Laboratory investigation of flow over and under a submerged cylindrical weir-gate in small canals

Combination of weir and gate as a hydraulic measuring structure has advantages such as passing the float and settling materials (ice, wood, sediments, etc) simultaneously in compression using weir and gate separately. The flow through combined devices may be submerged when the downstream water level affect on discharge coefficient. In this study, the authors describe new experiments of both submerged cylindrical and sharp edge weir-gate to investigate the effects of geometric and hydraulic parameters on flow discharge. The experiments have been done on rectangular and horizontal small laboratory flume with fore cylinder sizes and also same sharp edge sheet for several flow rates and downstream water level. The results demonstrate that the discharge coefficient are affected by ratio of upstream depth to gate opening H/a, the ratio of upstream depth to height of structure H/P and the ratio of downstream water depth to upstream depth. Also, two submergence limits can be defined for combinational model. The first one depends on gate and it occurs when HTW/H=0.55-0.65 and the second one belongs to weir in HTW/H=0.8-0.85. Moreover, in the both sharp- edged and cylindrical combination models with increasing the submergence ratio, the trend of discharge coefficient decreases similarly and in a constant submergence ratio, the relative discharge coefficients of both models are similar.