Tools for Environmental Analysis, Evaluation and Management 211
Let us suppose that the construction of a large hydroelectric or irrigation
work is being planned. Its main component is the construction of a dam in
a river bed with the purpose of creating an artificial lake that will serve as a
reservoir for the production of hydroelectric energy, for irrigation or water
supply. Throughout the world, thousands of large dams have been constructed (e.g. the Aswan dam in Egypt, the Itaipu dam in South America).
The following list is not complete but is indicative of the environmental
impacts’ variety and complexity of such a work:
• The artificial lake will inundate areas that may include settlements,
agricultural cultivations, other economic activities, historical monuments, remarkable landscapes, biotopes etc. If salvaging some of them
is deemed necessary, then they will have to be transferred somewhere
else if possible, or the extent of the lake should be reduced by suitable
auxiliary dams.
• The dam will cause retention of river sediments and their accumulation in the lake. This entails that the whole work will have a limited
life span. If the assessments about the inflow rate of sediments are
misjudged, there is a risk that the lake will be filled faster and that the
project will be prematurely rendered useless.
• Retention of sediments in the lake means that they will not reach
their normal destination, that is, the flat riparian areas and the delta
formed at the river mouth. Consequently, there will be a decrease of
nutrients in the riparian and marine areas of the river mouth, possibly
resulting in reduction of agricultural and piscatorial production. The
reduction of sediments also poses the risk of affecting the evolution of
the coastline and causing increased erosion of the banks downstream
of the dam.
• Creation of an artificial lake may cause alterations of the local climate,
with a possible humidity increase and temperature fluctuation decrease.
• In the area of the artificial lake, erosion and torrential phenomena
will be positively or negatively influenced.
• The river flow downstream of the dam will be artificially determined,
which can have negative consequences for the downstream eco systems.
This danger is increased during the filling of the lake.
• The lake water will have reduced oxygenation in relation to the river
water; therefore, it will have reduced pollution assimilation capacity,
especially if there is also lake stratification. There will be an increased
possibility for eutrophication. If the river upstream of the dam is a
receptor of pollution (municipal waste, livestock farming wastewater,
fertilizers etc.) there may be a need for more advanced wastewater
treatment due to a smaller self-purification capacity of the lake water.
Let us suppose that the construction of a large hydroelectric or irrigation
work is being planned. Its main component is the construction of a dam in
a river bed with the purpose of creating an artificial lake that will serve as a
reservoir for the production of hydroelectric energy, for irrigation or water
supply. Throughout the world, thousands of large dams have been constructed (e.g. the Aswan dam in Egypt, the Itaipu dam in South America).
The following list is not complete but is indicative of the environmental
impacts’ variety and complexity of such a work:
• The artificial lake will inundate areas that may include settlements,
agricultural cultivations, other economic activities, historical monuments, remarkable landscapes, biotopes etc. If salvaging some of them
is deemed necessary, then they will have to be transferred somewhere
else if possible, or the extent of the lake should be reduced by suitable
auxiliary dams.
• The dam will cause retention of river sediments and their accumulation in the lake. This entails that the whole work will have a limited
life span. If the assessments about the inflow rate of sediments are
misjudged, there is a risk that the lake will be filled faster and that the
project will be prematurely rendered useless.
• Retention of sediments in the lake means that they will not reach
their normal destination, that is, the flat riparian areas and the delta
formed at the river mouth. Consequently, there will be a decrease of
nutrients in the riparian and marine areas of the river mouth, possibly
resulting in reduction of agricultural and piscatorial production. The
reduction of sediments also poses the risk of affecting the evolution of
the coastline and causing increased erosion of the banks downstream
of the dam.
• Creation of an artificial lake may cause alterations of the local climate,
with a possible humidity increase and temperature fluctuation decrease.
• In the area of the artificial lake, erosion and torrential phenomena
will be positively or negatively influenced.
• The river flow downstream of the dam will be artificially determined,
which can have negative consequences for the downstream eco systems.
This danger is increased during the filling of the lake.
• The lake water will have reduced oxygenation in relation to the river
water; therefore, it will have reduced pollution assimilation capacity,
especially if there is also lake stratification. There will be an increased
possibility for eutrophication. If the river upstream of the dam is a
receptor of pollution (municipal waste, livestock farming wastewater,
fertilizers etc.) there may be a need for more advanced wastewater
treatment due to a smaller self-purification capacity of the lake water.