• Water for future
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• v.29 no.4
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• pp.119-129
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• 1996

The daily soil water contents were obtained from the time domain reflectometry (TDR) method and energy balance-water budget approach with eddy correlation at the two small semiarid watersheds of Lucky Hills and Kendall during the summer rainy period. There was a comparison of daily soil water content measured and estimated from these two different approaches. The comparison is valuable to evaluate the accuracy of current soil water content measuring system using TDR and energy balance-water budget approach using eddy correlation method at small watersheed scale. The degree of similarity between the regressions of these two methods of measuring soil water content was explained by determining the correlations between these methods. Simple linear regression analyses showed that soil water content measured from TDR method was responsible for 58% and 63% of the variations estimated from energy balance-water budget approach with eddy correlation at Lucky Hills and Kendall, respectively. The scatter plots and the regression analyses revealed that two different approaches for soil water content measurement at small watershed scale have no significant difference.

• Journal of Korea Water Resources Association
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• v.36 no.1
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• pp.117-128
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• 2003

The objectives of this study are to develop the total maximum daily loads simulation system, TOLOS that is capable of estimating annual nonpoint source pollution from small watersheds, to monitor the hydrology and water quality of the Balkan HP#6 watershed, and to validate TOLOS with the field data. TOLOS consists of three subsystems: the input data processor based on a geographic information system, the models, and the post processor. Land use pattern at the tested watershed was classified from the Landsat TM data using the artificial neutral network model that adopts an error back propagation algorithm. Paddy field components were added to SWAT model to simulate water balance at irrigated paddy blocks. SWAT model parameters were obtained from the GIS data base, and additional parameters calibrated with field data. TOLOS was then tested with ungauged conditions. The simulated runoff was reasonably good as compared with the observed data. And simulated water quality parameters appear to be reasonably comparable to the field data.

• Journal of Korean Society on Water Environment
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• v.20 no.3
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• pp.223-230
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• 2004

The QUAL2E and Box-Jenkins time series model were applied to the Miho river, a main tributary of the Geum river, to predict water quality. The models are widely used to predict water quality in rivers and watersheds because of its accuracy. As results of the study, we concluded as follows: Pollutant loadings in upper stream of Miho river were determined to 57,811 kgBOD/d, 19,350 kgTN/d, and 5,013 kgTP/d. The loading of TN in Mushim river was 19,450 kgTN/d, respectively. As the mass loadings were compared with pollutant sources, it concluded that the farming livestock contributed highly to mass emissions of BOD and TP and the population contributed to TN mass loading. The observed water quality values were applied to the models to verify and the models were used to predict the water quality. The QUAL2E Model predicted the concentrations of DO, BOD, TN and TP with high accuracy, but not for E-Coli. The Box-Jenkins time series model also showed high prediction for DO, BOD and TN. However, the concentrations of TP and E-Coli were poorly predicted. The result shows that the QUAL2E model is more applicable in Miho basin for prediction of water quality compared to Box-Jenkins time series model.

• Journal of Korean Society on Water Environment
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• v.32 no.2
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• pp.183-190
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• 2016

Monitored data (rainfall runoff and water quality) from 4 different paddy sites over 3 years were compared to analyze the effect of irrigation water management on irrigation supply and rainfall runoff quality in Korea. The system of rice intensification water management was adopted at one site (SRI) while the conventional water management method was used for rice culture at the other three sites (CT, SD and HD). The soil texture at SRI, CT and SD was sandy loam while that at HD was silt loam. The average reduction of irrigation supply at SRI compared with CT, SD and HD during the 3 years studied was 49%, 51% and 55%, respectively. The average event mean concentration (EMC) at SRI compared with that at CT, SD and HD was decreased by 35% (BOD), 44% (COD), 47% (SS), 19% (TN) and 38% (TP). The correlation between rainfall runoff and the measured non-point source (NPS) pollutants was very good in general. The comparison revealed that SRI water management significantly reduced both irrigation supply and EMC in rainfall runoff. Paddy NPS pollution was closely related to factors that induce runoff such as rainfall and irrigation supply. It was concluded that SRI management could be an effective and practical option to cope with both water shortage due to climate change and water quality improvement in rural watersheds. However, further studies are recommended in large irrigation districts for use in the development and implementation of NPS pollution policies since the data was collected from field sized paddies.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.17 no.3
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• pp.245-256
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• 1999

