Abstract:Due to the frequent occurrence of heavy rainfalls,landslides and debris flows in mountain regions,a large amount of sediments enter into rivers in different ways,silt up riverbed and change the river pattern,especially in wide-narrow reaches which cause water level to increase sharply and induce flood disasters.In order to study the mechanism of water level change under different river morphology and sediment supply changes in mountain rivers,the experiment was conducted.The correlation between the hydraulic parameters,the river morphology and the sediment supply was discussed.The experimental results showed that the hydraulic parameters were affected by river width and riverbed gradient under clear-water condition and the response of water flow to riverbed change was delayed.The sediment supply affected river morphology and further affected the flow parameters.The water depth changed more obviously compared to the clear-water condition.With the sediment supply being increased,more sediments silted in the riverbed,raised the riverbed towards the upstream.At the top of the siltation,a hydraulic jump was found to occur accompanied with a sharp increase of water level,leading the water up to the floodplain.Thus,the upstream sediment supply exacerbated the riverbed elevation,especially in the wide-narrow regions,where sediment was easily silted and water level increased steeply causing flood to occur.The flow-sediment disasters prevention should be the focus of these areas.