Why hydroelectric power is bad for environment?

In our country, there are attempts to increase the height of several existing dams like Tehri and Almati, dams across the Narmada.

Choose the correct statements among the following that are consequences of raising the height of dams.

(i) Terrestrial flora and fauna of the area are destroyed completely.
(ii) Dislocation of people and domestic animals living in the area.
(iii) Valuable agricultural land may be permanently lost.
(iv) It will generate permanent employment for people.