Sluice and radial radial gates are common devices used for flow control in hydraulic
structures. This paper demonstrates the variation of the contraction coefficient of sluice gates and
three types of radial gates (namely, Hard-Rubber, Sharp and Music Note gates) by using Energy
and Momentum Equations (EMEs). This paper presents a novel method for estimating the acting
force behind these gates under free and submerged flow conditions. A minimum value of the
contraction coefficient for sluice gates was obtained under a certain value of relative gate opening.
Under a specific condition, Hard-Rubber gates have a larger contraction than Sharp gates, while
Music Note gates have the least contraction. It is recognized that the contraction coefficient
decreases as the gate lip angle and the gate opening increase. Under submerged flow conditions,
the contraction coefficient of sluice and radial gates would be either increased or decreased
depending on the level of flow submergence. It is concluded that using the proposed contraction
coefficient in estimating the discharge coefficient demonstrates an acceptable accuracy.