Hydraulic Conditions Created by Passing Flow Through and Over a Combined Weir

In this study, a novel broad-crested weir was designed to investigate the effect of varying rectangular gate widths (vertical slots) on the discharge coefficient and free surface profile of a compound weir. Six weir models with vertical slots were theoretically and experimentally examined in a laboratory flume under uniform flow conditions. Each weir model measured 9.5 cm in height, 30 cm in length, and 10 cm in width. The vertical slots were uniformly 7.5 cm in height, with six different widths ranging from 0.5 cm to 3.0 cm, corresponding to a range of opening area ratios (OAR) from 10% to 60%. Under different head conditions, six flow rates between 10 and 35 m³/hr were tested. Dimensional analysis and multivariable regression techniques were applied to derive a formula relating the discharge coefficient to key influencing variables. These variables include the ratio of total energy head to flume width (Ht/B), the ratio of upstream water head to flume width (Hw/B), and the ratio of slot width to flume width (Bg/B). The results indicated that the discharge coefficient (C_d) of the compound weir increases with both Ht/B and Hw/B, and with increasing slot width (Bg/B). The proposed model, which describes the relationship between measured and computed discharge coefficients, demonstrated excellent accuracy, with R²= 0.998. Furthermore, the findings showed that the width of the weir openings has a significant impact on upstream water depth, downstream free surface profiles, and the hydraulic characteristics of the resulting flow transitions.

Doi: 10.28991/CEJ-2025-011-05-016

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