OVERBANK FLOOD FLOWS WITH TOPOGRAPHIC CHANGE IN FLOODPLAINS

We consider overbank flood flows with topographic change due to deposition offine sediment, which is one of the most difficult cases for computation. Takingaccount of a relationship between numerical viscosity and bottom friction in theprimitive model, horizontal viscosity must be introduced for finer computational gridof a few ten meters, in order to estimate bottom friction under movable bedconditions precisely. By using a vorticity model for overbank flood flow, transversevelocity distribution is found to be sensitive to the roughness in floodplains such asvegetation. To verify the results of the vorticity model, laboratory experiments onthe flows in compound channel of short reach were carried out. Additionalexperiments on the flows above vegetated bed were also carried out, where velocityprofiles in and over the roughness arrangement are well expressed by formal walllaw due to constant eddy viscosity. Some aspects of concentration profile arediscussed in relation to sedimentation.We consider overbank flood flows with topographic change due to deposition offine sediment, which is one of the most difficult cases for computation. Takingaccount of a relationship between numerical viscosity and bottom friction in theprimitive model, horizontal viscosity must be introduced for finer computational gridof a few ten meters, in order to estimate bottom friction under movable bedconditions precisely. By using a vorticity model for overbank flood flow, transversevelocity distribution is found to be sensitive to the roughness in floodplains such asvegetation. To verify the results of the vorticity model, laboratory experiments onthe flows in compound channel of short reach were carried out. Additionalexperiments on the flows above vegetated bed were also carried out, where velocityprofiles in and over the roughness arrangement are well expressed by formal walllaw due to constant eddy viscosity. Some aspects of concentration profile arediscussed in relation to sedimentation