Geomorphology of the River Nile

Mon, 09 Apr 2018



 

Dr.  Muhammad Fathalla Muhammad

Abstract:

This study addresses the aspects concerning geomorphological features of the River Nile. Meanwhile, the study follows the circumstances under which the River was originated in its High Sources. A simplified and adequate study is presented to explain these circumstances, for instance tectonic movements which impacted geological and geomorphological structure of the River sources in both Equatorial and Ethiopian Plateaus and, again, the impact of consequent geological and geomorphological developments on the water flow system of the River Nile. It is worth mentioning that the material of this study was collected from a group of sources and specialized scientific references which addressed aspects of the geography of the River Nile Basin. In this study, the researcher made some modifications and inserted his own opinions and field remarks. So, the study concludes that the River Nile Basin and its tributaries pose the more prominent geomorphological and hydrological feature in East and Central Africa, including the Sudan. Also, geological structure of the Nile Basin is divided between Basement Complex (among different parts of it) and sedimentary rocks represented by Nubian Series which cover about 50% of the area of the Sudan and on which Nubian Nile flows.

 

Introduction:

In fact, every river has a legend that illustrates circumstances and events by which this river is affected inside areas that include its basin and valley and the space through which water flows. In this respect, the legend or story of the Great Nile refers to difficulty and complication of the Nile flows in a way that all general rules to which other rivers are subject cannot, in the geomorphologic point of view, be applied to River Nile. This means that there are no typical sectors of the River in which features of the high, middle and near courses of the Nile are incorporated. However, this irregular distribution which is incompatible with general rules of flowing undoubtedly yet explicitly shows how much complicated the geomorphologic development of the River is. Similarly, incompatibility of history of rocks and configurations including the space of the River course on a hand and history of the River flow, on another, are also complicated. Notably, the former tends to be of recent history on the general axis from South to North. In this light, we should perceive modernity and youthfulness which some sectors of the River Nile course are marked with since these sectors are irregularly and asymmetrically distributed in a way inapplicable to origins of the normal riverine system. These sectors denote that the River Nile, in its current scene from sources to estuaries, represents a young river regarding age and geological history.

As regards the story of geomorphologic development of the River and history of the Nile flows in its current scene, it is important to shed light on whatever may explain modernity of those modern sectors of the River course or may, otherwise, reflect factors and events that created the sectors. Naturally, the end of research and explanation entails practicing temporal expansion at the vertical level which digs deep in previous geological ages and times during which structural factors and events emerged and, consequently, impacted features of climate as they affected the nature and amount of rain and its relationship with surface flowing. Likewise, the end of research and explanation entails practicing spatial expansion at the horizontal level which means getting out of the large space, including the Nile Basin, to the neighboring land and basins. This spatial expansion aims at studying linkage of structural factors and events and how these factors and events affected the Nile flows and featured its current scenery.

Geologically, the Nile is involved in factors and events that contributed to the structure of African continent. Notably, these structural factors and events were the same ones that were combined to form the largest part of Gondwana Landmass which represented the Core of this continent. This means that the core mass, on and around which grew the African Land, had represented a large part of the Southern Continent of Gondwana Land which had been compactly existent during ages of Pre-Cambrian and nearly during some ages of the Cambrian. It is worth noting that Gondwana Land, to which the core mass belong, had been formed of rocks that ranged between archaic crystalline rocks, metamorphic rocks and old igneous rocks on a hand and antique sediments which belonged to both Pre-Cambrian and Cambrian on another. Meanwhile, structural tectonic factors and movements had affect and severely demolished Gondwana Landmass in about an age of the Cambrian time.

The outcome of those esoteric factors is summed up in the following:

  • Demolishment that resulted in the core mass
  • budging that mass and other masses towards the north in a way that created the side pressure
  • impacting sea sediments which had accumulated and magnified on the seabed of Nets sea
  • emergence of modern contortions on the sides of north western African continent and in south Europe

In addition, outcome of those esoteric factors came as a group of cracks, fissures, local fractures and shallow flexions which occurred on specific axes. This group of factors helped external factors to curve, deepen and form terrain images and inject a big group of basins which are irregularly scattering on Africa surface. Also, from a terrain viewpoint, these latter factors lent the basins its specific features.  Whatever these outcomes caused by esoteric factors are, most areas of the Great Nile Basin, which scatters from heart of Africa and heading northwards, were directly or indirectly affected by those factors with disparate amounts and results from an area to another. Needless to say, being acquainted with these factors and their outcomes on African land in general and on the Nile Basin land in particular necessitates the follow-up of geological history and old structural events. In so doing, one can be aware of circumstances that brought about the Nile flow or that combined to create the Nile and render it take its course as it does today.

