1075| 17 | 18 | 17·71| 5·46 | 12 | 3 | 15·30| 3·05 |
| | | | +-----+-------+------+--------+
1076-1100| 18 | 16 | 18·07| 5·82 | 13 | 17 | 16·11| 3·86 |
1101-1125| 19 | 1 | 18·17| 5·92 | 16 | 12 | 17·48| 5·23 |
1126-1150| 18 | 18 | 18·09| 5·84 | 16 | 9 | 17·45| 5·20 |
1151-1175| 18 | 18 | 18·09| 5·84 | 15 | 1 | 16·83| 4·58 |
1176-1200| 18 | 14 | 18·05| 5·80 | 12 | 21 | 15·68| 3·43 |
| | | | +-----+-------+------+--------+
1201-1225| 18 | 8 | 17·98| 5·73 | 15 | 7 | 16·96| 4·71 |
1226-1250| 18 | 8 | 17·98| 5·73 | 14 | .. | 16·27| 4·02 |
1251-1275| 18 | 17 | 18·08| 5·83 | 16 | 12 | 17·48| 5·28 |
1276-1300| 19 | 7 | 18·24| 5·99 | 15 | 18 | 17·22| 4·97 |
1301-1325| 18 | 19 | 18·10| 5·85 | 16 | 2 | 17·37| 5·12 |
1326-1350| 18 | 21 | 18·13| 5·88 | 16 | 5 | 17·40| 5·15 |
1351-1375| 24 | .. | 20·05| 7·80 | 16 | 18 | 17·55| 5·30 |
+-----+-------+------+--------+ | | | |
1376-1400| 20 | 3 | 18·46| 6·21 | 16 | 13 | 17·50| 5·25 |
1401-1425| 20 | 12 | 18·56| 6·31 | 16 | 13 | 17·50| 5·25 |
1426-1450| 20 | 21 | 18·67| 6·42 | 15 | 7 | 16·96| 4·71 |
1451-1475| 18 | 8 | 17·98| 5·73 | .. | .. | .. | .. |
1476-1500| 20 | 21 | 18·67| 6·42 | 19 | 17 | 18·55| 6·30 |
1501-1525| 20 | 16 | 18·61| 6·36 | 16 | | 17·35| 5·10 |
1526-1550| .. | .. | .. | .. | .. | .. | .. | .. |
1551-1575| .. | .. | .. | .. | .. | .. | .. | .. |
1576-1600| 26 | .. | 21·13| 8·88 | 18 | 8 | 17·98| 5·73 |
+-----+-------+------+--------+ | | | |
1601-1625| 24 | 5 | 20·16| 7·91 | 17 | 23 | 17·88| 5·63 |
+-----+-------+------+--------+ | | | |
1626-1650| 19 | .. | 18·16| 5·91 | 15 | .. | 16·81| 4·56 |
1651-1675| 22 | .. | 18·97| 6·72 | .. | .. | .. | .. |
+-----+-------+------+--------+ | | | |
1676-1700| 24 | .. | 20·05| 7·80 | 22 | .. | 18·97| 6·72 |
+-----+-------+------+--------+ | | | |
1701-1725| 23 | 4 | 19·60| 7·35 | 16 | .. | 17·35| 5·10 |
1726-1750| 24 | 12 | 20·32| 8·07 | 20 | 14 | 18·58| 6·33 |
+-----+-------+------+--------+ | | | |
1751-1775| 24 | 12 | 20·32| 8·07 | 18 | 17 | 18·08| 5·83 |
+-----+-------+------+--------+ | | | |
1776-1800| 24 | .. | 20·05| 7·80 | 12 | 12 | 15·49| 3·24 |
+-----+-------+------+--------+ | | | |
1801-1825| 22 | .. | 18·97| 6·72 |[5]8 | .. | 13·14| 0·89 |
| | | | +-----+-------+------+--------+
1826-1850| 24 | 9 | 20·26| 8·01 | 18 | 23 | 18·15| 5·90 |
+-----+-------+------+--------+ | | | |
1851-1875| 26 | 12 | 21·40| 9·15 | 19 | 13 | 18·30| 6·05 |
+-----+-------+------+--------+ | | | |
1876-1900| 26 | 6 | 21·27| 9·02 | 17 | 3 | 17·65| 5·40 |
+-----+-------+------+--------+ | | | |
1901-1904| .. | .. | 19·18| 6·93 | .. | .. | 18·02| 5·97 |
=========+=====+=======+======+========+=====+=======+======+========+
=========+========+==============
Years |N^{o} of|Remarks.
