Why dams have broader base than bottom?

Question

Why dams have broader base than bottom?

Answer 1

do you mean 'than the top'?

Answer 2

Dams has to resist water pressure on one side

Water pressure at depth H = wH ( w unit weight of water)

Total pressure= wH^2/2

Moment of this pressure= wH^3/6

This moment will try to topple the dam. Then Dam has to resist this by its self weight. Here you can notice that Moment increases with Height ( varies as cube of H) and hence the boottom shall be obiviosly broader in order to keep the equilibrium.

Answer 3

They use their weight to hold back the water

We assume the pressure increases linearly with depth. so the bottom needs to be bigger.

Also, if the top were bigger, it would have a huge torque on the foundation of the dam.