• Proceedings of the Korea Water Resources Association Conference
• /
• 2015.05a
• /
• pp.173-173
• /
• 2015

The flood water level in tidal river is determined by the joint effects of flood discharge and tidal water levels at downstream boundary. Due to the variable tidal boundary conditions, the evaluated design water levels associated with a certain flood event can be significantly different. To avoid determining of design water levels just by a certain tidal boundary condition and remove the influence of variability in boundary condition from the evaluation of design water levels, a probabilistic approach is considered in this study. This study focuses on the development of a method to evaluate the realistic design water levels in tidal river with taking into account the combined effects of river discharge and tidal level. The flood water levels are described by the joint probability of two driving forces, river discharge and tidal water levels. The developed method is applied to determine design water levels for the tidal reach of the Han River. An unsteady flow model is used to simulate the flow in the reach. To determine design water levels associated with a certain flood event, first, possible boundary conditions are obtained by sampling starting times of tidal level time series; then for each tidal boundary condition, corresponding peak water levels along the channel are computed; and finally, design water levels are determined by computing the expectations of the peak water levels. Two types of tides which are composed by different constituents are assumed (one is composed by $M_2$, and the other one is composed by $M_2$ and $M_2$) at downstream boundary, and two flood events with different maximum flood discharges are considered in this study. It is found that (a) the computed design water levels with two assumed tides have no significant difference for a certain flood event, though variability of peak water levels due to the tidal effect is considerably different; (b) tidal effect can reach to the Jamsil submerged weir and the effect is obvious in the downstream reach of the Singok submerged weir; (c) in the tidally affected reach, the variability of peak water levels due to the tidal effect is greater if the maximum flood discharge is smaller.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.199-202
• /
• 2008

It is well-known fact that tidal difference between the ebb and flow in Yellow Sea is about 9 m so that it has largest value in the world. This wide range of tide level enables Yellow Sea water to intrude into main stream of Han River. However, the study of the tidal reach of Han River has not been carried out thoroughly since North and South Koreas share this region so that topography data and physical measurement are lacking. In this study, to examine the reverse flow and dispersion behavior by tidal effect at the tidal reach of Han River, 2-D river analysis models were applied. RMA-2 was applied to calculate the horizontal velocities and water surface elevation. With the results of velocities and water depth, RAM4, which is 2-D advection-dispersion model based on FEM was simulated to analyze the horizontal transport behavior of BOD.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.32 no.4
• /
• pp.81-88
• /
• 1990

The flow in a river reach where is influenced by tidal motion is characterized by unsteady flow. The flood analysis in the river reach needs depending upon the theory based on the complete unsteady flow equations. In this study the unsteady flow model which is called CRIUM (Channel Routing by Implicit Unsteady Flow Model) was developed and was applied to the Mankyong and Dongjin river in order to analyze the flood characteristics. The results, which were calibrated and verified by the flood records to be measured in the two rivers, show that unsteady flow mode] can be used for the derivation of the flood hydrograph. The peak flood discharges were estimated as 4,960 and $2,870m^3$/sec in 100 year frequency at the estuary of the Mankyong and Dongjin river, respectively. In addition, it was analyzed that the river reaches were not influenced by tidal motion when the discharge magnitude was larger than approximately $3,000m^3$/sec.

• Journal of the Korean Society of Safety
• /
• v.29 no.6
• /
• pp.104-110
• /
• 2014

The Han River is the only waterway in Korea where estuary is not blocked by dykes so that tidal water is flowing in and out through the tidal reach. The extreme tidal range in the Yellow Sea causes an intense flood current, stretching over horizontal extents of tens of kilometers into the rivers. To elucidate the flow reversal by discharge conditions and transient tidal level in the Han river, numerical simulations were conducted under 7 boundary conditions for two days with 10 minute time step. As the flow conditions changed from low discharge and high tidal difference to high discharge and low tidal difference, the flow reversals became weaker and the velocity of forward flow direction became higher due to the increased flow momentums and decreased tidal differences. In the case of normal flow, the maximum reverse velocity was 0.4 m/s, which was equivalent to the maximum forward velocity. In addition, the pattern of the development and decay of forward and reverse flow was presented.

• Water for future
• /
• v.21 no.1
• /
• pp.87-94
• /
• 1988

Tidal asymmetry in the Keum River Estuary has been investigated from the observed tides. Despite strong frictional attenuation within the estuary, the $M_4$ tides reach significant amplitude, resulting in strong tidal distortion. The observed asymmetry over the area shows that generally more intense flood flows transport more sediment that do less intense ebb flows of longer duration. This causes filling of the estaury as evidenced by sand flats spreaded over the inner area. The spatial distribution of peak bottom stress associated with the dominant $M_2$ and $M_4$ tides calculated via two-dimensional numerical tidal model suggest that present tidal sedimentation regimemay be altered, sepecially in the approach channel to outer Kunsan Port and downstream part of the dike, due to the construction of barrier.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.1 no.1
• /
• pp.31-43
• /
• 1989

Tidal asymmetry and the associated sediment dynamics in the Keum River Estuary has been investigated from a numerical tidal model. Modeling efforts were focussed on the simulation of large drying sandflat exposed at the mouth of the Estuary and dynamic combination of two-dimensional estuary model and one-dimensional river model. Despite strong frictional attenuation within the estuary, the M4 tides reach significant amplitude, resulting in strong tidal distortion. Model results show that the asymmetry over the area exhibit more intense flood flows transport than do less intense ebb flows of longer duration. This causes filling of the estuary as evidenced by large sandflats spread over the inner area. The spatial distribution of peak bottom stress computed from the tidal model suggest that present tidal sedimentation regime may be altered significantly, especially in the approach channel to outer Kunsan port and downstream part of the dike, due to the construction of cross-channel barrier.