 

Nile in Equatorial Plateau

To tackle the legend of flowing in the Equatorial Plateau, it is important to tackle the Nile flow which takes two courses which jointly drain the Nile water resource off this Plateau. These two courses are:

  • Albert  Nile which represents the starting point from which the water resource flows from Lake Albert towards the north
  • Aswa River, a revering branch draining water resource from a big basin which includes some areas north to Equatorial Plateau. These areas are not themselves included in any one of the basins comprising the Equatorial Nile system. Necessarily, there must be a comparative study on the two courses as they naturally drain waters from Equatorial Plateau or as they collect the permanent water resource that feeds the Nile flow and drain waters again from Equatorial Plateau to Bahr al-Ghazal Depression. Comparatively, the Albert Nile course is enjoyed with the most flowing from Equatorial Plateau while the share of Nile Aswa is meager if compared to the total resource drained to Bahr al-Jebel.  However, the feature of the space that includes Albert Nile flow is of two different parts as to the scenery, general shape and width and even to the length and all other basic features which confer riverine qualities. In this regard, the first and taller part stands out in the scenery of the hand extending on the general axle on which the Lake spreads out. On this hand, Albert Nile course is wide and expansive while the slope of running water here is quietly waddling on the groove bottom. As to the other part of Albert Nile, it includes the narrow course in which waterfalls and cataracts stick out and show that the Nile flow in this sector is more recent. 

The time when these waterfalls and cataracts emerged shows, in a way or another, the history of the Nile flow from Lake Albert and Equatorial Plateau as it also reflects the general scene of the current Nile flow. In this sector, the study discloses that the space of the newly born Nile course resulted in esoteric movements which themselves brought about cracking and fracture. Wiland sees that the likely suitable history for these esoteric movements and occurrence of cracking is recent in that it cannot date back beyond the middle Pleistocene Age for earliest estimate or the high Pleistocene Dawn for latest estimate. This means that these esoteric movements are extension to esoteric movements which created the water course of Victoria Nile between Kruma rapids and Victoria waterfalls. In this respect, there is a close relationship between upheavals in plateaus of East Africa and Abyssinian Plateau on a hand and those eruptions which had had impacts on sectors and areas of Equatorial Plateau on another. Undoubtedly, those upheavals and eruptions contributed to the complete panorama of the Nile flow. 

Aswa River, one of the important estuaries of the Nile to which it is connected immediately north to Nimule drains off a big basin which gathers, among other basins, on the surface of Equatorial Plateau. Aswa River is located north to Kuja basin and Victoria Nile where we see in it an example of riverine flow with special unparalleled features compared with all Nile riverine courses in this Plateau. With regard to general scenery, Aswa River is marked with features of the naturally grown river to which qualities and characteristics of normal river flow apply. Remarkably, general direction of the near course of the river is the general direction of the main course which includes Nile flow between Nimule and Gondokoro, namely the two courses keep running on a general axle where the riverine course is contained by the gorge resulted from cracking in the middle Pleistocene. This riverine course shows up as if continuing revering flow in Aswa course. 

The scenery of the Nile flow on the Equatorial Plateau had been a direct result for flowing of some riverine courses which made a group of basins, which are scattering on the surface of these courses, connected and associated. Geologically, this riverine flow brought about esoteric movements and eruptions that created cracking and fracture in more than one point and, also, determined space and axels and directions. Thus, one can perceive the actual launch that included the first stage of Nile flow during the period extending from late Pliocene Epoch to near Pleistocene Epoch. At that early stage, increased rain had obviously affected areas and levels of water bodies and, probably, boundaries that demarcated and divided basins might have been unclear or high. Perceptively, then occurring movements and eruptions had created and cleaved some cracks, fractures and gorges which included the space of Nile flow. Also, those same factors created the cracks that made Victoria Nile flow and fixed the relationship between Lakes Victoria and Albert, besides creating fissures which rendered water flow from Lake Albert towards the north. 

