Hydro Development in
Egypt, Lessons From High Aswan Dam
Eng : Hassan M.A. Osman This submission was presented at
the WCD Regional Consultation, Cairo, Egypt, 8 - 9 December 1999 Abstract High Aswan Dam is
undergone to the design criteria during the 29 years operation period and no
unfamiliar phenomena has been appeared all over this period. It is approved
that high Aswan Dam is the backbone of Egypt's socio-economic welfare.
Tremendous achievements have been realised by the project, in the field of water
control and management, in agriculture promotion, protecting the country from
perils of high floods and droughts, horizontal land expansion with new
communities, hydropower generation, electrification of ruler areas, and
promoting industry, which had a great impact over social and economical
progress of Egyptian peoples. In addition to that, the High Aswan Dam had a
positive impact on the rapid growing development of Aswan province, specially
influx of tourists, fishing wealth, and changing Aswan from a punishment area
to be the best winter resort all over the world. Within 10 years of High
Aswan Dam construction, Aswan area has changed from repulsive area to a very
attractive one. Introduction: Water is the
vital and most important element for development in Egypt and the River Nile
is the main source of water in Egypt. To meet the
demands of expanding population and economy, and to promote the level of
national prosperity, It is essential that water resources be developed and
utilised. Due to the great
variation of the flow of the river between flood and summer period, some
annual storage project were executed in the river basin, such as Old Aswan
Dam and Jebel Awlia Dam. Due to the great
change in the natural river flow from year to year. the annual discharge at
Aswan rises to 150 milliard m3 during high floods as happened in
year 1878 / 1879 which caused heavy damage to crops and property, while it
drops to 42 milliard m3 during low floods as happened in year 1913
/ 1914 which caused drought and privation, In additional, there was an
average of 32 milliard m3 wasted every year to the Mediterranean
Sea. For the above
reasons and due to the fact that the annual storage reservoirs with their
limited capacity cannot be filled with flood waters which contain big amounts
of silt, the only way for a comprehensive solution to the problem was found
to be in the use of the over year or long term storage by building large
reservoirs. Henceforth came the idea of constructing a High Dam on the Main
Nile at Aswan in order to control and preserve the discharge of high flood
seasons, for use during low flood seasons, as well as to ensure the release
of the river's average yearly discharge which is 84 milliard m3 in
the due time of water needs, beside flood protection of Wadi and Delta. Type and short
description of the Dam: The Aswan High
Dam is a rock-fill dam and blocks the River Nile at 7km upstream from the old Aswan Dam. The
Dam layout was determined to fit the topographical features of the chosen
site. The channel dam was positioned in the narrowest part of the river. The general
layout of the dam (fig. 1), its type, profile and design was developed to
suit the unique and specific conditions of the site and the vital importance
of the dam. The high Dam
length is 3830 m of which 530 m are within the river channel and the
rest in the shape of two wings along both sides of the river. The dam is
built in the shape of a pyramid where its width at the bottom of the river
bed is 980m and 40m at the crest The height of the dam above the river bed is
111 m. The bulk of materials used in building the High Dam reached 43 million
m3 about 17 times the size of the great Giza pyramid. The body of the
dam is constructed of granite blocks, sand and clay, in the midst of which is
a clay core to prevent the seepage of water connected in the front part with
a horizontal blanket of clay for the same purpose. Since the Nile
bed, on which the dam is built, consists of a sedimentary deposit, it was
provided with a vertical injected curtain extending 170m under the main core
until it reached the solid layer. The injected curtain has been built of
special materials like Aswan clay and other chemical materials in order to
prevent the seepage of water. The width of the injected curtain is 40 m under
the main core, and decreases until it reaches 5 m at the point where it meets
with the solid layer. The core is
penetrated by three galleries, constructed with reinforced concrete. The
