Stream Control Description Control code. United States Geological Survey, Surface Water User Group UNSP 1 true unspecified The streamflow control was not specified. CHAN 2 true channel control The streamflow control is a channel where the geometry and roughness of a long reach of channel downstream from the stage gage are the elements that control the relation of the stage-discharge. SECT 3 true section control The streamflow control type is defined by the geometry and composition of a single cross-section; for example, when the channel is constricted by a sand bar, rock outcropping, or man-made structures. A distinct downward break of the water surface can be detected at a section control. CMBN 4 true combined section and channel control The streamflow control during the discharge measurement was both section and channel control.