• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.390-396
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• 2000

The basic concept of the model is minimizing the error range between forecasted flood inflow and actual flood inflow, and accurately forecasting the flood discharge some hours in advance depending on the concentration time(Tc) and soil moisture retention storage(Sa). Simplex method that is a multi-level optimization technique was used to search for the determination of the best parameters of RETFLO (REal-Time FLOod forecasting)model. The flood forecasting model developed was applied to several strom events of Yedang reservoir during past 10 years. Model perfomance was very good with relative errors of 10% for comparison of total runoff volume and with one hour delayed peak time.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.2
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• pp.1-9
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• 2014

A modeling system is constructed by integrating an one-dimensional unsteady flow simulation model and a hydrologic model to simulate flood flows in drainage channel networks of paddy field districts. The modeling system's applicability is validated by simulating flood discharges from a paddy field district, which consists of nine paddy fields and one drainage channel. The simulation results are in good agreement with the observed. Particularly, in the verification stage, the relative errors of peak flows and peak depths between the observed and simulated hydrographs range 8.96 to 10.26 % and -10.26 to 2.97 %, respectively. The modeling system's capability is compared with that of a water balance equation-based model; it is revealed that the modeling system's accuracy is superior to the other model. In addition, the simulations of flood discharges from large-sized paddy fields through drainage channels show that the flood discharge patterns are affected by drainage outlet management for paddy fields and physical characteristics of the drainage channels. Finally, it is concluded that to efficiently design drainage channel networks, it is necessary to analyze the results from simulating flood discharges of the drainage channel networks according to their physical characteristics and connectivities.

• Journal of Korea Water Resources Association
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• v.48 no.3
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• pp.221-231
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• 2015

This is a continuous study on the dam effects for the spatial extension of flood data. In this study, flood reduction rates of dams and their influences on downstream using the spatially extended flood data were implemented. Nam-Han River was selected for measuring the impacts of ChoongJu and HoangSung dams. In the evaluations of flood reduction rate at dams, the larger flood events have the lower flood reduction rates for both dams. At the YeoJoo water level station, the analyses of the relations between flood reduction rates and the sizes of watersheds dams located were performed. the sizes of watersheds having a functional dam have highly influenced on the reduction rates of flood. The average of flood reduction rates was smaller than the area rate. For instances, area rates of HoangSung (0.02) and ChoongJu dams (0.6) are larger than the average flood reduction rates for HoangSung (0.01) and ChoongJu dams (0.51), respectively. However, the water level station follows the dam flood reduction characteristics of dams themselves. The spatial effects of dam flood reductions are analyzed based on the three water level stations (GangChun, YeoJoo, YangPyung). The distance of flood reduction rates lower than 0.1 as average flood reduction rate was the area 7 times of watershed having a dam with 0.02 as a minimum reduction rate.

• Ecology and Resilient Infrastructure
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• v.3 no.4
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• pp.294-301
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• 2016

The underflow type movable weirs were arranged in a multi-stage way at a section of the Chiseong River, a tributary of Geum River, where flooding is observed frequently. The flood control and the movable weir management levels were compared with the occasions of installing the existing weir for analysis. The peak discharge decreased by a maximum of 97% for the underflow type movable weir, and the downstream flood elevation decreased by a maximum of 82%. The amount of storage also increased by a maximum of 463% by the distribution and storage functions of the multi-stage arrangement of the underflow type movable weirs. It is possible to suggest that the management level of each movable weir for the target storage of the reach and the flood reduction level through the relationship among this storage, downstream peak flood elevation, and peak flow.

• Journal of Korea Water Resources Association
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• v.54 no.8
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• pp.629-641
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• 2021

In this study, a two-dimensional numerical model (Nays2DH) was applied to analyze the process of morphological changes in the river channel bed depending on the changes in the amount of flooding after fully opening the Sejong weir, which was constructed upstream of the Geum River. For this, numerical simulations were performed by assuming the flow conditions, such as a non-uniform flow (NF), unsteady flows (single flood event, SF), and a continuous flood event (CF). Here, in the cases of the SF and CF, the normalized hydrograph was calculated from real flood events, and then the hydrograph was reconfigured by the peak flow discharge according to the scenario, and then it was employed as the flow discharge at the upstream boundary condition. In this study, to quantitatively evaluate the morphological changes, we analyzed the time changes in the bed deformation the bed relief index (BRI), and we compared the aerial photographs of the study area and the numerical simulation results. As simulation results of the NF, when the steady flow discharge increases, the ratio of lower width to depth decreases and the speed of bar migration increases. The BRI initially increases, but the amount of change decreased with time. In addition, when the steady flow discharge increases, the BRI increased. In the case of SF, the speed of bar migration decreased with the change of the flow discharge. In terms of the morphological response to the peak flood discharge, the time lag also indicated. In other words, in the SF, the change of channel bed indicates a phase lag with respect to the hydraulic condition. In the result of numerical simulation of CF, the speed of bar migration depending on the peak flood discharges decreased exponentially despite the repeated flood occurrences. In addition, as in the result of SF, the phase lag indicated, and the speed of bar migration decreased exponentially. The BRI increased with time changes, but the rate of increase in the BRI was modest despite the continuous peak flooding. Through this study, the morphological changes based on the hydrological characteristics of the river were analyzed numerically, and the methodology suggested that a quantitative prediction for the river bed change according to the flow characteristic can be applied to the field.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.103-111
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• 2014

