• Journal of Korea Water Resources Association
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• v.54 no.6
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• pp.381-393
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• 2021

As part of the National Disaster Management Research Institute's Official Development Assistance (ODA) projects for transferring new technologies in the field of disaster-safety management, a flood forecasting and warning system was established in 2019 targeting the Borikhan in the Namxan River Basin in Bolikhamxai Province, Laos. In the target area, which is an ungauged small and medium river basin, observation stations for real-time monitoring of rainfall and runoff and alarm stations were installed, and a software that performs real-time data management and flood forecasting and warning functions was also developed. In order to establish a flood warning standard and develop a nomograph for flood prediction, hydraulic and hydrological analysis was performed based on the 30-year annual maximum daily rainfall data and river morphology survey results in the target area. This paper introduces the process and methodology used in this study, and presents the results of the system's applicability review based on the data observed and collected in 2020 after system installation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.5
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• pp.671-683
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• 2018

The flood damage caused by heavy rains in urban watershed is increasing, and, as evidenced by many previous studies, urban flooding usually exceeds the water capacity of drainage networks. The flood on the area which considerably urbanized and densely populated cause serious social and economic damage. To solve this problem, deterministic and probabilistic studies have been conducted for the prediction flooding in urban areas. However, it is insufficient to obtain lead times and to derive the prediction results for the flood volume in a short period of time. In this study, IDNN, TDNN and NARX were compared for real-time flood prediction based on urban runoff analysis to present the optimal real-time urban flood prediction technique. As a result of the flood prediction with rainfall event of 2010 and 2011 in Gangnam area, the Nash efficiency coefficient of the input delay artificial neural network, the time delay neural network and nonlinear autoregressive network with exogenous inputs are 0.86, 0.92, 0.99 and 0.53, 0.41, 0.98 respectively. Comparing with the result of the error analysis on the predicted result, it is revealed that the use of nonlinear autoregressive network with exogenous inputs must be appropriate for the establishment of urban flood response system in the future.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.3
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• pp.13-21
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• 2007

Recently, very short-term rainfall forecast using radar is required for regional flash flood according to climate change. This research is to evaluate the feasibility of GIS based distributed model using radar rainfall which can express temporal and spatial distribution in actual dam watershed during flood runoff period. Vflo model which was developed Oklahoma university was used as physical based distributed model, and Namgang dam watershed ($2,293km^2$) was applied as study site. Distributed rainfall according to grid resolution was generated by using K-RainVieux, preprocess program of radar rainfall, from JIN radar. Also, GIS hydrological parameters were extracted from basic GIS data such as DEM, land cover and soil map, and used as input data of distributed model(Vflo). Results of this research can provide a base for building of real-time short-term rainfall runoff forecast system according to flash flood in near future.

• Journal of Korean Society for Geospatial Information Science
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• v.16 no.1
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• pp.23-32
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• 2008

According to recent frequent local flash flood due to climate change, the very short-term rainfall forecast using remotely sensed rainfall like radar is necessary to establish. This research is to evaluate the feasibility of GIS-based distributed model coupled with radar rainfall, which can express temporal and spatial distribution, for multipurpose dam operation during flood season. $Vflo^{TM}$ model was used as physically based distributed hydrologic model. The study area was Yongdam dam basin ($930\;km^2$) and the 3 storm events of local convective rainfall in August 2005, and the typhoon.Ewiniar.and.Bilis.collected from Jindo radar was adopted for runoff simulation. Distributed rainfall consistent with hydrologic model grid resolution was generated by using K-RainVieux, pre-processor program for radar rainfall. The local bias correction for original radar rainfall shows reasonable results of which the percent error from the gauge observation is less than 2% and the bias value is $0.886{\sim}0.908$. The parameters for the $Vflo^{TM}$ were estimated from basic GIS data such as DEM, land cover and soil map. As a result of the 3 events of multiple peak hydrographs, the bias of total accumulated runoff and peak flow is less than 20%, which can provide a reasonable base for building operational real-time short-term rainfall-runoff forecast system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.6
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• pp.839-850
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• 2018

The flood damage in urban areas due to torrential rain is increasing with urbanization. For this reason, accurate and rapid flooding forecasting and expected inundation maps are needed. Predicting the extent of flooding for certain rainfalls is a very important issue in preparing flood in advance. Recently, government agencies are trying to provide expected inundation maps to the public. However, there is a lack of quantifying the extent of inundation caused by a particular rainfall scenario and the real-time prediction method for flood extent within a short time. Therefore the real-time prediction of flood extent is needed based on rainfall-runoff-inundation analysis. One/two dimensional model are continued to analyize drainage network, manhole overflow and inundation propagation by rainfall condition. By applying the various rainfall scenarios considering rainfall duration/distribution and return periods, the inundation volume and depth can be estimated and stored on a database. The Rainfall-Duration-Flooding Quantity (RDF) relationship curve based on the hydraulic analysis results and the Self-Organizing Map (SOM) that conducts unsupervised learning are applied to predict flooded area with particular rainfall condition. The validity of the proposed methodology was examined by comparing the results of the expected flood map with the 2-dimensional hydraulic model. Based on the result of the study, it is judged that this methodology will be useful to provide an unknown flood map according to medium-sized rainfall or frequency scenario. Furthermore, it will be used as a fundamental data for flood forecast by establishing the RDF curve which the relationship of rainfall-outflow-flood is considered and the database of expected inundation maps.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.105-115
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• 2008

Urbanization results in increased runoff volume and peak flowrate and shortening in time of concentration, which may cause frequent flooding downstream. There are various types of flow retardation methods including detention ponds, retention ponds, and infiltration ponds. In general, hydrologic models to design the detention pond are classified into planning model and design model. This study is comparing and analyzing of planning model to design the detention pond in urban area. Detention ponds data of Disaster Impact Assessment Report on 22 sites were analyzed to investigate proper planning models in this study. From this research, following conclusions are derived, 1) In case of on-line detention pond, Lee model(1991) is the best planning model and similar to real storage volume. 2) In case of off-line detention pond, Abt and Grigg model is much more proper model compared to other models.