A. D. | years |
| re- |
| corded.|
---------+--------+--------------
639- 650|11 years|
651- 675|25 „ |
676- 700|25 „ |
701- 725|25 „ |
726- 750|25 „ |
751- 775|25 „ |
776- 800|25 „ |
801- 825|25 „ |
826- 850|25 „ |
851- 875|25 „ |
876- 900|25 „ |
901- 925|25 „ |
926- 950|25 „ |
951- 975|24 „ |
976-1000|25 „ |Max. year 199
| |
1001-1025|25 „ |
1026-1050|25 „ |
1051-1075|25 „ |Min. year 1070
| |
1076-1100|24 „ |
1101-1125|25 „ |
1126-1150|24 „ |
1151-1175|25 „ |
1176-1200|25 „ |Min. year 1199
| |
1201-1225|25 „ |
1226-1250|25 „ |
1251-1275|23 „ |
1276-1300|25 „ |
1301-1325|25 „ |
1326-1350|25 „ |
1351-1375|24 „ |Max. year 1359
| |
1376-1400|25 „ |
1401-1425|24 „ |
1426-1450|23 „ |
1451-1475| 1 „ |
1476-1500| 2 „ |
1501-1525|19 „ |
1526-1550| .. |
1551-1575| .. | ..
1576-1600|11 years|Max. year 1587
| |
1601-1625|19 „ | „ 1602
| |
1626-1650| 3 „ |
1651-1675| 1 „ |Max. year 1669
| |
1676-1700| 3 „ | „ 1697
| |
1701-1725|18 „ |
1726-1750|24 „ |Max. year 1738
| |
1751-1775|25 „ | „ 1756
| |
1776-1800|25 „ | „ 1779
| |
1801-1825| 3 „ |Min. year 1809
| |
1826-1850|25 „ |Max. year 1850
| |
1851-1875|25 „ | „ 1874
| |
1876-1900|25 „ | „ 1878
| |
1901-1904| 4 „ |Min. year 1877
=========+========+==============
[5] There is an error here in the records.
At Assuân the Nile has a mean range of 7.90 metres between high and low
supply, with a maximum of 9.80 metres and a minimum of 6.40 metres. The
high supply varies between 13,200 and 6,500 cubic metres per second,
with a mean of 10,000 cubic metres per second, while the low supply
varies between 350 and 1400 cubic metres per second with a mean of 590
cubic metres per second. September is generally the highest month and
May the lowest. The mean low water level is R. L. 85.00.
At Cairo the Nile has a mean range of 7.00 metres with a maximum of 9.6
metres and a minimum of 5.3 metres. The high supply varies between
12,000 and 4,800 cubic metres per second with a mean of 7,600 cubic
metres per second, while the low supply varies between 1,300 and 250
cubic metres per second, with a mean of 500 cubic metres per second.
October is the highest month and June the lowest. The mean low water
level is at R. L. 12.25.
[Illustration: PLATE XI.
CROSS SECTIONS OF THE NILE & ITS TRIBUTARIES
_Horizontal Scale 1 : 2.000_
_Vertical Scale 1 : 500_
Lith. Sur. Dep. Cairo.
No. 19. _River Rahad at Khor Abou Seghire 20 km. above the Nile
junction_
No. 20. _Atbara River at Khashim al Girba 410 km. from Nile_
No. 21. _Atbara River at Khor Abadar 25 km. from Nile_
No. 22. _Nile at Manfalout_
No. 23. _Rosetta Branch at Khatatba_
No. 24. _Damietta Branch at Benha_]
Tables 41 to 52 refer to the Nile between Assuân and the Barrage at the
head of the Delta proper.
Table 46 gives the Reduced Level of the mean low water level of the Nile
at various points between Assuân and Cairo. If, for example, it is known
that the water surface at any time of the year at Assiout is R. L.
50.80, we know the mean low water by the Irrigation Department levels is
45.05. The gauge is therefore 5.75, and by turning to Table 37 we know
the discharge.
Table 37 gives the discharges of the river for gauges referred to the
mean low water level. Between Esna and Kena the table is in excess of
the truth, and between Assiout and Beni-Suef it is slightly under. Taken
all round the table is reliable, calculated from the means of hundreds
of discharges and carefully prepared.
Table 45 gives the slope of the water surface of the Nile in flood and
in summer between Assuân and Cairo. Owing to the more winding track of
the low supply than of the flood waters, the former is 948 kilometres
and the flood 900. The slope in summer is ¹⁄₁₃₀₀₀ and in high flood
¹⁄₁₂₂₀₀.
