Study On Parameterized River Pattern Classification Method And River Evolution Characteristics Based On Flow Resistance Law

When planning to protect and develop the water resources,it is necessary to maximize the relevant information about river,so as to do river planning scientifically and rationally.Natural rivers are very complex and fast-changing,but also follow many regularities,some of them are well-regulated and very similar.River morphology is the external reflection of river dynamics,and also the important expression form of river evolution characteristics.Based on flow resistance law,this paper gives creative research on river pattern discrimination,establishes a river pattern classification method based on flow resistance law;numerical and experimental investigations on the important meander hydrodynamics are carried out;the possible river pattern and development process under different parameters are studied in laboratory conditions.Many research methods,such as statistical analysis,theoretical analysis and model study,are used in this paper.Main contents and innovations are:1).Establish the relational expression of river resistance law.Flow resistance law for natural rivers directly determines river morphology,while different river morphology reflects different flow resistance law.Different from the flow resistance law for open channels,we take river morphology into consider,build the analytical expression of river resistance law,the method is described as follows: we extend the Darcy-Weisbach equation to the natural river cases,using some parameters,such as slope,discharge,velocity,grain size,river shape parameter,channel geometry,by the means of some technological means,such as data analysis and data fitting,we obtain the expression form of river resistance law.The river pattern parameter is defined as the discrimination criteria,inverting the river resistance law,a clear physical and simple river pattern discriminant method is established.Analysis reveals that single-thread channels are sensitive to bank strength in this river pattern discrimination,but not braided channels,in particular in overlarge width-depth ratio cases.Transient anabranching or braiding pattern could occur in single-thread typical zone following external disturbance,but would eventually return to dynamic equilibrium state.2).Typical river bend flow structure study.Meandering is the most basic river morphology,the simplest transformation of straight open channel,the meandering flow movement is also the driving force of river evolution.According to some research,the migration rate in local bends depends on the ratio of the local curvature radius(R)to local river width(B)and there is a peak migration rate at around R/B=3.In reaction to the phenomenon,we researched on numerical and experimental investigations of flow in a 180o mild bend,which is close to criticality with curvature ratio R/B =3.The variations of velocity components,streamlines,secondary flow,and wall shear stresses are analyzed in the study.Comparision between the numerical results and measurements indicated that RNG k-? model can successfully predict this flow phenomenon.The flow pattern in this bend is influenced widely by the secondary flow.3).The experimental study on river evolution.During the transformation of river patterns,flow resistance law is also changing,which show up as various parameters variations in flow structure,slope,particle size distribution,river-bank lines,bed topography and so on.We researched on the simulation of short-term development of sine-generated meandering river in laboratory conditions.The influences of initial system parameters on the evolution process of rivers are investigated,including control over channel sinuousness,channel width and dominant discharge.Measurements on the bank-line,flow field,bed topography and sediment transport rate were carried out.Different rivers have different development characteristics.Braided rivers are easy to produce using non-cohesive sediments in floodplains,whereas environmental temperatures and humidities could influence the fluvial process by their effects on material cohesion.The stability degree of sandbars formed in the channels reflects the adaption of channel morphology to hydrodynamic condition.The experiment results could be useful for verifying river pattern discriminant functions and offer a basis for further study on the morphological evolution of large-scale natural rivers.