Geoscience Reference
In-Depth Information
Ghana can store water within an area the size of Lebanon
and Lake Kariba on the Zambezi can cover over half a
million hectares ( Table 26.1 ). These artificial lakes have
become a feature of Earth's surface. There is no disputing
that the control of river systems by dams can have a
positive effect on the local area and the national economy.
If we take Egypt as an example, we see that the construc-
tion of the Aswan High Dam in 1970 has stabilized
the flow of the Nile ( Figure 26.8 ). It has also allowed
the generation of about 20 per cent of Egypt's electricity,
which saves on import costs of fossil fuel. The area of
perennially irrigated cropland has been increased, which
is of vital importance in a country with a high natural
increase of population. Less obviously the control of water
level on the Nile has had a beneficial impact on tourism.
Tourists can visit the Nile temples more easily with
improved navigation and assist the country's economy.
Unfortunately not all the results of big dam construc-
tion have been beneficial. There have been a number of
disadvantages, some natural, some unexpected and some
induced through subsequent human activities.
Siltation . Like all natural lakes, reservoirs are prone to
silting. Dams built in dryland environments are likely
to have large areas of partial vegetation cover, especially
Table 26.1 Hydro-power generated per hectare inundated and number of people displaced for selected big dam projects
Approx. rated
Normal area of
KW
People
Project and country
capacity (MW)
reservoir (ha)
per ha
relocated
Pehuenche (Chile)
570
400
1,250
400
Guavio (Colombia)
1,000
1,500
666
5,500
Itaipu (Brazil and Paraguay)
12,600
135,000
93
59,000
Sayanogorsk (Russia)
6,400
80,000
80
0
Churchill Falls (Canada)
5,225
66,500
79
0
Tarbela (Pakistan)
3,478
24,300
194
96,000
Grand Coulee (United States)
6,494
33,300
63
10,000
Tucurui (Brazil)
3,980
243,000
16
24,000
Ataturk (Turkey)
2,400
81,700
29
55,000
Three Gorges (China)
18,200
110,000
165
1,900,000
Batang Ai (Sarawak)
92
8,500
11
3,000
Cahora Bassa (Mozambique)
2,075
266,000
8
25,000
Aswan High Dam (Egypt)
2,100
400,000
5
100,000
BHA (Panama)
150
35,000
4
4,400
San Roque (Philippines)
345
87,000
4
20,000
Kariba (Zimbabwe and Zambia)
1,260
510,000
2.4
57,000
Volta or Akosombo (Ghana)
833
848,200
0.9
80,000
Brokopondo (Surinam)
30
160,000
0.2
5,000
From various sources. The figures are not precise.
Dongola (above Aswan Dam) 1912-1984
el Ekhsase (below Aswan Dam) 1973-84
8000
8000
6000
6000
4000
4000
2000
2000
0
0
Figure 26.8 Contrasting river discharges above and below the Aswan Dam (completed 1970).
 
 
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