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THE NILE IN 1904
BY
Sir WILLIAM WILLCOCKS, K.C.M.G., F.R.G.S.
LONDON
E. & F. N. SPON LIMITED, 57 HAYMARKET.
NEW YORK
SPON & CHAMBERLAIN, 123 LIBERTY STREET.
_=Price 9=s/- =net.=_
PRINTED AT THE NATIONAL PRINTING DEPARTMENT OF EGYPT, CAIRO
1904.
_Dedicated to my old Chief and Master in Irrigation, Sir Colin
Scott-Moncrieff, K.C.S.I., K.C.M.G., under whom I had the privilege of
working for 20 years in India and Egypt._
PREFACE
The publication of Sir William Garstin’s monumental work on the “Basin
of the Upper Nile” is an event of such importance in the history of the
Nile that the occasion should not be lost of bringing Lombardini’s work
on the Nile to date. The information utilised by me in this book as far
as the Upper Nile is concerned is obtained from Sir William’s Report;
for the Blue Nile and Atbara I am indebted to M. Dupuis’ interesting
appendix at the end of Sir William’s Report; and for the river north of
Khartum to my own studies and surveys. As Sir William employed Capt.
H.G. Lyons, R.E. to collaborate with him, the references to the works of
previous writers and geographical details may be accepted without any
misgivings. To M. Chélu Bey, Director of the Government Press, I am
indebted for his ever ready aid; to Mr. Hansard of the Survey Department
for the plates accompanying this work; and to Mr H.G.F. Beadnell, F.G.S,
F.R.G.S, for having kindly written the description of the Egyptian oases
and the geology of Egypt which form the fifth chapter of this book.
W. WILLCOCKS.
_Cairo, 12-10, 1904._
THE NILE IN 1904.
SUBJECT MATTER.
CHAPTER I. _The Nile_--(Page 11).
1. Introduction.
2. Nomenclature.
3. Description of the course of the Nile.
4. Slopes and velocities of the Nile in its different reaches.
5. Catchment basins of the Nile and its tributaries.
6. The climate of the Nile valley.
7. The geology of the Nile valley.
8. The discharges of the Nile and its tributaries.
CHAPTER II. _The tributaries of the Nile_--(Page 26).
9. Lake Victoria Nyanza.
10. The Victoria Nile.
11. The Semliki river.
12. Lake Albert Nyanza.
13. The Albert Nile.
14. The Gazelle river.
15. The Zeraf river.
16. The Sobat river.
17. The Sudd region.
18. The White Nile.
19. The Blue Nile.
20. The Atbara.
21. The Nile from Khartoum to Assuân.
22. The Nile from Assuân to the Barrage.
23. The Rosetta and Damietta Branches.
CHAPTER III. _The utilisation of the Nile_--(Page 56).
24. The Nile in flood.
25. The Nile in low supply.
26. Nile water.
27. The soil of the Nile Valley.
28. Basin irrigation.
29. Perennial irrigation.
30. Flood protection.
CHAPTER IV. _Projects_--(Page 73).
31. Projects.
32. The raising of the Assuân dam.
33. The Wady Rayan reservoir and escape.
34. The Albert Lake and Nile project.
35. Flood protection for Egypt.
36. Complete project for water storage and flood control.
37. Sir William Garstin’s projects.
38. The conversion of basin to perennial irrigation.
39. Development of the Sudan.
CHAPTER V. _The oases and the geology of Egypt by H.J.L.
Beadnell, F.G.S., F.R.G.S._--(Page 107).
40. The oases.
41. Dakhla oasis.
42. Kharga oasis.
43. Baharia oasis.
44. Farafra oasis.
45. The geology of Egypt.
46. Igneous rocks.
47. Sedimentary rocks.
48. Upper cretaceous.
49. Eocene.
50. Oligocene and Miocene.
51. Pliocene, Pleistocene and Recent.
52. Economic products.
Table of Appendices (Page 117).
Index (Page 221).
LIST OF PLATES.
PAGE.
I. Plan of the Nile Valley 12
II. Longitudinal Section of the Nile Valley 14
III. Outlet of Lake Victoria 26
IV. Cross sections of the Nile and its tributaries (1) 28
V. Gauge diagrams of Lakes Victoria and Albert 30
VI. The Sudd region 34
VII. Outlet of Tsana Lake 44
VIII. Gauge diagrams of the White and Blue Niles at Khartoum 46
IX. Cross sections of the Nile and its tributaries (2) 42
X. Longitudinal section of the Nile: Wady Halfa to Assuân 48
XI. Cross sections of the Nile and its tributaries (3) 52
XII. Longitudinal section of the Nile: Assuân to Cairo 50
XIII. Typical cross sections of the Nile Valley 50
XIV. Plan of typical basin irrigation in Egypt 66
XV. Plan of the Fayoum and the Wady Rayan 76
XVI. Longitudinal section of the Fayoum and the Wady Rayan 80
XVII. „ „ „ Rosetta Branch 54
XVIII. „ „ „ Damietta Branch 54
XIX. Plan of typical perennial irrigation in Egypt 68
XX. Possible tunnel at Lake Tsana 103
XXI. The Egyptian oases 108
THE NILE IN 1904.
