Abstract:With the existence of congeries in the river channel

the hydraulic characteristics were changed.In order to analyze the mechanism of accumulation in different water resistance

the flume experiment was carried out.The change of hydraulic characteristic caused by different sizes of congeries was obtained by controlling the slope of the bed surface

the size of the congeries and the flow of upstream.The result showed that the height and the range of backwater were larger due to the smaller flow and the larger congeries with the same slope of water channel.With the increasing of water channel slope

the water changed from subcritical flow to riffle

in the same conditions.The additional gradient increased with the increase of congeries size.But the additional gradient decreased with the increase of congeries size if the water turned into riffle.