• Water for future
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• v.26 no.2
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• pp.59-65
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• 1993

In the present study the methods proposed by Fuller and Sangal were evaluated to estimate the peak flood discharge based on the mean daily discharges during a flood period. The total of 198 flood events observed at seven stage gauging stations in the Han River basin were analyzed. The result showed that the peak flood discharges estimated based on the mean daily flows have a relatively high correlation with the observed peak floods. Hence, a regionalized relation and method is proposed for a possible application to estimate the peak flood discharges at the stage gauging stations with no hourly flood stage data, but with the mean daily stages.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.417-426
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• 2016

SWAT model usually underestimates daily peak discharges. To resolve this problem, in this study, the algorithm related with the surface flow simulation was modified by partitioning excessive infiltration based on the relative length between overland flow time of concentration and percolation travel time in soil water zone and by computing time of concentration varying with the amount of surface flow. The modified SWAT was applied to the Chungju dam watershed to assess the increasing effects of daily peak discharges. The daily peaks simulated by the modified SWAT were on average 10% higher than those by original SWAT for the peaks above $5,000m^3/s$. The modified SWAT was found to be able to more accurately reproduce daily peaks, particularly showing increase rates of 9.9%, 18.6% and 12.6%, respectively, for top three peaks that occurred in the years of 1990, 2002, and 2006.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.5
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• pp.81-89
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• 1995

One of the most difficult problem to estimate the flood inflow is how to understand the effective rainfall. The effective rainfall is absolutely influenced by the condition of soil moisture in the watershed just before the storm event. DAWAST model developed to simulate the daily streamflow considering the meteologic and geographic characteristics in the Korean watersheds was applied to understand the soil moisture and estimate the effective rainfall rather accurately through the daily water balance in the watershed. From this soil moisture and effective rainfall, concentration time, dimensionless hydrograph, and addition of baseflow, the rainfall-runoff model for flood flow was developed by converting the concept of long-term runoff into short-term runoff. And, real-time flood forecasting model was also developed to forecast the flood-inflow hydrograph to the river and reservoir, and called RETFLO model. According to the model verification, RETFLO model can be practically applied to the medium and small river and reservoir to forecast the flood hydrograph with peak discharge, peak time, and volume. Consequently, flood forecasting and warning system in the river and the reservoir can be greatly improved by using personal computer.

• Journal of Environmental Impact Assessment
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• v.10 no.4
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• pp.297-304
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• 2001

Recently the road traffic noise has appeared as a significant environmental issue because of dramatic increase of vehicles and expansion of newly constructed road. Therefore, this study proposes the method that improves prediction factors and models through analysis of the existing road traffic noise prediction model. Prediction factors can be improved by establishing guideline for diffraction attenuation and applying daily traffic discharge, peak traffic discharge, and average traveling speed through an analysis of level service. Prediction must be made by periods of one or five years during 20 years. Prediction models also can be improved to include better prediction model through setting the database, establishing functional relation between physical properties and noise levels by acoustic analysis, and developing models for road traffic noise prediction in residential areas.

• Magazine of the Korean Society of Agricultural Engineers
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• v.8 no.1
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• pp.1011-1034
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• 1966

