Which of the following statement is incorrect regarding the selection of dam site?

• A. For economy, the length of the dam should be as small as possible
• B. For a given height, it should store the maximum volume of water
• C. The river valley at the dam site should be narrow but should open out upstream to provide a large basin for a reservoir
• D. The general bed level at the dam site should preferably be lower than that of the river basin