Inverted V‐Notch: Practical Proportional Weir

This paper presents a practical linear proportional weir of simple geometric shape in the form of an inverted V‐notch or inward trapezium. The flow through this weir, of half‐width w and altitude d, for depths above $0.22d$ is proportional to the depth of flow measured above a reference plane situated at $0.08d$ for all heads in the range $0.22d⩽h⩽0.94d\text{,}$ with a maximum percentage deviation of $\pm 1.5$ from the theoretical discharge. The linear relationship between head and discharge is based on numerical optimization procedures. Nearly 75% of the depth of inverted V‐notch can be used effectively as the measuring range. Experiments with four weirs, with different vertex angles, show excellent agreement with the theory by giving an average coefficient of discharge for each weir varying from 0.61–0.62.