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Why is the upstream face of a buttress dam built at an angle?
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Itaipú Dam on the Upper Paraná River, north of Ciudad del Este, Paraguay.
The upstream face of a buttress dam is built at an angle—typically between 25° and 45°—to ensure that the thrust of the water is directed toward the foundation rather than acting horizontally.12
Unlike traditional gravity dams, which rely primarily on their own weight for stability, buttress dams utilize the bracing action of buttresses on the downstream side to support the load. By inclining the upstream face, the design effectively transfers the water pressure into the foundation, which is essential for the dam's overall stability.12