An arch dam is a type of dam that is curved and designed to hold back water in a reservoir. Its shape allows it to efficiently transfer the water pressure to the rock walls on either side, making it strong and stable. Arch dams are typically built in narrow canyons where the rock formations can support the structure. These dams are often made of concrete and can be quite tall, allowing them to store large amounts of water. Famous examples of arch dams include the Hoover Dam and the Glen Canyon Dam, both of which play crucial roles in water management and hydroelectric power generation in the United States.