Study On The Multiple Time Scales Of Inflow Condition And Fluvial Processes In Yellow River

With the purpose of studying the mechanism of multiple time scales of fluvialprocesses, the mainly indexes of fluvial processes, such as bankfull discharge andsedimentation rate of river bed, were chosen to study the multiple time scales offluvial processes using the methods of wavelet analysis and statistic analysis based onthe observed data of hydrological stations in the Yellow River basin. The delayedresponse mechanism of fluvial processes to incoming flow and sediment conditionswas also studied based on the multiple time scales analysis and the calculated methodof bankfull discharge was developed through relating the bankfull discharge to inflowconditions under different time scales. The results of this paper show a certain valuein discovering the multiple time scales of fluvial processes for alluvial rivers andenriching the theory of fluvial processes.The multiple time scales of flow discharge, sediment concentration and bankfulldischarge were analyzed using the continuous wavelet analysis and the domainanttime scales of these variables were also calculated basing on energy spectrum analysis.The variations of wavelet coefficients represented the variation of the original timeseries under certain time scale. The bankfull discharge and sediment concentrationhave main time scales of5-6years and19-20years and the sedimentation series has3-5years and35-36years for the main stations of the lower Yellow River. Thecorrelations of bankfull discharge and inflow conditions under the same time scaleswere analyzed. The results shown that there were obvious phases differencesbetween bankfull discharge and inflow conditions and the value of the phasedifferences were different for different river reaches. The calculated result wascoincided with delayed response model and artificial neural network and reflected themechanism of delayed response for bankfull discharge to inflow conditions from thepoint of multiple time scales.The driving and responding model of fluvial processes was built up based onmechanism of the variation rate of bankfull discharge was determined by the drivingforce comparing to the resistance force. In order to get the analytic solution of themodel the driving force was decomposed to series of functions using the waveletanalysis and the domainant functions can also be identified. The domainantfunctions of main time scales were used to replace the driving force after wavelet reconstruction. The model was applied to calculate the bankfull discharge of thelower Yellow River channel and the calculated results were compared with theobserved data. The driving and responding model played the role of expanding anddeveloping the delayed response model of bankfull discharge.The multiple time scales of sedimentation rate of the river bed of flood eventsrepresented the fluvial processes in the short-time scale were also analyzed. Therelationships between sedimentation rate and the inflow conditions under the sametime scale were analyzed too. These would supply references for predicting thetrend of sedimentation rate of the lower Yellow River reach. The statisticrelationship between sediment deliver ratio, which reflected the characteristics ofsedimentation and erosion of the river channel, and inflow conditions was built upbased on the multiple time scales analysis. It was also applied to calculate thesediment deliver ratio of the lower Yellow River channel in the flood season. Theequation reflected the nonlinear relationships between dependent and independentvariables. It would be useful for engineering application.