Watershed delineation is the process of tracing surface water flow across a landscape to identify hydrologic basins. Manual and automated techniques have been developed to trace surface waters and locate watersheds on a variety of landscape. Low topographic relief landscapes, however, are particulary problematic for automated watershed delineation techniques. Therefore, this study aims at focusing the watershed delineation algorithm of low topographic relief landscape. By using topogrid, which manages enforcement drainage algorithms and incorporates topographic data into stream data, this study delineates watershed boundary in low relief landscape. Based on this research, in a low topographic relief landscape, enforcement drainage algorithms using topogrid generate better source grid to delineate watershed boundary than using only TIN. Also, comparing automated watershed delineation which incorporates contours and elevations into stream data with manual watershed delineation, we can know that the incorporation of both elevation and stream data generate more effective results.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.123-133
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• 2009

In this study, we developed the GIS-based Geomorpho-hydrological Watershed Modeling System($G^{2}WMS$) which could consider both nonlilear rainfall-runoff relationship based on Geomorpho-Climatic Unit Hydrograph(GCUH) as well as watershed system inducing river routing. The developed new model was calibrated at the gaged rainfall events at natural watersheds and previewed to apply at the ungaged mountain basins, such as Sulma basin for small mountain basin and Andong-Dam basin for large scale basin, compared single with partitioned basin in the observed unit hydrographs and rainfall-discharge events. Finally, at the large scale Andong dam basin, we concluded that partitioned basin cases which including th nonlinear GCUH and river routing methods were superior to single basins which including the traditional methods in rainfall-discharge simulation at the mountain basins.

• Current Research on Agriculture and Life Sciences
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• v.5
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• pp.158-167
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• 1987

The purpose of this study is to inquire and analyse the relation between traveltime (Tc) and watetshed physical characteristics surveyed such as river length (L), Lea, river main slope (s), base length of time area diagram, and storage constant (k). The results obtained in this study are as follows. The average widths of watersheds were with the range from 4.6 kilometers to 16.7 kilometers. The shape factors of main stream ranged from 0.08 to 0.37. The average slopes to main 8tream were within the range of 1.7-5.5 meter per kilometer. The relation between the base length and traveltime from S. C. S. method, Rational method, and RZIHA+KRAVEN method were derived $Tc=0.524{\times}1.35^c$ (r=0.98), $Tc=0.628{\times}1.339^c$, (r=0.98), $Tc=0.667{\times}1.342^c$ (r=0.97). The base length of the time-area diagram (c) for the IUH was derived as $c=0.9(\frac{L.L_{ca}}{\sqrt{s}})^{0.35}$ and correlation coefficient was 0.98 which defined a high significance. The storage constant K, derived in this study was $K=8.32+0.0213{\frac{L}{\sqrt{s}}}$ with correlation coefficient (0.96). The relation between storage Constant and conventional formula were figured out $Tc=0.0003{\times}3.323^k$ (r=0.97). $Tc=0.00045{\times}3.268^k$ (r=0.99) and $Tc=0.0004{\times}3.26^k$ (r=0.963). The base length (c) and storage constant (k) of time-Area Diagram were very important parts that determined traveltime for flood events. In the estimate of travel time for predicting flood volume, the formula of $Tc=0.524{\times}1.35^c$ that would be available to apply the Nak - Dong river watershed area and homogeneous watershed characteristics was found.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.430-430
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• 2011

