A weir is a hydraulic structure designed to partially obstruct an open channel, enabling precise control and measurement of water flow. By forcing water to flow over or through it, a weir allows for accurate determination of discharge rates, making it an essential tool in water resource management. These structures are extensively used in regulating river flows, irrigation systems, and flood control channels.

Types of Weirs and Their Features

Weirs are categorized primarily into sharp-crested and broad-crested types, each suited to specific applications. Sharp-crested weirs consist of a thin, vertical plate with a sharp edge that causes water to flow over it, forming a free-falling sheet of water known as the nappe. Common shapes for sharp-crested weirs include rectangular, triangular (V-notch), and trapezoidal configurations, chosen based on the expected flow conditions. The discharge rate for these weirs depends on factors such as the weir coefficient, head (water height above the weir crest), channel width, and gravitational effects. In V-notch weirs, the notch angle is also critical in flow calculation.

Broad-crested weirs, on the other hand, feature a wide, flat crest that promotes near-uniform critical flow conditions. These weirs are particularly effective for larger channels, where their stable flow characteristics support reliable flow measurement and regulation. 

Due to their different geometries, the flow equations for broad-crested weirs and sharp-crested weirs differ significantly.

Applications in Flow Management

Weirs are indispensable in the management of natural and engineered waterways. By enabling controlled water discharge, they help prevent flooding, distribute irrigation water efficiently, and monitor river flows. Their adaptability to different flow conditions and precise measurement capabilities make them integral components in hydrological and engineering systems.