CHAPTER I.
The Nile.
1. =Introduction.=--In the introduction to his brilliant essay on the
Hydrology of the Nile[1], an essay, which, though written in 1865,
foreshadowed much of what we know to day, Lombardini remarked, with much
truth that, no river in the world lends itself to hydrological studies
on so majestic a scale as the Nile. The most interesting river of the
ancient world, it is still the most interesting river of our time; and,
in spite of all that ancient and modern discoveries have unfolded, its
discharges are to-day more difficult to unravel and weave together than
those of any other stream in either hemisphere. These discharges are
still a mystery, and it will need years and years of patient observation
and study, at the hands of the Sudan Irrigation Department, to enable us
to state with exactitude why its floods rise and fall with such regular
and stately precision, why they are never sudden and abrupt, and why its
summer supplies can never be completely cut off even in their traverse
of over 3000 kilometres through the burning and parched Sahara. Though
the mystery of the Nile is far from being solved to-day, still an
enormous step in advance has been made by the publication of Sir William
Garstin’s Report on the Basin of the Upper Nile[2]. This Report not only
contains the results of three years’ observations of the Egyptian Survey
Department in the Sudan, of Sir William Garstin’s own observations and
studies, but also a mass of information of the Nile and its tributaries
collected by Capt. H. G. Lyons. R. E., through four years of
uninterrupted study. Those who know the intelligence and method with
which Capt. Lyons works, will rate this information at its proper value.
[1] _Saggio idrolico sul Nilo_, by ELIA LOMBARDINI, Milan 1865.
[2] _Report on the Basin of the Upper Nile_ by SIR WILLIAM GARSTIN.
Blue Book Egypt (2) 1904.
Lombardini gathered together all the information available at the time
that Sir Samuel Baker announced the existence of the Albert Nyanza
shortly after Speke and Grant had proclaimed to the world that the
Victoria Nyanza was the true source of the Nile. From the information
then available he deduced the laws and operations of the great river.
About twenty years later, just before the rebellion in the Sudan closed
the Nile to the civilized world, a German savant, Joseph Chavanne[3], in
his book on the rivers of Africa, collected and tabulated on clear and
methodical lines much of the information available in 1883. Though many
of his facts are erroneous, his method is clear and his ideas just. Sir
William Garstin, in his Report, has developed the information at his
disposal on such practical lines as are needed to study the question of
insuring an abundant supply of water to the Nile in Egypt during the
times of low supply.
[3] “_Afrikas Ströme und Flüsse_” by JOSEPH CHAVANNE. Wien 1883.
Having myself studied the Nile for fifteen years in order to solve the
problems of water storage and flood control on the Nile, and having
devoted the whole of my life to this very science of Hydraulics, I have
been encouraged to attempt the continuation of Lombardini’s work; and,
to the utmost of my ability, to bring it to the level of the knowledge
of our day.
2. =Nomenclature.=--The nomenclature of the tributaries of the Nile is
difficult to follow. In this book I shall call the river _the Victoria
Nile_ from Lake Victoria to Lake Albert; _the Albert Nile_ from Lake
Albert to the Sobat mouth (this reach is known generally as the Bahr el
Gebel); _the White Nile_ from the Sobat mouth to Khartoum; and _the
Nile_ from Khartoum to the sea. _The Blue Nile_ stretches from Lake
Tsana in Abyssinia to Khartoum.
3. =Description of the course of the Nile.=--Chapters II and III contain
detailed descriptions of the Nile and its main tributaries, and this
paragraph is a short epitome of what is written there about the course
of the Nile. The Nile drains nearly the whole of north-eastern Africa,
an area comprising 3 million square kilometres. Its main tributary, the
White Nile, has its furthest sources in south latitude 4°, near Lake
Tanganyika. Known as the Kagera, it is one of the feeders of Lake
Victoria, and has a course of 600 kilometres before it reaches the lake.
Lake Victoria, covering 60,000 square kilometres, is the first reservoir
of the Nile. The Victoria Nile leaves Lake Victoria by the Ripon Falls
and after a course of 400 kilometres enters Lake Albert at its northern
corner. At its southern end Lake Albert is fed by the Semliki river
which has its sources in Lake Edward. Its own area is 4,500 square
kilometres. The Albert Nile leaves Lake Albert at its northern end and
has a course of 1280 kilometres to the mouth of the Sobat river. Of this
length, the first 200 kilometres up to Dufile have scarcely any slope,
the next 150 kilometres are down a series of severe cataracts. From the
foot of these cataracts to its tail the Albert Nile has a gentle slope
and traverses the Sudd region where the bed of the stream is often
barred by blocks of living vegetation. In this latter region the stream
divides into two, of which the right hand one is known as the Bahr
Zeraf. After a course of 270 kilometres the Bahr Zeraf joins the Albert
Nile again. In the interval the Albert Nile receives as a left-hand
feeder the Bahr Gazelle. The Sobat river has its sources in Gallaland
and joins the Albert Nile at the termination of the Sudd region. From
the junction of the Albert Nile and the Sobat, the river is known as the
White Nile, which, after a course of 840 kilometres, with an exceedingly
gentle slope, joins the Blue Nile at Khartoum.
