• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1B
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• pp.27-38
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• 2006

The storage function model (SFM) has been used for the flood forecasting in Korea. The SFM has a simple calculation process and it is known that the model is more reasonable than linear model because it considers non-linearity of flood runoff. However, the determination of parameters is very difficult. In general, the trial and error method which is an manual calibration by the decision of a model manager. This study calibrated the parameters by the trial and error method and optimization technique. The calibrated parameters were compared with the representative parameters which are used in the Flood Control Centers in Korea. Also, the evaluation indexes on objective functions and calibration methods for the comparative analysis of simulation efficiency. As a result, the Genetic Algorithm showed the smallest variation in objective functions and, in this study, it is known that the objective function of SSR (Sum of Squared of Residual) is the best one for the flood forecasting.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.188-191
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• 2008

The Tonle Sap, Cambodia, is a huge lake and periodically flooded due to monsoon climate. The incoming water causes intensive flooding that expands the lake over vast floodplain and wetland consisting mainly of forests and shrubs. Monitoring the water-level change over the floodplain is essential for flood prediction and water resource management. A main objective of this study is flood monitoring over Tonle Sap area using ALOS PALSAR. To study double-bounce effects in the lake, backscattering effect using ALOS PALSAR dual-polarization (HH, HV) data was examined. InSAR technique was applied for detection of water-level change. HH-polarization interferometric pairs between wet and dry seasons were best to measure water level change around northwestern parts of Tonle Sap. The seasonal pattern of water-level variations in Tonle Sap studied by InSAR method is similar to the past and altimeter data. However, water level variation measured by SAR was much smaller than that by altimeter because the DInSAR measurement only represents water level change at a given region of floodplain while altimeter provides water level variation at the central parts of the lake.

• The Journal of the Korea Contents Association
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• v.13 no.2
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• pp.498-504
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• 2013

Recently, the frequency of typhoons have increased due to the effects of climate change. As a result, in mountain streams, it has caused streamflow increase upstream and frequent water surface elevation downstream. This study analyzed the effects of the heavy rainfalls caused by Typhoon Sanba, which had a direct impact on Korea between September 17 and 18, on the water level variations downstream in mountainous streams. In addition, the drainage basin of Samcheok Oship stream was chosen as the object of this study. This study analyzed the flood level by applying HEC-RAS model. The observed water level measured in 2012 and the water level simulated by HEC-RAS model showed similar results. In addition, the simulation results showed the maximum flood level was 5.32m the mean flow velocity was 2.33m/sec and the maximum channel water depth was 7.51m. The analysis showed that the heavy rainfalls caused by Typhoon Sanba had an impact on the water surface elevation in Oship stream. The final results from this study will give a reasonable and important data to perform the Design of Hydraulic Structure.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.99-104
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• 2003

This study investigated the yearly variation of pollutant loads outflowing from six watershed of Yeong-il Bay and compared the relationship of pollutant load and water quality, and estimated the Inner productivity of Yeong-Il Bay by using ${\Delta}COD$ method which analysis nonlinear process of water quality. As the estimated results for the pollutant loads of Yeong-Il Bay, total COD load outflowing from Hyeong-san river in flood season(summer) of 2001 year was 2275.0 kg/hr and in dry(low water) season(winter) 852.8 kg/hr, respectively. Load quantity in flood season was about 2.67 times than that in dry season. And as the calculated results of the net-flux of water for seven divisions, it showed that the net-flux of water increased for the divisions of the north coast and inner sea of Yeong-Il Bay but decreased for the south coast. On the contrary, for the cases which water quantity increase from land, the net-flux of water in estuary front of Hyeong-san river decreased but outflowing quantity of that though division of the south coast of Homi-got increased. Finally, this study compared the Inner productions for flood and dry season of Yeong-il Bay by using ${\Delta}COD$ method.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.157-157
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• 2019

This study derived the Flood-Inducing-Rainfall (FIR) and the Flood-Inducing-Runoff (FIRO) from the radar-gage composite data to be used as the basis of the flood warning initiation for the urban area of Seoul. For this, we derived the rainfall depth-duration relationship for the 261 flood events at 239 watersheds during the years 2010 and 2011 based on the 10-minute 1km-1km radar-gauge composite rainfall field. The relationship was further refined by the discrete ranges of the proportion of the flooded area in the watershed (FP) and the coefficient variation of the rainfall time series (CV). Then, the slope of the straight line that contains all data points in the depth-duration relationship plot was determined as the FIR for the specified range of the FP and the CV. Similar methodology was applied to derive the FIRO, which used the runoff depths that were estimated using the NRCS Curve Number method. We found that FIR and FIRO vary at the range of 37mm/hr-63mm/hr and the range of 10mm/hr-42mm/hr, respectively. The large variability was well explained by the FP and the CV: As the FP increases, FIR and FIRO increased too, suggesting that the greater rainfall causes larger flooded area; as the rainfall CV increases, FIR and FIRO decreased, which suggests that the temporally concentrated rainfall requires less total of rainfall to cause the flood in the area. We verified our result against the 21 flood events that occurred for the period of 2012 through 2015 for the same study area. When the 5 percent of the flooded area was tolerated, the ratio of hit-and-miss of the warning system based on the rainfall was 44.2 percent and 9.5 percent, respectively. The ratio of hit-and-miss of the warning system based on the runoff was 67 percent and 4.7 percent, respectively. Lastly, we showed the importance of considering the radar-gauge composite rainfall data as well as rainfall and runoff temporal variability in flood warning system by comparing our results to the ones based on the gauge-only or radar-only rainfall data and to the one that does not account for the temporal variability.