This study was to develop the flood analysis module (FAM) for implementation of a web-based real-time agricultural flood management system. The FAM was developed to apply for an individual watershed, including agricultural reservoir. This module calculates the flood inflow hydrograph to the reservoir using effective rainfall by NRCS-CN method and unit hydrograph calculated by Clark, SCS, and Nakayasu synthetic unit hydrograph methods, and then perform the reservoir routing by modified Puls method. It was programmed to consider the automatic reservoir operation method (AutoROM) based on flood control water level of reservoir. For a $15.7km^2$ Gyeryong watershed including $472{\times}10^4m^3$ agricultural reservoir, rainfall loss, rainfall excess, peak inflow, total inflow, maximum discharge, and maximum water level for each duration time were compared between the FAM and HEC-HMS (applied SCS and Clark unit hydrograph methods). The FAM results showed entirely consistent for all components with simulated results by HEC-HMS. It means that the applied methods to the FAM were implemented properly.

• Journal of Industrial Technology
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• v.3
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• pp.95-101
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• 1983

This study aims at the determination of the coefficienties of runoff and infiltration affecting runoff. The rating curve is more available than the peak flood runoff to determine flood control plan of flood control reservoir and the volume of hydroelectric power plant, or to make multipurpose dam. In hydrologic analysis and design, it is necessary to develop relations between precipitation and runoff, possible using some of the factors affecting runoff as parameters. In order to calculate the runoff discharge, the runoff process constituting elements are divided to the surface runoff, the subsurface runoff and the groundwater runoff. By comparing the computed hydrograph with the measured hydrograph, determinned the watershed TANK Model constant Varying the tank model constant for approximating the computed hydrograph to the measured hydrograph.

• Journal of Korea Water Resources Association
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• v.45 no.10
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• pp.1035-1041
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• 2012

This paper is on the decision of design magnitude for flood control of urban basin, based on flooding characteristic values. In Korea, a design magnitude for flood control is established based on peak discharge of the outlet of basin. However, this method is inappropriate in an urban basin because sewerage only can flow out as much as it could and other discharge overflow to basin. In order to calculate a design magnitude for flood control of an urban basin, flooding characteristic values (peak discharge of pipe, average flooded depth, maximum flooded depths of an important point, flooded area, flooded volume, flooded time) were used as a tool. Using the Gwanghwamun Square as an example, a methodology was proposed that used XP-SWMM 2010 model as a platform to predict urban flood disaster. It can help other local government and residents to better understand, prepare for and manage a flood in urban environments.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.281-284
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• 2002

Geographic Information System (GIS) has advantage of analyzing spatial distributed data and handling spatial data for hydrologic analysis. Hydrologic Engineering Center's Hydrologic Modeling System(HEC-HMS) with HEC-GeoHMS was used to analyze flood runoff at agricultural small watershed. HEC-GeoHMS, which is an ArcView GIS extension designed to process geospatial data for HEC-HMS, is a useful tool for storing, managing, analyzing, and displaying spatially distributed data. Hydroligical component including peak discharge, time to peak, direct runoff, baseflow for Balhan study watershed, which is located in Whasung city, Kyunggi province, having an area of $29.79km^2$, were calculated using the HEC-HMS model with HEC-GeoHMS.

• Water for future
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• v.25 no.4
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• pp.97-107
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• 1992

The purpose of this study is to estimate the flood hydrograph and runoff at ungaged small watershed by using interactive program with geomorphologic and climatic data obtained from the topographic maps following the law of stream classification and ordering by Horton and Strahler. The present model is modified from Allam's interactive program which derives the geomorphologic instantaneous unit hydrograph(GIUH). This program uses the results of Laplace transformation and convolution integral of probability density function in travel time at each station, This program is used to estimate the time to peak, the flood discharge and the direct runoff at San seong station in Bocheong Stream.