Hence, that period had witnessed those movements which activated regressive curving in some riverbeds and completed the process of riverine containment whereby both Kajira and Simliki rivers have flowed and both Lakes Edward and Albert were completely connected. Therefore, it can be said that actual flow of waters in the Nile Course and hydrologic connection between lakes were completed in the second stage. This stage had included the scenery of complete flow of the Nile during the late Middle Pleistocene Age for earliest estimate or early High Pleistocene for latest estimate. Certainly, increased rain during that period and through the second Rainy Age boosted up flow levels higher than they are today.

High Pleistocene Age had experienced the actual linkage, runoff flowing and connection of lakes which represent the cornerstone of the Nile system in Equatorial Plateau. When this panorama was completed in that stage, waters of Equatorial Plateau had been running northwards from different courses, i.e. Aswa River and Albert River. It is likely calmness of flow was affected by increased rain in the second Rainy Age, known as Gamblian, or by increased rain in following stages. Nevertheless, all this could not make important or original changes in the scenery of the Nile flow in that stage.

 

Nile in Abyssinian Plateau:

Three different factors contributed to create and heighten the Abyssinian Plateau and confer special features on it. These factors are of disparate origin but are of integrated outcomes, yet they are all well connected with esoteric movements and eruption cases and instability which had long remained from about Cretaceous era to Pleistocene Age. These factors are as follows:

  1. Height of the Plateau mass which was affected by lifts and pushing movements from bottom up.
  2. Slide of what was about the Plateau under pressure of esoteric movements up-down.
  3. Accumulation ensuing volcanic activity and eruption of lava and volcanic rash out of points of cracks and fractures in the Plateau mass.

According to this, light can be shed on the study of the River and developments of surface flow to, lastly, connect all this with the Nile. It is worth noting that researches are not certain regarding the legend of both Rivers of Atbara and Subað but the Blue Nile course was deeply studied and researched concerning its geomorphologic development and stages of water flow.

Atbara River, on the northern parts of the Abyssinian Plateau, is an Abyssinian tributary which had remained far away from cores of eruption and instability which had affected the Plateau. Notably, the longest side of the main course of Atbara River runs on Sudanese plain. Certainly, all researches could not find out clear evidence referring to the history of its development and flow nor could they refer to how much the River course was affected by those eruptions and instability cases which had overridden most of the Abyssinian Plateau sectors. Nevertheless, Atbara River is certainly more regularly running in its riverbed than other riverbeds of the Abyssinian Plateau. Concerning its panorama, Atbara is the nearest one to normal rivers and, from this perspective; it is likely the oldest one of all Abyssinian rivers and the oldest one of them in relation to flowing into the greatest Nubian Nile.

Mainstream of researchers considers Atbara as one of old main high sources of the Nubian Nile at a stage when the current scenery of the Nile had not completed. This opinion builds on a set of evidence and outcomes, all of which refer to likelihood of flow of the River in earlier time than in some other Abyssinian tributaries. Probably, among material evidence are some sediments and side configurations in the River valley. The evidence is manmade stone tools dating back to early Old Stone Age and refers to ex istence of the River in that Age. So, it is more possible to perceive the flow of this comparatively old River than perceiving all other Abyssinian rivers since the flow of the River dated back to Pleistocene Age at earliest estimate. It is to be understood, out of this estimate, that high branches of Atbara River on northern ends of Abyssinian Plateau are seemingly affected by mountainous masses left by volcanic activity and accumulation of lava on earth surface. Also, there is the fact of heights that determined slope landmarks which are unlikely dated back earlier than Pleistocene Age. This hypothesis is built on knowing the past movements in consequence of which Red Sea Hills heightened and their basic features stood out in the Higher Miocene Age during which the legend of Atbara River was started. However, the increased rain in that age caused the flow of the River with curving and digging the space which included water flow in Atbara basin.

