Hydro Power Environment Impacts.
By Emil Bedi, CANCEE and Hakan Falk, "Energy Saving Now".
PROBLEMS OF HYDRO POWER
The main reasons that hydro power plants are not
build everywhere are that they are costly and require large bodies of water
relatively close to inhabitants. According to the World Bank, “developing
countries will need to raise an estimated USD 100 billion by the year 2000 for
hydroelectric plants currently in the planning stage.” Another arising problems
are the effects of dams on river ecosystems and social problems related to
relocation of inhabitants.
ENVIRONMENTAL ASPECTS OF HYDRO POWER PLANTS
 A watercourse is an ecological system
where changes within one component may create a series of spread-effects. For
instance, changes in the water flow may affect the quality of the water and the
production of fish downstream. Dam barriers may greatly change the living
conditions for fish. In addition to the emergence of a major or completely new
lake, the dam may divide upstream fish from downstream fish, and block their
migration routes.
Environmental changes may be traced far downstream, at times even out into
the sea. In the tropics there may be great seasonal variations as to the amount
of precipitation, and in dry periods evaporation from lakes and reservoirs may
be considerable. This may affect the water level of the reservoirs more
dramatically than in temperate areas. The watercourse and its watershed mutually
influence each other. The watercourse, for example, may affect the local climate
and the ground-water level in surrounding areas. The sedimentation taking place
in a reservoir can often lead to an increased erosion downstream, i.e. an
increase in the total erosion. Changes in water flow and water level will also
lead to changes in the transportation of sediments.
During the
construction phase the transport of mud and sediments will be especially large
downstream from the construction area. Excavation and tunnelling may lead to
greatly reduced water quality and problems for those dependent on the water.
GROUNDWATER
The
groundwater level is important for the ecosystem‘s composition and development
of plant and animal species. Groundwater is particularly important as a
drinking-water source in most countries. The filling of a reservoir of hydro
power plant and the flow of a watercourse are of great importance to the
groundwater level and for the feeding of the groundwater reservoirs. A
reservoir, together with the changes and variations of the water level caused by
its operation, will change the groundwater level in surrounding areas. These
areas may in turn influence the quality of the water and the sediment transport
of the watercourse as a result of area run-off and erosion.
EXCESSIVE FERTILIZATION
Whenever nutrients are trapped in a
reservoir, the result may be excessive fertilisation - eutrophication - in the
reservoir. It may lead to an increased growth of algae or large amounts of
higher-order aquatic plants. A substantial production of organic matter in the
reservoir, or the supply of external organic matter, may cause anaerobic
conditions - lack of oxygen - in the deep-water layers.
On the whole,
shallow lakes with a large surface area are most at risk, partly because the
reserve of oxygen in the deep-water layers is limited in proportion to the
productive area in the top layers. In deep, narrow lakes the oxygen content in
the deep-water layers will be sufficient to recycle organic matter sinking down,
provided there is a regular circulation of the waters. This is not always the
case in the tropics. If the watercourse is initially rich in nutrients, the risk
of eutrophication will increase.
Evaporation may cause a
concentration of nutrients, leading to excessive fertilisation or
eutrophication. Tropical soil normally has-a low humus content. This, combined
with the great seasonal variations as to the amount of precipitation, and the
fact that precipitation often comes in heavy showers, may cause considerable
erosion. The transportation of eroded sediments will be halted and deposited in
a reservoir. The reservoir’s lifetime may in this way be reduced. Transport of
sediments and nutrients tends to play a crucial role in the ecosystem of a
watercourse. The population’s utilization of nature and natural resources may be
completely dependent on floods and waterborne sediments and nutrients.
TRANSPORT OF NUTRIENTS
A reservoir serves as a trap for nutritious elements and mud flowing in,
possibly leading to a considerable reduction of the total transport of nutrients
downstream. In addition, the annual variations in supply downstream may undergo
changes. This may reduce the biological production all the way to the sea. There
are grave examples of marine fishing being impaired in the wake of a major dam
development.
FISH
The
composition of fish species may be altered, since reproduction for some species
may be hindered if the operation involves changes in the water level during the
spawning period. Artificial reservoir tends to contain a less varied composition
of species than a natural lake. Changes in the water flow and water-flow pattern
may radically alter nutrient and spawning conditions downstream. The primary
production as well as the direct accessibility of nutriment for fish will
change. Changes made to the downstream floods, as a result of water control, may
be decisive. At dam and turbine outlets a surfeit of gas may occur, principally
of nitrogen, which can cause death among fish.
