2. Dams are extremely expensive to build and must be built to a very high standard.
3.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.
2.Dams are designed to last many decades and so can contribute to the generation of electricity for many years / decades.
3.When in use, electricity produced by dam systems do not produce green house gases. They do not pollute the atmospherec