• Journal of Korea Water Resources Association
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• v.51 no.3
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• pp.263-272
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• 2018

For the design of hydraulic structures, the design flood discharge corresponding to a specific frequency is generally used by using the design storm calculated according to the rainfall-runoff relationship. In the past, empirical equations such as rational equations were used to calculate the peak flow rate. However, as the duration of rainfall is prolonged, the outflow patterns are different from the actual events, so the accuracy of the temporal distribution of the probability rainfall becomes important. In the present work, Huff's quartile method is used for the temporal distribution of rainfall, and the third quartile is generally used. The regression equation for Huff's quadratic curve applies a sixth order polynomial equation because of its high accuracy throughout the duration of rainfall. However, in statistical modeling, the regression equation needs to be concise in accordance with the principle of simplicity, and it is necessary to determine the regression coefficient based on the statistical significance level. Therefore, in this study, the statistical significance test for regression equation for temporal distribution of the Huff's quartile method, which is used as the temporal distribution method of design rainfall, is conducted for 69 rainfall observation stations under the jurisdiction of the Korea Meteorological Administration. It is statistically significant that the regression equation of the Huff's quartile method can be considered only up to the 4th order polynomial equation, as the regression coefficient is significant in most of the 69 rainfall observation stations.

• Journal of Industrial Technology
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• v.25 no.B
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• pp.27-35
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• 2005

Non-point source pollution, which is found in soil, urban area, and agricultural area, is difficult to have its amount to be estimated. Moreover, it is hard to come up with a counterplan to cope with this pollutant. Hence, the watershed of Mandae-cheon located at the upstream of Soyang Lake was chosen as our site of study. We analyzed the relationship between precipitation level of each month and pollution load in the watershed by using statistical methods: measuring BOD, T-N and T-P - which are the causes of eutrophication - in the water; and analyzing the changes in water quality caused by precipitation level of nth.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.509-512
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• 2001

In this study, pollutant load from paddy field was estimated by regression equation from 5 to 8 in 2001. During study period, total rainfall was 511.3mm and runoff discharge was 968.71mm. Regression equation between flow rate(m3/s) and pollutant loading rate(g/s) is exponential relationship. For site 1, coefficient of determination (R2) for $COD_{cr}$, T-P, T-N were 0.7068, 0.8441, 0.6806 respectively and site 2, 0.9369, 0.8855, 0.4262 respectively. Considering unit loads, Jun was the highest valus as 13.85 $COD_{c}kg/km2/day$, 0.24 T-Pkg/km2/day, 1.22 T-Nkg/km2/day. Until study period, total $COD_{cr}$ load estimated regression equation is 19.32kg/km2/day and, T-P, T-N were 0.264, 1.88 respectively

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.2095-2099
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• 2008

본 연구에서는 충분히 보정되고 검증되어진 SWAT-K 모형으로부터 생성된 자료를 이용하여 강우-유출-유사 사이의 상호 관계를 도출해 보았다. 소양댐 상류유역을 대상으로 유역내 각 지점별 강우에 따른 유출 및 유사, 유출과 유사의 상호 관계 등을 도시하여 검토한 결과, 약 40 mm 이하의 강우에 대해서는 유사 발생이 많지 않음을 알 수 있었으며, 그 이상의 강우에 대해서 강우와 유사 사이에 이차원 관계의 회귀식을 유도할 수 있었다. 또한, 유출과 유사 사이에도 거듭제곱 형태의 관계식을 유도할 수 있었으며 그에 따른 결정 계수도 높게 나타나 상호간의 회귀식이 매우 상관성이 높음을 알 수 있었다. 이와 같은 관계로부터 향후 복잡한 모형을 이용하지 않아도 대상유역의 특정 지역에 대해 강우로부터 유출이나 유사를 추정하는데 비교적 간편하고 신뢰성 있게 적용될 수 있을 것으로 판단된다.