As to Subaðt River, it comprises flowing and coupling of a group of riverine tributaries and courses, the more important of which flows from western slopes of Abyssinian Plateau towards northern end of Bahr al-Ghazal Depression. For this River, all researches and studies on its courses did not register an outcome of geomorphologic development which rendered its waters flow in the Nile. But, concerning general configuration, it is remarkable that the near course of the River is latest and embryonic. Accordingly, these qualities of the River course make us believe that this sector of the embryonic course is not, concerning geological age, dated back to far beyond High Pleistocene Age. It is likely this perception may not be sufficiently true since it is unconvincing that the flow of near sector of Subað  was only affected by Abyssinian tributaries, at the forefront of which is Baro River. Probably, there are other tributaries in which waters might have dug and flowed in pre-Pleistocene Age. This means that these riverine tributaries which flow on the eastern side of Bahr al-Ghazal basin, with their slopes affected by the nature of this land and their quiet and slow flow, are only remains of an old riverine system. However, all these premises remain lacking evidence founded on research and study. As a result, the outcome of these studies does not only shed light on Subat River and history of its flowing but go beyond that to prove pre-Pleistocene riverine flow system in Bahr al-Ghazal basin depression and its relationship with water flow system of the Nile riverine tributaries in the surrounding lands in all directions.

Blue Nile, master of Abyssinian tributaries, got the lion’s share in many studies and researches according to the great role played by its riverine flow since it supplies the River Nile with hydro capacity that helps the latter continue its long journey to the north. However, studies noted that the Blue Nile may not be an old tributary, notwithstanding its deep course and the deep valley through which the River runs, i.e. this valley is about 1500 meters deep in some points. But, it can be said that this initial estimate is supposedly submitted because digging, curving and deepening in configurations of which Abyssinian Plateau consists is a relatively easy thing. Again, volcanic rocks are not of the same type and also torrential rain and surface slopes help deepen configurations and create the space that includes the rapid flowing. From geological point of view, the remarkable depth seen in the valley which includes the course space does not prove that the River is old but, otherwise, the twists of the River seen around the hills in Gaujjam region and the River changing its direction more than once are apparent evidence that the River was lately created. In this light, it can be perceived that the Blue Nile or at least some of its parts are newer than terrain sceneries found on the surface of the Abyssinian Plateau. This means that the complete panorama of the Blue Nile we now see is supposed to be completed in ensuing date to the time when terrain sceneries of the Abyssinian Plateau had been completed, knowing that these terrains determined the River course.

According to some researches carried out on Lake Tana, for example Yeltsin study, 1880, the flow of the Blue Nile had been in gestation during the Middle Pleistocene Age. In the Near Pleistocene Age or about the first Rainy Age, the Abyssinian Plateau had included more completely different status and scenery than its scenery in the High Pleistocene Age. So, it can be said that Lake Tana had never been existent in the Near Pleistocene Age and, probably, there was no any trace of the lava barrier which stoutly closed the basin which, thereafter, included the Lake due to volcanic activity and flow of lava which contributed to creation and formation of some details which were added to terrain scenery on the Plateau surface. These changes stoutly closed the basin in which Lake Tana was formed and helped accumulate some of the latest lava in a way that affected general directions of the flow. Likewise, height of eastern end of the Plateau made basic changes in sloping levels on the Abyssinian Plateau at the general axle from east to west where these changes caused flowing and drainage of water through the Blue Nile. Yet, the new scenery included miniature details assimilated in the current complete scenery, because some details had not reached the stage which they reached later on. This means there was new scenery that emerged between the late Middle Pleistocene and early High Pleistocene eras other than the scenery of the Near Pleistocene which had included new details truly reflecting the flow of the Blue Nile even without linkage between the Blue Nile and Lake Tana which had not then been filled with waters and even waters had not flowed out of the southern outlet on barrier of the new lava.

