Abstract: A water control structure for a flow channel comprises a structure-mounted roller assembly having a pair of elongate, generally U-shaped frame members including an upstream leg, a downstream leg and a connecting web therebetween, the frame members adapted to be positioned on opposite sides of the flow channel with the openings in the U-shape facing each other for slidably receiving and supporting in vertically stacked relationship the ends of from one to a plurality of plain flashboards therewithin for providing a height-adjustable gate of flashboards for regulating water levels. A plurality of longitudinally spaced-apart rollers are mounted on the downstream leg for facilitating longitudinal sliding movement of the flashboards in the U-shaped members, each of the rollers comprising a split wheel roller assembly including first and second spaced apart, major diameter roller surfaces.