galleries were used in completing the vertical curtain during the construction
period, while they are being used now for inspection and maintenance
purposes. Various measuring apparatuses have been installed in these
galleries to measure vertical horizontal movements, pore pressure in clay and
seepage if any. The 3 inspection galleries in the clay core, rarely found in
other dams, are an excellent means for monitoring. The dam is provided before
the end of its toe with a row of vertical relief wells to drain the water
which might seep underneath the dam, while the second designed row will be
erected if necessary. (Fig. 2 ) shows
the cross section of dam along channel part. The diversion
canal on the eastern bank of the Nile is composed of in upstream and a
downstream canal linked by the main tunnels, which were dug in the rocks
underneath the right wing of the dam. The total length of the diversion canal
is 1950 m. Six spillway
tunnels have been constructed to link the upstream and downstream canals. The average
length of each tunnel is 282 m with a 15 m circular cross-secti6n of internal
diameter lined with reinforced concrete of a minimum thickness of one meter. Each tunnel is
divided vertically into two branches before its connection with the electric
power station. These branches are divided again by a horizontal wall into two
water passages, one of them supplies water to generating units and the
other is controlled by sector gates for passing the surplus water needed
during the period of peak water requirements. The six tunnels were designed
to release discharge of 11,000 m3 per second, i.e. about one
milliard m3. The
hydro-electric power station was built at the outlets of the tunnels. It
contains twelve generating units of Francis type, each with a capacity of
175,000kw. The total generating capacity Is 2.1 million KW producing ten
milliards KWH annually. The electric power generated at Aswan is transferred
to Cairo by two high voltage transmission lines of 500 kv. When the water
level upstream the dam reaches an elevation between 178 and 183 m. the
surplus water will be released, if necessary, by means of 30 sluices
emergency spillway, on the western bank of the Nile, to allow the passage of
5000 m3/s of water. This water pours back into the Nile downstream
of the dam. The darn forms a
large artificial lake of 500 km long, with an average width of 12 km over a,
surface area of 6000 k m2. It is considered one of the largest
man-made lakes in the world. Its maximum capacity, amounts to 162 milliard m3. The dam
construction started on 1960 and finished on 1970, during two main stages.
The 1st one was Finished on May 1964 during which the lower part of the dam
was filled under water up till elevation ranging between 107 to 128, also the
diversion canals and tunnels were completed. The upper part of the Dam and
the grout curtain were completed in the 2nd stage. Operation and
full water controlled: The operation of
the dam is done under specific regulation mentioned in the design documents.
Water released from Aswan High Dam is specified by Ministry of Public Works
and Water Resources to meet the requirements of irrigation and domestic uses. The filling of
the reservoir continued progressively since 1964 , as shown in fig ( 4 ). The
Nile flood in 1964 was a very high one, for the first time in the history of
Egypt the 1964 flood did not bring any damage to the country, this owing to
the construction of the First stage of the dam. Also very high floods
occurred in 1975, 1988 1998 and 1999. With the
completion of the High Dam, no losses have been sustained by the country in
years of high flood ( as years 1964, 1975, 1988, 1998 and 1999 ) and it has
been spared losses that would have cost millions of Egyptian pounds. Also the High Dam
preserved Egypt from droughts. The 1972 flood was very low, and without the
High Dam having been established, land would have been barren, poverty and
drought would have prevailed. Moreover, the
recent terrible drought and famine years from 1979 to 1987 which caused
immeasurable damage to human and animal life in many African countries,
without the High Dam there would have been a great shortage of irrigation
water and Egypt would have been exposed to such famine as many countries in
Africa. Egypt was not affected by the drought, due to over year storage in
Lake Nasser. The level of U.S. High Dam had dropped from 173.03 meters in
August, 1979 to 150.62 meters in July, 1988, and about to 72.8 milliards cu.