The complete image of the flow of Blue Nile emerged through some time during High Pleistocene, i.e. the second Rainy Time. It can be understood that increased rain in this age helped accumulate water in Lake Tana basin and lifted up surface level in the Lake to the extent that water could flow towards the direction that linked the Lake with Blue Nile. Hence, we can say that water flow of Abyssinian Plateau towards the west to connect with flow of the Nile had also coincided with connection of Equatorial Plateau with the Nile. So, no wonder that they were both affected by the same circumstances and esoteric movements linked factors which remained active in East Africa and the region of the Great African Rift. In this regard, we may get to a blatant coordination between consecutive sceneries which had emerged in every stage of Pleistocene and reflected factors that were combined to confer specific features on every one of those sceneries for both Equatorial and Abyssinian Plateaus. 

 

Geomorphology and Hydrology of the River Nile:

The Nile and its tributaries are of the more important water landmarks in the Sudan. The Nile consists of two main branches which are White Nile and Blue Nile where the former originates in Lake Victoria in Lakes Region. When the White Nile gets out of the Lake, it passes through Robin waterfalls on which Owen Dam was built for electricity generation. Thence, the Nile heads northwards to Lake Kiauva and to Lake Albert which is fed by Simliki coming from Lake Edward to the south. From Lake Albert, the Nile heads northwards to pass borders of Uganda and South Sudan at Nimule town. After that, the White Nile flows on a flat plain where its water spreads out on vast area on which grasses grow to form what is known by the Suds in which the River loses a lot of its waters due to evaporation. In this area of Suds, the Nile is called Bahr al-Jebel. On passing the Suds, it embraces Bahr al-Ghazal, which comes from the west, at Lake NŪ. From there, the River runs eastwards to meet Subāt River which slopes down from south east and then it heads northwards to Khartoum where it meets the Blue Nile. The latter originates in Lake Tana in the Ethiopian Plateau and brings large quantities of water during flood time. This Nile slopes so rapidly down to Sudan plains where both rivers of Dindir and Rahad flow into it before meeting the White Nile in Khartoum.

On confluence of White and Blue Niles, the Nile flows through the desert and pours water into Mediterranean Sea. During this journey, the River Nile is met only by Atbara River at Atbara town. This latter river comes down also from Abyssinian Plateau and feeds the Nile with large amounts of water and silt. However, north to Khartoum, the Nile is obstructed with a number of cataracts known as First Cataract at Aswan town and Sixth Cataract at Sabalauka area, immediately north to Khartoum (Hurst, 1946).

White Nile:

White Nile occupies the basin bed which is formed with connection of both Bahr al-Ghazal and Central Sudan basins. This basin includes, besides the two courses of White and Blue Niles, some areas extending westwards in Darfur and Kordofan to contain the wide semi-flat land of plateaus and extend eastwards to include most areas of land of Butāna. The land surface included by this longitudinal basin is marked with smoothly uneven height to the east and another one west to the sector occupied by the White Nile valley and a smooth slope along the longitudinal extension from Malakal to Khartoum. By time, dry valleys had torn down the surface while longitudinal sand hills gather on wide areas. Also, diversity in the surface shape increases with pervasion of some mountainous blocks whose levels are higher than the general surface level (MuÊammad, 1956).

White Nile occupies the basin bed which is situated on an average level of 380 meters above sea surface. As to Blue Nile, which penetrated the basin, it nearly keeps passing on relatively higher levels than the low basin bed since the River slopes from a level of 445.9 meters at Rusairis down to 375.88 meters at Khartoum. This means Blue Nile level won’t be equal to White Nile only in the last sector of its course north to Wad Madani.

The slope in the basin bed is largely slender and thin as the slant of White Nile reflects it and that difference of the Nile course levels at the beginning and end of the River in Malakal and Khartoum were counted. Perceivably, the slope between Malakāl and Gabalain reaches 1:60000 and then dwindles between Malakal and Khartoum to reach 1:20000 while the slope of the Blue Nile between Ruîairiî and Khartoum is 1:6700. However, the great difference between the slope degree in both Rivers are blatant in relation to the longitudinal sector of Central Sudan basin which is one of basins connected by the Nile flow on the general extension from south to north.

