148
Regular measurements and related water control,
however, can slow down the process and afforestation in the catchment area is favourable. (The
above mentioned authors note that deforestation
in catchment areas is unfortunately more
frequent.)
Basson (2009) carried out calculations regarding the average sedimentation rate of reservoirs
operated in different regions. His data can be
found in Table 4.12. It can be seen that most reservoirs for water power plants active today will
suffer from 80% of siltation by 2060–2100 that is
around the limit of operation. Annandale (2014)
calls attention to the fact that economic calculations for future generations mostly ignore that
this natural resource will suffer from a significant
loss in about 100 years’ time and less appropriate
space will be found for constructing new dams.
This runs opposite the idea of sustainable
development.
Large dams cause a number of other environmental effects. The load of the Nile, for example,
remains almost entirely in Lake Nasser and thus
the river without sediment load cannot build further its delta. Indeed, sea erosion “consumes” the
fertile and densely populated area. According to
certain estimations this process is so severe that
Egypt could lose 19% of its arable land within
50 years while its population will grow to 150
million from the current 97 million.
In the vicinity of water reservoirs groundwater
conditions generally change and this influences
soil properties as well: soils become too saturated
with water or if the subsoil is saline even secondary salinization may occur. In both cases soil fertility decreases. Even aquatic life changes since
formerly running water is replaced by aquatic
conditions more similar to lakes. When the reservoir is filled terrestrial life perishes and earthquakes occur due to the pressure of the water as
mentioned in Chap. 3. In certain cases residents
of several settlements have to be relocated as
their dwelling places are flooded.
The effects of water overuse on closed (without outlet) water systems below. As an example
major changes in the water system of Aral Sea
are presented first.
Aral Sea is located in continental desert conditions at moderate climate. Its two supplying rivers
(Amu Darya, Syr Darya) have their sources in the
Pamir and Tian Shan mountains and are mostly
supplied from meltwater. Water of the two rivers
was used in increasing ratio for intensifying cotton and rice production from the 1960s. Up to
90% of the total exploited water was used for irrigation (Fig. 4.52). Eventually water use became
so extensive that the two rivers never reached the
lake that, as a result, started to shrink rapidly
(Fig. 4.53). Changes in the size of the lake is illustrated by the fact that it was the fourth largest lake
in the world (66,400 km
2
) in 1960 and it became
seventeenth in 2004 with an area of 17,160 km
2
.
In the remaining two smaller depressions the typical value of the salt content of the water increased
to 130 g/L compared to the 10 g/L typical in the
1960s. The total water content of the two depressions was reduced to 98 km
3
from the former
1093 km
3
(Gaybullaev et al. 2012).
Dried out parts of Aral Sea turned to be saline
desert from where wind carries salt away to disTable 4.12 Average sedimentation rates of reservoirs in different regions (Basson 2009)
Region
%/year
Hydropower expected date of 80%
siltation
Other uses dams expected date of 70%
siltation
Africa
0.85
2100
2090
Asia
0.79
2035
2025
Australia + Oceania
0.94
2070
2080
Central America
0.74
2060
2040
Europe
0.73
2080
a
2060
a
Middle East
1.02
2060
2030
North America
0.68
2060
2070
South America
0.75
2080
2060
a
Europe + Russia
4 Changes on Earth as a Result of Interaction Between the Society and Nature
Regular measurements and related water control,
however, can slow down the process and afforestation in the catchment area is favourable. (The
above mentioned authors note that deforestation
in catchment areas is unfortunately more
frequent.)
Basson (2009) carried out calculations regarding the average sedimentation rate of reservoirs
operated in different regions. His data can be
found in Table 4.12. It can be seen that most reservoirs for water power plants active today will
suffer from 80% of siltation by 2060–2100 that is
around the limit of operation. Annandale (2014)
calls attention to the fact that economic calculations for future generations mostly ignore that
this natural resource will suffer from a significant
loss in about 100 years’ time and less appropriate
space will be found for constructing new dams.
This runs opposite the idea of sustainable
development.
Large dams cause a number of other environmental effects. The load of the Nile, for example,
remains almost entirely in Lake Nasser and thus
the river without sediment load cannot build further its delta. Indeed, sea erosion “consumes” the
fertile and densely populated area. According to
certain estimations this process is so severe that
Egypt could lose 19% of its arable land within
50 years while its population will grow to 150
million from the current 97 million.
In the vicinity of water reservoirs groundwater
conditions generally change and this influences
soil properties as well: soils become too saturated
with water or if the subsoil is saline even secondary salinization may occur. In both cases soil fertility decreases. Even aquatic life changes since
formerly running water is replaced by aquatic
conditions more similar to lakes. When the reservoir is filled terrestrial life perishes and earthquakes occur due to the pressure of the water as
mentioned in Chap. 3. In certain cases residents
of several settlements have to be relocated as
their dwelling places are flooded.
The effects of water overuse on closed (without outlet) water systems below. As an example
major changes in the water system of Aral Sea
are presented first.
Aral Sea is located in continental desert conditions at moderate climate. Its two supplying rivers
(Amu Darya, Syr Darya) have their sources in the
Pamir and Tian Shan mountains and are mostly
supplied from meltwater. Water of the two rivers
was used in increasing ratio for intensifying cotton and rice production from the 1960s. Up to
90% of the total exploited water was used for irrigation (Fig. 4.52). Eventually water use became
so extensive that the two rivers never reached the
lake that, as a result, started to shrink rapidly
(Fig. 4.53). Changes in the size of the lake is illustrated by the fact that it was the fourth largest lake
in the world (66,400 km
2
) in 1960 and it became
seventeenth in 2004 with an area of 17,160 km
2
.
In the remaining two smaller depressions the typical value of the salt content of the water increased
to 130 g/L compared to the 10 g/L typical in the
1960s. The total water content of the two depressions was reduced to 98 km
3
from the former
1093 km
3
(Gaybullaev et al. 2012).
Dried out parts of Aral Sea turned to be saline
desert from where wind carries salt away to disTable 4.12 Average sedimentation rates of reservoirs in different regions (Basson 2009)
Region
%/year
Hydropower expected date of 80%
siltation
Other uses dams expected date of 70%
siltation
Africa
0.85
2100
2090
Asia
0.79
2035
2025
Australia + Oceania
0.94
2070
2080
Central America
0.74
2060
2040
Europe
0.73
2080
a
2060
a
Middle East
1.02
2060
2030
North America
0.68
2060
2070
South America
0.75
2080
2060
a
Europe + Russia
4 Changes on Earth as a Result of Interaction Between the Society and Nature