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A study approach is developed to assess the longitudinal channel slope under the equilibrium condition as well as the transient evolution of a mixed alluvial-soft-bedrock stream. Both the historical field data and 2D mobile-bed numerical modeling are adopted. The proposed approach is applied to a 14 km reach downstream of the Ji-Ji Weir, Chuo-Shui River, Taiwan, where continuous maintenance works have been carried out to stabilize this reach. In this study, the temporal evolution of the longitudinal channel profile is assessed numerically with three spatial scales: The large (the entire study reach), the medium (four sub-reaches), and the local (cross-sections) scale. The large scale analysis is the approach for purely alluvial streams and is shown to be difficult to use to characterize mixed alluvial-bedrock streams. The local scale analysis shows that the soft-bedrock incision has a widely fluctuating slope, reflecting the compound environmental forcing and complex riverbed setting. With the medium scale analysis, the longitudinal channel profile is found to follow a predictive trend if the reach is partitioned into four distinctive sub-reaches. Characteristics of the dynamic channel slope evolution in different spatial scales are computed and presented. The study results can be used to select the proper locations and types of the engineering stabilizing structures in a mixed alluvial and soft bedrock stream
Kuowei Wu; Keh-Chia Yeh; Yong G. Lai; Wu; Yeh; Lai. A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream. Water 2019, 11, 735 .
AMA StyleKuowei Wu, Keh-Chia Yeh, Yong G. Lai, Wu, Yeh, Lai. A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream. Water. 2019; 11 (4):735.
Chicago/Turabian StyleKuowei Wu; Keh-Chia Yeh; Yong G. Lai; Wu; Yeh; Lai. 2019. "A Combined Field and Numerical Modeling Study to Assess the Longitudinal Channel Slope Evolution in a Mixed Alluvial and Soft Bedrock Stream." Water 11, no. 4: 735.
Three-dimensional (3D) hydrostatic-pressure-assumption numerical models are widely used for environmental flows with free surfaces and phase interfaces. In this study, a new flow and sediment transport model is developed, aiming to be general and more flexible than existing models. A general set of governing equations are used for the flow and suspended sediment transport, an improved solution algorithm is proposed, and a new mesh type is developed based on the unstructured polygonal mesh in the horizontal plane and a terrain-following sigma mesh in the vertical direction. The new flow model is verified first with the experimental cases, to ensure the validity of flow and free surface predictions. The model is then validated with cases having the suspended sediment transport. In particular, turbidity current flows are simulated to examine how the model predicts the interface between the fluid and sediments. The predicted results agree well with the available experimental data for all test cases. The model is generally applicable to all open-channel flows, such as rivers and reservoirs, with both flow and suspended sediment transport issues.
Yong G. Lai; Kuowei Wu. A Three-Dimensional Flow and Sediment Transport Model for Free-Surface Open Channel Flows on Unstructured Flexible Meshes. Fluids 2019, 4, 18 .
AMA StyleYong G. Lai, Kuowei Wu. A Three-Dimensional Flow and Sediment Transport Model for Free-Surface Open Channel Flows on Unstructured Flexible Meshes. Fluids. 2019; 4 (1):18.
Chicago/Turabian StyleYong G. Lai; Kuowei Wu. 2019. "A Three-Dimensional Flow and Sediment Transport Model for Free-Surface Open Channel Flows on Unstructured Flexible Meshes." Fluids 4, no. 1: 18.
Yong G. Lai; Robert E. Thomas; Yavuz Ozeren; Andrew Simon; Blair P. Greimann; Kuowei Wu. Modeling of multilayer cohesive bank erosion with a coupled bank stability and mobile-bed model. Geomorphology 2015, 243, 116 -129.
AMA StyleYong G. Lai, Robert E. Thomas, Yavuz Ozeren, Andrew Simon, Blair P. Greimann, Kuowei Wu. Modeling of multilayer cohesive bank erosion with a coupled bank stability and mobile-bed model. Geomorphology. 2015; 243 ():116-129.
Chicago/Turabian StyleYong G. Lai; Robert E. Thomas; Yavuz Ozeren; Andrew Simon; Blair P. Greimann; Kuowei Wu. 2015. "Modeling of multilayer cohesive bank erosion with a coupled bank stability and mobile-bed model." Geomorphology 243, no. : 116-129.
Many rivers in Taiwan have steep slopes, are subject to typhoon-induced flood flows, and contain soft bedrock that is exposed at many locations and easily erodible. The occurrence of extensive bedrock erosion has been a major threat to river infrastructure at many locations. Soft bedrock erosion, therefore, is an important process to consider for river projects in Taiwan. In this study, bedrock erosion models are reviewed. A specific model is proposed by combining two existing models incorporating both the hydraulic and abrasive scour mechanisms. The proposed bedrock erosion model is incorporated into a two-dimensional mobile-bed model, and the integrated model is tested by simulating bedrock erosion downstream of the Chi-Chi weir on the Choshui River in Taiwan. A calibration study is performed to determine appropriate values of the model parameters based on two and a half years of measured data. The model is then assessed based on a verification study that compares model predictions of bedrock erosion of the same reach to two additional years of measured data. The bedrock erosion model is found to be suitable for the river reach studied. Further improvement, however, is still necessary, which points to potential future research.
Yong G. Lai; Blair P. Greimann; Kuowei Wu. Soft Bedrock Erosion Modeling with a Two-Dimensional Depth-Averaged Model. Journal of Hydraulic Engineering 2011, 137, 804 -814.
