• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.141-141
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• 2021

This study proposed an equation for Rainfall Threshold for Flood Warning (RTFW) for urban areas based on computer simulations. First, a coupled 1D-2D dual-drainage model was developed for nine watersheds in Seoul, Korea. Next, the model simulation was repeated for a total of 540 combinations of the synthetic rainfall events and watershed imperviousness (9 watersheds × 4 NRCS Curve Number (CN) values × 15 rainfall events). Then, the results of the 101 simulations with the critical flooded depth (0.25m-0.35m) were used to develop the equation that relates the value of RTFW to the rainfall event temporal variability (represented as coefficient of variation) and the watershed Curve Number. The results suggest that 1) the rainfall with greater temporal variability causes critical floods with less amount of total rainfall; and that 2) the greater imperviousness requires less rainfall to have critical floods. For validation, the proposed equation was applied for the flood warning system with two storm events occurred in 2010 and 2011 over 239 watersheds in Seoul. The results of the application showed high performance of the warning system in issuing the flood warning, with the hit, false and missed alarm rates at 68%, 32% and 7.4% respectively for the 2010 event and 49%, 51% and 10.7% for the event in 2011.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.95-101
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• 2002

Much of domestic city is served by combined sewer system rather than separate sanitary or storm sewers. During wet weather, when the volume of sanitary sewage and storm water entering the combined sewers exceeds the system capacity, the system is designed to overflow at several designated CSOs. The objective of this research is to have grasp of characteristics of combined sewer runoff and to evaluate efficiently the intercepted volume of CSOs. During the wet weather in first rainfall, SS load at each site H-1, H-2, and H-3 were 600kg/event, 370kg/event, and 289kg/event, SS load at each site in second rainfall were 216kg/event, 113kg/event, and 37.2kg/event. EMCs at each site were 702mg/L, 816mg/L, 861mg/L in first rainfall and 99.9mg/L, 161.9mg/L, 103.6mg/L in second rainfall, respectively. First flush coefficients b at each site were 0.237, 0.166, and 0.151.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.4
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• pp.13-22
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• 2020

The Doam Lake watershed has a significant impact on the downstream water system due to nutrients and sediment outflow during rainfall caused by steep slopes, soil losses, and fertilization. These non-point sources are unclear in the discharge area and are affected by land use patterns, soil characteristics, and topographical features of the watershed. Therefore, this study conducted rainfall monitoring from July to October 2019 in Songcheon upstream of the Doam Lake watershed, one of the non-point pollution source management areas. Then, after analyzing rainfall runoff, Event Mean Concentration (EMC) and Mass First Flush ratio (MFFn) were calculated to compare and analyze the characteristics of rainfall and the non-point pollutant discharge. As a result of the analysis, it showed various non-point pollutant emission characteristics for each rainfall event. In addition, the concentration of EMC and the MFFn were affected by the average rainfall intensity and the maximum rainfall intensity, and were not significantly affected by the number of antecedent drying days. In the future, it is expected that effective non-point source reduction measures and management measures according to rainfall intensity through continuous monitoring and analysis will be needed.

• Journal of Korean Society on Water Environment
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• v.34 no.5
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• pp.487-493
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• 2018

Urban stormwater runoff is the one of the most extensive causes of deterioration of water quality in streams in urban areas. Especially, in the Suyeong River watershed, non-point sources from urban-residential areas are the most common cause of water pollution. Also, it has been ascertained that BOD and COD as indexes of organic matter, have limitation on management of Suyeong River's water quality. In this study, changes of organic matter properties of Suyeong River from inflow of non-point source during rainfall were investigated. Fractions of organic matters were analyzed using water samples collected at two sites (Suyeong River and Oncheon Stream) during a rain event. Variations of dissolved organic carbon (DOC) concentration by rainfall were similar to flow rate change in the river. Distribution of organic matter fraction according to change of rain duration revealed that while hydrophilic component increased at initial rainfall, the hydrophobic component was similar to change in dissolved organic carbon (DOC) concentration. Also, the relative proportion of hydrophilic components in organic matter in river water increased, due to rainfall. Results of biodegradation of organic matters revealed that decomposition rate of organic matters during rainfall was higher than that of during a non-rainfall event.

• Journal of Korean Society on Water Environment
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• v.29 no.1
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• pp.97-106
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• 2013

The temporal and spatial variations of water quality in a stratified reservoir are fully dependent on the characteristics of inflow loading from its watershed and the transport regimes of pollutants after entering the reservoir. Because of the meteorological and hydrological conditions in Korea, the pollutants loading to reservoirs are mostly occur during rainfall events. Therefore it is important to understand the characteristics of pollutants loading from upstream rivers and their spatial propagation through the stratified reservoir during the rainfall events. The objectives of this study were to characterize the water quality variations in upstream rivers of Imha Reservoir during a rainfall event, and the transport and spatial variations of pollutants in the reservoir through extensive field monitoring and laboratory analysis. The results showed that the event mean concentration (EMC) of SS, BOD, $COD_{Mn}$, T-N, T-P, $PO_4-P$ are 8.6 ~ 362.1, 2.5 ~ 5.1, 1.5 ~ 5.1, 1.1 ~ 1.9, 8.3 ~ 57.1, 5.6 ~ 25.7 times greater than the mean concentrations of these parameters during non-rainfall period. The turbidity and SS data showed good linear correlations, but the relationships between flow and SS showed large variations because of hysteresis effect during rising and falling periods of the flood. The ratio of POC to TOC were 12.6 ~ 14.7% during the non-rainfall periods, but increased up to 28.2 ~ 41.7% during the flood event. The turbid flood flow formed underflow and interflow after entering the reservoir, and delivered a great amount of non-point pollutants such as labile and refractory organic matters and nutrients to the metalimnion layer of reservoir, which is just above the thermocline. Spatially, the lateral variations of most water quality parameters were marginal but the vertical variations were significant.

