• Journal of Korean Society of Environmental Engineers
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• v.35 no.11
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• pp.795-802
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• 2013

According to the increase of impervious area due to the town development, the rate of infiltration generally lessens and that of runoff rises during wet weather events. And it is concerned that its impacts on water quality for the downstream water bodies due to the change of rainfall runoff patterns may also increase. To cope with these issues, LID (Low Impact Development) techniques which try to maintain the characteristics of rainfall runoff regardless of the town development have been introduced actively. However, the behaviors of each LID technique for rainfall runoff and pollutant loads is not understood sufficiently. In this study, considering the applications of some LID techniques, several sets of simulations using a distributed rainfall runoff model, SWMM-LID, have been conducted for D town whose development is progressing. As the results of the simulations, the rates of infiltration/storage have been decreased from 78% in the case before the town development to 15% after the development and increased again by 24% with LID techniques such as porous pavement, rain barrel and rain garden. The rates of runoff have been increased more than three times from 20% in the case before the development to 74% after the development, and they have also been decreased to 66% by the adoption of LID techniques. It has been simulated that porous pavement is more effective than others in the view point of the reduction of runoff and rain barrel is more attractive for the management of pollutant loads (TSS, BOD, COD, T-N and T-P). Therefore, if some LID techniques should be selected for the a new town, it could be concluded that some techniques with better infiltration functions are recommendable for the control of runoff, and ones with larger storage functions for the management of pollutant loads.

• Water for future
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• v.28 no.3
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• pp.159-173
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• 1995

This study is to develop the suitable hydrologic models for determination of the size and location of detention storage facilities to restrain stormwater runoff in urban areas. Fictitious areas of two levels are considered to seize the hydrologic response characteristics. A one-square-kilometer area is selected for the catchment level, and a 10-square-kilometer area consisting of 10 catchments is adapted at the watershed level as representative of urban drainage area. In this analysis, different rainfall frequencies, land uses, drainage patterns, basin shapes and detention storage policies are considered. Flow reduction effect of detention storage facilities is deduced from storage ratio and detention basin factor. A substantial saving in detention storage volumes is achieved when the detention storage is planned at the watershed level than the catchment level. For the application of real watersheds, two watersheds in Seoul metropolitan area-Jamshil 2, Seongnae 1-are selected on the basis of hydrologic response characteristics. Through the regression analysis between dimensionless detention storage volume, dimensionless upstream area ratio and reduction rate of storage ratio, the regression equations to determine the size and location of detention storage facilities are presented.

• Journal of Korea Water Resources Association
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• v.47 no.7
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• pp.615-628
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• 2014

The objectives of this study are to estimate the annual and monthly actual evapotranspiration for the Bokhacheon upper-middle watershed using the data from 1996 to 2012 simulated by SWAT-K model, and to evaluate the effect of storage change on the actual evapotranspiration based on water balance estimates. The simulated results of the annual actual evapotranspiration showed the range from 401 mm to 494 mm and the annual mean of 436 mm, about 31% of the annual mean of precipitation. The average monthly estimates of the actual evapotranspiration showed the range of 10 mm/month in Dec to 84 mm/month in Jul. From the analyses of annual mean storage changes according to data length, it was found out that more than four to five years of data of precipitation and runoff are needed to estimate the watershed based actual evapotranspiration with ignorance of the storage change for this study area. Furthermore, annual and monthly relations between the storage change and the difference of precipitation and runoff were derived which can be effectively used for estimating actual evapotranspiration based on water balance analysis.

• Water for future
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• v.26 no.1
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• pp.115-124
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• 1993

This study is to determine the critical duration of design rainfall and to utilize it for the design of detention pond with pump station. To examine the effect of the duration and temporal distribution of the design rainfall, Huff's quartile method is used for the 9 cases of durations ranging from 20 to 240 minutes with 10 years return period, and the ILLUDAS model is used for runoff analysis. The storage ration which is the ratio of maximum storage amounts to total runoff volume, is introduced to determine the critical duration of design rainfall. The duration which maximizes the storage ratio is adopted as the critical duration. This study is applied to 18 urban drainage watersheds with pump station in Seoul, of which the range of watershed area is $0.24-12.70\textrm{km}^2.$ The result of simulation shows that the duration which maximizes storage ration is 30 and 60 minutes on the whole. It is shown also that the storage ration of 2nd- and 3rd-quartile pattern is larger than that of 1st- and 4th-quartile pattern of temporal distribution. A simplified empirical formula for Seoul area is suggested by using the regression analysis between the maximum storage ration and the peak ratio, and can be utilized for the preliminary design and planning of detention pond with pump station.

• Journal of Wetlands Research
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• v.18 no.2
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• pp.121-131
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• 2016

The determination of feasible design flood is the most important to control flood damage in river management. Concentration time and storage constant in the Clark unit hydrograph method mainly affects magnitude of peak flood and shape of hydrograph. Model parameters should be calibrated using observed discharge but due to deficiency of observed data the parameters have been adopted by empirical formula. This study is to suggest concentration time and storage constant based on the observed rainfall-runoff data at GongDo stage station in the Ansung river basin. To do this, five criteria have been suggested to compute root mean square error(RMSE) and residual of oserved value and computed one. Once concentration time and storage constant have been determined from three rainfall-runoff event selected at the station, the five criteria based on observed hydrograph and computed hydrograph by the Clark model have been computed to determine the value of concentration time and storage constant. A criteria has been proposed to determine concentration time and storage constant based on the results of the observed hydrograph and the Clark model. It has also been shown that an exponent value of concentration time-cumulative area curve should be determined based on the shape of watershed.