The other tables need no explanation.
23. =The Rosetta and Damietta Branches.=--Plates XVII and XVIII give
longitudinal sections of the two branches of the Nile and their cross
sections are given on Plate XI.
During winter, summer, and low floods, regulation at the Barrage
interferes with the natural discharges of the two branches. The Damietta
branch is gradually silting up and decreasing in size, while the Rosetta
branch scours in high floods. The mean width of the Rosetta branch is
500 metres, and the mean area of the section in flood is 4000 square
metres. The mean width of the Damietta branch is 270 metres and the mean
section 2700 square metres. The mean velocity of the floods range from
1.00 metre to 1.60 metres per second. In summer the branches are
hermetically closed at their heads and receive only the water which
filters into them from the subsoil. This in the Rosetta branch amounts
to 20 cubic metres per second, and less in the Damietta branch. It may
be noted here that at Cairo the girder bridge at Kasr-el-Nil is 403
metres between the abutments and the smaller bridge is 178 metres,
making a total width of 581 metres. The width of the Kafr Zayat bridge
on the Rosetta branch is 530 metres, while the old Benha bridge on the
Damietta branch is 285 metres. The average depth of water in flood in
the two branches may be taken as 7 metres.
The barrage at the head of the Rosetta branch has 61 openings of 5
metres each and one lock 15 metres wide and the other 12 metres. They
are all open in high flood. The Damietta barrage has 61 openings of 5
metres and one lock of 12 metres. The depth of water in a high flood is
9 metres. The Rosetta barrage has 10 openings too few, and the Damietta
barrage 15 openings too many.
Before the construction of the Barrage in the middle of the 19th
century, the maximum discharges of the two branches at the head of the
Delta were nearly the same. A little lower down, however, the Rosetta
branch had considerably more water than the Damietta. About 2 kilometres
below the Barrage there was a branch called the Shalakan branch which
flowed from the Damietta into the Rosetta branch. About 20 kilometres
below the Barrage, the Bahr Ferounieh took about ¹⁄₃ the total discharge
of the Damietta branch and led it into the Rosetta branch. Both these
were closed by Mehemet Ali, while at the same time the Bahrs Sirsawiah,
Baguria, Shebin, Khadrawiah, Moes, Um-Salama, Bohia and Sogair were also
completely closed or provided with regulating heads, which very
considerably diminished their discharge. During the time that they had
been open the Damietta branch had lost water at every kilometre as it
approached the sea, and though 400 metres wide at the head it had a
channel only 200 metres wide in its lower reaches. The Rosetta branch on
the other hand received the tail waters of many Bahrs and had only one
escape, the Bahr Saidi near its tail.
The closing of so many escapes on the Damietta branch has caused this
branch in its upper reaches to carry so much water that its tail reaches
can not carry it without having the surface of the water raised
inordinately and dangerously above the level of the country. An
examination of the longitudinal sections will show that while the
Rosetta branch in its middle reaches is from 1.50 to 2.00 metres above
the level of the country in a high flood, the Damietta branch is from
2.50 to 3.00 metres. They will also show how the slope in the early
reaches of the Damietta branch is considerably less than that in the
early reaches of the Rosetta branch, which results in the gradual
silting up of the former as already noted. The Karanain regulator at the
head of the old Bahr Shebin, taking from the Damietta branch below the
Bahr Ferouniah, was built in 1842 by Linant Pasha, with its wing wall 60
centimetres higher than any previous flood. By 1870 the Damietta branch
had risen 70 centimetres above the wing wall as measured by Linant
Pasha. In 1878, though the Damietta branch was relieved by the Gizeh
breach in the left bank of the Main Nile which drained into the Rosetta
branch, the flood water surface of the Damietta branch at Karanain was
1.50 metres above the wing wall.
[Illustration: PLATE XVII.
LONGITUDINAL SECTION OF THE ROSETTA BRANCH
_Longitudinal Scale 1 : 100,000_
_Vertical Scale 1 : 1,000_
_Measurement along the right bank_]
[Illustration: PLATE XVIII.
LONGITUDINAL SECTION OF THE DAMIETTA BRANCH
_Longitudinal Scale 1 : 100,000_
_Vertical Scale 1 : 1,000_
_Measurement along the left bank_]
The maximum, minimum and mean floods in the Rosetta branch are 6,500,
2,600 and 4,000 cubic metres per second. In the Damietta branch they are
4,600, 1,300 and 2,300 cubic metres per second respectively.