최근 지구온난화, 엘리뇨 및 라니냐 등 지구환경 변화에 따른 기후변화의 영향으로 짧은 시간에 매우 높은 강도를 가진 이상호우에 의해 많은 인명과 재산피해가 발생하고 있다. 우리나라의 경우에도 1990년대 후반부터 과거와 달리 국지적 집중호우가 빈번히 발생하고 있으며 집중호우에 의한 홍수는 우리나라의 가장 빈번한 자연재해 중 하나가 되었다. 이러한 성격의 홍수는 소유역 규모의 좁은 지역과 급경사지역에서 짧은 지속시간과 집중적인 강우강도에 의해 발생하고, 빠른 유속과 토사를 동반하는 빠른 수문반응으로 홍수에 대비할 시간이 부족한 것이 특징이기 때문에 기존의 홍수예보모형을 이용하여 발생홍수의 특성을 예측하기에는 많은 어려움이 있다. 유출수문곡선의 특성을 분석하여 홍수의 특성을 분석하는 연구는 Kyiamah (1996)가 유출수문곡선의 기초적인 상승곡선, 지체시간, 첨두홍수량을 이용하여 돌발홍수사상에 대한 크기를 산정하였으며, 이를 바탕으로 Bhaskar 등 (2000)은 유출수문곡선의 상승부 기울기, 첨두 홍수량비, 홍수 반응시간을 이용하여 돌발홍수지수(Flash Flood Index)를 산정하고 이 지수에 의해 돌발홍수를 설명하고자 하였다. 국내에서는 정재철 (2000)이 보청천을 대상으로 단 몇 개의 사상만을 대상으로 Bhaskar 등 (2000)이 제시한 돌발홍수지수를 적용한 바가 있다. 그러나, 이들 연구에서는 소수의 수문사상만을 이용하였기 때문에 상대심도를 산정하는데 있어 문제가 있으며 상대심도를 산정하는데 있어 각 심도계수들의 임의적인 도수분포를 이용하였기 때문에 매우 주관적이라고 할 수 있다. 김병식 등 (2008)은 한강유역의 과거 101개의 홍수사상에 대해 돌발홍수의 상대심도를 파악하기 위하여 돌발홍수지수를 산정하고 2006년 7월의 집중호우에 의해 발행한 홍수사상의 돌발홍수 심도를 시간 및 공간적으로 정량화하였다. 이러한 기존의 연구는 홍수심도 산정시에 필요한 유출수문곡선을 실측된 자료를 이용하여 산정하였으나 국내의 소유역의 경우 실측된 유출수문곡선 자료가 그다지 많지 않은 관계로 인해 홍수심도를 산정하는데 많은 어려움을 내포하고 있다. 따라서 본 연구에서는 미계측 소유역중 시범유역을 선정하고 30년 이상 장기간 실측 강우의 기왕최대 시강우량 자료에 대하여 강우-유출모형을 통한 홍수유출수문곡선을 모의한 후, 빈도별 확률강우량에 대한 수문곡선 특성인자들의 비를 무차원 지수화하여 극한홍수사상에 대한 설계강우의 취약성을 평가하기 위한 홍수위험지수 (Flood Hazard Index) 산정방법을 제시하였다.

• Korean Journal of Remote Sensing
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• v.23 no.2
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• pp.119-124
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• 2007

The few observed data related snowmelt was the major cause of difficulty in extracting snowmelt factors such as snow cover area, snow depth and depletion curve. Remote sensing technology is very effective to observe a wide area. Although many researchers have used remote sensing for snow observation, there were a few discussions on the characteristics of spatial and temporal variation. Snow cover maps were derived from NOAA AVHRR images for the winter seasons from 1997 to 2006. Distributed snow depth was mapped by overlapping between snow cover maps and interpolated snowfall maps from 69 meteorological observation stations. Model parameters (Snow Cover Area: SCA, snow depth, Snow cover Depletion Curve: SDC) building for 5 major watersheds in South Korea. Especially SDC is important parameter of snowmelt model.

• 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.