Browsing by Author "Liao, Chung-Ta"

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3D Simulation of Softrock Erosion in Chuoshui Creek
(2015)
Zhang, Yaoxin
;
Jia, Yafei
;
Yeh, Keh-Chia
;
Liao, Chung-Ta
;
Wang, Sam S. Y.
This paper presents a study of soft rock erosion in Chuoshui Creek, Taiwan, using CCHE3D hydrodynamic model. The geological condition of Chuoshui Creek is complex; one reach of the river is flowing through a zone of base rock which is highly weathered and erodible, resulting in tremendous channel incision and headcut propagation particularly by high floods during typhoon seasons. A semi-empirical soft-rock erosion mechanism is implemented, in which the softrock properties, flow shear stress, and stream power, etc. are considered. The erosion rate coefficients of the formulation have been calibrated by field data in separate studies. In this study, the event of typhoon Morakot in 2012 was utilized to simulate the softrock erosion process in a 1.6km-long reach downstream of a large cross-river infrastructure, JiJi Weir, where serious soft rock erosion has occurred, threatening the integrity of the weir. The 3D model performed well under the conditions of highly unsteady, supercritical flows and complex channel topography. Comparing to the field data, the simulation results agreed well with the observations. The calibrated CCHE3D softrock model is then applied for evaluating the effectiveness of planned erosion control structures in the river.
Coupled geo-fluvial channel evolution and bedrock erosion modeling on the river in Taiwan
(2015)
Wu, Kuowei
;
Lai, Yong G.
;
Yeh, Keh-Chia
;
Liao, Chung-Ta
;
環境工程研究所
Cross-stream structures such as weirs are widely used for water intake in many alluvial rivers in Taiwan. Use of these structures, however, leads to severe scour downstream as rivers in Taiwan typically have steep slopes and are subject to flood flows caused by typhoon. The 7.3-magnitude earthquake in 1999 caused a differential uplift of river channel near several weir sites, which led to accelerated river width and slope adjustments. This study concerns with a reach downstream of Ji-Ji weir that consists of mostly soft bedrock and has experienced significant vertical and lateral erosion. Extensive bank failure occurred during Typhoon Saola in 2012. Vertical erosion of upto 14 meters was recorded since the weir operation in 2000. A number of engineering schemes have been proposed to stabilize the reach or to reduce the erosion in the bedrock exposed reach. In this study, a new two-dimensional geo-fluvial numerical model, SRH-2D, was used to simulate combined vertical and lateral erosion in alluvial stream. The geo-fluvial model is coupled with a bedrock erosion module to predict both vertical and lateral alluvial erosion and bedrock incision. The model is used to simulate a 15.5-kilometer reach of Cho-Shui River over a three-year period. The results are then compared with the field data for model assessment. The simulated results show that the coupled geo-fluvial and bedrock model could correctly capture major erosion and deposition patterns. However, this study also points to the need for future improvement.
Development and application of 2-D mobile-bed model with bedrock river evolution mechanism
(2014-08-01)
Liao, Chung-Ta
;
Yeh, Keh-Chia
;
Huang, Ming-Wan
;
土木工程學系
;
Department of Civil Engineering
Steep slope and severe bed change are the characteristics of mountain rivers. These characteristics often cause the bed armour layer flushed away, make the bedrock exposed, and then increase the channel incision. Most mobile-bed models of past few decades aimed at the sediment transport of alluvial channel. In this paper, a bedrock river evolution mechanism is proposed, and included in a 2-D mobile-bed model, called the explicit finite analytic model (EFA). The EFA model can consider both incision and deposition over the bedrock, by combining a new stream power type of bedrock erosion rate formula with the flow and sediment transport modules. An uplifted reach of Taan River, Taiwan, caused by the Chi-Chi earthquake occurred in 1999 is chosen as the study site. Rapid bedrock incision since the uplift provides a rare chance to explore its mechanism and evolution process. The field and numerical results show that the proposed model has the capability of simulating morphological changes for bedrock rivers. (C) 2013 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.