Transport Of Nonuniform Suspended Load In Yangtze Estuary

Nonuniform sediment transport is the frontier problem of river dynamics and sediment transport capacity is the key to solving the problem of siltation and erosion of rivers,estuaries and coastal waters,as it is a key parameter or bottom boundary condition for 2D/3D mathematical models.This paper studies the transport of nonuniform suspended load in Yangtze estuary,which has important theoretical significance and application value.A new formula for the arbitrary k-th fractional transport capacity of nonuniform sediment was developed as a function of Froude number and the particle Reynolds number based on dimensional analysis.The coefficient for interaction was introduced into the present formula to consider these shelter-hindering effects between different size particles.The proposed formula is organically combined with critical condition of suspension,which is more reasonable and reliable.The formula provides a consistent formulation in which the fractional transport capacity is unified with the total transport capacity of nonuniform sediment.This unification is obtained since the mean fall velocity in the total transport capacity is equal to the geometric average of the fractional fall velocity.And the formula has the adaptability to uniform sediment,which is more reasonable in theory.A formula of maximum particle Reynolds number expressed by flow parameters and boundary conditions was proposed as a new critical condition of suspension,which is more intuitive to judge the suspension state of sediment.The coefficient of the formula was determined by the high-speed camera and the graded dyeing method,and the formula was verified by the van Rijn formula.The coefficients in the formula of sediment transport capacity were determined with laboratory data of uniform sediment,and the formula was verified by measured field data from alluvial rivers.The concept of instantaneous equilibrium was put forward so that applicability of the formula extended to estuaries with the the critical sediment concentration and the corresponding flow and sediment parameters chosen from the field data in the Yangtze,Jiaojiang and Qiantang estuaries.A nonconstant nonuniform sediment scouring and silting mode in estuaries was constructed base on the riverbed deformation equation and the formula for transport capacity of nonuniform sediment.According to this mode,the scouring and silting in the north channel of the Yangtze estuary were calculated and analyzed,which shows that the north channel had undergone a process from scouring to silting and then to significant silting in time domain and the middle section(CSW)had the largest silting and the upstream and downstream silting decreased or even scoured in space.In addition,it was found that the difference of scouring and silting during flood and ebb tide is significant,presenting the phenomenon of silting during flood tide and scouring during ebb tide.The hydraulic geometry of branching river for arbitrary cross-sectional shape was proposed based on the formula for transport capacity of nonuniform sediment.The ratio of cross-sectional area of a distributary channel and the main stream is a power function of its bifurcation ratio with an exponent of 6/7.The hydraulic geometry was applied to the branching channel of Yangtze River,and the equilibrium water depth calculated was consistent with the multi-year average water depth,indicating that the proposed hydraulic geometry was reliable.Based on this,the equilibrium water depth of several branching channels after projects was predicted,which provides new ideas for channel regulation.