• Journal of Korea Water Resources Association
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• v.49 no.8
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• pp.673-683
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• 2016

An Idea to estimate flexible criteria for river water use permits was proposed that takes the spatio-temporal flow variation along the river into account, which was applied to the Keumho River, one of the tributary of the Nakdong River in Korea. This idea implies the temporal division of four periods with different criteria, combining flood/non-flood seasons and irrigation/non-irrigation periods, while a single one has been applied throughout the year in the current practice. Through flow regime analysis of daily natural flow simulations at Dongchon and Seongseo, the control points of the study area, Q355 and 1Q10 for non-flood and non-irrigation period, Q275 for non-flood and irrigation period, Q185 for flood and irrigation period were suggested respectively. So, those values that subtract instream flow were determined as the flexible criteria in each season. From the comparison of current practice and the proposed method, it was estimated that $10.6\;million\;m^3/year$ is available for more water use permits without additional development of water storage. Therefore, it is conceived that flexible criteria for river water use permission suggested in this study can contribute to improve the national policies for more efficient water resources management in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.133-139
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• 1987

Three disastrous floods experienced over the tidal reaches of the Han River are investigated numerically with the use of one-dimensional finite-difference tidal flow model. The hindcast scheme involves processing flood hydrograph at Indogyo to provide the necessary discharge variation at upstream boundary and predicting tidal elevations at downstream boundary that computes the response in terms of flood levels and discharges within the tidal reaches. Computed results of 1925, 1972 and 1984 floods are presented and discussed.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.325-343
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• 2003

In this study, several types of rainfall time distribution of the probabilistic rainfall amount have been applied to the Sihwa Lake, located in Gyounggi Province, Korea and their runoff characteristics, obtained by the Hec-Hms program, according to the rainfall distribution types, were compared and analysed. And then, the influences of the above rainfall distribution types of the highest water level of the reservoir, computed through the reservoir flood routing, were analysed. The tidal variation was considered, performing the flood routing and, in addition, the new program, called “IWSEA”, which can compute the reservoir water level, was developed. To conclude, when the Mononobe type of the rainfall distribution was used, the largest inflow flood discharge into the reservoir was performed and the highest reservoir water level was obtained when the Pilgrim-Cordery type of the rainfall distribution was applied.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.164-164
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• 2016

Radar rainfall estimates have been widely used in calculating rainfall amount approximately and predicting flood risks. The radar rainfall estimates have a number of error sources such as beam blockage and ground clutter hinder their applications to hydrological flood forecasting. Moreover, it has been reported in paper that those errors are inter-correlated spatially and temporally. Therefore, in the current study, we tested influence about spatio-temporal errors in radar rainfall estimates. Spatio-temporal errors were simulated through a stochastic simulation model, called Multivariate Autoregressive (MAR). For runoff simulation, the Nam River basin in South Korea was used with the distributed rainfall-runoff model, Vflo. The results indicated that spatio-temporal dependent errors caused much higher variations in peak discharge than spatial dependent errors. To further investigate the effect of the magnitude of time correlation among radar errors, different magnitudes of temporal correlations were employed during the rainfall-runoff simulation. The results indicated that strong correlation caused a higher variation in peak discharge. This concluded that the effects on reducing temporal and spatial correlation must be taken in addition to correcting the biases in radar rainfall estimates. Acknowledgements This research was supported by a grant from a Strategic Research Project (Development of Flood Warning and Snowfall Estimation Platform Using Hydrological Radars), which was funded by the Korea Institute of Construction Technology.

• Journal of Korea Water Resources Association
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• v.48 no.8
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• pp.673-683
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• 2015

The existing flood protection in rivers has shown the limitation due to the urbanization around rivers and the abnormal climate. Thus, the demand for the constructions of side-weir detention basin are being increased as a part of integrated watershed flood protection plan. It is necessary to estimate the quantitative flood-control effect for including the side-weir detention basin in flood-control measures. For the determination, it is required to reduce the uncertainty of the design factors which can affect the flood-control effect of side-weir detention basin. Among the factors, however, the water level in river always contains uncertainty. Therefore, the design method considering the uncertainty is required. For the reasons, the design method considering uncertainty of the water level in river is suggested in this study with using the length of side-weir which is relatively easy-determinable by designers. Therefore, it is examined how the variation of the length of side-weir can affect the flood-control effect, using HEC-RAS, and then the method to determine the side-weir length considering the uncertainty of the water level in river through results from analyses. Since the uncertainty of the water level in river can be taken into account in the suggested design method, it is evaluated that the design method is more effective to suggest the flood-control effect of the side-weir type detention basin with higher safety side.