[Illustration: PLATE I.
THE NILE
Lith. Sur. Dep. Cairo.]
The Blue Nile is the true parent of the land of Egypt. The deposits of
its muddy waters have made Egypt. The Atbara has added its quota, but
the Blue Nile is incomparably the chief contributor; fed by the timely
and plentiful rains of southern and south-eastern Abyssinia, it
contributes 65 per cent of the waters which pass Assuân. The furthest
sources are those of the Abai, which, after a course of 110 kilometres
falls into Lake Tsana. This lake has an area of 3,000 square kilometres
and lies about 1,760 metres above sea level. The Blue Nile leaves it at
its south-eastern corner and hurries down to the Sudan, fed by numerous
Abyssinian rivers. At Rosaires, after a course of 750 kilometres, it has
fallen 1,260 metres; and below the Rosaires cataract enters the plain
country south of Khartoum. For its remaining 615 kilometres on to
Khartoum, where it meets the White Nile, it is navigable for the greater
part of the year. North of Sennaar it is fed by the Dinder and Rahad
rivers.
Between Khartoum and El Damer, on a length of 320 kilometres, the Nile
has its even passage broken by the 6th cataract at Shabluka. At El Damer
the Nile receives the Atbara as a right hand tributary.
The Atbara is a very muddy torrent fed by the rains of north-eastern
Abyssinia. It runs for 4 months per annum and is dry for 8 months.
Rising within a few kilometres of Lake Tsana, it falls 1500 metres in
its first 300 kilometres, and is then joined by the Salaama, and, 100
kilometres lower down, by the Settit river. After the junction with the
Settit, the Atbara flows for 480 kilometres and joins the Nile at El
Damer, contributing a fair quantity of water and a very considerable
quantity of Nile mud to the river.
From the Atbara junction to the sea, the Nile has a course of 2,700
kilometres. In its first length of 1480 kilometres to Assuân it
traverses the 5th and 4th cataracts between Berber and Dongola, the 3rd
and 2nd cataracts between Dongola and Wady Halfa, and the 1st cataract
at Assuân. All these cataracts are navigable in flood, but not so in
summer. From Assuân to the Barrage at the head of the Delta north of
Cairo, the Nile has a length of 970 kilometres and traverses Egypt
without a cataract or interruption of any kind. At the Barrage, the Nile
divides into the Rosetta and Damietta branches, and after a further
course of about 240 kilometres in either branch, flows into the
Mediterranean sea. Its greatest length from the sources of the Kagera
river to the sea is 6350 kilometres, constituting it one of the longest
rivers in the world.
4. =The Slopes and velocities of the Nile in its different
reaches.=--Table 2 of Appendix B and Plate II comprise all the
information available under this head which I have been able to collect.
For the slopes I have adopted the following data:
R. L. of Lake Victoria 1129 metres above mean sea
„ Fowera 1060 „ „
„ Lake Albert 680 „ „
„ Khartoum (flood) 389 „ „
From Khartoum to Wady Halfa I have adopted the generally accepted levels
of the original Soudan railway survey. From Wady Halfa to the sea I have
levelled myself. Upstream and downstream from the adopted levels I have
carried the levels by the aid of slopes calculated from velocity and
hydraulic mean depth data. It seems to me absurd to adopt a level for
Lake Choga 50 metres above that for Fowera, and then to add, that in the
140 kilometres between the two places the Victoria Nile has a gentle
slope, wide bed and gentle velocity. By a strange fatality, this very
error has crept into the figures under Lake Choga on Plate II. The error
is noted in the corrigenda attached to the Plate. The Section is drawn
correctly but these wrong figures have been interpolated by an
oversight.
The Victoria Nile Falls 450 metres in 400 kilometres, but has four
reaches; the first ¹⁄₁₂₀₀, the second ¹⁄₂₀₀₀₀, the third ¹⁄₁₈₀ past the
Murchison Falls, and the fourth ¹⁄₁₀₀₀₀.
The Albert Nile falls 277 metres in 1290 kilometres. The first reach
past Wadelai has a slope of ¹⁄₂₅₀₀₀, the second over the Fola and
following cataracts has a slope of ¹⁄₇₀₀, the third ¹⁄₁₂₀₀₀, the fourth
¹⁄₂₀₀₀₀, the fifth ¹⁄₂₅₀₀₀, and the last below lake No of ¹⁄₇₅₀₀₀ in
flood.
[Illustration: PLATE II.
ERRATUM.
Erase the two figures under Lake Choga in the “Height” column.
LONGITUDINAL SECTION OF THE NILE,
THE BLUE NILE, THE WHITE NILE, THE ALBERT NILE, THE VICTORIA NILE & THE
SEMLIKI RIVER
Lith. Sur. Dep. Cairo.]