• Journal of Korea Water Resources Association
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• v.46 no.1
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• pp.73-85
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• 2013

The researches on the parameter estimation for storage function method have been conducted for a long time using different methods. However, the determination of the optimal parameters takes a long time and there is a controversy that the proposed optimal parameters do not likely represent the physical characteristics of watershed. In this study, the characteristics of the continuity and storage function equation was analyzed and sensitivities were evaluated. As the result, the only optimal solution is suggested among several local optimums. It is also shown that the lag time is able to be determined using the direct runoff starting time of the watershed. From the sensitivity analysis, it is also proved that the determination of the lag time is very important and the only optimal solution could be found easily after selecting the lag time. Therefore, unlike the traditional optimization method, the proposed method does not take a long time to find the optimal solution which is depending on the characteristics of the rainfall events. The fixed coefficient method which is a method to estimate the optimal parameters of storage function method has been modified using the proposed method. Therefore, the practical efficiency to apply storage function method could be enhanced by applying the proposed method. While the traditional method takes care only the error of the runoff hydrograph, it is very important that the proposed method considers the characteristics of the watershed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.859-866
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• 1994

It is difficult to make an exact estimate of the peak discharge or the runoff depth of flood and establish the proper measure for the flood protection since the water stage or discharge has been nearly measured at most medium or small river basins. The objective of this study is to estimate parameters of the discrete, linear, input-output model for medium or small river basin. The On-Cheon River basin in Pusan was selected for the study area. The runoff data used in the study has been observed since June 1993, and the effective rainfall was determined using the storage function method. The parameter sets of the discrete, linear, input-output model were estimated using the least squares method and the correlation function method, respectively. The calculated hydrographs by the discrete, linear, input-output model regenerated the observed outflow hydrographs well, and also the simulated flood hydrograph was comparable to the observed one. Therefore, it is believed that the discrete, linear, input-output model is simpler than other runoff analysis methods, and can be applied to a medium or small river basin.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.434-442
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• 2019

Low Impact Development(LID) techniques has been attracting attention as a countermeasure to solve frequent flood damage in urban areas. LID is a techniques for returning to the natural hydrological cycle system by infiltrating the runoff from the impervious surface into the soil. The Bio-retention, one of the LID element technology has outflow reduction effect by reserving and infiltrating storm water runoff from watersheds. Recently, a number of studies have been carried out as interest in the reduction of storm water runoff and non-point pollutants in Bio-retention has increased. However, quantitative analysis on the outflow reduction of Bio-retention applied to small watershed is insufficient. In this study, Bio-retention model was constructed in a small watershed using K-LIDM which is capable of hydrologic analysis. When the storage capacity was increased or dividing the Bio-retention and watershed, the outflow reduction effect was 20% according to the storage capacity increase and 5~15% in the distributed Bio-retention system. The results of this analysis will be used as the basic data of future Bio-retention research related to watershed characteristics, vegetation type and soil condition.

• Current Research on Agriculture and Life Sciences
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• v.17
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• pp.31-38
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• 1999

Trend of some hydrologic features such as precipitation, runoff and reservoir storage rates in the five great river systems of Han, Nakdong, Keum, Yeongsan and Seomjin river watershed areas were surveyed and analysed. The sample period of Sept. 1994 to Aug. 1998 (four years) was chracterized by unusual climatic features such as El Nino, La Nina and areal terrible storms. And also average values of rainfall and runoff of the priod of 1961 to 1990 (30 years) were surveyed and analysed compared with the sample preiod events for the same river systems. In case of the monthly mean rainfall of the sample period (Sept. 1994 to Aug. 1998 : 48 months) in the five great river systems, 20 months, 19 months, 20 months, 21 months and 18 months in the Han, Nakdong, Keum, Yeongsan and Seomjin river system respectively were higher than monthly average rainfall records of the 30 year records. For the monthly runoff in the same river systems, 7 months, 9 months, 7 months, 11 months and 11 month in the Han, Nakdong, Keum, Yeongsan and Seomjin river systems respectively were higher than the monthly average runoff of the period of 30 years. For the storage rates, most of the dams in the Han river systems were highly stored through the year continuously and Paldang dam was specially higher than the other dams in the same river system. And most of the dams in the other river systems were stored irregularly but getting much better than early time during the 48 months. And special climatic features were not found during the sample period of 48 months, Sept. 1994 to Aug. 1998.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.127-137
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• 1992

For the real-time control of a multi-purpose reservoir in case of a storm, it is absolutely necessary to forecast accurate flood inflows through a good rainfall-runoff model by calibrating the parameters with the on-line rainfall and water level data transmitted by the telemetering systems. To calibrate the parameters of a runoff model. the trial and error method of manual calibration has been adopted from the subjective view point of a model user. The object of this study is to develop a automatic calibration method using an optimization technique. The pattern-search algorithm was applied as an optimization technique because of the stability of the solution under various conditions. The object function was selected as the sum of the squares of differences between observed and fitted ordinates of the hydrograph. Two historical flood events were applied to verify the developed technique for the automatic calibration of the parameters of the storage-function rainfall-runoff model which has been used for the flood control of the Soyanggang multi-purpose reservoir by the Korea Water Resources Corporation. The developed method was verified to be much more suitable than the manual method in flood forecasting and real-time reservoir controlling because it saves calibration time and efforts in addition to the better flood forecasting capability.