Modification Of Mathematical Model For Sediment Transport Of The Lower Weihe River

In recent years, many flood control problems resulting from small river flux with high river stage and lengthen in the time of flood wave travel have happened because of the condition change of river water , sediment and variation of channel boundary in the downstream reach of Weihe River, which brings the case of small discharge but a heavy flood damage. The frequently occurring unordinary flood stage increases the difficulty of flood control practice in the river. For the river regulation, the rational determination of design flood table and building a study base of flood forecast for the lower reaches of Weihe River, it is quite important to study systematically the flood travel and to recognize the flood character appearing under the existing river bed conditions of Weihe River. In order to improve the forecasting risk management and make a safe flood control, there is a active demand to explore the many phenomena and probing problems existing in hyper-concentration sediment flood travel by mathematical model in the lower reaches of Weihe River, which could supply a reference for monitoring flood and directing actions on flood control.At the present, many 1-D and 2-D mathematical models being used in the middle and lower reaches of Yellow River build with the flow equation, the continuous equation, the sediment continuous equation and the channel bed deformation equation. The differences among them come from the special parameters used and the method of model operation, such as sediment-carrying capacity of flow, movable-bed resistance, and the way of exchange between the suspended load and the bed load and so on, which reflect non-equilibrium transportation of sediment in stream channel. In contrast with Yellow River, the lower reaches of Wei River happen more frequently the hyper-concentration flood. The flood has the character of long wave travel time, hyper-concentration sediments and more manifest static shearing stress which results in abrupt change of the river bed cross section, especially in the lateral deformation. Now, the mathematical model for the lower reaches of Wei River is mainly the one of 1-D mathematical model used in middle and lower reaches of Yellow River. So the model more reflects the character of river sediment delivery of general muddy flow in Yellow River but that of hyper-concentration flow in lower Wei River. In order to explain the characteristic of Wei River, it is necessary to improve the model according to the character of sediment delivery and the lateral deformation in the Wei River. This thesis builds up a common 1-D mechanical model with modifications as follows so as to hopefully reach the goal.1.In the aspect of sediment computation, considering the existing of different exchange mechanics between suspended load and bed load under the condition of water scouring and silting process in flood travel, this thesis adopt firstly the marginal scouring and marginal silting sediment concentration capacity formula which possess more definite physical meaning and developed a methods for its application. 2.In the part of evolution of river bed, the specific phenomena of integral depositing at the channel boundary often occurred at downstream river reach of Weihe River has been probed into from a physical base, and the results of this analysis and study indicated that one of the most important causes that cause the river channel of the downstream channel of Weihe River deform rapidly is the static yield stress of hyper-concentration flood. And this static share stress is a product of muddy water stream pattern changing from Newtonian into gel.3. For fitting the characteristic of hyper-concentration flood with mathematic model, in the process of simulation, the integral depositing was been made a generalized disposal through building empirical formula according to observed data.4. Lastly, the model verification has been carried out using the hydrograph of observed flood of year 1994, and the results of the simulation indicated that the model has preferably simulation capability. Comparison with the same kind models, the modified model in this thesis is more distinct, exact and practicable at the aspect of reflecting the physical base conception.