【作者】 陈杰；

【导师】 秦毅；

【作者基本信息】 西安理工大学 ， 水文学及水资源， 2007， 硕士

【摘要】 近年来，由于水沙条件发生变化，以及河槽边界条件的改变，使得渭河出现了许多新的防洪问题，其特点是：“流量小、水位高、灾害大”。频繁发生的异常洪水位现象给渭河下游防洪增加了困难。针对这种现状，有必要系统地研究渭河下游的洪水行进规律，认清渭河现有河床中发生的洪水特性，这对于渭河下游的河道治理、设计洪水位的合理确定及对渭河下游的洪水预报研究都具有重要的意义。因此，为促进渭河下游洪水的预测预报和风险管理，确保防洪安全，迫切需要利用数学模型来研究渭河下游洪水演进的各种现象和问题，为洪水的监测、防洪和抢险指挥提供参考。目前，在黄河中下游上得到应用的一、二维水沙模型有多个，基本上都是由描述水沙运动的四个基本方程构成，即水流连续方程、水流运动方程、泥沙连续方程与河床变形方程，不同之处在于各模型在求解基本方程时，对某些参数的具体取值和计算方法有所不同，如反映不平衡输沙规律中的挟沙力问题、动床阻力、悬移质泥沙与床沙的交换机理等。然而，与黄河中下游相比，渭河下游发生高含沙洪水的频率高，洪水历时长，含沙量大，高含沙水流的静态剪切应力作用明显，造成河床断面形态变形剧烈，尤其在横向变形上显得更为突出。而现有的渭河下游数学模型，主要是沿用黄河中下游的一维数学模型，模型结构反映更多的是黄河中下游一般高含沙挟沙水流的输沙特性，并不能合理地反映出渭河下游的输沙特性。因此，有必要针对渭河下游泥沙问题，在挟沙规律和横向冲淤变形等方面去改进现有的渭河下游一维恒定流泥沙数学模型。本研究论文建立了常规一维数学模型，并对其作了部分改进，以期达到适应渭河特点的目的。工作主要表现在以下几方面。1、在泥沙计算中，考虑到行洪过程中泥沙在冲刷和淤积情况下，悬移质泥沙与床沙交换机理的不同，首次在冲淤计算中采用物理含义更明确的双值挟沙力公式，并对双值挟沙力公式中的系数计算问题进行了详细的分析及开发出与该公式应用相配套的应用方法。2、在河床演变部分，对渭河下游特有的“贴边淤积”现象进行了机理探讨，分析研究表明，造成渭河下游河槽急剧淤积萎缩变形的重要原因之一为高含沙洪水的静态剪切应力，它是浑水的流型从牛顿体转变成凝胶体后的产物。3、为了使数学模型在模拟过程中能反映出高含沙洪水静态剪切应力造成的“贴边淤积”，作者根据实测资料建立经验公式对“贴边淤积”进行了概化处理。4、最后利用1994年高含沙小洪水过程对模型进行验证，模拟结果表明模型具有一定的模拟能力。相比较而言，经本论文改进后的模型在反映物理成因概念方面较同类型模型清晰、准确，也更接近渭河下游实际情况。更多还原

【Abstract】 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.更多还原