Effects of water discharge and sediment supply on deformation of riverbed with sand bars

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Effects of water discharge and sediment supply on deformation of sandbar beds are investigated. The effect of grain sorting on the bad deformation is also investigated. The summary of results is as follows :1. Effects of change in water discharge on growth and transformation of alternate bars(1) Effect of change rate on the transformation is relatively small in case of a long wave period, whereas it is large in case of a short one.(2) Wave height of an individual alternate bar in the non-uniform sediment bed is lower than that in the uniform one during the flood period.(3) Response-lag of the wavelength and height, flow depth and sediment transport rate to discharge change are small when the wave period is long, whereas they are large when the wave period is short. And, response-lag of alternate bars to discharge change in the non-uniform sediment bed is smaller than that in the uniform one.2. Effects of sediment supply on alternate bar transformation and meandering stream formation(1) The centralization of flow at pools of alternate bars due to decrease of water discharge makes emerged bars appear, and forms meandering streams. The meandering streams in case with sediment supply are shallow and vary actively, whereas those in case without sediment supply are deep and stable.(2) The emerged bars in the non-uniform sediment bed are formed with grain sorting, and are more stable than those in the uniform one.3. Effects of water discharge on meandering stream deformation and alternate bar reformation(1) Alternate bars are formed easily in the non-uniform sediment bed because the emerged bars in that bed are eroded easily than those in the uniform one.(2) The meandering streams are transformed into more large alternate bars by the riverbed aggradation and the low water discharge.