Study On Recovery Saturation Coefficient Of Suspended Sediment In Unidirectional Scouring River Downstream Of Reservoir

After the construction of the reservoir project,the "clean water" with low sediment concentration discharged from the reservoir will scour the downstream channel,and the sediment on the bed will move as suspended load under the influence of the flow,and the sediment concentration of the flow will enter the process of saturation recovery.As the main form of non-equilibrium sediment transport,the study of the movement mechanism of suspended load is of great significance to the analysis of the process of recovering saturation of suspended load sediment concentration and the evolution of riverbed scouring and silting.Therefore,from the perspective of suspended dynamics of sediment particles,this paper adopts the idea of combining energy conservation theory and mechanical analysis to study the characteristics of suspended force of sediment particles,the law of suspended movement of sediment particles,the distribution law of critical suspended height and maximum suspended height of sediment particles,and the mathematical model of suspended sediment concentration recovery saturation coefficient.In this paper,the main research work and achievements are as follows:(1)In this paper,a series of flume tests are designed and completed with sediment particles and coal particles as the experimental observation objects.The variation of the maximum suspended height of sediment particles with the particle size and flow conditions is studied,and the average maximum suspended height of sediment particles under different particle size and flow friction velocity conditions is obtained.Using coal particles instead of sediment particles for partial similarity tests,the variation rule of the relative suspension height of sediment particles with particle sizes ranging from 0.03 to 1.44 mm in the range of 19.85 to 76.86 mm/s frictional velocity is summarized.(2)based on the distribution law of vertical turbulence intensity of flow,the force balance condition of suspended sediment is analyzed,the energy conservation equation of suspended sediment movement is established,and the turbulent energy transfer coefficient is put forward and calibrated.The conversion relationship between sediment suspension energy and flow turbulence energy is analyzed,and the formula for calculating the maximum suspension height of sediment particles is derived.The calculated value of the maximum suspension height of sediment is in good agreement with the experimental value.(3)By substituting the sediment suspension height and single-step suspension step formula derived from the sediment energy conservation formula,the calculation formula of Hanqi to restore saturation coefficient is improved and perfected.In terms of the single-step suspension step of sediment particles,the effect that the transport velocity of sediment particles lags behind the flow velocity is considered.The main factors affecting the change of recovery saturation coefficient are analyzed,and the calculation results of the improved recovery saturation coefficient formula are compared with the classical formula.It provides a basis for the selection of the recovery coefficient of the mathematical model of unbalanced sediment transport,and can be used to calculate the recovery saturation process of suspended sediment concentration in the pebble sand-entrained channel in the lower reaches of the reservoir.