The White Nile falls 14 metres in 840 kilometres and has two slopes in
flood; ¹⁄₅₀₀₀₀ in its upper reach, and then ¹⁄₁₀₀₀₀₀.
The Blue Nile falls 1370 metres in 1370 kilometres, which may roughly be
divided into three reaches. The first from Lake Tsana to Rosaires on a
length of 750 kilometres ¹⁄₆₀₀, the second Rosaires to Sennaar ¹⁄₄₅₀₀,
and the third ¹⁄₇₀₀₀. These are very approximate indeed.
The Atbara falls 1640 metres in 880 kilometres. In the first 300
kilometres the slope is ¹⁄₂₀₀; in the next 300 kilometres the slope is
¹⁄₂₅₀₀, and in the last reach of 280 kilometres it is ¹⁄₆₀₀₀. These are
approximate.
The Main Nile from Khartoum to Assuan falls 295 metres in 1810
kilometres; the so-called six cataracts occupy 565 kilometres with a
slope of ¹⁄₃₀₀₀; and the ordinary channel occupies 1245 kilometres and
has a slope of ¹⁄₁₂₀₀₀. From Assuân to the Barrage, on a length of 970
kilometres, the Nile falls 76 metres with a mean slope of ¹⁄₁₃₀₀₀. The
Rosetta and Damietta branches are each about 240 kilometres long and
have a slope in flood of ¹⁄₁₃₀₀₀, and of ¹⁄₁₂₅₀₀ in extraordinarily high
floods.
From the sources of the Kagera river to the sea, on a length of 6350
kilometres, the Nile falls 2000 metres, or has a slope of ¹⁄₃₂₀₀. From
Lake Victoria to the sea the length is 5535 kilometres and the fall 1129
metres, or the slope is ¹⁄₅₀₀₀.
Table III of Appendix C. gives the velocities of the river in flood and
low supply, in metres per second and kilometres per day, and also the
time occupied in traversing the different reaches. There are two breaks.
The first is at Lake Choga and the second is at Lake Albert. As the
Victoria Nile traverses the eastern arm of the many-armed and peculiar
Lake Choga with a perceptible current, and as, moreover, the lake is
very shallow, we may give some figure to the velocity and make it half
that of the Bahr Gazelle which is ·20 metres per second and is
considered perceptible. With a velocity of ·10 metres per second or 8
kilometres per day, the 80 kilometres of the lake would be traversed in
10 days. The time of traverse from Lake Victoria to Lake Albert would be
15 days. With Lake Albert it is very different. A reference to Plate V
will show that it takes the Victoria Nile 5 months to fill up Lake
Albert before the Albert Nile can carry off the waters of the Victoria
Nile, gauge for gauge. Under these conditions it will be wise to stop at
Lake Albert and begin a new calculation from this lake.
The Albert Nile takes 22 days in flood and 25 days in low supply to
traverse the distance from Lake Albert to the Sobat mouth. The White
Nile takes 21 days in flood and 28 days in low supply to reach
Khartoum. Consequently from Lake Albert to Khartoum we have 43 days in
flood and 53 days in low supply.
From Khartoum to Assuân the Nile takes 11 days in flood and 22 days in
low supply, and consequently from Lake Albert to Assuân we have 54 days
in flood and 75 days in low supply.
From Assuân to Cairo we have 6 days in flood and 12 days in low supply.
Table III is very interesting and well worth study. Through the Sudd
region we have a velocity of ·6 metres per second, but only of ·35
metres per second in the White Nile. In Egypt the Nile in flood has a
velocity of 1·75 metres per second, and in low supply of ·85 metres per
second.
5. =Catchment basins of the Nile and its tributaries.=--Table I, of
Appendix A gives the areas of the catchment basins of the Nile. The
total area according to the table is 3,007,000 square kilometres. The
limits of the basin are depicted on Plate I, and, with rare exceptions,
they are now fairly well known everywhere. North of the 20th parallel of
latitude the watershed on the west of the Nile is not far removed from
the edge of the plateau skirting the Nile valley. The plateau falls away
to the west, and occasional ravines find their way to the Nile down the
reverse slope. On the east of the Nile the crest of the hills skirting
the Red sea is the watershed. South of the 20th parallel of latitude the
eastern watershed follows the crest of the hills on the west of the Red
sea as far as Suakin. South of Suakin the watershed leaves the Red sea,
to allow the Khor Barraka to flow into this sea. From the south east of
Kassala, round by Addis Ababa, the watershed follows the crest of the
high hills forming the eastern backbone of Abyssinia, and dividing the
waters of the Nile from those flowing into the Indian Ocean. South west
of Abyssinia the watershed travels in a south-westerly direction to the
east of Gondokoro, and divides the Sobat from the rivers draining into
Lake Rudolf. The watershed then moves due south to the western
escarpment east of Lake Victoria. Mounts Kenia and Kilmanjaro are not
within the basin of the Nile. Sweeping in a rough curve round Lake
Victoria and nearly touching Lake Tangangyika in 4° south latitude, the
watershed keeps close to the western shores of Lakes Edward and Albert
to nearly opposite Wadelai. All the slopes of the Ruenzori mountains
drain into the Nile.
