A methodology for locating the hydraulic controls for layered flow when both the bed elevation and flow width are varying, is presented. The model, based on singular points in the solution of the gradually varying flow equations for the free surface and interface slopes, reviews the basic hydraulic principles behind hydraulic control. A number of different types of control are identified depending upon the depth-discharge relationship at the control, its location relative to the point of maximum constriction and the relationship between the maxima and minima of the internal energy at different locations within the flow. The pair of internal controls for two-layer exchange flow are shown to be a special solution to the model where the exchange flowrate adjusts to match the maximum internal energy at one control with the minimum internal energy at the other.