World's largest dam Three Gorges

The world's largest dam in China is called the three gorges dam. It is by far very expensive at 39 billion US dollars and also the most notorious dam ever made, drawing criticism from many environmental activists. The building of the dam has caused many problems on the source of the Yangtze river. Pros and cons include:

Pros

• Flooding control: for many years the Yangtze has overflowed its banks due to monsoon rains, and building the dam reduces water flow into the mouth of the river, controlling flooding and blocking excess water. Many industries are built by the river and farmers also farm near as water is plentiful. To prevent a huge flood means many billions of dollars in damages can be avoided.
• Environmental impact(positive): Hydro electricity by building the dam would reduce the country's dependence on coal, there for cutting carbon emissions. China is the largest emitter of carbon, and achieving clean hydro electric energy would bring China one step closer to stopping global warming. Also, Industries have been reminded to treat toxic waste before dumping it in the river and up to 65% (confirmed) of factories have done so. Also waste treatment sites have been built.
• Reforestation has also been accelerated by the China government to prevent huge floods near the river basin.

Cons

• Relocation: Relocation of many farmers would also have to take place, as water levels would obviously rise and flood many homes. Farmers are put off by the lack of assistance by local governments and sometimes even corruption can be a obstacle to farmers where tax money is taken and not paid as compensation to farmers.
• Pollution and erosion : when water levels rise before the dam the ability to flush out pollutants by the river is slowed down so pollutants accumulate and may affect ecosystems. Also trees which are removed cannot hold on to soil with roots so erosion might occur. Sedimentation would affect water quality, and even, the silt may decrease the efficiency of the turbines. To clean up the entire river, over a billion yuan is needed. Also the sediments may block the entrance and cause dam failure and an overflow of water causing more floods.
• Cultural and aesthetic problems: The dam causes many different cultural or historical artefacts to be submerged. Although some of them are removable, many historical locations cannot be removed because of its size or other factors.

references: http://en.wikipedia.org/wiki/Three_Gorges_Dam