Investigating the flow through parallel sluice gates on a broad-crested weir

When dealing with the challenges of large conduit widths or high upstream depths in irrigation and drainage networks, installing parallel sluice gates on a broad-crested weir can be a practical solution to reduce construction, maintenance, and operational costs. However, the complex flow dynamics of this composite structure differ from a single-gated weir, warranting a closer investigation. This study built a laboratory model with three parallel sluice gates on a trapezoidal weir sill. Various combinations of gate openings were tested to understand how this design choice impacts the discharge coefficient, which is a crucial parameter for engineers. Under free-flow conditions, the researchers used two different methodologies to estimate the discharge coefficient, both achieving low average errors of around 2 %. Interestingly, the result showed that adding parallel gates significantly influences the discharge coefficient compared to a single-gated weir design. Three new methodologies were developed for submerged-flow conditions to determine the submerged discharge coefficient, with average errors ranging from 5.4 % to 8.3 %. By examining the different gate opening combinations, the most suitable configurations were identified in terms of accuracy for submerged discharge determination. Also, the manner in which parallel gates impact other important factors like water surface elevation, energy dissipation, and flow patterns were investigated. Finally, three relationships were derived to help engineers determine the critical submergence threshold for identifying submerged-flow conditions.