The Project Gutenberg EBook of The Nile in 1904, by William Willcocks This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org. If you are not located in the United States, you'll have to check the laws of the country where you are located before using this ebook. Title: The Nile in 1904 Author: William Willcocks Release Date: June 23, 2018 [EBook #57379] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK THE NILE IN 1904 *** Produced by Chris Curnow, Harry Lamé and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive) Please see the Transcriber’s Notes at the end of this text. Cover 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 9s/- 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. P R E FA C E 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. [3] [5] [6] [7] 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. [8] 1. Introduction. 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. Longitudinal section of the Rosetta Branch 54 XVIII. Longitudinal section of the 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. —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. [9] [10] [11] [12] 2. Nomenclature. 3. Description of the course of the Nile. [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. —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. —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. PLATE I. Lith. Sur. Dep. Cairo. Larger map (240 kB) THE NILE 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. [13] [14] 4. The Slopes and velocities of the Nile in its different reaches. 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. —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. PLATE II. Lith. Sur. Dep. Cairo. Larger illustration (180 kB) 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 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. [14] [15] [16] 5. Catchment basins of the Nile and its tributaries. 6. The climate of the Nile valley. —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. —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 [17] [18] [19] 7. The Geology of the Nile Valley. 8. The discharges of the Nile and its tributaries. 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:— Month ALEXANDRIA CAIRO ASSUAN THERMOMETER Centigrade. Rain- fall. THERMOMETER Centigrade. Rain- fall. THERMOMETER Centigrade. Rain- 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. —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. —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 [20] [21] [22] 9. Lake Victoria Nyanza. 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. CHAPTER II. The tributaries of the Nile. —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, [23] [24] [25] [26] 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. PLATE III. RIPON FALLS Plan and Section Scale 1 : 6.000 Lith. Sur. Dep. Cairo. Larger illustration (210 kB) 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, [27] [28] 10. The Victoria Nile. 11. The Semliki River. 12. Lake Albert Nyanza. (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. —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. PLATE IV. CROSS SECTIONS of the NILE & its TRIBUTARIES Horizontal Scale 1 : 2.000 Vertical Scale 1 : 600 Lith. Sur. Dep. Cairo. Larger illustration (300 kB) 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...