Question

What is dam ? Write two main advantages and two ill effects of constructing a big dam.

Answer 1

dam is a barrier that impounds water or underground streams.

advantages:
1. Once a dam is constructed, electricity can be produced at a constant rate.
2. The lake's water can be used for irrigation purposes. 

disadvantages:

1. they are extremely expensive to build and must be built to a very high standard. 

2. it needs a large area to be construction for this so many obstacles as chop down.by this natural environment gets destroyed.

Answer 2

a human construction at the end of a river or lake,  that aims to store water for later use , is described as dam.
     advantage   1. act as a source which can be used at the time of crises.
                         2. construction of dam require labour , which provide employment.
        disadvantage     1. leads to destruction of natural resources as it require huge amount of it.
                                  2. decrease fertlity of soil as all the fertile soil is traped in the dam and get settled at the end.