White Nile is about 840 km long but the difference of water level in its high and low parts, when Blue Nile levels are low, is about 12 meters or about 1:100000. Reversely, this difference is decreased to 8 meters on the flooding of the Blue Nile. However, tributaries of the White Nile are extremely few in southern parts, including Khaur A'dār which drains off Machār swamps. Even if amounts of water drained by these khors are unknown, they certainly add to the River since it was proved that loss of the River between Rank and Malakal, South Sudan, is negligible, i.e. 0.25%. This is attributed to the fact that evaporated and leaking water to the neighboring swamps, during water flooding season, returns once more to the River.

Notwithstanding Jabal Awlia Dam, study of water drainage of the White Nile notes that the River is not only affected by drained water from Malakal, South Sudan, but is also affected by Blue Nile waters which hold back waters of the White Nile due to the weak current of the latter.  However, the higher waters of the Blue Nile are in Khartoum, the farther waters of White Nile are held back. So, when waters of the Blue Nile are at their zenith, waters of the White Nile become in horizontal level in the last 200 km with its waters level getting higher for 30—40 cm in the first 100 km from the Confluence. In this struggle, impact of water levels extends southwards upstream to Jabalain, about 400 km south to Confluence of the Niles. Here, Jabal Awliya Dam, being filled from July to October, confines these waters in order to be regularly drained when needed (Lyons, 1916).

Blue Nile and tributaries:   

Blue Nile has a unique advantage among the Nile tributaries as it is responsible for 70% of the Nile waters. Known as Abbay River in its source at Lake Tana, the Blue Nile originates at 1840 meters above sea level. In itself, Lake Tana is a basin lake in which tributaries gathered to form the Blue Nile but the nature of the volcanic plateau and flow of lava to the south of the depression had formed a barrier extending from east to west to stop flow of water which again gathered beyond the barrier and formed the Lake.

Blue Nile travels for 975 km between the Plateau and Ruîairiî  town and this part, regarding amount of water, is one of the more important parts of the River. Notably, this part the River is marked with many twists and extreme depth which sometimes reaches 1500 meters in addition to many waterfalls and cataracts through which the River passes. The more important waterfalls here are Tissat which show up shortly after origination of the Blue Nile. At these waterfalls, waters drop from a height of 50 meters and these landscapes have their own causes and effects. Naturally, their causes are attributed to structure and terrain of Abyssinian Plateau. Therefore, given irregular accumulation of the mammoth volcanic masses comprising the Plateau, the enormous volcanic masses, whose diameter gets sometimes to 70 or 80 km, have posed hurdles before the River which, more than once, is forced to deviate and avoid these obstacles. On another hand, the extreme depth of the River in the Plateau is attributed to nature of rocks which are apt to weathering and to nature of high surface. As to effects of these landscapes, gyration of the Blue Nile and its reaches in Abyssinia has a big impact on collection of those huge amounts of waters which the River annually carries. Actually, while originating from Lake Tana, the River doesn’t carry but about 6% of its waters while the many tributaries embracing it, particularly those which meet the River at its left bank, supply the Blue Nile with about 90% of water (Hurst, 1952).

Given the extreme slope of the River between Lake Tāna and Ruîairiî, i.e. 994 m along a distance equaling roughly 975 km, only little part of its water evaporated in this area. But what is certain is that there is no loss of water caused by swamps or floods in this part.

On getting out of DamāzÌn town, the River seems barely sloping compared to what it is in the former case, i.e. about 100 m for 640 km. Here, the River flows on old sedimentary clay plains which were formed when the River had once been flooding and submerging vast areas. Then, before reaching latitude circle of Sinnār, the Blue Nile is marked with a group of khors which had dug their courses on ancient riverine terracing, some of which was covered with water when Ruîairiî Dam was built. On passing Sinnār, the River gets marked with many twists while sporadic lakes stand out. These lakes are filled with water in rain and flood season and may keep up their waters for many months after flood season of the River.

Remarkably, the River banks in this part are several meters high where the River is connected here with its two branches, Dindir and Rahad, which are nearer to khaurs than to genuine rivers. These two branches nearly get dry in the period when the River levels of water become low, i.e. period of TaÊāriq, and are changed to scattering pools separated by sediments of sand. In the rain season, the two branches are rapidly filled with water and the biggest one of the two branches, i.e. Dindir, will supply the Blue Nile with about 3% of its waters, namely a proportion equivalent to the amount supplied with White Nile and Subāð combined. As to Rahad, it doesn’t supply the Blue Nile but by one third of this amount of water (Saudi, 1983). 

