Generalized Experimental Study On The Flow Movement And River-bed Scouring In The Bank Slope

Navigation regulation projects in river channels not only change channel boundaries,flow characteristics and sediment transport but also can be reacted by flows.Flows and channel evolutions caused by flows can result in deformed or even damaged regulation projects.After the Three Gorges Dam(TGD),channel scouring in the middle-lower Yangtze River has made more complicated interactions between flows and regulation projects.Understanding damage mechanisms of different kinds of regulation projects and proposing reasonable optimized design principles and maintenance measures can reduce their damage levels and improve maintenance efficiencies.Therefore,it is meaningful for better understanding the interactions laws between flow,riverbed and bank protections and also damage mechanisms of bank protections by studying flow structures and channel deformations in the bank slopes.Conceptual flume experiments and theory analysis are used in this paper to study flow speed distributions,eddy structures and local scouring.Also,influences of hydrodynamic incipient conditions of sediment,sediment concentrations and various distances of bottom protections on riverbed scouring are studied.The main conclusions can be drawn as follows:Under the same flow conditions,vertical flow velocities reduce from main channel to bank but keep steady turbulence intensity and turbulent energy.Flow velocities,turbulence intensity and turbulent energy increase with flow Reynolds numbers.Moreover,increasing extent of flow velocities,turbulence intensity and turbulent energy is lager in the bank sides.Bottom protections on riverbed change vertical flow distributions and longiitudinal flow velocities.Flow velocities decrease and turbulent energy increase in the lower region of the two vertical bottom protections.While,flow velocities increase in the upper section of bottom protections and along two bank sides.Also,flow velocities in the lower region decrease and circulation flows even occur with distance reduction between bottom protections.However,turbulent energy increases firstly and then decreases with different distances.Also,turbulent energy reaches its maximum at different distances under different incoming flows.When ratio of flow velocities to incipient sediment flow velocities is increasing,scouring area,maximum scouring depth and its increasing extent between two bottom protections also will increase.Also,when sediment concentration is increasing,scouring area,maximum scouring depth will decrease,which means the larger unsaturation of flows,the greater scouring extent of riverbed along the banks.When distances between bottom protections are reduced,the maximum scouring depth between two bottom protections decreases.And reduction extent increases with decreasing bottom protection distances,which means that bottom protections with particular distances have significant influences on preventing riverbed scouring.