• The KSFM Journal of Fluid Machinery
• /
• v.18 no.1
• /
• pp.51-58
• /
• 2015

This paper presents a study on Vane Tidal Turbine (VTT) focusing on analysis of two types of blade arrangement originated from the previous studies where the original design was examined and performance-tested for different numbers of blades (six, eight and twelve). Compared to conventional tidal turbines, VTT has several special features and potential advantages which have been being thoroughly developed. The purpose of this study is to analyze VTT's capability of extracting and converting the hydrokinetic energy of tidal currents into electricity at given arrangement of blades (single and double rows, six and twelve blades) using CFD. From the calculation results, the six-blade single row turbine shows the best performance, in which the highest power and torque coefficients reach up to about 34 % and 36 %, respectively, at TSR=0.94. However, despite of lower power coefficient, by adding more blades, the torque's extraction of twelve-blade turbine, especially the double row type, is less fluctuate than that of the six-blade setups.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.4
• /
• pp.207-218
• /
• 2013

This study is based on a series of numerical modeling experiments to understand the circulation and its change in the Chunsu Bay (CSB), Yellow Sea of Korea. A skill analysis was performed for the tidal height and tidal current of the observation data using the amplitude and phase of the 4 major tidal constituents respectively for verification of modeling experimental results. As a result, most of the skill score was seen to be over 90%, so numerical model experiment results can be said to be in good agreement with the observed tidal height and tidal current. Tidal wave proceeded from the entrance of the CSB towards inside, and the tidal range gradually increased to the north. It took about 10 to 30 minutes for the tidal wave to reach to northern end. The tidal wave showed a characteristic to rotate counter-clockwise in the southern part. The tidal current flowed to the north-south direction along the bottom topography; the angle of the major axis appeared alongside the isobath. It showed the characteristics of reversing tidal current with the minor axis less than 10% of the major axis. The strength of the tidal residual current that is influenced by geographical factors including bathymetry and coastline showed the range of 1~30 cm/sec, greater in the south channel and smaller in northern Bay. Two pairs of cyclonic/anti-cyclonic eddies around Jukdo and 3~4 pairs of strong eddies at the southern part of CSB in hundreds of m to a few km size by relative vorticity derived from the tidal residual current.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6B
• /
• pp.523-529
• /
• 2011

A tidal river is a river affected by tides causing the water level to rise and fall. In the river, the velocity induced by tides at a dry season can be a more dominant factor than that at a flood season in designing hydraulic structures. In this study, flow velocities and water levels were observed in the downstream of Han River at the dry season, and they are used for verification of numerically predicted results. The behaviors of flow were also analyzed by using UNET, a commercial model managing unsteady flows. To estimate the roughness coefficients of the tidal river reach near the Shingok submerged weir, a statistical method is employed. In the method, the discrepancy ratio between the measured and calculated water levels was implemented.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6B
• /
• pp.731-741
• /
• 2008

Previous studies on the numerical simulation at the tidal reach of Han River tend to restrict downstream boundary as Jeon-ryu station due to difficulties in gaining cross section data and tidal elevation values at Yu-do. But, in this study, geometries beyond the confluence of Gok-reung stream and Im-jin River are constructed based on the numerical sea map; tidal elevation at the downstream boundary, Yu-do is estimated by harmonic analysis of In-cheon tide gage station so that hydrodynamic and diffusion behavior have been analyzed. The domain ranging from Shin-gok submerged weir to Yu-do is selected (which is 36.8 km in length). RMA-2 and RAM4 developed by Il Won Seo (2008) are applied to simulate flow and diffusion behavior, respectively. Numerical results of flow characteristic are compared with the measured data at Jeon-ryu station. Simulation is carried out from June 23 to 25 in 2006 on the ground that hydrologic data is satisfactory and tidal difference is huge during that period. The result shows that reverse flow occurs 5 times according to the tidal elevation at Yu-do and the maximum reverse flow is observed up to Jang-hang IC, which is 32.9 km in length. Also analysis is focused on the process of generation and disappearance of reverse flow, the distribution of water surface elevation and velocity along the maximum velocity line, and the transport of nonconservative pollutant. Pollutant injected from Gul-po stream spreads widely across the river; however, the size of BOD cloud entering from Gok-reung stream is relatively small because water depth at the mid and left side becomes deeper and maximum velocity occurs along the right bank so that transverse mixing is completed quickly. Finally, mixing characteristic of horizontal salinity distribution is obtained by estimating the salinity input with analytical solution of 1D advection-dispersion equation.