Energy Dissipation Rate Theory And Its Application In The Lower Yellow River

The energy dissipation rate（shorted as EDR thereafter）in a river is one of the important factors that reflect the laws governing sediment transport capacity and morphological changes.However,in the case of the Lower Yellow River（shorted as LYR）,which is characterized both by complex and rapid morphological changes like cross-sectional forms changing longitudinally significantly and extremely irregularly,and non-smooth sediment transport during floods,consequently tending to make some local reaches become unstable,very little is known about both EDRs distributing along the channel and the quantitative relationships between EDRs and cross-sectional forms.Therefore,using EDRs to study the channel form changings is of important theoretical significance and great practical value in the decision making about how to train the Lower Yellow River so as to shape a highly efficient channel for flood conveyance and sediment transport.First,in the thesis,theoretical formulas for EDRs are developed,which are convenient for applications in the field,based on the energy equation of fluid mechanics.The correction coefficients involved in the EDRs formulas are determined as well as the effects of flow structure and sediment concentration on EDRs,using experimental data obtained on a pipeline model and a channel model.Second,the formulas,helped with a one-dimensional and two-dimensional hydrodynamic numerical models,are used to calculate EDRs along a typical reach of the LYR.With the EDR values,a relationship between EDR and cross-sectional forms is established,with the mechanism governing the feedback between EDR,sediment carrying capacity,and cross-sectional form revealed.Third,using the EDR formulas,flow continuity equation,resistance equation,and the modified formula for sediment carrying capacity,intervals for the thresholds about the values of channel cross-sectional form index and sediment carrying capacity for floods of scales are given.The main research findings and conclusions are given as follows:（1）Theoretical formulas for EDRs are made for the LYR based on the basic equations of fluid mechanics and different energy dissipation modes.One formula is for the whole cross section EDR and the other for the internal main-stream zone EDR.A reduction is done,using the filed data about the LYR,to a formula for sediment carrying capacity,the latter based on water-sediment two-phase energy theory.Then it is compared with the other typical formulas.The efforts verify sound reliability of the formulas.（2）The coefficients in the formulas for EDRs are determined by using the experimental data obtained on physical models for a pipeline and a curved channel.Also,with the data,investigated are the characteristics of flow,sediment transport,circulating flow structures,and the laws about changing of the EDRs in the LYR.Both the coefficients for the two EDRs are found approximately 1.0.The pipeline model experiments show the whole cross section EDR and pulse pressure amplitudes increase but the frequency decreases,when sediment concentration increases.The curved channel experiments show that internal main-stream EDR is strongly affected by secondary flow,and the region near the secondary flow usually produce a high value of EDR.Within a bend,secondary flows are found to occur alternately in the cross sections in the downstream direction,and the whole cross section EDR is found to fluctuate along the flow path.（3）Based on the topographic characteristics of the Huayuankou-Gaocun reach of LYR,i.e.,cross-sections being wide-shallow coumpound,a two-dimensional hydrodynamic model is made to find flow velocity,flow depth,and EDR distribution laws along the continuous curved reach.The results show that the floods in the Doumen-Jiahetan reach are still restricted to run within the channel without the overflow for a flood of less than 4000 m³/s.The whole cross section EDR and the internal main-stream EDR are found to increase with increasing flow velocity.For a flow rate,the high EDR zone and high-velocity zone are found to occur generally downstream of the bent apex and be of a low value in the approach arm of the bend and a high value in the exist arm.（4）Relationships between EDRs and index for cross-sectional forms and riverbed stability in the Gaocun-Sunkou reach of the LYR for the stable flow are established.It is found that the whole cross section EDR fluctuates about the average value with larger amplitudes for larger floods,but decreases first,and increases then as the flow area or width-depth ratio increases,and has a significant positive correlation with the riverbed stability index.When the EDR changes to the smallest and the riverbed stability index is found to be somewhere between 0.8 and 1.0,and the cross-section is found to be able to keep stable.The internal main-stream zone EDR is found much less than the whole cross section EDR,and has an increasing ratio of the latter as width-depth ratio(B^1/2/H)increasing.（5）In-depth research is done on the law governing the responding of EDR to the incoming flow and sediment conditions and changings in cross section forms in the Huayuankou-Sunkou reach of the LYR.The threshold intervals for the cross-sectional form and sediment transport capacity are given for floods of different scales.The incoming flow rate is found to be the main factor for the whole cross section EDR while sediment concentration is found to be the main factor in the internal main-stream zone EDR while channel is becoming narrower and deeper.With the continuous adjustment of cross-sectional forms,the whole cross section EDR is found to run in the opposite relation to changing in sediment transport capacity but in a non-synchronous（i.e.,lag）phase.The threshold intervals of sediment transport capacity and width-depth ratio are found to between 20.5～56 kg/m³ and 18～38,respectively,considering the condition for riverbed stability.