Final answer:
The base of a dam is thicker than the top to withstand the increasing water pressure at greater depths, ensuring the dam's structural integrity against the forces exerted by the water it retains.
Step-by-step explanation:
The thickness of a dam must increase from the top to the base due to the pressure exerted by the water it holds back. Water pressure increases with the depth of the water because the water at the bottom has the weight of all the water above pressing down on it. According to physics, pressure is calculated as the force per unit area, and with increasing depth, the force due to the water's weight increases. Therefore, the base of the dam must be thicker to withstand the increasing force and to maintain structural integrity, otherwise the dam could fail.
Furthermore, the weight of the water itself in the reservoir exerts a significant force on the dam structure. While this force is a fraction of the water's total weight, the dam design must account for it to prevent potential damage or collapse. The base's thickness is a crucial factor in the dam's capability to withstand these forces without breaking.