The design and structural support of a buttress dam differ from that of a gravity dam. Instead than relying solely on the weight of the dam, a buttress dam uses many sloping supports, or buttresses, to shift the water pressure to the base of the structure. The basic framework is a very thin concrete wall, which is supported by these buttresses. This design is effective in situations when the foundation is strong but the base is narrow. It allows for a lighter structure than gravity dams, which is advantageous in areas with limited resources or space. Buttress dams are commonly used in tiny valleys when the rock base is solid.