From near Wadelai the watershed moves in a north-westerly direction
along the hills dividing the waters of the tributaries of the Gazelle
river from the Welle. Due west of the Sudd region the watershed has
reached its most westerly position and from there turns northwards along
the Marrah hills in Darfur, dividing the scanty waters of the
Bahr-el-Arab and its tributaries from the rivers draining into Lake
Chad. From the Marrah hills the watershed travels in a north-easterly
direction to a point close to the Nile on the 20th parallel of latitude
near Hannek.
Of the lands enclosed within this watershed, all that are drained
directly into the Main Nile are desert. There are occasional showers,
and some of the valleys and ravines carry water for a few hours every
year, others every second, third or fourth year, but they contribute
practically nothing to the volume of the Nile. The rains generally come
in the winter when the Nile is falling every day, and the steady fall of
the Nile is never arrested by the waters of any or all of these
watercourses. The country west of the White Nile past Kordofan and
Darfur to the Marrah hills is steppe land producing scanty grasses and
forests of low accacias in the south, and rising to a general height of
about 600 metres at the Marrah hills. The lands drained by the Gazelle
river and the Albert Nile north of Gondokoro are flat plains or swamps
in the north and east, and wooded and broken ground in the west and
south-west, where the tributaries of the Gazelle river rise in the Blue
mountains at a general height of 1500 metres. The upper waters of the
Sobat and its tributaries drain the well wooded and cultivated mountain
masses of Gallaland and then traverse the marshes and flat lands which
lie east of the Sudd region. The Blue Nile and its upper tributaries
drain the choicest portions of the high Abyssinian mountain plateau
lying over 2000 metres above sea level, and rising in places to 2500
metres and upwards. The lower courses of the Blue Nile, the Rahad and
the Dinder are through the black cotton soil plains of the eastern
Sudan, which are either wooded or covered with dense grass in the south.
The Atbara and its tributaries in their upper courses drain the northern
slopes of the Abyssinian plateau, and traverse the level plains of the
eastern Sudan in a direction parallel to the Blue Nile.
The Albert Nile and its tributaries between Gondokoro and Lake Albert
traverse the broken and hilly country which is cut through by the Albert
Nile at the Fola and succeeding rapids. The catchment basins of Lakes
Victoria and Albert are the undulating hills, the flat marshy valleys,
the great lakes and, in parts, high hills which constitute the
highlands of Central Africa. The general level of the area may be taken
as 1400 metres above sea level.
The area draining into Lake Victoria is 240,000 square kilometres. At
the outlet of Lake Albert this has increased to 380,000, and at
Gondokoro to 470,000. The Gazelle river drains 470,000 square
kilometres, and the Sobat 160,000. The White Nile drains altogether
1,690,000 square kilometres, or more than half the total area of the
catchment basin of the Nile. The Blue Nile drains 300,000 square
kilometres and the Atbara 240,000. The Nile below the Atbara junction is
draining 2,290,000 square kilometres. Between the Atbara mouth and the
sea, the Nile drains whatever falls on a desert area of 720,000 square
kilometres.
If we take 3,000 cubic metres per second as the average annual flow past
Assuân we may say that the White Nile supplies 24% off more than half
the area of the whole basin, the Blue Nile 65% off ¹⁄₁₀ the area, and
the Atbara 11% off ¹⁄₁₂ the area. The Gazelle river drains about ¹⁄₆ the
total area and adds practically nothing to the discharge. Table 24
should be very carefully studied by any man who wants to understand the
Nile. It does not pretend to exactitude, but embodies the best
information I have been able to obtain.
6. =The climate of the Nile valley.=--This paragraph would have been
much more complete if Capt. Lyons’ monograph on the Meteorology of the
Nile valley had been published. In considering the climate I shall
follow the subdivisions of the catchment basin of the Nile contained in
Table I.
In the catchment basins of Lakes Victoria and Albert, the mean annual
rainfall may be taken as 1.25 metres, with great fluctuations between
good and bad years. Neglecting here and through this paragraph, the
light occasional falls of rain which are trying to travellers but which
have no effect on the rivers, it may be said that in these basins there
are two rainy seasons, the greater in March, April and May, and the
lesser in October, November and December. The former are followed by dry
southern winds, while north winds blow in the winter.
Along the whole of the Albert Nile, the mean annual rainfall may be
taken as 1 metre, with severe famines in occasional years and heavy
rainfall in others. The principal rains are between May and November,
with the maximum between August 15 and September 15. In years of
deficient rainfall, the June, July and August rains seem to fail. The
catchment basin of the Gazelle river may be credited with a mean annual
rainfall of 75 centimetres between May and October, while the mean
annual rainfall on the Arab river cannot be more than 30 centimetres
between June and September. The Sobat river in its upper reaches enjoys
an annual rainfall of about 1.25 metres and of ·75 metres in its lower
reaches. The time of rain is between March and September. The lands
draining into the White Nile north of Tewfikieh have an annual rainfall
of about 20 centimetres between June and September.