At the summit of flooding of Blue Nile, the drainage of the River, at Suba suburb of Khartoum, reaches about 6000 cubic meters per second which is equivalent to 50 times the least drainage of it. Besides level of water, impact of flood is reflected in speed of the current and in the amount of hanging clay in water to the extent that proportion of hanging clay gets to 3600 ppm at Khartoum where difference will be clear between the dark brown waters of Blue Nile and the fresh grey waters of White Nile.

Sinnār Dam doesn’t impact drainage system of the Blue Nile because the Dam's capacity, when filled, doesn’t equal but the amounts of flowing waters in one day during flooding. The Blue Nile resources of waters, which reach in total about 52 billion cubic meters in the year at Khartoum, can be summed up as follows as shown in Table 1(Ibid):

Table 1:  Blue Nile resource of water 

Source

Percent

From Lake Tana

6%

From branches between Tana and Ruîairiî

90%

From Dindir

3%

From Rahad

1%

 (Source: azÌn, 1953)

 

Nubian Nile

The Nile derived this appellation from Confluence of White and Blue Niles down to town of Aswan, namely about 1900 km. however, the Nile course through this area is clear-cut and can carry any amount of flowing waters except in some locations like Sabalauka, Shandi and Atbara in the River Nile State, and in towns of KarÌma, Marawi, Dungola and Karma in the Northern State. At these points, some tucks in the shape of English letter “S” mark the Nile. On its journey, the River Nile heads north east and then North West from Khartoum to Abu amad where it takes a south western direction from Abu amad to al Dabba, then it slightly turns to head northwards. Arguably, opinions differ with regard to these tucks and two opinions explain them as follows: 

  1. Cracks had occurred in the crustal in this district, some of which from south west to north east and some were parallel to the Red Sea. These cracks took place at the time when the Red Sea was cleaved to consequently form the refractive course through which the Nile is now running.
  2. Nothing refers to occurrence of cracks in the crustal here, but only cause of these inflexions was recessive erosion and the River load of grit and gravel.

As to the second event in the Nubian Nile is a group of six cataracts which begin from Sabalauka Gorge north of Khartoum and end south of Aswan. Geologically, these cataracts are attributed to juvenility of the Nile in this place where igneous rocks, which stand out in the middle of the Nubian sandstone, are overlapping except for Sabalauka Cataract which is located in the middle of igneous rocks. However, the River could erode soft rocks, i.e. Nubian grit, till it reached granite rocks which the River took a long time to weather and, consequently, these latter rocks remained as rocky islands obstructing the Nile course (azÌn, 1953).

Some kilometers north of Atbara, there is the Fifth Cataract extending for 100 km to end up in Muqrāt island, after which the Nile runs in a course free from obstacles and, then, it heads south west till features of the Fourth Cataract stand out after Shiri island which extends for about 110 km and where the River extremely slopes down to reach 1:3200 meters. Then, the River gets into an area where sloping decreases until the Third Cataract at Abu Fātima which nearly connects to the Second Cataract 9 kilometers south to town of alfa. Then, after about 345 km, the River reaches the First Cataract south to town of Aswan. Notably, of late, the First Cataract and Fourth Cataract were covered by waters of the High Dam and amdāb Dam respectively. On the whole, the Nubian Nile is relatively of extreme slope and rapid current where these cataracts played a great part in this. Helpfully, this latter fact helps reduce the loss of evaporating water in one of the most arid districts in the world. It is worth noting that no tributary other than Atbara River is connected with the Nubian Nile all through its flow north of Khartoum.

Atbara River:

Atbara River originates from the Ethiopian region of Gondar. In fact, the River is a group of tributaries combined with each other near town of Gallabāt to form Atbara River. The more important one of these branches is Takzi or Sitait River which originates from east Ethiopian Plateau at latitude 12° north. This river course draws two big bends between latitude 12° and 14° north in a way resembling English letter “Z”. The distance between the confluence of Takzi River and Atbara River is about 500 km. comparatively; Atbara River is different in its sloping from that of the Blue Nile as the slope of the former is 1:4000 meters while the slope of the Blue Nile is 1:10000 meters. Accordingly, Atbara River carries 3 kg of clay in every cubic meter of water while the Blue Nile holds only one kg of clay and big islands disappear in this River because of its extreme slope.