• Magazine of the Korean Society of Agricultural Engineers
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• v.8 no.1
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• pp.1011-1034
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• 1966

This thesis is the final report which has long been studied by the author to obtain the design basis for various hydrological constructions with the specific system suitable to the natural environmental conditions in Korea. This report is divided into two parts: one is to estimate runoff volume from watersheds and the other to estimate the peak discharge for a single storm. According to the result of observed runoff record from watersheds, it is known that Kajiyama formula is useful instrument in estimating runoff volume from watersheds in this country. But it has been found that this formula shows us 20-30% less than the actual flow. Therefore, when wihed to bring a better result, the watershed characteristics coefficient in this formula, that is, f-value, should be corrected to 0.5-0.8. As for the method to estimate peak discharge from drainage basin, the author proposes to classify it in two ways; one is small size watershed and the other large size watershed. The maximum -flood discharge rate $Q_p$ and time to peak Pt obtained from the observed record on the small size watershed are compared by various methods and formulas which are based upon the modern hydrological knowledge. But it was fou.d that it. was not a satisfied result. Therefore, the author proposes. tocomputate $Q_p$, to present 4.0-5.0% for the total runoff volume ${\Sigma}Q$.${\Sigma}Q$ is computed under the assumption of 30mm 103s in watershed per day and to change the theoritical total flow volume to one hour dura tion total flow rate when design daily storm is given. Time to peak Pt is derived from three parameters which are u,w,k. These are computed by relationship between total runoff volume (ha-m unit)and $Q_p$. (C.M.S. unit). Finally, the author checked out these results obtained from 51 hydrographs and got a satisfied result. Therefore the author suggested the model of design dimensionless unit-hydrograph. And the author believes that this model will be much available at none runoff record river site. In the large size watersheds in Korea when the maximum discharge occurs, the effective rainfall is two consequtive stormy days. So the loss in watershed was assutned as 6Omm/2days,and the author proposed 3-hour-daration hydrograph flow distribution percentage. This distribution percentage will be sure to form the hydrograph coordinate.

• Journal of Korean Society on Water Environment
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• v.28 no.2
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• pp.255-268
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• 2012

Nonpoint source pollution has become a concern for water quality in the Han River system, especially during the high runoff events during the monsoon season. The patterns in nonpoint source runoff the relationships with land use, rainfall intensity, and stream nutrients concentrations were surveyed in 19 streams in the Han River watershed. The results show that the magnitude of NPS inputs of nutrients and sediment in the Han River watershed are of a serious concern. In the South Han River watershed, event mean concentrations (EMC) for biochemical oxygen demand (BOD), suspended sediment (SS), dissolved organic carbon (DOC), dissolved total phosphorus (DTP), total nitrogen (TN) Nitrate ($NO_3$-N) and total phosphorus (TP) were $1.94mg{\cdot}L^{-1},\;251mg{\cdot}L^{-1},\;2.75mg{\cdot}L^{-1},\;0.076mg{\cdot}L^{-1},\;2.82mg{\cdot}L^{-1},\;2.40mg{\cdot}L^{-1}$ and $0.232mg{\cdot}L^{-1}$, respectively. In the North Han River watershed, EMCs for BOD, SS, DOC, DTP, TN, $NO_3$-N and TP were $1.34mg{\cdot}L^{-1},\;172mg{\cdot}L^{-1},\;2.63mg{\cdot}L^{-1},\;0.032mg{\cdot}L^{-1},\;1.97mg{\cdot}L^{-1},\;1.55mg{\cdot}L^{-1}$ and $0.148mg{\cdot}L^{-1}$, respectively. The specific export coefficients of nutrient and sediments were much higher than those of other reports. Our study also found that the proportion of agricultural field area was significantly correlated with the EMCs for nutrients. Therefore, efforts to reduce NPS loading must focus on agricultural practices in the watershed. The relationships between land use and nutrient and sediment export found in this study can be used to derive estimates of runoff coefficients for agricultural field and as input data for modeling works and to develop total maximum daily load and best management practices in the Han River watershed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1171-1180
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• 2014

The NRCS-CN method is generally used to estimate effective rainfalls in a basin. However, since the curve number which plays a critical role in the NRCS-CN method was originally developed for US watersheds, it is limited to be directly applied to other basins outside the United States. Therefore various modifications have been suggested to revise the NRCS-CN for specific watershed condition. This study introduced the weighted average method and the slope-based CN to estimate effective rainfalls available for Korean watersheds and compared with the observed direct runoff. The overall results achieved from this study indicated that the adjusted slope-based CN considerably increases effective rainfalls in general and makes the duration of effective storm longer. Based on the statistical error analysis performed for various modifications of NRCS-CN, the weighted average method with the adjusted slope-based CN has highest precision with the observed direct runoff. In addition, after analyzing the relation between the initial loss estimated from rainfall-runoff observations and the potential maximum retention from GIS-based data, it turns out that the assumption of linear relationship between the initial loss and the potential maximum retention is not available for Korean watersheds.

