Aerial view of the Grand Coulee Dam,Washington State,USA. The dam was constructed in 1933-42 on the Columbia River,and is one of the largest concrete structures in the world. The dam itself is 216m high and 1,272m long,with a thickness of 200m at the base and 12m at the top. The dam holds back the Franklin D Roosevelt Lake,named after the US President who initiated the project. The lake extends for over 240km,with a surface of 202,000 hectares. The dam was built to provide irrigation and flood control,and to serve as a 6.2MW hydroelectric power station |