Although the River Nile Basin receives annually ca.
1600 billion cubic meters of rainfall, yet some countries within
the Basin are suffering much from lack of water. The great
changes in the physiography of the Nile Basin are well
displayed on its many high mountains, mostly basement rocks
that are overlain by clastic sediments and capped by volcanics
in eastern and western Sudan. The central part of the Nile Basin
is nearly flat including volcanics in the Bayuda Mountains and
volcanic cones and plateaus in southwestern Egypt. The high
mountains bordering the Nile Basin range in elevation from
3300 to 4600 m.a.s.l. in the Ethiopian volcanic plateau in the
east to ca. 3070 m.a.s.l. in the western Gebel Marra, and
1310 m.a.s.l. in the Ennedi Mountains in northwestern Sudan.
In central Sudan, the Nile Valley rises approximately 200–
300 m.a.s.l. In Egypt, the River Nile is bounded by the Red
Sea Mountains in the east, assuming ca. 1000–2600 m.a.s.l.,
mostly of basement rocks, which are covered to the north of
Aswan by Phanerozoic sediments sloping to the west, passing
by the Nile Valley and continuing through the Western Desert.
The Phanerozoic cover on both sides of the Nile is known as the
Eastern and Western Limestone Plateaus. These plateaus assume
elevations varying from 300 to 350 m.a.s.l. near the eastern
bank of the Nile to 400–500 m.a.s.l. south Luxor at Esna
and west of Aswan. The nearly flat Sahara west of the Nile
Valley rises gradually westward until it reaches Gebel
Uweinat in the triple junction between Egypt, Sudan, and
Libya. Gebel Uweinat has an elevation of 1900 m.a.s.l. sloping
northward towards the Gilf Kebir Plateau, which is
1100 m.a.s.l. The high mountains and plateaus in the southern
and western Egypt slope gradually northward where the Qattara
Depression is located near the Mediterranean coast. The depression
is −134m.b.s.l., which is the lowest natural point in Africa.
All these physiographic features in Sudan and Egypt are related
to (i) the separation of South America from Africa, which
started in the Late Paleozoic and continued up to the
Cretaceous, giving rise to several generally E–W-oriented tectonic
features inside Africa, (ii) the uplift of the Red Sea
Mountains and their continuation inside Africa resulted in the
East African Rift System (EARS), (iii) the Guinea–Nubia
Lineament crossing Africa from the Atlantic to the Red Sea
where many havoc trends, mostly E–W-trending faults, and
uplifted basement features pierce the overlying sediments, (iv)
parallel and longitudinal structures associated with volcanic
plateaus and cones extend from west Sudan (Gebel Marra) to
Ethiopian Plateau, passing by volcanics and plume features in
between and the basins in east Africa were subjected to wrench
related inversions, and (v) the Sudd linear E–Warea stretching
more than 1000 km between Gebel Marra in the west, passing
by South Sudan and reaching southwestern Ethiopia. Here,
fluviatile and subsurface waters led to ponds, lakes, and wet
areas that are hard to exploit. The impact of these features led to
the present south to north River Nile, but passing by many
changes in the direction of its many tributaries and slope reversal
of some of the major extinct rivers, either sectors of themain
Nile or the rivers once flowed into the main river. The paleoclimatic
changes during the Quaternary period: wet and dry
have a great effect on the physiographic features and slope
reversal of the Nile Basin drainage system. |