Some hydro power plants are equipped with fish
ladders. 
FLORA AND FAUNA
Submerging and water-flow changes, moreover, will lead to changes in the
fauna and vegetation beyond the watercourse as such. Large reservoirs will exert
a considerable direct impact on the flora and fauna of the hydro power plant
area through submerging the area permanently or periodically. Animals may to
some extent move to new habitats beyond the reservoir area, provided that
suitable conditions are to be found. But normally the types and species of
nature existing in areas being submerged must be considered as lost.
It is difficult to predict in general terms how changes beyond the
submerged area will turn out. Local climatic changes and changes to the
ground-water level may affect the flora and fauna. Valuable types and species of
nature may be lost. A general activity increase in the area, such as traffic,
noise etc., may also affect the fauna in a negative way. This especially
pertains to the construction period.
Further, a reduced water flow or
changed flow pattern downstream may influence the flora and fauna. The effects
may be direct ones in that the flora and fauna react to the water flow, or the
effects may be indirect owing to changes in the ground-water level and the
transport of nutrients.
POPULATION MOVEMENTS
Large hydro power plants with dams require large reservoir and discharge
areas. Many people have to be evacuated to make room for these areas. This could
lead to a completely new situation for people who have lived in a relatively
small, protected environment. Housing, land distribution, working conditions and
way of life may change radically. The impacts will depend upon the size and
location of the project. With major dam developments they can be serious.
Social consequences are likely to arise if the population concerned
should be pressured into settling down in, or exploiting, more marginal and
ecologically vulnerable areas than the ones they have traditionally utilized.
These impacts may further aggravate their situation. Such indirect environmental
effects can cause considerable ecological problems, with consequences for the
entire project area.
Indigenous groups affected by hydropower
development may be particularly deprived. Their principle socio-cultural
conditions together with their traditional connection to land, water and other
natural resources, tend to make them unadaptable to changes and new activities.
The size of many hydropower projects and the rapid alterations in ecological
conditions that may arise, usually allow little room for readjustment. The
transfer of indigenous groups may endanger their entire cultural system. Such
minorities are particularly exposed, as they tend to have little political
influence and possibility of securing their own interests.
As a
whole, the consequences of dam development can involve great damage to
traditional ways of life and cultural expressions. Changes in terms of social,
economic and religious organisation can create a series of indirect social
impacts which are difficult to foresee during the planning of the project.
Cultural landscapes, ancient monuments, holy places, burial grounds etc. are
often areas and objects of great importance to a local population’s cultural
activities. Should such areas and objects be affected by a project, the cultural
identity of the population might be at risk.
HEALTH
Large hydro power plants can increase the extent of water-related
diseases. The reservoir may improve the living and breeding conditions of
disease-causing organisms (pathogens) and their intermediate hosts. Among
water-related diseases one could mention typhus, cholera, dysentery and several
tapeworm and roundworm diseases. Several serious diseases have intermediate
hosts linked to water. This applies to bilharzia, malaria, filariasis, sleeping
sickness and yellow fever.
Reservoirs with large, stagnant waters and
slow water-level variations offer favourable living conditions to pathogens.
Vegetation in the reservoir also affords improved living conditions for several
types of infection-carriers. The vegetation may provide infection-carriers with
an increased supply of nutrients, improved conditions for breeding and
protection in periods of a low water level. Moreover, the aquatic vegetation
shields snails - which are carriers of bilharzia infection - from strong
sunlight. In addition, research reveals that mosquito species carrying malaria
and filariasis due to vegetation in dams. If the reservoir is employed both for
irrigation and as the industrial and drinking water supply, there will be a risk
of infection spread by pathogens living in the water. Such infection may spread
over large areas.
DAM BREACH -UNCONTROLLED FLOODING
A dam breach seldom occurs, but owing to the
enormous consequences which it may involve, the impacts of a breach should be
assessed. The risk of casualties and damaged property or technical installations
must be considered the most serious consequences, but the impacts on the natural
environment can also be considerable.
Statistically, the combination
of a flood in the upstream watershed of the dam and faults in the spillway are
the most frequent causes of accidents. Secondary causes are foundation errors or
water seepage. At high water levels in the reservoirs, landslides of earth and
rocks from the embankment above or inside the reservoir may cause flood waves so
massive that water may spill over the total or partial width of the dam. If the
dam is an embankment dam, this may lead to the dam itself being damaged. Special
care should be taken if a major dam is planned in an area exposed to
earthquakes.
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