Siwan Lyu

A study on the optimal sediment discharge formula for Hyeongsan river.

In order to determine the optimal sediment discharge formula for Hyeongsan river, some statistical approaches have been applied to analyze the simulated results of long-term bed change by HEC-6. The field measurements have been conducted to obtain the data for model calibration and verification such as sediment discharge, bed material, and channel geometry. Several sediment discharge formulae have been verified according to the bias, RMSE, RRMSE, discrepancy ratio, and S/N ratio of bed change along the thalweg. Comparing the formulae, Laursen formula(modified by Copeland) have shown the best performance to simulate the long-term bed change of Hyeongsan river.

A Study on Application of 2-Dimensional Flow Models to Inundation on Underground Space System

In order to increase the utilization of limited space in urban area, it can be a good solution to make use of underground space. For the last few decades, underground space systems, such as underground passages, subway stations, and underground shopping arcades, have been constructed in many cities all over the country. Despite of the advantages on the utilization of space in urban area, underground space systems have always been exposed to the risk of inundations resulted from severe rain storms. In this study, it has been examined to apply 2-D flow models (TUFLOW and FLUMEN) to establishing the preventive measures to the risk of flood. For the part with relatively complex configuration, such as a corridor junction, 2-D flow models present the detailed information about the effect of geometry on the inundation events and the temporal and spatial distribution of inundation over the space. From the result, it can be concluded that the 2-D flow model can be the effective implement for establishing the proper measure to the inundation on underground

Analysis of the Effect of Dredging and Weirs on Bed Change in the Nakdong River and its Tributary using HEC-6

It is necessary to evaluate the effect of dredging and weir operation on the flow and long-term bed change for river management. Especially, large scale river treatment project, with dredging or weir installation and operation, can increase the instability of riverbed in tributaries as well as mainstream. This study focuses on the effect of weir installation and dredging on the long-term bed change in Nakdong river (Gangjeong- Goryeong Weir~Dalseong Weir) and its tributary (Geumho river). HEC-6 model has been used to analyze the amount of long-term bed change and sediment transport resulted from the river treatment including dredging or weir installation. From the result, it was concluded that a large scale river treatment can accelerate and increase the long-term bed change both in mainstream and tributary.

Numerical Modeling of Two-Dimensional Pollutnant Transport in Nakdong River

The transport and dispersion of pollutants in natural rivers is a principal issue in river management. To study the pollutant transport in natural rivers, the effects of meandering and confluence of tributary on mixing processes have to be analyzed. Two-dimensional depth-averaged schemes are used to represent variations in the velocity distribution and water quality in a channel. The objective of this study is to evaluate the impacts of operating water gate of Nakdong Estuary Barrage on the river environment. The Nakdong River being used as drinking water sources for Busan and Gyeongnam province has been contaminated due to inflow of inadequately treated wastewater from the tributaries into the river. The computational domain includes the cross sections from the Miryang river junction to the downstream barrage end of the Nakdong River. The length of the reach is 45 km. Mulgeum intake station is located west side of applied domain. During the operating of the water gate, the velocity magnitude and concentration are analyzed around intake. The effect of the pollutant flow from the Daepo stream, tributary of the Nakdong river, which is located opposite intake, is also analyzed.

Flowrate and Velocity Measurement in Nakdong River Using ADCP

ADCP is the equipment for flowrate measurement using the Doppler Effect that transmits supersonic waves in the fixed frequency into the water and gathers reverberations which are diffused by particles suspended without interrupting a lowing stream. The flowrate measurement using ADCP is now widely used for the measurement of surveying the flowrate by crossing the river for a dry period. This method can cut the manpower and the time down compared to velocity-area method. Consequently, many kinds of ADCPs that are suitable for various scales of the rivers have been developed. There have been many-sided analyses and studies on the consequences of measuring the velocity and flowrate by using these methods. In this study, the RIO Grande ADCP of RDI Co. is applied for measuring the flowrate in Seonakdong River. The characteristics of velocity and flowrate data using ADCP, which is measured by employing a wireless controlled small boat equipped with ADCP, are compared with the result of the velocity-area method on the Seonakdong River. Seonakdong River is reservoir like river which blocked with upstream Daejeo water-gate and downstream Noksan water-gate. It has little flowrate in ordinary times, however, it has the maximum 250 CMS record of the flowrate during the water gate opening.