The Abyssinian part of the catchment basin of the Blue Nile enjoys a
good rainfall throughout nine months of the year from February to
October, with generally heavy rain between May and September, and very
occasionally in October. The rainfall here may be taken as 1.25 metres
per annum. In the plains of the eastern Sudan traversed by the lower
reaches of the Blue Nile and the Atbara the rainfall is very much
lighter and may be considered as 30 centimetres between July and
September; fairly constant and heavier in the south, and very inconstant
and lighter in the north. The Atbara and its tributaries in their upper
reaches on the northern slopes of Abyssinia, have rain from May to the
end of August and occasionally into September. There are great
fluctuations in the rainfall. The mean annual rainfall may be taken as
75 centimetres.
The desert area between Khartoum and Cairo has occasional winter rains
especially in the parts near the Red sea, but as these rains are nearly
all soaked up by the desert, and very little, here and there, reaches
the Nile, we may neglect them altogether. Railways have to be provided
with culverts and bridges where they cross the terminal reaches of the
khors and wadis which run considerable bodies of water for a few hours
after rain; but the effect on the Nile is practically nothing. Along the
sea-board of the Mediterranean there are a few inches of rain every
winter, sufficient as a rule to raise poor crops of barley.
In the catchment basins of Lakes Victoria and Albert the direction of
the winds may be taken as north-east in winter and south-east in summer.
The maximum monthly temperature may be taken as 35° and the minimum as
12°, with a mean for the year of 21°.
Along the Albert Nile the north wind blows through the winter, and
southerly winds prevail from about the 15th of April to October. The
temperature may be taken as ranging from a monthly maximum of 38° to a
monthly minimum of 16°, with a mean of 27°.
Tables 75 to 81 give the principal meteorological data for many places
in the Nile valley and compare the Bombay rainfall with the Assuân
gauges. The latter show how closely the Assuân gauge in flood follows
the rainfall at Bombay.
At Addis Ababa in the highlands of Abyssinia, the mean monthly
temperature ranges between 19° and 15°, with a mean of 17°. The winds
are south-east and east through the year. In 1902 the rainfall was 980
millimetres, and in 1903 it was 1340 millimetres. (Table 75).
At Wad Medani in the Grezireh south of Khartoum, the mean monthly
temperature ranges between 35° and 24°, with a mean of 30°. The winds
from October to April are from the north and from May to September from
the south. In 1902 there were 350 millimetres of rain and in 1903 there
were 310. (Table 76).
At Khartoum the mean monthly temperature ranges between 34° and 19°,
with a mean of 28°. The winds from October to April are from the north
and from May to September from the south. In 1902 there were 120
millimetres of rain and in 1903 there were 70. (Table 77).
For Alexandria, Cairo and Assuân, representing the Nile valley in Egypt,
I have prepared the following table:--
=========+====================+====================+====================
| ALEXANDRIA | CAIRO | ASSUAN
+--------------+-----+--------------+-----+--------------+-----
MONTH | THERMOMETER |Rain-| THERMOMETER |Rain-| THERMOMETER |Rain-
| Centigrade. |fall.| Centigrade. |fall.| Centigrade. |fall.
+----+----+----+ +----+----+----+ +----+----+----+
|Max.|Min.|Mean| |Max.|Min.|Mean| |Max.|Min.|Mean|
---------+----+----+----+-----+----+----+----+-----+----+----+----+-----
| | | |MILL.| | | |MILL.| | | |MILL.
January |25·0| 5·4|24·1| 54 |26·6|-0·7|12·4| 6 |32·5| 4·0|14·8| ..
February |29·7| 6·2|14·8| 22 |35·3| 1·2|14·2| 3 |37·0| 5·0|22·0| ..
March |37·0| 5·5|16·1| 17 |41·2| 3·2|16·9| 5 |42·0| 8·0|24·3| ..
April |38·9|11·0|18·5| 2 |42·6| 5·7|20·9| 2 |46·6|11·0|27·3| ..
May |38·9|13·3|21·3| 13 |44·2| 9·0|24·4| 2 |46·0|17·0|29·6| ..
June |39·4|13·8|24·0| .. |45·2|13·7|27·3| .. |47·0|20·0|34·2| ..
July |37·0|20·5|26·1| .. |44·3|17·4|28·5| .. |46·0|23·0|33·6| ..
August |35·0|20·3|26·6| .. |41·6|16·5|27·7| .. |46·0|21·0|35·1| ..
September|40·0|18·7|25·6| .. |40·6|14·0|25·3| .. |47·0|17·0|31·0| ..
October |37·8|15·0|23·7| 9 |42·1|12·1|23·2| 1 |42·0|18·0|28·7| ..
November |32·2|10·8|20·0| 38 |33·6| 3·5|18·1| 6 |40·0|11·0|23·1| ..
December |28·9| 6·8|16·0| 80 |29·4| 1·3|14·4| 6 |34·0| 6·0|19·0| ..
