| The Analysis of the risk of dam-break flood can provide a basis for flood control decision-making.For river with high sediment concentration,dam-break flood is sediment-laden flow.The sediment-laden dam-break flood could cause flooding accompanied with silt erosion and deposition at the same time.Large amounts of sediment deposition aggravate the risk of dam-break and property losses.Moreover,the variations in bed erosion and deposition caused by dam-break flood can affect the flood routing process.Therefore,it has practical significance for the evaluation of the disaster caused by the joint action of water and sediment when the sandy rivers suffer from dam-break.Base on previous studies,we developed dam-break flood mathematical models which are suitable for sandy rivers,according to the actual situation of flood plains.And we use the model to compute the dam-break flood on one of the dam-breaks of Yellow River,analyze the water and sediment movement characteristics of the sediment-laden dam-break flood,we study the impact of silt erosion-deposition on levee breaches outflows and the speed of flood propagation,we assess the risk under the joint action of water and sediment.The main research contents are as following:(1)We develop a two-dimensional flow-sediment mathematical model which are suitable for sandy river and complex flood plains based on the unstructured triangular mesh.Buildings in the flood plains like road and villages were generalized,considering the effects of variations in bed erosion-deposition to water-sediment movement.We simulate the development process of the horizontal extension and vertical erosion of the dam-break through timely changing its length and height.The Roe scheme based on approximate Riemann is adopted to compute the hydrodynamic flux,the TVD-MUSCL scheme is adopted to compute the sediment flux.(2)Fixed bed dam-break test data and punch press dam-break test data are used respectively to verify this model.From the contrastive analysis of the model data and the test data,we find that the model not only can well simulate the water current movement of dam-break under the condition of fixed bed,but also can well simulate the water-sediment movement and the variations in bed erosion-deposition under the condition of movable bed.(3)We use the model to simulate the dam-break of sediment-laden flow happened once in two hundred years on one of the dangerous sections of Yellow River.Then analyze the calculation results of the model,like the water level,flow velocity,sediment concentration and bed erosion-deposition etc.And summarize the characteristics of water and sediment movement and silt erosion-deposition.(4)To analyze the impact of silt erosion-deposition on levee breaches outflows,we compare the results calculated from the clear water fixed bed model,clear water movable bed model,sediment-laden flood fixed bed model and sediment-laden flood movable bed model,analyze the reason that sediment deposition impact levee breaches outflows and assess the risk under the joint action of water and sediment.The results show that sediment concentration of the dam-break flood decrease along river-way.A larger range of sediment deposition is formed in the flood submerging range the sediment body mainly concentrates near the scour pit periphery of dam-break,and the sediment body is distributed in ring form.Near the dam-break,silt erosion and deposition could affect the levee breache outflows and the flood routing process.The formation of the scour pit could increase levee breaches outflows and submerged scope,while the sediment body tends to decrease levee breaches outflows and submerged scope.The results of the study provide certain guiding value for the decision-making of flood and sediment control of the sandy river. |
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