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

• Water for future
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• v.17 no.2
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• pp.85-97
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• 1984

Measuring the river flow and water quality in the midstream of the Nakdong River, the natural purification status in examined through the analyses of the elements which affect the variation of dissolved oxygen, and DO model is evaluated to the midstream reach of the river. The major results of this study are as follows; the pruification factor of the of the river is relatively high, it is worried over eutrophication considering much production of algae, and it is evaluated that important factor affecting the DO value computed by the proposed DO model are in order of reaeration coefficient, carbonaceous BOD and deoxygenation constant.

• Journal of Korea Water Resources Association
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• v.49 no.7
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• pp.589-597
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• 2016

In this study, we investigated the use of satellite-derived flow (SDF) signals and a data-based model for the estimation of outflow for the river reach where in situ measurements are either completely unavailable or are difficult to access for hydraulic and hydrology analysis such as the upper basin of Imjin River. It has been demonstrated by many studies that the SDF signals can be used as the river width estimates and the correlation between SDF signals and river width is related to the shape of cross sections. To extract the nonlinear relationship between SDF signals and river outflow, Artificial Neural Network (ANN) model with SDF signals as its inputs were applied for the computation of flow discharge at Imjin Bridge located in Imjin River. 15 pixels were considered to extract SDF signals and Partial Mutual Information (PMI) algorithm was applied to identify the most relevant input variables among 150 candidate SDF signals (including 0~10 day lagged observations). The estimated discharges by ANN model were compared with the measured ones at Imjin Bridge gauging station and correlation coefficients of the training and validation were 0.86 and 0.72, respectively. It was found that if the 1 day previous discharge at Imjin bridge is considered as an input variable for ANN model, the correlation coefficients were improved to 0.90 and 0.83, respectively. Based on the results in this study, SDF signals along with some local measured data can play an useful role in river flow estimation and especially in flood forecasting for data-scarce regions as it can simulate the peak discharge and peak time of flood events with satisfactory accuracy.

• Journal of Industrial Technology
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• v.19
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• pp.369-377
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• 1999

The determination of the design flood based on probabilistic concepts is one of the important matters of the general field of hydrology. Until now, Most of any existing formulas to predict the flood flow were estimated by very different values with each other when we applied these formulas to the small basin, in extreme case, which were estimated over top be 400% of a difference because these have been developed by foreigners or derived from the big basin. The objective of this thesis is to examine closely the characteristics of frequency flood flow for reliable prediction of the flood flow through the probabilistic method in hydrology and to develop the ($Q_T=27.74T^{0.178}A^{0.594}$) applicable to the river of Kangwon province.

• Journal of Korean Society on Water Environment
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• v.25 no.4
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• pp.580-588
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• 2009

In this study daily flow rates and delivered pollutant loads of Nakdong river basin are simulated with modified TANK model and minimum variance unbiased estimator. Based on the simulation results, flow duration curves, load duration curves, and delivery ratio duration curves have been established. Then GIS analysis is performed to obtain several hydrological geomorphic characteristics such as watershed area, stream length, watershed slope and runoff curve number. Finally, multiple regression analysis is carried out to estimate empirical equations for pollutants delivery ratio. The results show that there is positive relation between the flow rates and delivery ratios, and the proposed empirical formulas for delivery ratio can predict well river pollutant loads.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.179-192
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• 1993

Three-dimensional cohesive sediment transport model, COSETM-3, is develpoed using a finite difference method. The model results are compared with the physical experimental results for the relative concentration with time at the mid-depth of the recirculating flume and are found to be in good agreement. This model is applied to Suyoung Bay in Pusan of Korea to verify the field applicability of the model and to investigate on the SS (suspended solids) diffusion phenomena at the bay. Behaviors of discharging SS from Suyoung River at normal river flow and flood river flow are predicted. The numerical results appear to be reasonable and qualitative agreement with field data. The influence of settling velocity on the concentration distribution of SS is also investigated. In case of not considering settling velocity, SS concentration at surface layer is higher than that at lower layer, but in case of considering settling velocity, SS concentration at lower layer is higher than that at surface layer. The fluctuation of SS concentration at surface layer is large due to the strong mixing, but the fluctuation of the concentration at lower layer is small due to the weak mixing. SS diffusion patterns at flood river flow are similar to those at normal river flow, while the concentration at that flow is so much higher than that at this flow. SS concentration increases with time until the peak discharge occurs, but the concentration decreases with time with decreasing river flow after the peak discharge.

• Journal of Korea Water Resources Association
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• v.43 no.10
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• pp.865-881
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• 2010

To evaluate influence of the future climate change on water environment, it is necessary to use a rainfall-runoff model, or a basin model allowing us to simultaneously simulate water quality factors such as sediment and nutrient material. Thus, SWAT is selected as a watershed-based model and Nakdong river basin is chosen as a target basin for this study. To apply climate change scenarios as input data to SWAT, Australian model (CSIRO: Mk3.0, CSMK) and Canadian models (CCCma: CGCM3-T47, CT47) of GCMs are used. Each GCMs which have A2, B1, and A1B scenarios effectively represent the climate characteristics of the Korean peninsula. For detecting climate change in Nakdong river basin, precipitation and temperature, increasing rate of these were analyzed in each scenarios. By simulation results, flow and increasing rate of these were analyzed at particular points which are important in the object basin. Flow and variation of flow in the scenarios for present and future climate changes were compared and analyzed by years, seasons, divided into mid terms. In most of the points temperature and flow rate are increased, because climate change is expected to have a significant effect on rising water temperature and flow rate of river and lake, further on the basis of this study result should set enhancing up water control project of hydraulic structures caused by increasing outer discharge of the Nakdong River Basin due to climate change.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.117-123
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• 2008

In this study, PHABSIM which is a sample for 1D physical habitat and River2D, which is a sample for 2D physical habitat were applied to the main streams of Han River in order to calculate an optimum flow considering the habitats of fishes in determining the instream flow. Moreover, the Weighted Usable Area (WUA) of the two samples in each growth step (adults and spawning) of the target fish type was compared and reviewed. The optimal flow value was calculated by considering the conditions for inhabiting fishes. As a result of the correlation analysis for WUA from 1D and 2D samples was 0.87 to 0.99. The optimum flow considering the conditions of inhabiting fishes showed insignificant difference of $3m^3/s\;to\;5m^3/s$ with the exception of adults in Moon-Mak and spawning in Dal-Chun.

• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.3
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• pp.21-34
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• 2009

Usually in flood flow problems, one-dimensional approach does not provide the required details of complex flow phenomena such as the flow in braided rivers and river junction. In this study, two-dimensional finite element mesh is constructed using DEM and GIS tool, and applied to RMA-2model. The purpose of this study is to investigate the applicability of the two dimensional model in natural rivers and to analyze characteristics of river flow due to the change of cross section. For model calibration, the result of unsteady flow analysis was compared with the observed data. Accordingly, the SMS model in this study prove to be very effective and reliable tool for the simulation of hydrodynamic characteristics under the various flow conditions.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.283-284
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• 2005