why are the dams made thicker at the bottom??
Dams are built broader at the base for two reasons. The first is because it needs to be stable enough to support the dam, and two, the bottom of the dam needs to be able to deal with the increased pressure of the water, as you get further down.
So basically, they're thicker at the bottom mostly for aesthetic reasons, but luckily this also means they're stronger at the bottom which is where the water pressure is greatest - definitely a bonus.
- Particular to dams, the lower part of the structure must hold back the lower levels of water, which are at higher pressure than the upper levels of the water. Higher water pressure on the base of the dam needs greater strength to hold it back.
- The base of the dam must support the weight of all the structure above it. Even if it was not a dam, but just a tower (or a pyramid), the lower sections must be stronger, and higher sections can be weaker because there is less weight above them.