• Ecology and Resilient Infrastructure
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• v.3 no.1
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• pp.35-45
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• 2016

The correlation relationships and their corresponding equations between the geomorphological parameters and the Soil Water Assessment Tool (SWAT) model parameters by Sequential Uncertainty Fitting - version 2 (SUFI-2) algorithm of SWAT Calibration and Uncertainty Programs (SWAT-CUP) were developed at the Seom-river experimental watershed. The parameters of the SWAT model at the Soksa-river experimental watershed were estimated by the developed equations. The SWAT model parameters were estimated by SUFI-2 algorithm of SWAT-CUP with rainfall-runoff data from the Soksa-river experimental watershed from 2000 to 2007. Rainfall-runoff simulation of the SWAT model was carried out at the Soksa-river experimental watershed from 2000 to 2007 for the applicability of the estimated parameters by the developed equations. The root mean square errors (RMSE) between the observed and the simulated rainfall-runoffs using the estimated parameters by developed equations of correlation analysis and the optimum parameters by SUFI-2 of SWAT-CUP were $1.09m^3/s$ and $0.93m^3/s$ respectively at the Soksa-river experimental watershed from 2000 to 2007. Therefore, it is considered that the parameter estimation of the SWAT model by the geomorphological characteristics parameters has applicability.

• Journal of Korea Water Resources Association
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• v.55 no.5
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• pp.333-343
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• 2022

For water resource management, the design flood is calculated using the flood frequency analysis technique and the rainfall runoff model. The method by design flood frequency analysis calculates the stochastic design flood by directly analyzing the actual discharge data and is theoretically evaluated as the most accurate method. Actual discharge data frequency analysis of the measured flow was limited due to data limitations in the existing flood flow analysis. In this study, design flood frequency analysis was performed using the measured flow data stably secured through the water level-discharge relationship curve formula. For the frequency analysis of design flood, the parameters were calculated by applying the bayesian inference, and the uncertainty of flood volume by frequency was quantified. It was confirmed that the result of calculating the design flood was close to that calculated by the rainfall-runoff model by applying long-term rainfall data. It is judged that hydrological analysis can be done from various perspectives by using long-term actual flow data through hydrological survey.

• Water for future
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• v.9 no.2
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• pp.87-100
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• 1976

These studies are aimed at the analysis of systematic variation pattern of water resources in Korean river catchments and the development of their simulation models from the stochastic analysis of monthly and annual hydrologic data as main elements of water resources, i.e. rainfall and streamflow. In the analysis, monthly & annual rainfall records in Soul, Taegu, Pusan and Kwangju and streamflow records at the main gauging stations in Han, Nakdong and Geum river were used. Firstly, the systematic variation pattern of annual streamflow was found by the exponential function relationship between their standard deviations and mean values of log-annual runoff. Secondly, stochastic characteristics of annual rainfall & streamflow series were studied by the correlogram Monte Carlo method and a single season model of 1st-order Markov type were applied and compared in the simulation of annual hydrologic series. In the simulation, single season model of Markov type showed better results than LN-model and the simulated data were fit well with historical data. But it was noticed that LN-model gave quite better results in the simulation of annual rainfall. Thirdly, stochastic characteristics of monthly rainfall & streamflow series were also studied by the correlogram and spectrum analysis, and then the Model-C, which was developed and applied for the synthesis of monthly perennial streamflow by lst author and is a Markov type model with transformed skewed random number, was used in the simulation of monthly hydrologic series. In the simulation, it was proved that Model-C was fit well for extended area in Korea and also applicable for menthly rainfall as well as monthly streamflow.