Atbara River differs from the rest of Abyssinian tributaries of the Nile in that it nearly gets dry for five months in the year (January—May) and is broken into rivulets and pools. Then, it is refilled with water in rain season of Abyssinian Plateau where its drainage reaches 173 million cubic meters per day in August.

This River adds to the main River Nile about annually 12 billion cubic meters, i.e. about 17% of flood waters where water position becomes, on the supply of Atbara River, as shown in Table 2 (Ibid):

 

Table 2: Water resource of the Nubian Nile (post-Khartoum Nile):

Water Source

Amount of water (Cubic Meters)

Water resource of White Nile

26 billion

Water resource of Blue Nile

52 billion

Loss of evaporation and leak, Khartoum -- Atbara

2 billion

Water resource of Atbara River

12 billion

total

88 billion

(Source: MuÊammad, 1956)

 

Thus, the permanent source of Nile waters and Lakes Region are contributing in feeding the Nile with about 16%; while the seasonal source, Abyssinian Plateau contributes to the Nile with about 84% arithmetically. If we take the 84 billion cubic meters as 14 units with six billion cubic meters for each unit, hence drainage of tributaries presented in Table 3: 

  Table3:  Amount of drainage of the River Nile and its tributaries

Drainage (unit equals six billion cubic meters

tributary

4

Bahr al-Jebel after Lake Albert

2

Bahr al-Jebel at Lake No

2

Subāð River at its mouth

4

White Nile at Khartoum

8

Blue Nile at Khartoum

2

Atbara River

14

Nubian Nile on entering Egypt

              (Source: Shāmi, 1983)

 

Generally, it can be said that the River Nile is more than 6000 km long on the general semi-regular axle from south to north. The River and its tributaries occupy a basin of great area extending between latitude circle 3°.30' south and 31°.30' north with extension of 34 latitudinal degree. The area of this basin is about 2.9 million square kilometers and the River itself is considered as the longest riverian course in the world.

(Footnotes are needed)

 

Sources, references and appendixes:

Firstly: Sources and references:

  • Al Tom. Mahdi AmÌn and Bābikir Abdel RaÊmān (2010) – Natural and Human Geography of Sudan, publications of the Open University of Sudan – Khartoum – Sudan.
  • al Shāmi. îalāh AddÌn A'li (1983) – North Eastern Sudan. a Study on the Red Sea Hills and their Dry Valleys – Cairo – Egypt. Ì
  • al Shami. îalāÊ AddÌn A'li (1983) – Sudan – Geographical Study – Al Maa'ārif Establishment – Alexandria – Egypt. î
  • HazÌn. Sulaiman AÊmed Sulaimān (1946) – River Nile, its Geological Development and Impact of this on Birth of Early Civilization – Dar Al Maa'ārif – Egypt.
  • Saudi. MuÊammed A'bd el Ghani (1983) – Geography of the Sudan – Anglo-Misri Library – Cairo – Egypt.
  • MuÊammed. A'wad MuÊammed (1965) – River Nile -- Cairo – Egypt.
  • Hurst. (1946) – a Brief on Nile Basin (Arabic copy) -- Cairo – Egypt.
  • Andrew, G. (1952); Geology of the Sudan, In Agric .In the   Sudan, London.                                                   - Barber, K.M.(1961) ; The Republic of the Sudan, London      .
  • Ball .j. (1939); Contributions to the Geography of Egypt .Cairo.                                                                                               
  • Richards. C .H; The Gash Delta, Ministry of Agriculture -- Khartoum.                                                                                     
  • World, G. A. (1957); A simple Introduction to the Geology of the Sudan, in S. N. R.                                                               
  • Lyons. G. (1916); the Physiography of the River Nile and Its Basin, Cairo.                                                                                
  • Hurst, H. E. (1952); the Nile, London.

 

Secondly: Appendixes:

A Map showing River Nile Course and its main tributaries

Source: Sudan Survey Authority

 

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