• Journal of Korea Water Resources Association
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• v.42 no.11
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• pp.963-972
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• 2009

The objective of this study is to evaluate an application of stochastic continuous storage function model with ensemble Kalman filter technique. The case study is performed at the upstream basin of Jibo streamflow gauge including Andong and Imha dam. Test period is for the rainy season during 2006 and 2007. Long term runoff analysis is feasible in the case of using deterministic model. Ensemble members for input data and parameters are generated using Monte Carlo simulation for the purpose of applying ensemble Kalman filter technique. The cumulative absolute errors of stochastic model to the deterministic one are improved for the amount of 17.5 %, 18.3 % and more than 40.0 % for Andong dam, Imha dam and Jibo station, respectively. The results indicate that the stochastic model improves the accuracy of the simulated discharge considerably.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.315-330
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• 2000

The GIUH (Geomorphologic Instantaneous Unit Hydrograph) is to be applied to the ungauged or insufficiently gauged basins. For tIris purpose, an accurate estimation of the charactenstlc velocity is one very important part, but any proper method for this has not been developed yet. In case that we have enough rainfall and runoff clata, the estimation of the characteristic velocity may be an easy job, but it is out of the purpose of the GIUH. Remindmg that the purpose of GIUH the characterisbc veloclty should be estimated based on the geomorpholog1c analysis and also be snnple for easy apphcation. In tIris research analysis cmd application of the GruH was given to several sub-basins in Wi-stream river basin, Gono, Donggok and Hyoryung. After deriving the characteristic velocity througn a optimizatlOn process with real data, it is compared w1th several velOCIties der1ved from geOlnoI1Jhoclimatic instantaneous unit hydrograph theory and several other concentration time formulae. The estimated charactenstic velocities using Kerby, Kim, KInematic Wave, and Brasby- Williams formulae found to g1ve the appropriate results. Hmvever, as the Kerby, and the Kinematic Wave require user's decision of the IvIanning's n value, the K1m and the Braby-Williams seem to be more applicable and recommended as characteristic velocity formula.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.9
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• pp.952-957
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• 2005

A sensitivity analysis study was performed to examine the effects of cell size on a distributed non-point source pollution model. The model, AnnAGNPS, whiff is a modified version of USDA's AGNPS, was applied to Eung stream watershed, a tributary of Cheongmi stream located in the South Branch of Han River System. The model components and results, such as channel length, slope, land use, and delivery ratio, were analyzed according to the various cell sizes from 10 to 200 ha. As cell sire increases, channel length decreases due to short-circuiting of meandering creek. The decreased channel length has more significant effects on the model results than any other geomorphological change. When the effects of land use and soil distribution are excluded, sediment delivery loads increase due to shorter time to reach the outlet of the watershed in larger tell size. When those effects are included, however, sediment delivery loads decrease in larger fell size because the variety of land use types can not be inputted. The predominant land use in the applied watershed is forest with very low soil erosion such that the predicted sediment delivery might be much lower than real system. The cell size of 30 ha was determined to produce the most appropriate resolution. Surface runoff and non-point source loads of TN, TP and BOD were predicted and the results agree well with the field measurements. From this study, it was shown that the model results would be very dependent on variations of topography, land use, and soil distribution, as a function of cell size, and the optimum cell size is very important for successful application of distributed non-point source pollution model.

• Journal of Korea Water Resources Association
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• v.34 no.6
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• pp.659-672
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• 2001

Generally, design flood for a hydraulic structure is estimated using statistical analysis of runoff data. However, due to the lack of runoff data, it is difficult that the statistical method is applied for estimation of design flood. In this case, the synthetic unit hydrograph method is used generally and the models such as NYMO method, Snyder method, SCS method, and HYMO method have been widely used in Korea. In this study, these methods and KICT method, which is developed in year 2000, are compared and analyzed in 10 study areas. Firstly, peak flow and peak time of representative unit hydrograph and synthetic unit hydrograph in study area are compared, and secondly, the shape of unit hydrograph is compared using a root mean square error(RMSE). In Nakayasu method developed in Japan, synthetic unit hydrograph is very different from peak flow, peak time, and the shape of representative unit hydrograph, and KICT method(2000) is superior to others. Also, KICT method(2000) is superior to others in the aspects of using hydrologic and topographical data. Therefore, Nakayasu method is not a proper in hydrological practice. Moreover, it is considered that KICT model is a better method for the estimation of design flood. However, if other model, i.e. SCS method, Nakayasu method, and HYMO method, is used, parameters or regression equations must be adjusted by analysis of real data in Korea.