Zifta, Asyut,
Isna, Naj'Hammadi Diversion Dams, Aswan First Dam
In 1843 work begun on diversion dams
(barrages or weirs) across the Nile at the head of the
delta about 12 miles downstream from Cairo, so as to
raise the level of water upstream to supply the
irrigation canals and to regulate navigation. The work
was not completed until 1861, after which it was extended
and improved it was the beginning of modern irrigation
dam building in the Nile valley. The Zifta dam, on the
Damietta branch of the Nile, was added in 1901. In 1902
the Asyut , 200 miles upstream from Cairo, in 1909
the Isna 160 miles above Asyut, and in 1930 the
Naj' Hammadi, 150 miles above Asyut were completed.
Construction on the first Aswan Dam begun 3 years after
Emperor Menelik's Defeat of the Italians at Adwa and
ended in 1902; it has a series of four locks to allow
navigation. The dam has twice been enlarged--first
between 1908 and 1911 and again between 1929 and 1934,
raising the water level and increasing the dam's capacity.
It is also equipped with a hydroelectric plant with an
installed power of more than 345 megawatts.
Aswan High Dam
The Aswan High Dam is located about
600 miles upstream from Cairo and 4 miles upstream from
the first Aswan Dam. It is built at a place where the
river is 1,800 feet wide and has steep banks of granite.
The dam is designed to control the Nile water for the
expansion of cultivation and for the generation of
hydroelectric power and to provide protection downstream
for both crops and population against unusually high
floods. The work began in 1959 and was completed in 1970.
The High Dam is 12,562 feet long at crest level and 3,280
feet wide at the base, with a height of 364 feet above
the riverbed. It has a hydroelectric plant with an
installed capacity of 2,100 megawatts. Lake Nasser
stretches some 310 miles upstream from the dam site,
extending 125 miles into The Sudan.
The principal objective behind the construction of the
High Dam is to store sufficient water in the reservoir in
order to protect Egypt from the dangers of a series of
years of drought. An agreement concluded in 1959 between
the two countries sets a maximum amount that can be drawn
per year and apportions it in a ratio of three to one,
with Egypt receiving the larger share. The quantities of
water maintained and apportioned are based on the
estimated worst possible sequence of flood and drought
events over a period of 100 years; and generally, one-fourth
of the total capacity of Lake Nasser is reserved as
relief storage for the highest anticipated flood during
such a period (called "century storage").
The High Dam was a source of considerable controversy
during its construction, and since it began operation it
has continued to have its critics. Opponents have charged
that silt-free water flowing below the dam has caused
erosion of the downstream barrages and bridge foundations;
that the loss of silt downstream has caused coastal
erosion in the delta; that the overall reduction in the
flow of the Nile resulting from the construction of the
dam has caused the inundation of the lower reaches of the
river by saltwater from the Mediterranean Sea, with
resulting deposition of salt in the delta soils; and that
the creation of Lake Nasser has caused the water table
along the river to rise, resulting in waterlogging and an
increase in soil salinity in some areas. Already the fish
population offshore of the delta has been reduced
dramatically by the loss of the nutrient-laden silt.
Proponents of the dam have maintained that these harmful
effects are worth the security of dependable water and
power supplies; and, indeed, Egypt would have suffered a
severe water shortage in 1984-88 without the dam.
Sannar, Jabal Al Awliya, Khashm Al Qirbah, Ar
Rusarys Dams
In The Sudan the Sannar Dam on the
Blue Nile provides water for the Al-Jazirah plain at the
time of year when the water level of the Blue Nile is low.
It also produces hydroelectric power. Another dam, at
Jabal al-Awliya' on the White Nile, was completed in 1937;
it was built to increase the water available to Egypt
during the period of low water (January to June) and was
not intended to provide irrigation water for The Sudan.
Other dams--including one on the Atbara at Khashm al-Qirbah
(completed in 1964) and the Ar-Rusayris Dam
on the Blue Nile (1966)--have enabled The Sudan to take
maximum advantage of its allocation of waters from Lake
Nasser.
Owens falls Dam
In Uganda, Lake Victoria was made
into a reservoir by the completion in 1954 of the Owen
Falls Dam; the dam is situated on the Victoria Nile just
below the point where the lake waters flow into the river.
This permits the storage of surplus water in high-flood
years to meet the deficit in years when the waters are
low. The fall from the lake is harnessed by a
hydroelectric plant that provides power for industries in
Uganda and Kenya. |