It has previously been shown that the transition from supercritical to subcritical behavior in granular chute flows often results in the formation of stagnant zones which limit the mass flow and eventually clog the chute. This paper reports an analysis of previously unpublished data for the flow of cohesionless granular material in inclined open channels. Three regimes of mass flow behavior, supercritical and two regimes of subcritical flow, were observed and are characterized by their dependence on chute inclination and geometry. (This paper represents the first report of the third how regime.) Analysis of the experimental findings lead into empirical/mathematical expressions for the mass flow in the first two regimes as well as a prediction of the regime transition points for all three regimes. This last gives insight into the effect of chute geometry on regime transition and the subsequent clogging of chutes.