---------+----+----+----+-----+----+----+----+-----+----+----+----+-----
Year |40·0| 5·5|20·6| 235 |45·2|-0·7|21·1| 31 |47·0| 4·0|26·9| 0
=========+====+====+====+=====+====+====+====+=====+====+====+====+=====
From the above table we may conclude that at Alexandria, Cairo and
Assuân the absolute maximum thermometers may be taken as 40°, 45° and
47° Centigrade; or 104°, 113°, 116°, Farenheit. The minimum thermometers
as 5·5°, -0·7°, 4·0° Centigrade; or 42°, 31°, 39° Farenheit. The
rainfall at Alexandria, Cairo and Assuân respectively may be taken as
235, 31, and 0 millimetres; or 9, 1¹⁄₄, and 0 inches. The heaviest
rainfall in any individual year at Alexandria and Cairo respectively has
been 308 and 55 millimetres; or 12 and 2 inches. The lightest rainfall
at Alexandria and Cairo respectively in any individual year has been 108
and 7 millimetres; or 4¹⁄₄ and ¹⁄₄ inches. Assuân is practically
rainless. It does rain sometimes at Assuân, but there has been no rain
during the last three years while meteorological observations have been
taken.
7. =The Geology of the Nile Valley.=--South of Gondokoro along the
Victoria and Albert Niles, and at the lakes, the rocks are generally
granites, crystalline schists and quartzites. The hills of Uganda are
covered with red clay and marl on the higher lands, while the valleys
consist of a rich black loam. All the cataracts are granites and
granitic rocks or diorites. The Ruenzori range consists of lofty
volcanoes. The surface of the ground is covered with a fine Kankar
(nodulated limestone) in many places. North of Gondokoro the plains are
formed of sandy deposits mixed with coarse peat in places. The hills of
the Bahr-el-Gazelle and Arab river are all crystalline. Abyssinia is a
volcanic plateau. It is the detritus of this rich volcanic soil swept
down by the Blue Nile and Atbara which constitutes the richness of the
soil of Egypt and of the water of the Nile. Those parts of the eastern
Sudan south of Khartoum and El-Damer and at Kassala, which are the
deltas of the Blue Nile, the Dinder, the Rahad, the Atbara, and the
Gaäsh, are possessed of a soil in every sense similar to that of Egypt
itself. At Khartoum and in the bed of the Blue Nile at Kamlin are
extensive deposits of nodular limestone corresponding to the Kankars of
India.
The main Nile from Khartoum to Assuân flows between low hills and tables
of Nubian sandstone overlying crystalline rocks of gneiss, mica schists,
hornblendic granite and red granite. Where the crystalline rocks come to
the surface we have cataracts; where the Nubian sandstone is at the
surface we have reaches of unbroken water.
From Assuân[4] to near Edfu the Nile flows between hills of Nubian
sandstone, the best known of which is Gebel Silsila. From Edfu to near
Luxor, the Nubian sandstone which overlies the crystalline rocks dips
under the Nile and its place along the Nile Valley is taken by green and
grey clays containing nitrate and phosphate deposits. The former are
inexhaustible and have constituted the manure of this part of the valley
for thousands of years. With these deposits are thick banks of soft
white limestone.
[4] Condensed from a description of the geology of the Nile Valley in
Egypt written by Capt. Lyons for the second edition of “Egyptian
Irrigation”.
From Luxor northwards the clays dip under the Nile and the Nile Valley
is bounded by the superposed white eocene limestone up to Cairo.
The Nubian sandstone is always soft and porous. The limestone is
generally soft, though hard siliceous beds are sometimes met with. North
of Cairo there is no building stone of any value except the siliceous
sandstone of Gebel Ahmar near Cairo and the basalt of Abu Zabel, a
recent outcrop furnishing a black rock of great durability. The area
covered by this rock is small.
Thick deposits of sand and gravel underlie the Nile mud deposits of the
Nile Valley. All along the Nile, but especially south of Luxor, river
deposits of dark sandy mud exist on either side of the Nile Valley
considerably above the level of the deposit of to-day. The best known of
these is the plain of Kom Ombos. The thickness of the layer of Nile mud
in the valley is as much as 18 metres in places, but the average depth
is, I should say, 10 metres.
8. =The discharges of the Nile and its tributaries.=--Reference should
be made to tables 24 and 25 which embody the results of an exhaustive
examination of the observed discharges, the cross sections, the gauges
of the Nile Valley, and the calculated discharge tables made for these
gauges. Many of these tables are founded on only two or three discharges
and some on only one, but they have been prepared with the greatest care
and referred to all the existing gauge observations, and are good
working tables, which can be modified and improved as time places more
information at our disposal. Until then they may be used as about the
best approximations available to-day.
In 1902 the Albert Nile discharged 600 cubic metres per second as
against 520 discharged by the Victoria Nile. In 1903 the Victoria Nile
discharged 730 cubic metres per second and the Albert Nile 800. Leaving
a poor year like 1902 which was much below the average, and taking 1903
which was all round a good average year and only slightly below the
mean, we have the following results:--
The Victoria Nile was at its highest in July with 840 cubic metres per
second, while the Albert Nile at its head was at its highest in December
with 1,060 cubic metres per second. Lake Albert took 5 months to fill
up. At Gondokoro the Albert Nile was at its lowest in April when it
discharged 700 cubic metres per second as against 550 cubic metres in
the previous year. Swollen by timely and good rains south of Gondokoro
the discharge at Gondokoro rose to 2,100 cubic metres per second in
September after the river had scoured out its bed over a metre in depth.
