Egypt: The Aswan High Dam

kayakjokeMechanics

Feb 22, 2014 (3 years and 3 months ago)

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Egypt: The Aswan High Dam

The Environmental Impact
of the dam

Background


The Aswan Dam is an embankment dam situated across
the Nile River in Aswan, Egypt. Since the 1950s, the
name commonly refers to the High Dam, which is larger
and newer than the Aswan Low Dam, which was first
completed in 1902. Following Egypt's independence
from the United Kingdom, the High Dam was constructed
between 1960 and 1970. It aimed to increase economic
production by further regulating the annual river flooding
and providing storage of water for agriculture, and later,
to generate hydroelectricity. The dam has had a
significant impact on the economy and culture of Egypt.



Before the dams were built, the Nile River flooded each
year during late summer, as water flowed down the
valley from its East African drainage basin. These floods
brought high water and natural nutrients and minerals
that annually enriched the fertile soil along the floodplain
and delta; this made the Nile valley ideal for farming
since ancient times. Because floods vary, in high
-
water
years, the whole crop might be wiped out, while in low
-
water years widespread drought and famine occasionally
occurred. As Egypt's population grew and conditions
changed, both a desire and ability developed to control
the floods, and thus both protect and support farmland
and the economically important cotton crop. With the
reservoir storage provided by these dams, the floods
could be lessened, and the water could be stored for
later release.



ENVIRONMENTAL IMPACT

Resettlement of People


Lake Nasser flooded much of lower Nubia and 100,000
to 120,000 people were resettled in Sudan and
Egypt.[18] The majority of the 50,000 Nubians resettled
in Egypt were resettled three to ten kilometers from the
Nile near
Kom

Ombo

45 kilometers downstream from
Aswan in what was called " New Nubia". Housing and
facilities were built for 47 village units whose relationship
to each other approximated that in Old Nubia. Irrigated
land was provided to grow mainly sugar cane.


The Aswan High Dam, when it was build created Lake
Nasser, Lake Nasser
Streches

back 270
kilometres

from
the Dam. The Lake has also created
alot

more land for
people to farm on. This is because a lot of water is
stored in the lake, and in turn this water can be used to
irrigate land around the lake. Lake Nasser has also
created a big fishing industry, which produces 25,000
tonnes

of fish a year, the fishing industry is aiming to
produce 100,000
tonnes

by the year 2000.


Unfortunately this dam has caused a big change to the
lifes

of farmers downstream from the dam. Usually when
the river flooded once a year before the dam was built. It
deposited fertile soil from upstream on its banks
downstream. This washed up soil was extremely
furtile
,
and renewed itself every year at in flood season. But
now, since the dam was built the annual flood has been
stopped. Causing all the farmers downstream to have to
use fertilizers to grow their crops, which makes it more
expensive.

The Aswan High Dam is also used to create
hydro
-
electricity for Egypt,


In
the 1980's this dam was providing half of Egypt's
Electricity, but by the 1990's this had fallen as energy
demands increased. The electric power capacity of the
Aswan High Dam is: 2.1
gigawatts

(GW). It consists of
12 Hydro
-
Generators each rated at 175 MW. Egypt
currently has a total installed generating capacity of 16.6
gigawatts

(GW) compared to 3.8 GW in 1976, thus the
percentage contribution by the High dam has decreased
from over half the total electricity generation to less than
13%. This percentage will continue to decrease as more
thermal power plants are added. Total capacity expected
to be 26 GW by 2010
.

Waterlogging and increase in soil salinity


Before the construction of the High Dam, groundwater
levels in the Nile Valley fluctuated 8
-
9m per year with the
water level of the Nile. During summer when evaporation
was highest, the groundwater level was too deep to
allow salts dissolved in the water to be pulled to the
surface through capillary action.
With heavy
year
-
round
irrigation, groundwater levels remained high with little
fluctuation leading to waterlogging. Soil salinity also
increased because the distance between the surface
and the groundwater table was small enough (1

2 m
depending on soil conditions and temperature) to allow
water to be pulled up by evaporation so that the
relatively small concentrations of salt in the groundwater
accumulated on the soil surface over the years.

Losses due to salinization


Since most of the farmland did not have proper
subsurface drainage to lower the groundwater table,
salinization gradually affected crop yields.[16] A total of
2.1 million hectares thus required subsurface drainage at
a cost that exceeded the construction cost of the High
Dam. Only 20 years after completion of the High Dam
the problem was seriously addressed and a large
-
scale
drainage program was initiated.