• Journal of Korea Water Resources Association
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• v.52 no.2
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• pp.141-148
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• 2019

When simulating the daily rainfall amount by existing Markov Chain model, it is general to simulate the rainfall occurrence and to estimate the rainfall amount randomly from the distribution which is similar to the daily rainfall distribution characteristic using Monte Carlo simulation. At this time, there is a limitation that the characteristics of rainfall intensity and distribution by time according to the rainfall duration are not reflected in the results. In this study, 1-day, 2-day, 3-day, 4-day rainfall event are classified, and the rainfall amount is estimated by rainfall duration. In other words, the distributions of the total amount of rainfall event by the duration are set using the Kernel Density Estimation (KDE), the daily rainfall in each day are estimated from the distribution of each duration. Total rainfall amount determined for each event are divided into each daily rainfall considering the type of daily distribution of the rainfall event which has most similar rainfall amount of the observed rainfall using the k-Nearest Neighbor algorithm (KNN). This study is to develop the limitation of the existing rainfall estimation method, and it is expected that this results can use for the future rainfall estimation and as the primary data in water resource design.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.235-235
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• 2015

This study investigates the impact of event characteristics on runoff dynamics during extreme flood events observed in a $8.5km^2$ experimental watershed located in South Korea. The 37 most extreme flood events with event rainfall in excess of 50 mm were analysed using an event-based rainfall-runoff model; the Revitalised Flood Hydrograph (ReFH) routinely used for design flood estimation in the United Kingdom. The ReFH model was fitted to each event in turn, and links were investigated between each of the two model parameters controlling runoff production and response time, respectively, and event characteristics such as rainfall depth, duration, intensity and also antecedent soil moisture. The results show that the structure of the ReFH model can effectively accommodate any nonlinearity in runoff production, but that the linear unit hydrograph fails to adequately represent a reduction in watershed response time observed for the more extreme events. By linking the unit hydrograph shape directly to rainfall depth, the consequence of the observed nonlinearity in response time is to increase design peak flow by between 50% for a 10 year return period, and up to 80% when considering the probable maximum flood (PMF).

• Korean Journal of Hydrosciences
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• v.6
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• pp.81-98
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• 1995

A linear reservoir rainfall-runoff system was developed as a rainfall-runoff event simulation model. It was achieved from large modification of runoff function method. There are six parameters in the model. Hydrologic losses consist of some quantity of initial loss and some ratio of rainfall intensity followed by initial loss. The model has analytical routing equations. Hooke and Jaeves algorithm was used for model calibration. Parameters were estimated for flood events from '84 to '89 at Seomyeon and Munmak stream gauges, and the trends of major parameters were analyzed. Using the trends, verifications were performed for the flood event in September 1990. Because antecedent rainfalls affect initial loss, future researches are required on such effects. The estimation method of major parameters should also be studied for real-time forecasting.

• Journal of Environmental Science International
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• v.26 no.3
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• pp.401-410
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• 2017

This study analyzed the changes in the concentrations of organic matters in constructed treatment wetlands, coming from discharge water from a sewage treatment plant and non-point pollutant sources during rainfall events. At the beginning of a rainfall event, a massive amount of particulate organic matter flowed in, and was removed from the sedimentation basin (S1, S2); dissolved organic matter was removed after passing through stepwise treatment processes in the wetland. During dry period in the wetland, the removal efficiency rate for COD and TOC was -21 and -7%, respectively; during the rainfall event, the removal efficiency rate for COD and TOC were 47 and 43%, respectively. The highly-concentrated organic matters that flowd in at the beginning of the rainfall event was stabilized by various structures in the wetland before water discharge. Cyanobacteria blooms annually at the confluence of the So-ok stream and Daecheong Lake. Therefore, it is expected that the wetland will contribute significantly to reducing cyanobacteria and improving water quality in the area.

• Atmosphere
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• v.23 no.1
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• pp.23-32
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• 2013

Ensemble sensitivity has been recently proposed as a method to analyze the dynamics of severe weather events. We adopt it to investigate the physical mechanism which caused the heavy rainfall over the Korean Peninsula on 6th August 2003. Two rainfall peaks existed in this severe weather event. The selected response functions are 1 hour accumulated rainfall amount of each rainfall peak. Sensitivity fields were calculated using 36 ensemble members which were generated by WRFDA. The sensitive regions for the first rainfall peak are located over the Shandong Peninsula and the Yellow Sea at 12 hours before the first rainfall peak. However, the 12-h forecast sensitivity for the second rainfall peak is revealed near Typhoon ETAU (0310) and midlatitude trough. These results show that the first rainfall peak was induced by low pressure which located over the northern part of the Korean Peninsula while the second rainfall peak was caused by the interaction between typhoon ETAU and midlatitude trough.