dinsdag 28 december 2010

Pros and Cons of dams

Pros and Cons of Dams In Developing and Developed countries
The world has about 46,000 dams that are higher than 15 meters.
Well over 70% of large dams around the world are used for the irrigation of agricultural land to secure food supply
Drinking water for citizens,
Processing water for industry and commerce and cooling water for thermal power stations.
A further function is flow control for flood protection and electricity generation from hydropower, the most effective use of this constantly regenerating energy.
According to world health organization:
Nearly 1 billion of the world's people do not have an "adequate" supply of water, and roughly 2 billion do not have access to "adequate" sanitation facilities Most of these people are in the world's developing nations. United Nations estimates that 900 million people each year suffer from diarrheal illnesses or other diseases spread by contaminated water Many barriers to better water management in the developing countries are rooted in economic, institutional, and policy issues These dams have provided significant benefits to the developing countries but have also caused complex physical, biological, and societal changes
Reservoirs thus often require the resettlement of large numbers of people. For example, China is building the Three Gorges Dam
ENVIRONMENTAL FRIENDLINESS
CONS:
A) Dams modify the existing natural conditions of life for animals and plants as well as the habitat of local population, primarily through the relocation of people who must leave the area where they settled, live and cultivate land.
B) Through increased water evaporation, and the slack water near dams facilitates development of life-threatening diseases.
C) we cannot ignore security risks resulting from the storage of large quantities of water, or possible collapse of the barrage construction.
D) large hydropower dams flood a lot of land.
E) Large dams alter the natural flow of rivers and cause problems with migrating fish
F) hydropower dams in forested areas can actually produce more greenhouse gasses
G) Many hydropower dams also eliminate vast forested areas that had been removing CO2 from the atmosphere
H) the consequences to the geologic and biologic systems are severe: sediment is deposited behind the dams, and so erosion is increased downstream.
I) Failure of a dam could cause massive floods.
J) dams constructed can decrease the flow in a river, and this can affect people who rely on water downstream.
K) One other concern is that damming rivers can impact wildlife, especially fish. Salmon migrate upstream to spawn and a dam is of course an impenetrable barrier.
L) Dams are usually built to benefit a large population of people at the expense of the environment
1. Subject to failure
2. Alters natural river flow 3. Interferes with life cycle of fish. 4. Surface area of reservoir evaporates large quantity of water. 5. Vulnerable to terrorist attack.
E Resettlement and relocation
E Socioeconomic impacts
E Environmental concerns
E Sedimentation issues
E Safety aspects
PROS:
A) Hydropower dams create recreation areas and large fish habitats (species have no problem adapting to impounded waters)
B) the power generated by flowing water produces no carbon dioxide or pollutants.
C) Millions of people are served with water that would not be available without dams
D) helping communities and economies harness water resources for food production, energy generation, flood control and domestic use
E) some 30.40% of irrigated land worldwide now relies on dams and that dams generate 19% of world electricity.
1. Store water 2. Regulate run off rate. Preventing flood, providing water in time of drought.
3. Provide recreation area, if large enough. 4. Generate power.
5.Domestic and economic benefits
6. employment opportunities
DEVELOPING AND DEVELOPED COUNTRIES
Benefits from dams:
1- Water Supply for domestic and industrial use (water stored in reservoirs)
The worldwide per capita water demand for water is expected to be about 750liter/day.
Dams and reservoirs are needed to store water and then provide consistent yearly supply (because most of the precipitated water evaporates or infiltrates to the atmosphere and only 36% is left for general use).
2- Meeting the agricultural demand for food supply
It is estimated that 80% of additional food production by the year 2025 will come from
irrigated land.
Most of the areas in need of irrigation are in arid zones, which represent
a major portion of the developing countries. So more reservoirs are needed to be constructed.
3-Flood control
regulate river levels
storing the flood volume and releasing it later
benefits such as water supply, irrigation, hydropower and water quality
4-Hydropower
Energy is essential for the socio-economic development of a nation.
Conditions often exist for renewable energy sources
Economical source of renewable energy is hydropower.
Less than 20% of the worldfs estimated feasible hydropower potential has been developed.
The greatest amount of potential remains to be developed in Asia, South America and Africa.
5- Recreation
The attractiveness of reservoirs for tourism (such as boating, swimming, fishing, bird watching and nature walks)
Concerns, Impacts and Mitigation
Safety aspects
Comprehensive plan for operation, maintenance and rehabilitation
Dams become older
(inspections, evaluations, modifications and upgrades of the older dams to meet current technology,
statutes and regulations)
Monitoring structural performance,
Developing emergency action plans,
Training of dam operators
Socio-economic impacts
Macro economic benefits are highlighted but Local economic and social impacts have not been adequately evaluated
Ensure that share of the benefits go to the population, directly affected.
Resettlement programs must involve the identification of the affected activities (people, industry, forestry etc)
Sanitation problems
Reservoirs can create an environment favorable for the transmission of water-related diseases.
(preventive measures are sanitation and health-care programs for the population)
Environmental concerns
Concerns about environmental issues and implementation of mitigation measures
Appropriate site selection, together with the implementation of these techniques.
Sedimentation problems
The capacity to erode and transport soil, sand, gravel and stones to the reservoir\
A positive impact of sedimentation is the improved water quality downstream of the dam
Improved local living conditions and facilitating aquatic wildlife
The negative aspects of reservoir sedimentation are progressive loss of
storage capacity, and increased erosion in downstream river channels.
How to handle sedimentation problem?
¡erosion control
¡ fostering and safeguarding the natural vegetation cover
COST
A) Some projects could not exist without government involvement
B) hydropower dams can be profitable in a pure economic sense ,
E.g. Grand Coulee Dam in the U.S. has generated about $15 Billion in revenues actual operating costs of $5.7 Billion. This dam is a good example of a multiple use project that generates electricity and provides irrigation water.
Pros and Cons of developed Countries Benefits of dams
Water storage
Flood control
Floods affected the lives of 65 million people between 1972 and 1996.
Irrigation
Dams contribute to 12-16% of world food production.
Electrical Power Generation
19% of the worlds total electricy supply, in 150 countries. 24 countries depend on dams for 90% of their power supply.
Industrialization
Increased croplands
Improved navigation
Stabilized annual flows
Improved domestic water availability
In 1990, over a billion people had access to less than the minimum required of 50 litres per person per day.
Recreation
Fishing cab be improved esp. in lakes but also in rivers with introduced species, leisure (e.g., boating on lakes, extended rafting season on the Colorado River)
Ecological
Increased riparian vegetation if dam discharges are steady
CONS OF DAMS
Ecological disruption
Fragmentation of 60% of the worlds rivers;
Disruption of movement of species (e.g., destruction of up to 75% of riparian bird species on the Colorado)
Destruction of riparian vegetation if discharges are irregular, e.g., peak-power of flood control types of operations; loss of beaches and marshes
Seepage and evaporation
15% for Nile system
Groundwater table effects
Groundlevel can be effected
Erosion downstream by sediment-starved waters
Flucuation vs. steady releases
Flucuations strand fish, reduce habitat for larval native fishes; deny access to tributaries;
Clogging of rivers by side-canyon floods
Peak floods required to clear channel may be eliminated
CONSEQUENCES OF DAMS
ecological
cultural
economic

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