河道堤防在洪水灾害防治、水利资源利用等方面起到了重要作用。但是当洪水超过一定界限后，堤防工程将会面临失效的风险。一旦河道溃堤发生，洪水的泛滥将带来巨大的生命财产损失。对河道溃堤水流特点和规律进行研究，有助于做好防灾减灾预案，应对可能引发的灾害。现有针对溃堤的研究多集中于应用数学模型进行模拟，而现场观测和物理实验等直接观测察的成果非常有限。溃堤问题具有其自身特性，河道内流速、水位的变化和溃堤过程相互耦合，也不能简单地将溃坝的研究成果直接应用于溃堤研究中。目前针对溃堤水流特性的深入分析仍较为缺乏。 本研究采用物理实验与数学模型相结合的方法，从水动力学的基础研究出发，在简化条件下着重研究溃堤发生后河道和洪泛区水流的演变特性。物理模型实验在大型室内水槽中进行，模拟了溃堤后洪水在溃口外洪泛区内的演进和落水波在河道内的传播过程，通过压力传感器阵列和声学多普勒流速仪对溃堤引发的水位、流量波动和演变过程进行了测量和研究。数学模型采用基于二维浅水方程的DIVEST-TVD模型，该模型可模拟从亚临界流到超临界流的复杂流态及其演变过程。模型结果应用实测数据进行了较为全面的验证，并对溃堤水流的流速分布、溃口流量等影响因素方面进行了分析和研究。 研究结果表明：（1）河道溃堤水流的变化主要有三个不同的阶段，分别为：以重力坍塌作用为主的溃堤初期、河道流量逐渐替代重力成为主导作用的过渡期和以来流流量为主导作用的稳定分流期；（2）在洪泛区，河道来流流量对溃堤水流的传播产生向下游偏移的影响，在一定范围内，河道来流流量越大，则偏移的程度越大；（3）河道内，溃堤产生的落水波向上下游的传播存在明显的不对称性，落水波向上游的传播速度较下游慢，但受到落水波影响上游水位骤降幅度较大且流量增加；（4）溃口流量过程在溃堤不同阶段有不同的表现，在溃堤初期出现峰值，而到了稳定分流期，溃口分流的大小主要取决于由上、下游流量差，同时受到溃口宽度和底部糙率的影响。 本文研究成果可为溃堤洪水动力学分析提供可靠的数据，为其他数学模型提供较为完整的验证资料，对河道溃堤洪水的预防和灾害控制提供科学的支撑作用。
River dikes play important roles in flood control and water resource utilization. While dike projects will face the risk of failure when the flood exceeds the design level. Dike breaking is one kind of the frequent disasters in the world and it could cause enormous losses. Therefore, attention should be attached to the study of dike-break induced flows.So far, numerical models are widely used to simulate the flooding due to dike-break, while direct observations from field surveys and physical models are rather limited. Moreover, unlike the dam break from reservoirs at rest, the dike-break flood is influenced by the main flow direction of the river. The research results of dam-break could not apply to dike-break directly.In this study, both physical experiments and numerical models are used and focus on the basic dynamics of water. Boundary conditions are simplified to highlight the propagation characteristic of the flow in different areas. Physical experiments have been conducted in a large laboratory flume to simulate dike-break induced flood wave propagations in flooded area and flow fluctuations in channel. The variations of water level and discharge are measured and investigated by using a pressure sensor array and two ADVs (Acoustic Doppler Velocimetry). DIVAST-TVD numerical model is adopted which base on Shallow Water Equations. These equations are broadly used to describe coastal, estuarine, inland water flows and will be solved by the TVD- MacCormack numerical scheme. Model calculation results are compared with the measured data to ensure its reliability. Then the numerical model is used to describe the velocity distribution of the dike-break flood and explore factors affecting the flow through the breach as complement and extension to experiments.The results show that: (a) the change process of water flow induced by dike-break can be divided into three different stages: the initial stage when the gravity has the main impact on flow, the transitional stage when the river discharge replace gravity guadually becoming the leading role, and the stable stage when the river discharge has the main affect; (b) in flood plains, river discharge makes the dike-break indued flow deflected downstream, and greater river discharge makes greater degree of deviation within a certain range; (c) in river channel the dike-break induced water dropping caused asymmetrical waves, which propagate slower upstream with greater amplitude and propagate faster downstream with smaller amplitude; (d) the rate of flow through the breach varied over time, the peak appears in the initial stage and the steady flood flow rate is related to the difference of discharges between the upstream and downstream sections. The study results could provide reliable materials for dynamics analysis of dike-break flows, for verifications of other numerical models and then for the benefit of flood prevention and disaster control in riverine managements.
