The unit consists of an inclinable channel mounted on a frame, together with a discharge tank and recirculating pump. To commence a demonstration, sand is placed evenly along the channel bed, between the inlet tank and the overfall discharge weir. Water is circulated around the system at one of the three selectable flow rates. The channel slope is adjusted by means of a fine screw jack to which an accurate slope indicator is attached. The channel sides are transparent in order that bed profile changes can be observed, and a section of one side is provided with graphical grid markings to permit quantitative assessments to be made of bedform dynamics.