meter were taken from reservoir to fulfil the irrigation requirements. This
amount represents almost1.3 of the yearly consumption of Egypt, which is 55.5
milliards cu. meter. Power Generation: The hydroelectric
power station is built at the outlet of tunnels. It contains 12 generating
units, each with a capacity of 175.000 KW. The total generating capacity is
2,1 million KW producing 10 milliard KWH annually. The power station
was started on 15th October, 1967 after the Arab-Israeli War of June 1967. So
the station was from the very moment of beginning a great support for the
national economy by sparing the foreign currency needed for generating an
equal amount of energy from steam power stations, The power
generation has been successfully used in the electrification of Egypt's
country. It's supporting the industry, agriculture, culture, education and
raising the standard of living and improving the efficiency and extension of
the two Aswan Dam Hydropower stations. It generated a
clean and cheap power needed for development, which represent 54 % of total
generated power in Egypt in 1978, and 16 % in 1998. The total annual capacity
in 1998 exceeded 10 milliard KWH. Dam Safety: According to the
design, the behaviour of each element of the dam would be monitored during
both construction and operation period. Different types of instruments have
been erected for monitoring seepage, discharge, piezometer measurements,
vertical settlement, total stresses and pore pressures. The measured
values after about 29 years of operation, including filling and draw down of
the dam reservoir are still less than the design limits as mentioned in the
following table. ·
The
maximum observed settlement up till now for dam body is only about 59 cm,
while according to design is 220 cm. ·
The
max. observed settlement for the dam foundation is only about 12 cm, while
according to design is 40 cm. ·
The
max. observed horizontal displacement up till now is only about 7 cm., while
according to design is 110 cm. ·
Max
observed head loss of the grout curtain till now is 96 %, and according to
design is 60%. Table showing the
max. observed values and design limits of measuring devices of High Dam
Good water
Qualitv: Samples of water
from different locations and depths along the whole length of the lake, are
taken periodically, to determine its physical and chemical properties. The
results of the physical and chemical analysis, for lake samples collected
after and before flood, indicated a good quality of the lake water. Protection of the
downstream Canal slopes : In the first
years of operation, when there was an excess of water needed for irrigation
above the power needs, a part of the discharge was passed through the
irrigation spillways, the water was pushed by the wind to fall on the slopes
of the downstream canal. This caused the reduction of the stability factor of
the rocks of the eastern slope and the slide of some of the slope blocks. So, the following
two methods were adopted a- As an urgent
measure, the two outer irrigation spillways were plugged permanently with
concrete keeping the passage to the turbine free to avoid any possible fault
in operation. b- Flattening and
treatment of eastern of the outlet canal : To avoid excess
falling of rocks, especially after the occurrences of earthquake on November
14th, 1981, permanent solution was executed during 1984 ~ 1988 includes as
shown in Fig ( 5 ). ·
Trimming
the right side to softer slope. ·
Strengthening
some parts of the slope by cement grouting using low pressure grout. ·
Increase
the stability of the slope by anchoring the rock mass. ·
Constructing
drainage system to depressurise the seepage water hydrostatic pressure and to
drain he collected water to D.S. canal. ·
Protect
the final slope by a layer of sprayed concrete. ·
Relocate
a new emergency road of capacity 70 t. The total cost of the project was
about LE. 18 million. Protecting the
Nile course against overall degradation The problem of
protecting the Nile course downstream Aswan against overall degradation after
the construction of High Dam and reserving the Nile silt in the reservoir,
has been the interest of those who have been engaged with the project. The
actual results of the observation on degradation showed that the rate
decreased significantly since year 1968 when the discharges released were
limited by irrigation requirement with a maximum of 230 Million m3
/day. According to instruction of operation for the High Dam issued by
"Hydroproject institute Moscow 1970". The flood control capacity
must be emptied down to level 175 m. before the arrival of the following
flood, this will result in releasing high discharges, that may reach 350 ~
360 million m3/ day. In this case, further degradation is
expected. This may affect the river bed, downstream the control structures
existing on the river, the canal intakes and water pumping stations etc. To
avoid this it was decided to make use of one of the western valleys ( khor
Toshka ), Connecting a huge depression ( Toshka depression ) on the western
desert to the reservoir to act as additional spillway as shown in Fig ( 6 ). Toshka project
includes: ·
Digging
Toshka canal, 22 km length, to connect Nasser Lake to Toshka depression. ·
Canal
inlet as a free sill at elev. 178 with a width of 750 m. located at 250 km
south of High Dam on the left side of the Nile. ·
Outlet
Ogee type weir at the connection of the canal with Toshka depression, ·
The
maximum discharge of Toshka canal is 250 million m3/ day at elev.
