• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.271-276
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• 2009

Under current design standard, sewers are designed to drain stormwater generated up to 10 year return period of storms. This implies sewer flooding could occur from rainfall exceeding a 10 year return period. 5, 10, 20 and 30 year return period of storm intensities were calculated for 22 locations (cities) of meterological stations over the nation and compared to the recorded rainfall intensities for the last 30 years. The comparison resulted in the numbers of year maximum rainfall intensities exceeded each return period. Using the questionnaire survey for "the incidences of flooding since 1980" of the previous paper (Survey on sewerage operation/management planning for flooding (I)), the actual rainfall records on the date of flooding events were analyzed to demonstrate the number of flooding events caused by the exceedance of sewer capacity. For the last 30 years, more than 6 years of year maximum rainfall intensity (20%) were larger than the 10 year return period of storm in 4 cities of the 22 used for the first analysis. The number of rainfall records that exceeded the 10 year return period was 50 of the 260 actual flooding events investigated from the survey.

• Membrane and Water Treatment
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• v.10 no.1
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• pp.45-55
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• 2019

Climate change has significantly affected the rainfall characteristics which can influence the pollutant build-up and wash-off patterns from the catchment. Therefore, this study explored the influence of varying rainfall characteristics on urban and agricultural runoff pollutant export using statistical approaches. For this purpose, Mann-Kendall and Pettitt's test were applied to detect the trend and breakpoint in rainfall characteristics time series. In addition, double mass curve and correlation analysis were used to drive the relationship between rainfall-runoff and pollutant exports from both catchments. The results indicate a significant decreased in total rainfall and average rainfall intensity, while a significant increased trend for antecedents dry days and total storm duration over the study periods. The breakpoint was determined to be 2013 which shows remarkable trend shifts for total rainfall, average rainfall intensity and antecedents dry days except total duration. Double mass curve exhibited a straight line with significant rainfall-runoff relationship indicates a climate change effect on both sites. Overall, higher pollutant exports were observed at both sites during the baseline period as compared to change periods. In agricultural site, most of the pollutants exhibited significant (p< 0.05) association with total rainfall, average rainfall intensity and total storm duration. In contrast, pollutants from urban site significantly correlated with antecedent dry days and average rainfall intensity. Thus, total rainfall, average rainfall intensity and total duration were the significant factors for the agricultural catchment while, antecedents dry days and average rainfall intensity were key factors in build-up and wash-off from the urban catchment.

• Water for future
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• v.22 no.2
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• pp.201-211
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• 1989

Using the storm data which was augmented by the stochastic correlation with it's neighbors, the multiquadric equation of random surface of total storm depth is constructed. And to separate the local components from it's regionals and find the regional characteristics, a double Fourier analysis was applied to the total depths of storm data. The local components, storm residuals of each storm was assumed to be homogeneous random field and investigated with it's autocorrelation function. For the practical application, isotropic was assumed and that was identified with emprical data. Coefficients of normalized autocorrelation for all storms showed similar apperance. Using this emprical result, an example of the radial spectral distribution function which represints the spatial characteristics of rainfall over Han River Basin during 1975-1983 is presented.

• Journal of the Korean Geographical Society
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• v.33 no.3
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• pp.395-409
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• 1998

The purpose of this paper is to determine the atmospheric conditions in whih urban areas affect the precipitation processes and to evaluate whether certain weather types show more apparent urban effect on precipitation modification over five cities in the southem United States. Each heavy rainstorm is classified into one of three synoptic weather types (frontal storm, airmass storm or tropical disturbance storm). Heavy rainstorm day is defined as day producing rainfall totals that equal o exceed 2 inches (50.08 mm). Houston, Dallass and San Antonio show possible urban effects on rainfall totals and frequencies of heavy rainstorms by airmass storm type while New Orleans and Memphis do not reveal any distinct precipitation enhancements through the synoptic analysis. The results of TSA (Trend Surface Analysis) show that frontal and tropical disturbance storm types have stronger climatic gradients than airmass types and the patterns of rainfall totals have stronger trends than those of rainfall frequencies for the five cities. The results suggest that airmass type events may well reveal possible precipitation enhancements due to urban effects since they are less influenced by a strong climate gradient and they provide favorable conditions for development of urban heat islands. Residual analysis confirms that rainfall totals and frequencies of heavy rainstorms by airmass storm type have positive residuals over the city or the major effect area.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.3
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• pp.58-68
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• 1988

Most of the Korean watersheds are mountaineous and consist of various soil types and land uses And seldom watersheds are found to have long term hydrologic records. The SNUA, a hydrologic watershed model was developed to meet the unique characteristics of Korean watershed and simulate the storm hydrographs from a small mountaineous watershed. Also the applicability of the model was tested by comparing the simulated storm hydrographs and the observed from Dochuk watershed, Gwangjugun, Kyunggido The conclusions obtained in this study could be summarized as follows ; 1. The model includes the simulation of interception, evaporation and infiltration for land surface hydrologic cycle on the single storm basis and the flow routing features for both overland and channel systems. 2. Net rainfall is estimated from the continuous computation of water balance at the surface of interception storage accounting for the rainfall intensities and the evaporation losses at each time step. 3. Excess rainfall is calculated by the abstraction of infiltration loss estimated by the Green and Ainpt Model from the net rainfall. 4. A momentum equation in the form of kinematic wave representation is solved by the finite differential method to obtain the runoff rate at the exit of the watershed. 5. The developed SNUA Model is a type of distributed and event model that considers the spatial distribution of the watershed parameters and simulates the hydrograph on a single storm basis. 6. The results of verification test show that the simulated peak flows agree with the observed in the occurence time but have relative enors in the range of 5.4-40.6% in various flow rates and also show that the simulated total runoff have 6.9-32% of relative errors against the observed. 7. To improve the applicability of the model, it was thought that more studies like the application test to the other watersheds of various types or the addition of the other hydrologk components describing subsurface storages are needed.

• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.563-571
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• 2017

Because of the rapid progress of urbanization in recent decades, the proportion of impervious areas in cities has increased. As a result, hydrological properties of urban streams have changed and non-point pollution sources have increased, that have had considerable influence on human life and ecosystems. To manage these situations, application of non-point pollution reduction facilities and LID facilities are expanding recently. In this study, it is investigated if rainfall interception rate used in design of non-point pollution reduction facilities can be applied to design of LID facilities. For this purpose, EPA SWMM is constructed for part of Noksan National Industrial Complex area wherein long-term observed storm water data can be obtained and storm water interception rates for various design capacities of a bio-retention LID facility reservoirs are estimated. While sensitivity of storm water interception rate according to design specifications of bio-retention facility is not large, sensitivity of storm water interception rate according to regional rainfall characteristics is relatively large. As a result of comparing present rainfall interception rate estimation method with the one proposed in this study, the present method is highly likely to overestimate performance of the bio-retention facility. Finally, a new storm water interception rate formula for bio-retention LID facility is proposed.

• Journal of Environmental Impact Assessment
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• v.24 no.2
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• pp.163-174
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• 2015

Urbanization caused various environmental problems like destruction of natural water cycle and increased urban flood. To solve these problems, LID(Low Impact Development) deserves attention. The main objective of LID is to restore the water circulation to the state before the development. In the previous studies about the LID, the runoff reduction effect is mainly discussed and the effects of each techniques of LID depending on rainfall types have not fully investigated. The objective of this research is to evaluate the effect of LID using the quantitative simulation of rainwater runoff as well as an amount of infiltration according to the rainfall and LID techniques. To evaluate the water circulation of LID on the development area, new land development areas of Hanam in South Korea is decided as the study site. In this research, hydrological model named STORM is used for the simulation of water balance associated with LID. Rainfall types are separated into two categories based on the rainfall intensity. And simulated LID techniques are green roof, permeable pavement and swale. Results of this research indicate that LID is effective on improvement of water balance in case of the low intensity rainfall event rather than the extreme event. The most effective LID technique is permeable pavement in case of the low intensity rainfall event and swale is effective in case of the high intensity rainfall event. The results of this study could be used as a reference when the spatial plan is made considering the water circulation.

• Journal of Wetlands Research
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• v.11 no.2
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• pp.67-76
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• 2009

The contribution of pollutant loadings from non-point source (NPS) to the four major rivers in Korea exceeded 22~37 % of the total loadings in 2004 and is expected to reach 60 % in 2020. Most of NPS loadings are coming from urban areas, especially from paved areas. Because of high imperviousness rate, many types of NPS pollutant are accumulating on the surface during dry periods. The accumulated pollutants are wash-off during a storm and highly degrading the water quality of receiving water bodies. For this reason, the Korean Ministry of Environment (MOE) developed the Total Maximum Daily Load (TMDL) program to protect the water quality by managing the point source and NPS loadings. NPS has high uncertainties during a storm because of the characteristics of rainfall and watershed areas. The rainfall characteristics can affect on event mean concentrations (EMCs), mass loadings, flow rate, etc. Therefore, this research was performed to determine EMCs for rainfall ranges from transportation landuses such as road and parking lot. Two sites were monitored over 45 storm events during the 2006/06 through 2008/10 storm seasons. Mean TSS EMCs decrease as rainfall ranges increase and highest at less than 10mm rainfall. The results of this study can be used to determine the efficient scale of BMP facility considering specific rainfall range.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.3
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• pp.65-72
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• 2002

Rainfall and runoff data from a forested watershed and irrigated rice paddies at the Bal-an experimental watershed were monitored and analyzed to investigate the variations of runoff characteristics with different land use. The comparisons were conducted fourteen storm events ranging 21.8∼190.2 mm of rainfall. Field data showed that direct runoff from paddies and forested watershed are not significantly different in volume. The peak discharge from forest watershed was less than that from paddies far lighter storms, but became greater fur heavier storms. The peak runoff from the forest watershed was 39 percent greater than from the paddies. The results demonstrate that paddies play an important role to reduce peak discharge from heavy storms as compared to forest.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.109-116
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• 1991

In recent years, hydrologists have been interested in the radial spectrum and its estimation in two dimensional storm field to construct simulation model of the rainfall. This paper deals with the problem of transformation from the spectrum or isotropic covariance function to two dimensional random field. The extended turning band method for the generation of random field is applied to the problem using the line generation method of one dimensional stochastic process by G.Matheron. Examples of this generation is chosen in the random components of the multidimensional rainfall model suggested by Bras and are given with a comparison between theoretical and sample statistics. In this numerical experiments it is observed that first and second order statistics can be conserved. Also the example of moving storm simulation through Bras model is presented with the appropriate parameters and sample size.