Dam

Structure that crosses more than the low-water channel of a permanent or intermittent watercourse or a thalweg. We can also say that it bars up a river cachtment area. But a dam can be outside a watercourse. The reservoir it makes upstream is gravity fed by the river basin waters. The body of a dam can be made of earth, masonry, concrete, wood, metal, etc. There are several types of dams, according to their function: hydropower dam, reservoir dam, dam for pollution control, dam for navigation.