Two-Dimensional Flood And Sediment Transport Model Over Movable Bed Considering Infiltration Effect

In reality, flood propagation is often accompanied by infiltration phenomenon. The exist of infiltration effect can have significant impacts on flow and sediment transport due to mass exchange. In this thesis, a complete two-dimensional hydrodynamic and sediment transport model is developed to simulate the flood and sediment movement with the consideration of infiltration effect. The effects of infiltration on flow and sediment are considered by introducing the Green-Ampt infiltration equation in governing equations of flow and sediment transport. The main research results in this study are summarized as follows:(1) The paper summarizes the characteristics and the applicable conditions of Green-Ampt infiltration model, and implements the Green-Ampt infiltration model to simulate infiltration phenomenon during rainfall and flooding process. The saturated hydraulic conductivity and wetting front average suction are the most critical parameter in Green-Ampt infiltration equation to describe soil infiltration. The fitting function formula is used to express the relationship between saturated hydraulic conductivity coefficient and the head and the relationship between the average wetting front suction and water sediment concentration respectively. The functional relationship is substituted into the traditional Green-Ampt infiltration model to improve the infiltration model which is suitable for different infiltration heads.(2) The Green-Ampt infiltration equation is introduced into the two-dimensional shallow water equations to consider the infiltration effect on flow flux, thus a new two-dimensional hydrodynamic and sediment transport model based on infiltration effect is developed. In the model, a central-upwind scheme is used to calculate the flow and momentum fluxes across the interface of computational mesh, and then the linear reconstruction of flow variables is adopted to achieve the second-order accuracy in space. An upwind scheme is used to calculate the sediment transport. A central difference method is used to discretize the bed slope source term to maintain the well-balanced property. The friction source term and resistance term are calculated using a semi-implicit method to ensure the stability of model. The diffusion terms in the model are processed using central difference scheme. The model can guarantee the positivity of water depth when the courant number meets the certain condition, which means no need is required to handle the negative water depth problem.(3) The paper introduces an improved Green-Ampt model which is suitable for different infiltration heads without taking into account the movement of sand. The flood model which is suitable for different infiltration heads is validated by rainfall example. The results show that the calculation of variable head permeability flood model and traditional infiltration flood model and measured values are in good agreement. The coastal waves climbing example is used to analyze the impact of infiltration effect on the process of climbing the wave, infiltration effect is found to reduce the maximum climbing wave height and slow down water flow rate on the climb and recession process, but also can catch jump phenomenon in recession process well, which show the reasonableness of the model.(4) The Green-Ampt model is introduced in the water and sediment coupled model in order to establish a movable bed model coupling flow and sediment transport and infiltration effect. The model is validated by examples to analyze the hydrodynamic characteristics, sediment movement and bed deformation characteristics, and also used to explore the effect on flood motion, sediment transport and seabed erosion by the different soil types. The results show that with the bed particle size increasing, the infiltration effect is more significant, and the bed deformation increases.