AMA StyleYong G. Lai, Blair P. Greimann, Kuowei Wu. Soft Bedrock Erosion Modeling with a Two-Dimensional Depth-Averaged Model. Journal of Hydraulic Engineering. 2011; 137 (8):804-814.
Chicago/Turabian StyleYong G. Lai; Blair P. Greimann; Kuowei Wu. 2011. "Soft Bedrock Erosion Modeling with a Two-Dimensional Depth-Averaged Model." Journal of Hydraulic Engineering 137, no. 8: 804-814.
Many rivers in Taiwan have steep slopes, are subject to typhoon induced flood flows, and contain soft bedrock that is weak and exposed at many locations. Soft bedrock erosion, therefore, is an important river process to consider for river projects. In this study, the bedrock erosion modeling is reviewed and a specific model is proposed by combining two existing models. The proposed bedrock erosion model is then incorporated into a two-dimensional mobile-bed model, SRH-2D. The model is used to simulate the bedrock erosion downstream of the Chi-Chi Weir on the Choshui River. A calibration study is carried out first to determine the appropriate values of the model parameters over a two and a half year period. The calibrated model is then used to predict bedrock erosion of the same reach for the next two years. Comparisons of both the calibration and verification model results with measured data lead to an assessment of the model performance. The study reports the current progress of bedrock erosion modeling; it also points to limitations and potential future research needs.
Yong G. Lai; Blair P. Greimann; Kuowei Wu. Soft Bedrock Erosion Modeling with a Two-Dimensional Model. World Environmental and Water Resources Congress 2010 2010, 1421 -1432.
AMA StyleYong G. Lai, Blair P. Greimann, Kuowei Wu. Soft Bedrock Erosion Modeling with a Two-Dimensional Model. World Environmental and Water Resources Congress 2010. 2010; ():1421-1432.
Chicago/Turabian StyleYong G. Lai; Blair P. Greimann; Kuowei Wu. 2010. "Soft Bedrock Erosion Modeling with a Two-Dimensional Model." World Environmental and Water Resources Congress 2010 , no. : 1421-1432.
Taiwan rivers generally have steep slopes, are subject to high flows, have frequent earthquake activity, and have relatively weak bedrock. Bedrock is often exposed and rock scour is an important river process. For example, the river channel downstream of the Shih-Gang on the Tachia River experienced severe rock scour since the Chi-Chi earthquake of 1999 uplifted a portion of the river approximately 10 m. The occurrence of deep rock scour has been a major threat to river infrastructure at many other locations in Taiwan. In this study, a rock scour model is implemented into a one-dimensional (1D) hydraulic and sediment transport model. The rock scour model has components to predict the potential scour due to direct flow hydraulic forces and scour due to sediment abrasion. The resultant 1D model is capable of simulating the combined effects of rock erosion and alluvial river erosion and deposition. The new model is applied to the Tachia River in the reach affected by the Chi-Chi earthquake in 1999. Findings related to the applicability and limitations of the current rock scour models are reported.
Blair P. Greimann; Yong G. Lai; Kuowei Wu. Predicting Rock Scour in an Alluvial River with a One-Dimensional Model. World Environmental and Water Resources Congress 2009 2009, 1 -9.
AMA StyleBlair P. Greimann, Yong G. Lai, Kuowei Wu. Predicting Rock Scour in an Alluvial River with a One-Dimensional Model. World Environmental and Water Resources Congress 2009. 2009; ():1-9.
Chicago/Turabian StyleBlair P. Greimann; Yong G. Lai; Kuowei Wu. 2009. "Predicting Rock Scour in an Alluvial River with a One-Dimensional Model." World Environmental and Water Resources Congress 2009 , no. : 1-9.
Most rivers in Taiwan have a steep slope, subject to high flows, and have relatively weak bedrock. Bedrock is often exposed and rock scour is an important river process. For example, the river channel downstream of the Chi-Chi Weir on the Choshui River experienced up to 10 meters of rock scour since the construction of the weir in 2001. The occurrence of deep rock scour has been a major threat to river infrastructure at many other locations in Taiwan. In this study, rock scour models are reviewed and a specific rock scour model is proposed. Among rock scour mechanisms, those due to flow hydraulic force and sediment abrasion are considered to be important. The rock scour model is incorporated into an existing two-dimensional (2D) mobile bed model, SRH-2D version 3. The resultant 2D model is capable of simulating the combined effects of rock erosion and alluvial river erosion and deposition. The new model is applied to the river reach at the Chi-Chi Weir in an attempt to test and verify the applicability of the rock scour model. Findings related to the applicability and limitations of the current rock scour models are reported.
Yong G. Lai; Blair P. Greimann; Kuowei Wu. Predicting Rock Scour in an Alluvial River with a Two-Dimensional Model. World Environmental and Water Resources Congress 2009 2009, 1 .
AMA StyleYong G. Lai, Blair P. Greimann, Kuowei Wu. Predicting Rock Scour in an Alluvial River with a Two-Dimensional Model. World Environmental and Water Resources Congress 2009. 2009; ():1.
Chicago/Turabian StyleYong G. Lai; Blair P. Greimann; Kuowei Wu. 2009. "Predicting Rock Scour in an Alluvial River with a Two-Dimensional Model." World Environmental and Water Resources Congress 2009 , no. : 1.