* Dams are extremely expensive to build and must be built to a very high standard. * The high cost of dam construction means that they must operate for many decades to become profitable. * The flooding of large areas of land means that the natural environment is destroyed. * People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead. * The building of large dams can cause serious geological damage. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earth's surface at its location. * Although modern planning and design of dams is good, in the past old dams have been known to be breached (the dam gives under the weight of water in the lake). This has led to deaths and flooding. * Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighboring countries. * Building a large dam alters the natural water table level. For example, the building of the Aswan Dam in Egypt has altered the level of the water table. This is slowly leading to damage of many of its ancient monuments as salts and destructive minerals are deposited in the stone work from 'rising damp' caused by the changing water table level * Hydro powerdams can damage the surrounding environment and alter the quality of the water by creating low dissolved oxygen levels, which impacts fish and the surrounding ecosystems. They also take up a great deal of space and can impose on animal, plant, and even human environments. * Fish populations can be impacted if fish cannot migrate upstream past impoundments dams to spawning grounds or if they cannot migrate downstream to the ocean. Upstream fish passage can be aided using fish ladders or elevators, or by trapping and hauling the fish upstream by truck. Downstream fish passage is aided by diverting fish from turbine intakes using screens or racks or even underwater lights and sounds, and by maintaining a minimum spill flow past the turbine. * Hydro powercan impact water quality and flow. Hydro power plants can cause low dissolved oxygen levels in the water, a problem that is harmful to riparian (riverbank) habitats and is addressed using various aeration techniques, which oxygenate the water. Maintaining minimum flows of water downstream of a hydro power installation is also critical for the survival of riparian habitats. * Hydro power plants can be impacted by drought. When water is not available, the hydro power plants can't produce electricity. * New hydro power facilities impact the local environment and may compete with other uses for the land. Those alternative uses may be more highly valued than electricity generation. Humans, flora, and fauna may lose their natural habitat. Local cultures and historical sites may be flooded. Some older hydro power facilities may have historic value, so renovations of these facilities must also be sensitive to such preservation concerns and to impacts on plant and animal life. * By 2020, it is projected that the percentage of power obtained from hydro power dams will decrease to around four percent because no new plants are in the works, and because more money is being invested in other alternative energy sources such as solar power and wind power. dams detract from natural settings, ruin nature's work dams have inundated the spawning grounds of fish dams have inhibited the seasonal migration of fish dams have endangered some species of fish dams may have inundated the potential for archaeological findings reservoirs can foster diseases if not properly maintained reservoir water can evaporate significantly some researchers believe that reservoirs can cause earthquakes the reservoir created by the dam may inundate land, crops, cities and villages people may be displaced by the reservoir and have to find new homes the reservoir may cause instability of the hillsides 1) Expensive to build and maintain - most dams can be very expensive to build, and even more expensive to maintain. Every dam has a design life. What happens when the design life of the dam expires? Nobody wants to pay to retrofit the dam, but they just want it to keep working forever.
2) Endagering to many wildlife species - while some species of wildlife thrive in a reservoir environment, most are affected in a negative way. Creative (...and expensive) solutions usually need to be engineered to minimize the effect on the wildlife. Effect on water resources as precipitation and evaporation may change
The advantages and disadvantages of water supply from river reservoirs and groundwater are one in the same. It could be a good source of water, but if it is contaminated, it could make you sick.
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disadvantages *not to scale *there are limitations