This thesis is the final report which has long been studied by the author to obtain the design basis for various hydrological constructions with the specific system suitable to the natural environmental conditions in Korea. This report is divided into two parts: one is to estimate runoff volume from watersheds and the other to estimate the peak discharge for a single storm. According to the result of observed runoff record from watersheds, it is known that Kajiyama formula is useful instrument in estimating runoff volume from watersheds in this country. But it has been found that this formula shows us 20-30% less than the actual flow. Therefore, when wihed to bring a better result, the watershed characteristics coefficient in this formula, that is, f-value, should be corrected to 0.5-0.8. As for the method to estimate peak discharge from drainage basin, the author proposes to classify it in two ways; one is small size watershed and the other large size watershed. The maximum -flood discharge rate $Q_p$ and time to peak Pt obtained from the observed record on the small size watershed are compared by various methods and formulas which are based upon the modern hydrological knowledge. But it was fou.d that it. was not a satisfied result. Therefore, the author proposes. tocomputate $Q_p$, to present 4.0-5.0% for the total runoff volume ${\Sigma}Q$.${\Sigma}Q$ is computed under the assumption of 30mm 103s in watershed per day and to change the theoritical total flow volume to one hour dura tion total flow rate when design daily storm is given. Time to peak Pt is derived from three parameters which are u,w,k. These are computed by relationship between total runoff volume (ha-m unit)and $Q_p$. (C.M.S. unit). Finally, the author checked out these results obtained from 51 hydrographs and got a satisfied result. Therefore the author suggested the model of design dimensionless unit-hydrograph. And the author believes that this model will be much available at none runoff record river site. In the large size watersheds in Korea when the maximum discharge occurs, the effective rainfall is two consequtive stormy days. So the loss in watershed was assutned as 6Omm/2days,and the author proposed 3-hour-daration hydrograph flow distribution percentage. This distribution percentage will be sure to form the hydrograph coordinate.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.2
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• pp.81-91
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• 1998

Water level of irrigation reservoir during the flood season could be kept to a certain level, so called, flood control level by releasing the flood inflow in advance in order to reduce the peak discharge of next coming flood and the damage of inundation. Concept of restriction intensity of water supply was introduced to evaluate the influence of flood control volume on the irrigation water supply. Restriction intensity can be calculated by multiplying the ratio of restriction to the days of restriction which are obtained from the operation rule curve and daily water level of irrigation reservoir and it has the dimension of % day. The method of restriction intensity was applied to the Yedang irrigation reservoir with the observed data of 30 years to review whether the present flood control volume is reasonable or not, and suggest the optimal flood control volume, if possible.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.223-237
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• 2011

The intermittent freshwater discharge has an critical influence upon the biophysical environments and the ecosystems of the Yeongsan Estuary where the estuary dam altered the continuous mixing of saltwater and freshwater. Though freshwater discharge is controlled by human, the extreme events are mainly driven by the heavy rainfall in the river basin, and provide various impacts, depending on its magnitude and frequency. This research aims to evaluate the magnitude and frequency of extreme freshwater discharges, and to establish the magnitude-frequency relationships between basin-wide rainfall and freshwater inflow. Daily discharge and daily basin-averaged rainfall from Jan 1, 1997 to Aug 31, 2010 were used to determine the relations between discharge and rainfall. Consecutive daily discharges were grouped into independent events using well-defined event-separation algorithm. Partial duration series were extracted to obtain the proper probability distribution function for extreme discharges and corresponding rainfall events. Extreme discharge events over the threshold 133,656,000 $m^3$ count up to 46 for 13.7y years, following the Weibull distribution with k=1.4. The 3-day accumulated rain-falls which occurred one day before peak discharges (1day-before-3day -sum rainfall), are determined as a control variable for discharge, because their magnitude is best correlated with that of the extreme discharge events. The minimum value of the corresponding 1day-before-3day-sum rainfall, 50.98mm is initially set to a threshold for the selection of discharge-inducing rainfall cases. The number of 1day-before-3day-sum rainfall groups after selection, however, exceeds that of the extreme discharge events. The canonical discriminant analysis indicates that water level over target level (-1.35 m EL.) can be useful to divide the 1day-before-3day-sum rainfall groups into discharge-induced and non-discharge ones. It also shows that the newly-set threshold, 104mm, can just separate these two cases without errors. The magnitude-frequency relationships between rainfall and discharge are established with the newly-selected lday-before-3day-sum rainfalls: $D=1.111{\times}10^8+1.677{\times}10^6{\overline{r_{3day}}$, (${\overline{r_{3day}}{\geqq}104$, $R^2=0.459$), $T_d=1.326T^{0.683}_{r3}$, $T_d=0.117{\exp}[0.0155{\overline{r_{3day}}]$, where D is the quantity of discharge, ${\overline{r_{3day}}$ the 1day-before-3day-sum rainfall, $T_{r3}$ and $T_d$, are respectively return periods of 1day-before-3day-sum rainfall and freshwater discharge. These relations provide the framework to evaluate the effect of freshwater discharge on estuarine flow structure, water quality, responses of ecosystems from the perspective of magnitude and frequency.

