How is a buttress dam different from a gravity dam?

A gravity dam and a buttress dam differ primarily in how they resist the horizontal thrust of water and manage foundation forces:

• Resistance Mechanism: Gravity dams are designed to resist overturning and sliding forces entirely through their own massive weight. In contrast, buttress dams do not rely solely on their weight; instead, they use an inclined upstream face (typically 25° to 45°) that directs the water's thrust toward the foundation, where the bracing action of the buttresses provides stability.123
• Uplift Forces: A significant advantage of buttress dams over traditional gravity dams is that they experience smaller uplift forces. Gravity dams, due to their large footprints, are more susceptible to destabilization from water seeping under the structure, requiring extensive drainage and grouting systems to manage uplift pressure.231
• Design and Construction: Gravity dams are typically constructed with unreinforced concrete and run in a straight line across a valley. Buttress dams feature a series of supports (buttresses) on the downstream side and may incorporate variations such as arches or domes to link buttress heads.123