Coastal Erosion


The High Dam has accelerated erosion of coastlines
(due to lack of sediment, which was once brought by the
Nile) in Egypt and, according to some sources even all
along the eastern Mediterranean. Coastal erosion
occurred and efforts to control it were made even before
the construction of the High Dam. This erosion may to
some extent have been caused by the limited trapping of
sediments behind the Old Aswan Dam. The High Dam
accelerated erosion and made the construction of further
expensive coastal protection works in the Nile Delta
necessary.

Health Impact


The standing water in irrigation canals is a breeding
ground for snails carrying the parasite bilharzia
.
The
incidence of bilharzia increased due to the Aswan High
Dam inhibiting the natural fluctuations in water height.
Important factors contributing to the prevalence of
schistosomiasis

were poor sanitation and limited
awareness of how the disease was transmitted.
Provision of clean water, sanitation, health education
and rural clinics has reduced the overall
prevalences

of
schistosomiasis

from more than 40 per cent during the
pre
-
dam period to 10 per cent in 1995 and only 2% in
2002
.

Reservoir sedimentation


Reservoir sedimentation. Sediment deposited in the
reservoir is lowering the water storage capacity of Lake
Nasser. The reservoir storage capacity is 162 km3, including
31 km3 dead storage at the bottom of the lake below 147m
above sea level, 90 km3 live storage, and 41 km3 of storage
for high flood waters above 175m above sea level. The
annual sediment load of the Nile is about 134 million tons.
This means that the dead storage volume would be filled up
after 300

500 years if the sediment accumulated at the
same rate throughout the area of the lake. Obviously
sediment accumulates much faster at the upper reaches of
the Lake where sedimentation has already affected the live
storage zone.[20] It would take about another 900 years until
the live storage zone would be completely
sedimented

and
operation of the dam would become impossible some time
before that.

Reservoir
evaporation;
Aquatic
weeds
;
Pollution from fertilizers


Evaporation from Lake Nasser is estimated at 10

km
3

per year,
varying mainly as a function of the lake area. While the
absolute amount of water lost to evaporation is enormous, it is
only 11% of the average volume stored in the Lake and 18% of
Egypt's share of the annual flow of the Nile
.


Before the
dam was built,
the 50,000 km of irrigation and
drainage canals in Egypt had to be dredged regularly to remove
sediments. After construction of the dam, aquatic weeds grew
much faster in the clearer water, helped by fertilizer residues.
The total length of the infested waterways was about 27,000 km
in the mid
-
90s. Weeds have been gradually brought under
control by manual, mechanical and biological methods
.


The increased use of artificial
fertilizers

has
caused chemical
pollution which the traditional river sediment did not do.

Fishery in the Delta and the Mediterranean


Mediterranean fishing and brackish water lake fishery
declined after the dam was finished because nutrients
that used to flow down the Nile to the Mediterranean
were trapped behind the dam. For example, the Sardine
catch off the Egyptian coast declined from 18,000 tons in
1962 to a mere 460 tons in 1968, but then gradually
recovered to 8,590 tons in 1992. A scientific article in the
mid
-
1990s noted that " the mismatch between low
primary productivity and relatively high levels of fish
production in the region still presents a puzzle to
scientist
.“


The
Aswan Dam tends to increase the salinity of the
Mediterranean Sea, and this affects the Mediterranean's
outflow current into the Atlantic
Ocean. This
current can
be traced thousands of kilometers into the Atlantic.

Algae Growth


Because of the lower turbidity of the water sunlight
penetrates deeper in the Nile water. Because of this and
the increased presence of nutrients from fertilizers in the
water, more algae grow in the Nile. This in turn increases
the costs of drinking water treatment. Apparently few
experts had anticipated that water quality in the Nile
would actually decrease because of the High Dam.


Irrigated
Farmland in
Egypt

Dam Specifications


The Aswan High Dam is 3,830
metres

long, 980
metres

wide at the base, 40
metres

wide at the crest and 111
metres

tall. It contains 43 million cubic
metres

of
material. At maximum, 11,000 cubic
metres

per second
of water can pass through the dam. There are further
emergency spillways for an extra 5,000 cubic
metres

per
second and the
Toshka

Canal links the reservoir to the
Toshka

Depression. The reservoir, named Lake Nasser,
is 550 km long and 35 km at its widest with a surface
area of 5,250 square
kilometres
. It holds 111 cubic
kilometres

of water.

A Panoramic View & Lake Nasser


Cross Section of the Dam