• Journal of the Korean Association of Geographic Information Studies
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• v.20 no.3
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• pp.141-152
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• 2017

This paper presents a technical method for flood estimation based on satellite rainfall and satellite rainfall correction method for watersheds lacking measurement data. The study area was the Sebou Watershed, Morocco. The Integrated Flood Analysis System(IFAS) and Grid-based Rainfall-Runoff Model(GRM) were applied to estimate watershed runoff. Daily rainfall from ground gauges and satellite-derived hourly data were used. In the runoff simulation using satellite rainfall data, the composites of the daily gauge rainfall and the hourly satellite data were applied. The Shuttle Radar Topographic Mission Digital Elevation Model(SRTM DEM) with a 90m spatial resolution and 1km resolution data from Global map land cover and United States Food and Agriculture Organization(US FAO) Harmonized World Soil Database(HWSD) were used. Underestimated satellite rainfall data were calibrated using ground gauge data. The simulation results using the revised satellite rainfall data were $5,878{\sim}7,434m^3/s$ and $6,140{\sim}7,437m^3/s$ based on the IFAS and GRM, respectively. The peak discharge during flooding of Sebou River Watershed in 2009~2010 was estimated to range from $5,800m^3/s$ to $7,500m^3/s$. The flood estimations from the two hydrologic models using satellite-derived rainfall data were similar. Therefore, the calibration method using satellite rainfall suggested in this study can be applied to estimate the flood discharge of watersheds lacking observational data.

• Journal of Korea Water Resources Association
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• v.38 no.9 s.158
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• pp.791-800
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• 2005

An ILLUDAS-NPS model was developed which is able to compute pollutant loadings and the concentrations of water quality constituents. This model is based on the existing ILLUDAS model, and added for use in the water quality analysis process during dry and rainy periods. For dry period, the specifications of coefficients for discharge and water quality were used. During rainfall, we used the daily pollutant accumulation method and the washoff equation for computing water quality each time. According to the results of verification, the ILLUDAS-NPS model provides generally similar outputs with the measured data on total loadings, peak concentration and time of peak concentration for three rainfall events in the Hong-je Basin. In comparison with the SWMM and STORM models, it was shown that there is little difference between ILLUDAS-NPS and SWMM.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.1
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• pp.53-62
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• 1982

An effort of preliminary type has been made to develope a practical method for the waterway area determination of a drainage outlet in rural or agricultural areas. The Seoul meteorological station was selected as tile index station, and the maximum rainfalls-duration-frequency (R-D-F) relation of short-time intense rainfalls was first established. A frequency analysis of the daily rainfalls for the 75 stations selected throughout the country resulted the 50-year daily rainfall for each station. The rainfall factor, which is defined here as the ration of 50-year daily rainfalls of individual station and the index station, was determined for the 8 climatological regions divided in this study. Following the US SCS method the runoff number of a watershed was given based on the soil type, land-use pattern, and the surface treatment. With this runoff number and the R-D-F relationship the runoff factors for the index station were computed and hence a nomogram could be drawn which makes it possible to determine the runoff factor for a given rainfall number and a rainfall of specific duration and frequency. With this done, the potential runoff of a watershed for a given rainfall duration could be calculated, based on the unit hydrograph theory, by multiplying the rainfall factor, the runoff factor, and the drainage area of the watershed under consideration. Then, the maximum runoff potential was determined by varying the rainfall duration and finding out the duration which results the peak discharge of a gived return period.