• Journal of Environmental Science International
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• v.23 no.4
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• pp.553-560
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• 2014

The rainfall-runoff characteristics in Jeju Island significantly differ from those in inland, due to highly permeable geologic features driven by volcanic island. Streams are usually sustained in the dry conditions and thereby the rainfall-runoff characteristics changes in terms of initiating stream discharge and its types, depending highly on the antecedent precipitation. Among various the rainfall-runoff characteristics, lag time mainly used for flood warning system in river and direct runoff ratio for determining water budget to estimate groundwater recharge quantity are practically crucial. They are expected to vary accordingly with the given antecedent precipitation. This study assessed the lag time in the measured hydrograph and direct runoff ratio, which are especially in the upstream watershed having the outlet as $2^{nd}$ Dongsan bridge of Han stream, Jeju, based upon several typhoon events such as Khanun, Bolaven, Tembin, Sanba as well as a specific heavy rainfall event in August 23, 2012. As results, considering that the lag time changed a bit over the rainfall events, the averaged lag time without antecedent precipitation was around 1.5 hour, but it became increased with antecedent precipitation. Though the direct run-off ratio showed similar percentages (i.e., 23%)without antecedent precipitation, it was substantially increased up to around 45% when antecedent precipitation existed. In addition, the direct run-off ration without antecedent precipitation was also very high (43.8%), especially when there was extremely heavy rainfall event in the more than five hundreds return period such as typhoon Sanba.

• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.285-288
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• 2008

This study aims to rout optimized design flood discharge through prediction of the frequency-based precipitation from the frequency analysis with density of rainfall gage networks in urban watershed. Frequency analysis was examined for the measured rainfall depth with low density of a point and high density of the sub-basin divided into 13 points in watershed. The used rainfall data in order to analyze consists of two groups based on measured rainfall depth for a day duration with 39years of a point and 6years of 13 points by an extending as annual exceedance series, respectively. Selected rainfall data in this analysis show that low-network has maximum rainfall depth with duration 1hr-79.1mm and 24hrs-329.1mm, and high-networks have ones with duration of 1hr-93.0 mm and 24 hrs-245.0 mm, respectively. As the result, probability of the best in this study determined the Gumbel method from the goodness of fit test and the method of prime 6 probability distributions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5330-5336
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• 2011

It becomes more and more important to develop various infiltration facilities for healthy water cycle and reduction of urban storm water runoff. In this study, a infiltration facility by utilizing tree box was developed. The developed facility is capable of reducing storm water road runoff, improving urban water cycle, and performing other sustainable and environmental functions. Because the facility can be manufactured to a smaller size than an existing runoff reduction facility, it can be installed at various road types of not only existing urban areas, but new developed areas. If the facility is applied to four-lane roadways, it is expected to reduce 65% of rainfall runoff discharge. Urban flood control improvement can be accomplished by a wide application of the developed technique.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.155-155
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• 2019

The Agricultural Policy/Environmental eXtender (APEX) models have been developed for assessing agricultural management efforts and their effects on soil and water at the field scale as well as more complex multi-subarea landscapes, whole farms, and watersheds. National Academy of Agricultural Sciences, Wanju, Korea, has modified a key component of APEX application, named APEX-Paddy for simulating water quality with considering appropriate paddy management practices, such as puddling and flood irrigation management. Calibration and validation are an anticipated step before any model application. Simple techniques are essential to assess whether or not a parameter should be adjusted for calibration. However, very few study has been done to evaluate the ability of APEX-Paddy to simulate the impact of multiple management scenarios on nutrients loss. In this study, the observation data from experimental fields at Iksan in South Kora was used in calibration and evaluation process during 2013-2015. The APEX auto- calibration tool (APEX-CUTE) was used for model calibration and sensitivity analysis. Four quantitative statistics, the coefficient of determination ($R^2$),Nash-Sutcliffe(NSE),percentbias(PBIAS)androotmeansquareerror(RMSE)were used in model evaluation. In this study, the hydrological process of the modified model, APEX-Paddy, is being calibrated and tested in predicting runoff discharge rate and nutrient yield. Field-scale calibration and validation processes are described with an emphasis on essential calibration parameters and direction regarding logical sequences of calibration steps. This study helps to understand the calibration and validation way is further provided for applications of APEX-Paddy at the field scales.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.250-250
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• 2017

