Yaoxin Zhang

By Yafei Jia, Yaoxin Zhang, Keh-Chia Yeh and Chung-Ta Liao

Bank erosion is a dominant river morphodynamic process resulting in encroaching valuable farming land and channel migration. Prediction of bank erosion and channel migration requires understanding of the morphodynamics of the entire river system. Numerical modeling is an ideal method for this task. However, models with full capabilities and applications on complex real-world problems are rare. In this study the finite element-based computational model, CCHE2D, and its flow, sediment transport, and bank erosion modules are introduced. The model is capable of simulating unsteady flows with nonuniform sediment transport and cohesive/non-cohesive material bank erosion. The effects of helical secondary current on sediment transport induced by flow curvatures are reflected in both bed load and suspended sediment formulations. This model is validated using multiple sets of experimental data and applied to bank erosion problems of the Chuoshui River, a real-world mountain river in Taiwan. Characterized by typhoon floods, steep channel slopes, and high sediment load and mobility, this river often exhibits a braided pattern consisting of multiple curved channels. Channel bed change and bank erosion caused by 10 years of typhoon floods in a selected reach have been simulated, and the computed bank erosion results agreed with the field observation.

Part of the book: Current Practice in Fluvial Geomorphology

By Yaoxin Zhang, Yafei Jia, Keh-Chia Yeh and Chung-Ta Liao

As low-head hydraulic structures, instream weirs are built across rivers to control the upstream water surface elevation and the downstream flow conditions. This chapter presents a study of erosion control using instream weirs at downstream of a reservoir; JiJi Weir was built across the longest river in Taiwan, Chuoshui Creek, a mountainous river with steep slopes. Due to the easy-to-be-eroded fine lithology layers of mud, shiver, and sandstones on channel bed, the downstream of JiJi Weir had suffered from severe channel incision and head-cut development problems, which greatly threatens the integrity of the dam. To protect the JiJi Weir and its downstream channel from serious channel erosions, the Water Resources Agency (WRA) of Taiwan proposed erosion control plans that multiple instream weir structures were to be installed along the downstream channel of JiJi Weir. A three-dimensional (3D) numerical model, CCHE3D model with capabilities of simulating bedrock erosions, was used to evaluate those erosion control plans and thus explore for the optimal design.

Part of the book: Hydraulic Structures - Impact on River Flow and Sediment Transport-Dimensioning