Answer: Because the wall has to withstand more pressure on the bed of the dam than on the surface.
Step-by-step explanation:
The question in english is written below:
A dam is a wall that contains a large amount of water whose depth exceeds 100 m. Why is the base of a dam wall much thicker than the part that is close to the surface?
Let's start by explaining that pressure changes with height. In the case of the water dam, the pressure at the bottom is much higher than on the surface of the water.
That is, the pressure decreases as we approach the surface.
Then, the fact that the thickness of the wall is much greater at the base than at the surface is because the wall has to withstand more pressure on the bed of the channel than on the surface.