The quality of surface waters in the Nile Basin
is influenced by both natural and human
factors, with human influences having far
greater impact. Although the chemical
quality of the water is good, its physical and
bacteriological quality is generally poor.
Evapotranspiration (ET), which is the sum of evaporation and plant
transpiration, is an important element of the water cycle. Evaporation
accounts for the movement of water from sources such as soil
The Main Nile Zone: This encompasses the downstream river reach,
starting at the Blue–White Nile confluence at Khartoum. This large
area generates virtually no runoff, and in-stream evaporation results
in a net loss. River flow in the lower reaches is controlled by Lake
Nasser, which is subject to significant evaporation losses.
As well as surface waters, the Nile Basin countries have considerable
groundwater resources occurring in localized and regional basins.
The term ‘basin’ refers to the geographical
area drained by a river or lake. The Nile Basin,
in the context of this report, refers not only
to the physical drainage area of the Nile with
its associated biophysical and ecological
elements, but also to the people living within
the basin and features of their social, cultural,
and economic development.
THE MAIN SUB-BASINS
AND THEIR CONTRIBUTION
TO THE NILE
billion cubic metres per year
The NBI is not an authority on
(Map prepared by the NBI; source of data: Blackmore
and Whittington 2008)
Rainfall over the basin is characterized
by highly uneven seasonal and
spatial distribution. Most of the basin
experiences only one rainy season typically in the summer months.
From analysis of sediment accumulation in Sudanese
reservoirs, the total load of sediment in the Nile is
estimated to be about 230 million t/yr.
With a growing population and increasing calorie intake associated
with rising prosperity, demand for food in the Nile Basin is set to
There are 22 main soil types and nearly
twice as many soil sub-types in the Nile
Basin according to the FAO-UNESCO soil
categorization scheme (see map opposite).
The Nile drainage network, which
is described in Chapter 2, comprises
many rivers, small and large. Among the
bigger rivers are the Kagera, Nzoia, Victoria
Nile, Semliki, Albert Nile, Bahr el Jabal,
Bahr el Ghazal, Sobat, Blue Nile (Abay),
Atbara (Tekezze) and Main Nile. The rivers
are commonly fringed by gallery forests
and herbaceous littoral vegetation.