Question

Why walls of a dam are made thicker at the bottom than at the top?

Answer 1

This is because the pressure of the water is much greater deeper down and the dam needs to be thick at the bottom so that it is strong enough to withstand this larger pressure.

Answer 2

What really happens is that flowing water has a greater amout of force towards the bottom...and dam should be able to retort the force of that water...Hence dams have their bottom walls thicker.!!
                                                   Peace..!!