Development of numerical models for wave deformation and sediment transport in wave-current coexisting field near river mouth

对波浪特征和河口周围相应沉积物输送的物理了解对于维护沿海地区的自然环境和预防自然灾害至关重要。在本研究中，针对河口附近波流共存场的波浪变换、粘性水流、粘性泥石流和海底形态变化建立了数值和统计模型。本研究取得的主要成果总结如下：建立了一种基于波浪作用平衡方程的波浪预测模型，用于分析大面积的波浪变形。该模型包括波流共存场中的波破碎和衍射效应。为了详细分析较小区域内的波浪变换，推导了改进的 Boussinesq 方程并构建了相应的数值模型。此外，基于广义曲线坐标中的纳维-斯托克斯方程，对沿海结构周围的二维和三维粘性流场进行了数值研究。还检查了由水和小泥浆颗粒组成的泥浆流的特征。此外，还通过一系列实地调查研究了日本手取河口附近海底剖面的长期变化。研究了大坝建设和挖沙等沿河沉积物管理对河口附近海底形态的影响。日本白川河口附近的泥滩剖面也采用二次剖面法进行了分析。

Physical understanding of wave characteristics and corresponding sediment transports around river mouths is essentially important in order to maintain physical environments and to prevent natural disasters in coastal areas. In this study, numerical and statistical models are developed for the wave transformation, viscous water flows, cohesive mudflows, and morphological seabed changes in the wave-current coexisting fields near river mouths. The main results obtained in this study are summarized as follows.A wave prediction model based on the wave action balance equation has been developed for analysis of wave deformation in large areas. This model includes the effects of wave breaking and diffraction in the wave-current coexisting fields. For detailed analysis of wave transformation in smaller areas, improved Boussinesq equations are derived and the corresponding numerical model has been constructed. In addition, the two-and three-dimensional viscous flow fields around coastal structures are numerically investigated on the basis of the Navier-Stokes equations in a generalized curvilinear coordinates. The characteristics of mudflows consisting of water and small mud particles are also examined.Furthermore, long-term variations of the seabed profile near Tedori river mouth, Japan, are investigated using a set of field surveys. The effects of the sediment management along the river such as dam construction and sand dredging on the seabed morphology near the river mouth is examined. The mudflat profiles near the Shirakawa river mouth, Japan, have also been analyzed by using a quadratic profile approach.