V‐Shaped Short‐Crested Weir With Semicircular Cross Section

The v‐shaped short‐crested weir with a semicircular cross section is used to measure discharges in open channels. Its truncated triangular shape provides a rather wide measuring range. Data obtained from laboratory experiments provide information on the head‐discharge relations for the bottom angle, $\alpha =150°\text{,}$ under free‐flow conditions. Drowned flow starts at a submergence ratio of 20‐30%. The maximum discharge depends on the dimensions chosen, but may reach a rate of $1.5m^3/s\text{,}$ making the structure suitable for small and moderate discharges. The lightweight weir is portable, and can be fixed at the front side of an existing structure or in vertical slots. If required, the weir can be constructed with a movable crest to act as a vertical gate with overflow. Results of investigations, design rules and limits of application are given. The dimensions and rating curves are presented for a typical weir designed for a capacity of $1m^3/s\text{.}$