针对河口水动力学特征和泥沙输移特点，建立了三维水动力学与泥沙运动数值模型，探讨河口水动力学过程，泥沙输移和床面形态发展之间的相互关系。本文的数值模型是基于国际上影响较大的ECOMSED三维水沙数学模型，在前人已有工作的基础上进行创新，增加了新的功能模块使之适应河口区域潮流运动和泥沙输移过程的数值模拟，主要创新点如下：1）侧向固壁边界在天然大尺度水域的计算中设置为滑移边界，但是在计算精度要求较高的小尺度水体问题时，侧向固壁边界采用类似底面边界的处理方式，设置为半滑移边界，不但提高了模型的使用范围，也适合河口和湖泊水流运动的数值模拟；2）加入干湿边界处理模块，定义低于给定临界水深的区域为干网格，在整个模拟区域内对原始方程进行求解；3）加入推移质输沙的不平衡输运模块，并将推移质输沙引起的床面变化加入到床面变形方程。采用航槽水流、丁坝绕流、松散床面泥沙冲刷试验和一个具有解析解的抛物面水面振荡过程对数学模型进行了验证，充分显示了建立的三维水动力学和泥沙输移数学模型的适用性。分析了渐扩水槽模型试验的泥沙冲刷过程的实测数据，根据动床沙波阻力与其几何尺寸的关系，研究了试验模型的床面粗糙高度动态变化过程，并利用本文提出的数值模型对物理模型试验的水流和泥沙输移过程进行了模拟。将数值模拟得到的流场、紊动能、床面切应力、水体含沙浓度、床面冲淤变形过程与实测资料进行了比较，两者结果符合较好。结合实际河口的地形、水文和潮位观测资料，对大潮河口的水沙输移过程进行了三维数值模拟，模型参数通过野外监测数据进行率定。得到了潮流条件下的流速分布，水深随时间变化过程和床底的冲淤过程。模拟结果表明，河口区处于微弱冲刷状态，主要冲刷位置发生在河口上游的河道缩窄处，河口区的滩地比较稳定。河口区内的盐度和泥沙输移均受潮流支配。研究结果为河口地区水环境治理提供了技术支撑。
According to the water flow and sediment transport properties in the estuary, an integrated 3-D numerical model study is conducted to investigate the interaction between the hydrodynamic, morphological and sediment transport processes occurring in the estuary. The numerical model is established based on the widely used in environmental sediment transport studies worldwide model- namely ECOMSED, which is modified to facilitate for the study of the hydrodynamic, morphological and sediment transport processes occurring in the estuary. Major innovations are as follows,1) For large-scale simulations, the influence of the shear-stresses along closed boundaries can be neglected. Free slip is then applied for all closed boundaries. For simulations of small-scale flow (e.g. laboratory scale), Partial slip is set for the influence of the side walls on the flow may no longer be neglected. 2) A wetting and drying scheme is proposed and applied to the model, which defines ‘dry’ cells as regions with a thin film of fluid O(cm). The primitive equations are solved in the thin film as well as in other regular wet cells. 3) A model for the bed load transport is included in the code to account for the dynamics of the mobile bed boundary. The bed evolution due to bed load transport is obtained by solving the sediment mass-balance equation. The model is validated by the trench flume flow, the spur dyke flume flow, sediment suspension over a loose sand bed and a water level over parabolic bed with free oscillations, which show that the model can be used in a wide range.The bed form development processes in an estuary-related laboratory flume experiment are concerned to study the bed roughness height distribution based on the Coleman method, which is included in the numerical model to simulate the water flow and sediment transport processes in the flume experiment. The comparisons between the numerical results and measured data of water velocities, turbulence energies, bed shear stresses, sediment concentrations in the water column and the bed level change processes show good agreements. The 3-D numerical model then is used to predict the sediment transport processes in a macro-tidal estuary with parameters of the model are calibrated first based on the field measured data of morphology, hydrology and tide cycle. The numerical results show the water velocities, water levels and bed level changes during the tide cycle. Tiny bed erosion is occurred in the estuary, most serious place is in the upper narrow river, and the tidal flat in the estuary is stable. The salinity distribution and sediment transport are significantly influenced by the tidal level change. The study can provide technical support for the water environmental management in estuaries.
