# River Hydraulic Computation

## Analysis of Hyper Concentrated Flow

### Analyze the properties of hyper concentrated flow such as the stagnation and bed evolution by the conjunction of numerical simulation and experiment.

Hyper concentrated flow refers the sediment concentration above 63,250 ppm. Due to the decrease of falling velocity and friction, the particle behaviors in hyper concentrated flow can not be analyzed through the conventional sediment transport theory. The hyper concentrated flow simulation model is developed based on the suitable theory as well as the experimental studies which enables the determination of bed evolution for rivers with hyper concentrated flow.

### Immersed Boundary Method

Incorporate the immersed boundary method into river hydraulic computation which simplifies the simulation of flow field around the in-stream structure.

The saw-toothed grids can not be avoided for traditional structured grid.

The immersed boundary method simplifies the processes of grid generation through an additional, independent coordinate system. The independent coordinate system calculates thefeed-back force around the boundaries of structures, then the force is incorporated into the momentum equation which enforces the water changing its direction around the structures.

### Soft Bedrock Incision Computation

The mechanism of soft bedrock incision is significantly different from alluvial sedimentation. The DPWE analyzes behaviors of soft bedrock incision at different channels in Taiwan based on the in-situ monitoring along with developed horizontal 2-D numerical model.

### Channel Migration Model Development

Based on the mechanism of lateral sedimentation, groundwater flow, and Mohr-Coulomb theorem, the horizontal 2D channel migration model is developed which can simulate the bank erosion and sliding simultaneously.

### Layered Semi-3D Hydraulic Model

With the assumption that the velocity and shear stress satisfy the quadratic polynomial function in the vertical direction, the unstructured layered semi-3D hydraulic and sediment model is developed. Owning to the superior computation efficiency, this model is especially suitable for density current and salt concentration simulations in reservoir, estuary, etc.

## Hydraulic Experiment

### Vegetated Channel Flow Field Analysis

The non-intrusive color particle image velocimety (CPIV) method is developed to measure the vertical 2-D flow field in the vegetated channel. Furthermore, the measured data are adopted to analyze the relationship between the resistance and density of planting and channel roughness.

### Collapse Behavior of Cavitation Bubbles

After a single cavitation bubble is generated through the U-shape platform device, the pressure wave during bubble collapse is monitored to analyze the flow field characteristics and the structure of counter jet near the solid boundary.

## Slope Stability Simulation

### River Bank Failure Analysis

With the developed numerical model, the behavior and potential for river bank failure are analyzed under different conditions, such as soil properties, planting, toe erosion, river stage, groundwater table, and rainfall pattern, etc.

### Rainfall Triggered Shallow Landslide

Rainfall triggered shallow landslide is one of the most seriously disaster in Taiwan. Based on the mechanisms of rainfall-runoff, infiltration, and Mohr-Coulomb theorem, the 1-D, 2-D, and 3-D shallow landslide model are developed which could offer an efficient assistance in disaster prevention and mitigation.

## Hydrological Data Analysis

### Rainfall Estimation by Meteorological Satellite

DPWE presents the rainfall estimation method with high accuracy and spatial resolution by meteorological satellite which incorporates the microwave and infrared rays.

### River Stage-Discharge Rating

Based on the hydraulic performance graph (HPG) along with hydraulic computation, the analytical method for deriving river stage-discharge rating curve is established, which could improve the accuracy during extremely high flow.