Discharge Coefficient of Rectangular Broad-Crested Weirs in Narrow Channels with High Relative Length of the Threshold

Abstract

Broad-crested weirs (BCW) are commonly used elements of stormwater systems and of different open-channel hydraulic structures. Specific features of stormwater drainage channels are small width, low flow depths and, accordingly, small overflow heads at weirs. Dependences of the discharge coefficient of narrow (b = 0.224 m) rectangular sharp-edged broad-crested weirs with vertical walls, threshold height of 0.05 m and threshold length of 0.05 – 0.2 m are obtained experimentally. Experimental values of the discharge coefficient are approximated by the power-law functions of relative length of the weir. At large values of the relative length of the threshold (L/h> 10) for all weirs obtained the same tendency of decreasing the discharge coefficient with increasing L/h ratio that can be explained by the enlargement of the hydraulic friction along the weir with increasing L/h ratio.

Keywords

• discharge coefficient
• broad-crested weir
• narrow channel
• relative length of the threshold