The mean discharge for the year at Gondokoro was 1,200 cubic metres per
second.
The Gazelle river gave no discharge in the first half of the year and
about 30 cubic metres per second in the latter half. Its mean discharge
was 10 cubic metres per second for the year.
The Albert Nile at its tail above the Sobat junction gave as a minimum
350 cubic metres per second in March, which discharge rose to 430 cubic
metres per second in September, but could not rise higher as the Saubat
river was then in flood and the White Nile could not carry off much more
than the discharge of the Sobat without putting the northern part of the
Sudd region under 2 metres of water. This held back water helped later
to maintain the discharge of the White Nile in January and February.
The Sobat river gave as a minimum a discharge of 40 cubic metres per
second in April, and then rose to a maximum in November of 1,080 cubic
metres per second.
At its tail, the Albert Nile gave a mean discharge for the year of 390
cubic metres per second and the Sobat of 550.
The White Nile at its head was at its lowest in April with 400 cubic
metres per second and at its highest in December with 1,460 cubic metres
per second, with a mean discharge of 940 cubic metres per second. At its
tail near Khartoum the White Nile was at its lowest in May with 420
cubic metres per second and at its highest in October with about 1,700
cubic metres per second. As this latter figure was about 400 cubic
metres per second more than it was receiving at its head, the additional
water represented Blue Nile water which had run up the valley of the
White Nile, been stored there while the Blue Nile was high and then been
discharged into the Main Nile when the Blue Nile had fallen. The mean
discharge at the tail of the White Nile was 830 cubic metres per second.
This figure was much below that at the head and was due to the fact that
in July, August and September the Blue Nile water was flowing up the
White Nile.
The Blue Nile was at its lowest in April when it was discharging 120
cubic metres per second. During its maximum in August and September it
was discharging 8,200 cubic metres per second. Of the discharge of the
Blue Nile in July, August and September, a considerable part flowed up
the White Nile which here has a slope of ¹⁄₁₀₀₀₀₀ and a bed from 3,000
to 1,500 metres wide. It is for these reasons that the Blue Nile water
does not hurry on to Assuân in its full strength. The mean discharge of
the Blue Nile for the year was 2,350 cubic metres per second. Gauges and
discharge tables at Kamlin on the Blue Nile, and north of Omdurman on
the Main Nile, would be very much better than the Khartoum or Duem
gauges of to-day which are both in back waters.
The Atbara river was dry from January to May, in June the discharge was
200 cubic metres per second, rising to 2,300 cubic metres per second in
August. In October, November and December it was dry. The mean discharge
for the year was 380 cubic metres per second. When the Atbara river
rises in flood it cannot flow down the Nile to Egypt in its strength
until it has filled up the trough of the Nile as far as the 6th
Cataract. Gauges up and down stream of the 6th Cataract and at Shendy
would be interesting when compared with Berber.
The minimum combined discharges of the White Nile, Blue Nile and Atbara
river were 540 cubic metres per second in April. The maximum combined
discharges of 10,900 cubic metres per second were in August. The mean
combined discharges for the year were 3,560 cubic metres per second.
The minimum discharge of the main Nile above Assuân was 440 cubic metres
per second in May and the maximum of 8,600 cubic metres per second was
in September. The mean discharge for the year was 2,650 cubic metres per
second.
Table 25 gives the actual daily minimum and maximum discharges during
1902 and 1903 for each stream, with their dates. For the Blue Nile in
1903 they were 100 and 9,600 cubic metres per second; for the White Nile
380 and 1,470; for the Atbara 0 and 3,100; and for the Nile above Assuân
420 and 9,000 cubic metres per second.
Table 26 compares the discharges for a maximum year like 1878, a minimum
year like 1877, and a mean year, at Khartoum, Assuân and Cairo. The
maximum discharges in 1877 were 5,300, 5,900 and 4,400 cubic metres per
second, at Khartoum, Assuân and Cairo. In 1878 they were 12,500, 12,100
and 10,300 cubic metres per second respectively, while for a mean year
they are 8,500, 9,200 and 7,200 cubic metres per second.
The modulus of the river at Assuân is 3,040 cubic metres per second, and
at Cairo 2,640. After the very high flood of 1878, the lowest discharge
in May 1879 at Assuân was 1,500 cubic metres per second.
The behaviour of the Nile after passing Assuân and entering Egypt may be
described as follows:--of the mean discharge of 3,040 cubic metres per
second which passes Assuân 400 cubic metres per second are utilised in
Upper Egypt in the irrigation of 2,320,000 acres and 2,640 cubic metres
per second pass Cairo. Of these again 540 cubic metres per second are
utilised in the irrigation of 3,430,000 acres in Lower Egypt, and only
2,100 cubic metres per second reach the Mediterranean sea.