147
Zambia and Zimbabwe (Postel 2000,
2011). According to experience, such drip
systems increase the productivity of water
twofold by increasing crop yield and reducing evaporation loss. In the above cases
water is accessed with pumps operated by
manpower. In Africa just south the Sahara
and in Bangladesh pedal pumps are capable of pumping water even from a depth of
6–7 m (Bill and Melinda Gates Foundation
2009). Nowadays such pumps are produced
and distributed by several non-profit organisations in many countries in Africa.
Small-scale micro-irrigation systems
using solar panels are even more effective
and require no manpower for bringing
water to the surface. Their disadvantage is
the cost of investment amounting to 18,000
dollars for an area of half hectare and 5750
dollars or operational cost each year.
Although the investment returns in
2–3 years and its advantages (more healthy
food, reducing child work thus regular education of children) are invaluable most
farmers in the poor countries of Africa cannot make such investments. Loan systems
supporting such investments and establishing local production opportunities of such
irrigation systems including the training of
skilled labour show the way for solution
(Postel 2011).
cooling and steam generation. Nuclear power
plant cooling requires especially large amount of
water thus such power plants are generally constructed near river banks.
Inhabitants consume also vast amount of
water using drinking quality water sometimes for
purposes (e.g. flushing toilet) that would not
require necessarily potable water quality. The socalled grey water (slightly polluted water from
bath tubs, showers and wash-basins with limited
reuse potential) accumulated in separate drainage
networks would be suitable for flushing toilets.
Unfortunately such household reuse systems
have been installed only rarely as it requires
excess costs; however, such systems would save
a vast amount of water.
Since the water discharge of rivers depends on
the regional specifics of the climate water reservoirs are constructed in many regions for secure
water supply and water power plants are operated
frequently in their dams.
Unfortunately from ecological perspective,
there are only a few water networks on Earth that
can be regarded natural. Discussing the global
water cycle it was mentioned that there are
around half a million reservoirs and artificial
lakes on Earth. Largest reservoirs (above
100,000,000 m
3
) can be found in China, the USA,
Brazil and Russia totalling to a number of 6862
(Lehner et al. 2011). Large reservoirs are registered by a separate organisation, the International
Commission on Large Dams (ICOLD). The definition of a “large dam” is as follows:
• a dam with height of 15 m or greater from lowest foundation to crest or a dam between 5 m
and 15 m impounding more than 3 million m
3
.
The number of such dams is 59,071 (ICOLD
2019). Most large dams were constructed for irrigation purposes (9718) while 7615 were built for
water supply and the number of dams for flood
control is roughly the same (7302). However,
most large dams—even though constructed for a
special purpose—serve several purposes at the
same time. The above numbers suggest that
humanity works hard to transform nature to his
own use but frequently success is only
temporary.
According to a former report, around 40% of
the reservoirs in the USA would operate for less
than 50 years due to sedimentation. Sediment
transported from the catchment area is deposited
at a high rate in many large reservoirs in the Earth
and this process endangers the operation of the
turbines installed in the dams and even other
functions of the reservoir as well in the long term.
The problem has been discussed in several
papers (Basson 2009; Schleiss 2013; Annandale
2014; Schleiss et al. 2016). These papers stated
that currently there are no adequate prevention
methods available for hindering sedimentation.
4.3 Changes in the Hydrosphere
Zambia and Zimbabwe (Postel 2000,
2011). According to experience, such drip
systems increase the productivity of water
twofold by increasing crop yield and reducing evaporation loss. In the above cases
water is accessed with pumps operated by
manpower. In Africa just south the Sahara
and in Bangladesh pedal pumps are capable of pumping water even from a depth of
6–7 m (Bill and Melinda Gates Foundation
2009). Nowadays such pumps are produced
and distributed by several non-profit organisations in many countries in Africa.
Small-scale micro-irrigation systems
using solar panels are even more effective
and require no manpower for bringing
water to the surface. Their disadvantage is
the cost of investment amounting to 18,000
dollars for an area of half hectare and 5750
dollars or operational cost each year.
Although the investment returns in
2–3 years and its advantages (more healthy
food, reducing child work thus regular education of children) are invaluable most
farmers in the poor countries of Africa cannot make such investments. Loan systems
supporting such investments and establishing local production opportunities of such
irrigation systems including the training of
skilled labour show the way for solution
(Postel 2011).
cooling and steam generation. Nuclear power
plant cooling requires especially large amount of
water thus such power plants are generally constructed near river banks.
Inhabitants consume also vast amount of
water using drinking quality water sometimes for
purposes (e.g. flushing toilet) that would not
require necessarily potable water quality. The socalled grey water (slightly polluted water from
bath tubs, showers and wash-basins with limited
reuse potential) accumulated in separate drainage
networks would be suitable for flushing toilets.
Unfortunately such household reuse systems
have been installed only rarely as it requires
excess costs; however, such systems would save
a vast amount of water.
Since the water discharge of rivers depends on
the regional specifics of the climate water reservoirs are constructed in many regions for secure
water supply and water power plants are operated
frequently in their dams.
Unfortunately from ecological perspective,
there are only a few water networks on Earth that
can be regarded natural. Discussing the global
water cycle it was mentioned that there are
around half a million reservoirs and artificial
lakes on Earth. Largest reservoirs (above
100,000,000 m
3
) can be found in China, the USA,
Brazil and Russia totalling to a number of 6862
(Lehner et al. 2011). Large reservoirs are registered by a separate organisation, the International
Commission on Large Dams (ICOLD). The definition of a “large dam” is as follows:
• a dam with height of 15 m or greater from lowest foundation to crest or a dam between 5 m
and 15 m impounding more than 3 million m
3
.
The number of such dams is 59,071 (ICOLD
2019). Most large dams were constructed for irrigation purposes (9718) while 7615 were built for
water supply and the number of dams for flood
control is roughly the same (7302). However,
most large dams—even though constructed for a
special purpose—serve several purposes at the
same time. The above numbers suggest that
humanity works hard to transform nature to his
own use but frequently success is only
temporary.
According to a former report, around 40% of
the reservoirs in the USA would operate for less
than 50 years due to sedimentation. Sediment
transported from the catchment area is deposited
at a high rate in many large reservoirs in the Earth
and this process endangers the operation of the
turbines installed in the dams and even other
functions of the reservoir as well in the long term.
The problem has been discussed in several
papers (Basson 2009; Schleiss 2013; Annandale
2014; Schleiss et al. 2016). These papers stated
that currently there are no adequate prevention
methods available for hindering sedimentation.
4.3 Changes in the Hydrosphere