measuring have been broadly studied. Since the nature of flow on the weirs is highly complicated, mostly the driven equations are taken in account a series of simplifier hypothesis that are on the base of empirical experiments. On the other hand most of the weirs cause a relatively calm zone of water on their upstream, which is a place of waste material and sediments to precipitate that is the disadvantage of the device. With gradual storage of sediments, the condition of flow changed and driven equations will lose their precision. In this case composition of weir and gate can be a useful solution for passage of floating materials over the weir and transmission of sediment materials from the lower part of the gate. In this study, hydraulic characteristics of the 18 combined model of trapezoidal weir-gate in the tree groups with three different opening gates at the end of an open channel with a circular cross section were studied. Also, a series of complementary experiments in a circular channel without combined model included 18 single trapezoidal sharp crested weirs model and a single sharp crested sluice gates model with three different opening at the end of channel was performed, in order to evaluating the properties of this type of model in circular channel. Using dimensional analysis, analytical solutions and statistical analysis, an equation for combined discharge by combined model of weir-gate was introduced. The equation was evaluated by experimental data. Finally, Flow-3D software was used to evaluate the denotative flow from under and over of the combined models. Passing flow from single weir model and single gate separately were simulated and analyzed. Dimensional and statistical analysis showed that discharge coefficient of the trapezoidal weir-gate combined model depends on the factors such as a opening angle of the weir in the combined model ( ), ratio of flow depth in the upstream to diameter of circular cha