글로벌 위성 기반의 강수량 관측에 대한 역사는 1979년에 Arkin의 의해 제안된 IR방법에 의해 위성으로부터 강우자료를 유도하는 개념이 도입된 이후 1987년 해양에서의 비교적 정확한 강수량 추정이 가능한 다중 채널의 마이크로파(MW) 복사계를 이용한 방법으로 위성강수 추정에 대한 연구가 활발히 진행되었다. 이후 두 IR과 MW를 혼합한 방법에서, 또다시 1997년 TRMM위성의 PR(Precpipitation Radar)의 레이더를 이용하는 방법, 그리고 2014년 GPM 핵심 위성(GPM Core Observatory)에 탑재된 Dual PR에 의한 방법으로 위성강수의 정확도를 매우 높여가고 있다. 본 연구는 KOICA 사업으로 진행중인 모로코 세부강 유역 홍수방지 마스터플랜 사업에서 모로코 세부강 유역의 2010년 홍수사상에 대한 위성강우 및 지상계측 일일자료를 이용하여 홍수유출량을 추정하는 것으로 목적으로 하고 있다. 모로코 세부강(Oued Sebou) 유역은 모로코의 서북부에 위치하며 유역면적은 한강유역과 유사한 $38,380km^2$이고 하천연장은 450km로 모로코 국토면적의 약 7% 정도를 차지하며 모로코 농업생산의 중심지역이고 유역의 기후 및 기상 특성은 겨울철 온난다습하고 여름에 고온 건조한 지중해성 기후를 나타내며, 연강수량은 400mm이상으로 보고하고 있다(이산 등, 2015). 유역내 49개 관측소의 일일 강우량 자료를 분석한 결과 2000년부터 2010년까지의 유역 산술평균 강수량은 607.1mm/yr로 분석되었고, 2010년 가장 많은 강수를 기록한 지역은 Jbel oudka로 1874.1mm/yr였고, 가장 적은 강수량을 기록한 지역은 Allal Al Fassi - Barrage로 289.9mm/yr로 나타났다. 2010년 홍수가 발생한 시기인 2009년 12월 19일부터 2010년 1월 18일까지의 1시간 간격의 위성강우자료와 1일 관측 지상계측자료를 합성하여 위성보정강우량을 추정하였다. 보정 방법은 순위상관방법을 적용하였다. 사용한 모형은 일본 ICHARM에서 개발한 IFAS와 한국건설기술연구원의 MapWindow 기반 GRM 모형(mwGRM)을 이용하였다. 모형의 적용 결과 세부강 유역 본류의 첨두유출량은 $6,010m^3/s$(mwGRM)과 $5,878m^3/s$(IFAS)로 분석되었다. 향후 위성강우 및 지상계측 강우의 시계열적 정확도와 총강우량 등의 정확도 평가를 수행할 계획이다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.74-74
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• 2019

수문조사를 통한 유량자료는 물의 이수, 치수, 환경 등 홍수피해 방지, 수자원의 관리 및 계획을 위한 기초자료로 이용되고 있다. 하지만 예산, 인력, 안전 및 하천공사 등의 문제로 매년 모든 지점에서 유량 측정을 실시하지 못하는 어려움이 있다. 특히 홍수기의 태풍 등 큰 호우사상 발생 시 수위-유량관계 변화 검토가 필요하지만 홍수기 계획지점 이외 지점에서 측정은 위와 같은 문제로 어려움이 있다. 따라서 본 연구에서는 이런 문제점을 개선하기 위해 최소 인력이 단시간 간편하게 드론을 활용하여 유량을 측정할 수 있는 방법을 도입하였다. 드론을 활용한 유량측정방법은 드론 사진측량 개념에서 접근하였으며 드론 사진측량의 정확도는 다양한 분야에서 많은 연구를 통해 입증된 바가 있다. 본 연구의 대상지점은 중랑천 상류에 위치한 의정부시(신곡교) 지점에서 보급형 회전익 드론 (DJI, 팬텀4 pro)을 활용하여 검증 목적을 위해 측정하였다. 유량측정은 드론으로 촬영된 항공사진 상에서 지상에 위치확인 가능한 지상기준점(GCP, Ground Control Point) 4개점을 선점하고 RTK-VRS 장비를 이용하여 측량을 수행하였다. 항공사진 촬영은 드론을 일정높이의 공중에 정지되어 있는 호버링(Hovering) 상태에서 카메라 타임랩스 기능으로 3초 간격 하도 내 수표면을 촬영하였다. 항공사진 수표면에 유하하는 부유물의 3초 간격 이동위치와 GCP 자료를 활용하여 X, Y 좌표 분석을 통해 3초간 이동거리를 표면유속으로 산정하고 통수단면적을 적용하여 유량을 산정하였다. 이와 같이 드론 사진측량으로 산정된 유량과 일반적인 유량측정 방법을 통해 개발된 수위-유량관계곡선식과의 비교를 통해 드론을 활용한 유량측정 방법의 적용성을 확인하였다. 다만, 드론이라는 기계적인 장비의 한계로 야간, 바람 및 강우 등 환경적인 요인에 의해 측정의 제한이 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.396-396
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• 2015

