The development and application of numerical model of riverbank retreat

• Main Author: 姜世偉
• Other Authors: 楊錦釧
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/09792368696716498554

博士 === 國立交通大學 === 土木工程學系 === 99 === In this study, a numerical model of riverbank retreat has been developed and applied to a practical case. The governing equation of unsaturated groundwater flow is solved by implementing numerical method to obtain the transient distribution of the pore water pressure to evaluate riverbank stability with respect to mass failure. However, previous studies to compute the pore water pressure were usually based on groundwater table with hydrostatic pressure distribution hypothesis. The approach proposed in this study not only improves this shortcoming but also takes the effects of river stage variations and rainfall into account by defining boundary conditions. In addition, cantilever failure and fluvial erosion are incorporated into the model in order to further understand the interaction and the process of riverbank retreat. First, mass failure, cantilever failure and fluvial erosion are respectively investigated by a series of hypothetical scenarios. The simulated results indicate that the occurrence of mass failure and cantilever failure mainly depend on the fluctuations in pore water pressure determined by river stage variations, soil permeability and rainfall condition. Fluvial erosion is determined by hydraulic conditions (i.e. channel slope, river stage and stage hydrograph) and soil erodibility (i.e. critical shear stress and erodibility coefficient). Subsequently, mass failure, cantilever failure and fluvial erosion are combined to estimate riverbank retreat. According to the conclusions of analyses, riverbank retreat is the process of repeated failure events and is primarily influenced by the magnitude and range of fluvial erosion with remarkable fluvial erosion. Finally, the results of the study reach of Jhuoshuei River reveal that the proposed model is capable of quantifying sediment yield and well predicting riverbank retreat length.