• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1361-1375
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• 2013

The design flow considering nonstationarity is estimated to determine the design flood related to hydraulic structure quantitatively based on the design process for stream restoration in the Mokgamcheon watershed proposed by Lee et al. (2011). The purpose of this research is to suggest new ways that the design flood was calculated considering nonstationarity at the Mokgamcheon watershed. Storm-unit hydrograph method to calculate design flood and direct frequency analysis were applied and nonstationarity was considered for the frequency analysis through extRemes toolkit developed at NCAR (National Center for Atmospheric Research). Although the method of direct flood frequency analysis due to dealing with flowrates directly has a more reliable than strom-unit hydrograph method, as a result, the method of direct flood frequency analysis underestimated the design flood than strom-unit hydrograph method due to the characteristics of the flow data. Therefore, the flood of storm-unit hydrograph method (100 years frequency) was determined as the design flood in the Mokgamcheon watershed.

• Journal of Korea Water Resources Association
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• v.41 no.2
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• pp.185-196
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• 2008

The flash flood has been studied in the climatological aspect which considers temporal and spatial characteristics of rainfall. However, we have not interested in runoff hydrograph for flash flood study. Therefore, our objectives of this study are to apply a work of Bhaskar et. al (2000) which studied runoff hydrograph to represent the flash flood to Korea and also to distinguish flash flood event from general flood event. That is, we quantified the severity of flash flood by estimation of flash flood index using runoff hydrograph. This study estimated the flash flood index for investigating the relative severity of flash flood in Han river basin with 101 flood events. Also we quantified the flash flood severity for flood event by heavy rainfall occurred in July of 2006. As a result, Kangwon-do province showed more severe flash flood than other areas in Han river basin and urban area such as Jungrang cheon stream also showed severe flash flood. We analyzed a flash flood of July of 2006 by dividing July into 1st to 3rd terms. From the analysis we knew that the 1st term of July showed the severe flash flood was occurred in Seoul area and the 2nd term showed it was occurred in Kangwon-do province.

• Journal of Korea Water Resources Association
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• v.47 no.1
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• pp.83-93
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• 2014

This research was carried out for suggesting design criteria and procedure for maximizing flood control capacity by building flood control facilities like flood retention basin built in connection with existing facilities in order to cope with increased uncertainty due to factors such as urbanization and climate change. We suggested the procedure for the analysis under the various scenarios applicable for the cases of determining retention basin capacity as provision for the flood water level increase in main river channel or estimating flood water level reduction effect when retention basin capacity is given. Procedure for estimating design flood hydrograph at any duration using Intensity-Duration-Quantity (IDQ) originated from the existing IDF, and its application example were provided. Based on rainfall estimated by the IDQ analysis, it is possible to calculate an equivalent peak hydrographs under various scenarios, e.g. lower frequency hydrograph under same rainfall duration with water level higher than existing hydrograph, hydrograph with same peak and higher volume due to increased rainfall duration, hydrograph with higher peak and volume than existing hydrograph, etc.

• Journal of Korea Water Resources Association
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• v.30 no.4
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• pp.327-334
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• 1997

The purpose of this study is to calibrate the parameters of tank model for the derivation of a design flood hydrograph at a certain river basin outlet. The selected stations are Gongju and Naju station which are located in the Keum and the Youngsan river basin, respectively. The results of parameters calibration for tank model are represented a little different values comparing with the proposed values at Gongju station through the verification of flood hydrograph in modeling procedure but the values of tank parameters at Naju station are fitted well for the derivation of flood hydrograph using the proposed design parameters of tank model.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.346-349
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• 2010

In this study several unit hydrographs by rainfall storms are derived and moving averaged unit hydrograph is extracted from them based on the rainfall-runoff data in a small basin 8.5 $km^2$ wide. And peak discharges and peak times of the unit hydrographs are investigated and reviewed. And then a representative unit hydrograph of the moving averaged one is applied to the linear convolution integration for obtaining the flood discharge hydrograph and peak discharge and time of its result are researched and inspected. Variance in application of the representative unit hydrograph in a basin on assumption of linearity is appeared and this is given as a counterevidence about that the runoff response from rainfall on a basin has nonlinear characteristics. And As a result of application of derived representative unit hydrograph the errors in peak discharge and time are investigated.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.125-131
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• 2009

The aim of this study is to quantify the severity of flash food for a study watershed in Korea by estimation of flash food index using flood runoff hydrograph following Bhaskar et. al (2000). As an extension of the previous research, we examine the relation between flash food index and rainfall intensity, rainfall duration, and total runoff, respectively. This study has estimated the flash food index through simulated flood hydrographs to investigate the relative severity of flash flood in an ungauged basin, Megok river basin for 31 flood events.

• 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.

• Water for future
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• v.9 no.2
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• pp.76-86
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• 1976

The 30-year design flood hydrograph for the Musim Representative Basin, one of the study basins of the International Hydrological Program, is synthesized by the method of unit hydrograph. The theory of unit hydrograph has been well known for a long time. However, the synthesis of flood hydrograph by this method for a basin with insufficient hydrologic data is not an easy task and hence, assumptions and engineering judgement must be exercized. In this paper, the problems often encountered in applying the unit hydrograph method are exposed and solved in detail based on the theory and rational judgement. The probability rainfall for Cheonju Station is transposed to the Musim Basin since it has not been analyzed due to short period of rainfall record. The duration of design rainfall was estimated based on the time of concentration for the watershed. The effective rainfall was determined from the design rainfall using the SCS method which is commonly used for a small basin. The spatial distribution of significant storms was expressed as a dimensionless rainfall mass curve and hence, it was possible to determine the hyetograph of effective design storm. To synthesize the direct runoff hydrograph the 15-min. unit hydrograph was derived by the S-Curve method from the 1-hr unit hydrograph which was obtained from the observed rainfall and runoff data, and then it was applied to the design hyetograph. The exsisting maximum groundwater depletion curve was derived by the base flow seperation. Hence, the design flood hydrograph was obtained by superimposing the groundwater depletion curve to the computed direct runoff hydrograph resulting from the design storm.

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

• 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.