182.70. ·
The
project was executed during 1978 ~ 1982. ·
The
total cost of the project was L.E. 46,6 million. Toshka spilllway
has played an important part in flood control and management, during 1998 and
1999 high floods. In 1998 the total discharges passed through it were 12.4 milliard
m3, During the present flood 1999 it is expected to pass about 16
milliard m3. Dam stability
against seismic hazard On 14th November
1981, the surprise occurrence of moderate earthquake 5.6 on Richter scale in
an area near the reservoir of the Aswan High Dam caused significant concern
about the stability of the High Dam and its relevant structures during
possible future earthquakes. A detailed study extended for two years
beginning in Feb. 1984 conducted by distinguished American Consultant. The study
was reviewed and endorsed by a distinguished International advisory panel of
experts on seismic geology, seismology and earth dam engineering. The studies have
concluded that: ·
The
occurrence of largest (conservative ) potential earthquake of magnitude 7 on
Richter scale, assumed on Kalabsha fault, would not jeopardise the safety and
integrity of the High Dam and its appurtenant structure. ·
No
precautions have to be taken either in lake water level or impounding or in
the planned programme of operation. ·
The
trigger of the Kalabsha fault is mainly due to seismo-geological reasons and
that it would have happened whether the lake was there or not. Sediment load
Deposition in Lake Nasser: Due to the
formation of the lake since 1964, the majority of the transported sediments
were trapped in the reservoir, and only a small portion used to flow to the
downstream. It is taken into design, that a dead storage capacity of 31.6
milliard cu.m. ( up to elevation 147.0m.) is used for silt deposition along
500 years. The reservoir is surveyed annually to study this phenomenon and
determine location and extent of the sediment deposits, The first mission was
sent in 1973 and continued after that year. These
measurements covered 500 Km, in which selected stations were fixed, shows
that the progress of sediment deposition along Nasser Lake, as follows: I- Sediment
deposition occurs at the tail zone of the reservoir. 2- Movement of
sediment deposition will be extended along the riverbed in downstream
direction (north). 3- Sediment
deposition near the dam will occur after a long time. It is very
early to make forecast for the useful life of the dead storage capacity of
the High Dam Reservoir. Recently
feasibility study is going on to determine the most economical and effective
method to use the sediment deposition. Conclusion: The high Aswan
Dam is one of the largest rock-fill dams in the world and impounds one of the
world's largest man-made lakes. It's the most important and vital element to
social and economical development of Egypt. The High Aswan
Dam is still and for hundreds of coming years, would be the corner stone for
comprehensive Nile water control and management in Egypt, for water policy
and future planning. It was built as
an over year storage in order to control and preserve the discharge of the
high flood seasons for use during low flood seasons, as well as to ensure the
releasing of water requirements in the adequate time. In addition to generate
cheap and clean hydro-electric power needed for development. Now after 29
years of operation of High Aswan Dam, we can say with certainly that the main
learned lessons from the project, that the objects of the project have been
greatly realised and that many social and economical objects have been gained
and practised by Egyptian people. ·
The
most important impact of this great project was safe guarding of Egyptian
people from damaging results of successive years of low floods during 9 years
successively. Starting from 1979 till 1987, more than seventy milliard m3
of the storage were taken from reservoir to fulfil the irrigation
requirements in these 9 years. One may evaluate the loss of the country of
this water quantity if it was not available. ·
On
the other hand, the High Dam has already saved Egypt from 4 cycles of
dangerous floods in years 1975, 1988, 1998 and 1999 in additional to high
flood of year 1964 during construction period. ·
The
behaviour of each element of the dam according to the monitoring system
showed that the measured values after successive years including filling and
draw down of the Dam reservoir are still less than the design limits. ·
Toshka
spillway is considered to be a complementary project to the High Dam. Its
object is mainly to achieve full control of discharges released to Nile
course D.S. according to actual requirements. ·
The
High Dam return in ten years was not less than 20 times of its cost of
construction |
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