The aim of this study is to investigate the coefficient of discharge for a combined hydraulic measuring device. For this purpose nine combined models were constructed and manufactured of an aluminum plates of 2 mm thick, the shapes of the models are of rectangular weir with different width ( )is used over a semi-circular gate of a constant diameter ( )the distance below the weir edge and the semi-circular gate y is changed three times( . The analysis of results show that increase as ( increase and for a constant value of ( increase as the width increase, the values of range from around 0.522 to 0.853 with an average of 0.695. Also decrease as the parameter ( ) ,( ) and ( ) increase and at a constant values of that parameters increase as increase, and the values of range from around 0.61 to 0.74. A multi regression model to estimate for the combined device is estimated with percentage of error .
Keywords: combined orifice, combined weirs.