Frequent urban floods affect the human safety and economic properties due to a lack of the capacity of drainage system and the increased frequency of torrential rainfall. The drainage system has played an important role in flooding control, so it is necessary to establish the effective countermeasures considering the connection between drainage system and surface flow. To consider the connection, we selected SWMM5 model for analyzing transportation capacity of drainage system and FLUMEN model for calculating inundation depth and time variation of inundation area. First, Thiessen method is used to delineate the sub-catchments effectively base on drainage network data in SWMM5. Then, the output data of SWMM5, hydrograph of each manhole, were used to simulate FLUMEN to obtain inundation depth and time variation of inundation area. The proposed method is applied to Sadang area for the event occurred in $27^{th}$ of July, 2011. A total of 11 manholes, we could check the overflow from the manholes during that event as a result of the SWMM5 simulation. After that, FLUMEN was utilized to simulate overland flow using the overflow discharge to calculate inundation depth and area on ground surface. The simulated results showed reasonable agreements with observed data. Through the simulations, we confirmed that the main reason of the inundation was the insufficient transportation capacities of drainage system. Therefore cooperation of both models can be used for not only estimating inundation damages in urban areas but also for providing the theoretical supports of the urban network reconstruction. As a future works, it is recommended to decide optimized pipe diameters for efficient urban inundation simulations.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.133-141
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• 2011

Urban development of basin causes increasing runoff volume and peak flowrate and shortening in time of concentration, which may cause frequent flooding downstream. An infiltration facilities are operated as a method of reducing flood discharge of urban rivers and peak flowrate. There are various types of infiltration facilities like infiltration trench and porous pavement. In this study, runoff reduction effect due to installation of infiltration facilities are performed and focused on $0.18km^2$ residential area of Ok-kye dong and $0.67km^2$ industrial area of Gong-dan dong in Gumi City. The analysis is fulfilled with comparison of total runoff volume and runoff reduction volume by using the WinSLAMM and the relation equation between area ratio of infiltration facilities and ratio of runoff reduction are derived and peak flow reduction effect for installation of infiltration facilities is analyzed.

• Journal of Korean Society of Disaster and Security
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• v.11 no.2
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• pp.83-89
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• 2018

The significant sedimentation at the estuary in the eastern coast of Korea frequently causes river mouth occlusion where disconnection between the river and sea is observed. River mouth occlusion causing watershed retention raises the environmental risk of the area as it impairs water quality and threatens the area's safety in the event of floods. This study proposes a plan to maintain stability of river channel and flow of flood discharge at the estuary with loss of its function for disaster prevention. To this end, the study tries to change the location and width of stream path, focusing on the center line of stream near the sand bar of river mouth. This allows to identify a shape of stream path that leads the most stable flow. To review the result, this study uses the SRH-2D, a model for two-dimensional hydraulic analysis, and conduct numeric simulation. The simulation result showed that the most effective plan for maintaining the stable flow of running water without having the area sensitive to changes in hydraulic characteristics is to lower the overall river bed height of the sand bar near the center line of stream to a equal level.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.203-215
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• 2021

In the present study, hydrologic data and topographical data from 2010 to 2019 were collected from three gauging stations placed in the watershed of Naeseong stream to determine changes and rates of changes in rainfall, water level & mean velocity, and water level & discharge, together with changes in rates of erosion and deposition at cross-sections of the river. Besides, effects of regulated and non-regulated rivers according to the presence of artificial regulation of flow rate of the river via artificial structure located at Seo stream (Yeongju si (Wolhogyo) station), the tributary free from construction of dams, were compared and analyzed. Results of analyses conducted in the present study revealed vegetational establishment and landforming due to increasing area of vegetational sandbar evolved in the flood plain (intermediate- or high- water level) by the drought sustained from 2013 to 2015. Continuous erosion of river bed was appeared because of narrowed flow area with low water level and increased velocity and tractive force on river bed.