Which type of dam relies primarily on its weight to resist water pressure?

A gravity dam is designed to rely on its own weight to withstand the forces exerted by the water it holds back. The fundamental principle behind a gravity dam is that its mass and the material used in its construction, typically concrete or masonry, provide the necessary resistance against the hydrostatic pressure from the water. The weight of the dam pushes it downwards into the foundation, effectively counteracting the lateral forces of the water.

In contrast, an arch dam primarily utilizes its curved shape to distribute water pressure; it directs these forces onto the canyon walls, relying less on weight and more on structural design. An embankment dam is composed of earth and rock materials and is designed to provide stability through its geometry and the material properties rather than sheer weight alone. A roller-compacted dam is a specialized type of concrete dam that is built using a method that consolidates materials into a dense structure, but it doesn’t rely solely on weight as a gravity dam does.

Thus, the key aspect that makes a gravity dam distinct and the correct choice is its reliance on its substantial weight to resist water pressure effectively.