What is a Weir?

A weir is defined as a barrier or dam built across an open channel to control the flow of water, typically in rivers or streams. Its primary function is to regulate water levels upstream and to measure flow rates. By creating a slight elevation in the water level, it effectively manages the discharge of water and can help in various applications such as irrigation, flood control, and water resource management.

The design of a weir allows for precise calculations of discharge based on the height of the water flowing over it, making it an essential structure in hydraulic engineering and environmental management. In contrast, the other options provided do not accurately represent the function or purpose of a weir. The correct choice emphasizes its role as a structural element in fluid dynamics, demonstrating its significance in managing water flow and levels.