• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.4
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• pp.89-93
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• 2010

It is well known that the drastic change of hydrological characteristics of an urbanized basin causes severe runoff, sediment yield, and peak flow. High vulnerability of urban flood disasters is caused by land-use change and development of a basin. A typical site suffering urbanization was selected and the experimental site has being operated last three years. Hydrological and hydraulic characteristics of the urbanizing basin were examined by observation of runoff, sediment loads and precipitation with T/M. The effects of land-use change were analyzed by examination of the hydrological characteristics, such as run-off ratio (runoff volume/rainfall volume), sediment yields. Runoff coefficient of rational equation was increased as basin was urbanized. Suspended sediment yields due to a urban development activities were raised almost 10 times compare to undisturbed condition for small runoff less than 1 cms. Meanwhile, no big change could be detected for bed loads.

• Journal of Wetlands Research
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• v.21 no.3
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• pp.191-198
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• 2019

High impervious surfaces increase the surface runoff during rainfall and reduces the underground infiltration thereby leading to water cycle distortion. The distortion of water cycle causes various urban environmental problems such as urban flooding, drought, water pollutant due to non-point pollution runoff, and water ecosystem damage. Climate change intensified seasonal biases in urban rainfall and affected urban microclimate, thereby increasing the intensity and frequency of urban floods and droughts. Low impact development(LID) technology has been applied to various purposes as a technique to reduce urban environmental problems caused by water by restoring the natural water cycle in the city. This study evaluated the contribution of hydrologic characteristics and water cycle recovery after LID application using long-term monitoring results of various LID technology applied in urban areas. Based on the results, the high retention and infiltration rate of the LID facility was found to contribute significantly to peak flow reduction and runoff delay during rainfall. The average runoff reduction effect was more than 60% at the LID facility. The surface area of the LID facility area ratio(SA/CA) was evaluated as an important factor affecting peak flow reduction and runoff delay effect.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.1
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• pp.97-109
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• 2004

The disposal of stormwater is one of the major problems in urban water management. One method of reducing peak runoff rates and other detrimental impacts of stormwater is detention storage. Detention ponds as a water quality control alternatives have been investigated by a number of researchers. Recognizing multiple roles such as flood peak attenuation, pollution removal and aesthetic enhancement, the design and management of detentions ponds deserve more research. The purpose of this research is to establish design criteria wet detention ponds to improve water quality. Water quality in detention pond discharge might be improve with physical, chemical and biological alterations. Physical alteration was focused in this study. There are several methods for estimating the suspended solid control capability of wet detention ponds. Existing models of suspended solids removal are based on sedimentation and gravity settling theory. The pollutant trap efficiency of pond is a function of several interrelating factors. Detention time is the most important factor, because it determine gravity settling quantities of pollutants. Desirable modification of physical factors for improvement of water quality in wet detention ponds are volume ratio, area ratio, length to width ratio, depth, out let location, bottom soil type. In order to apply design procedure in actual site, Namak new town development area was selected.

• Korean Journal of Ecology and Environment
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• v.54 no.1
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• pp.49-60
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• 2021

We examined the flow characteristics by direct runoff and base flow in a headwater stream during observed 59 rainfall events of flood season (June~September) from 2017 to 2020 yrs. Total precipitation ranged from 5.0 to 400.8 mm, total runoff ranged from 0.1 to 176.5 mm, and runoff ratio ranged from 0.1 to 242.9% during the rainfall events. From hydrograph separation, flow duration in base flow (139.3 days) was tended to be longer than direct runoff (78.3 days), while the contribution of direct runoff in total runoff (54.2%) was greater than base flow (45.8%). The total amount and peak flow of direct runoff and base flow had the highest correlation (p<0.05) with total precipitation and duration of rain among rainfall and soil moisture conditions. Dominant rainfall events for the total amount and peak flow of base flow were generated under 5.0~200.4 and 10.5~110.5 mm in total precipitation. However, when direct runoff occurred as dominant rainfall events, total amount and peak flow were increased by 267.4~400.8 and 169.0~400.8 mm in total precipitation. Therefore, the unique aspects of our study design permitted us to draw inferences about flow characteristic analysis with the contribution of base flow and/or direct runoff in the total runoff in a headwater stream. Furthermore, it will be useful for the long-term strategy of effective water management for integrated surface-groundwater in the forested headwater stream.

• Journal of Environmental Science International
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• v.22 no.3
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• pp.259-267
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• 2013

In this study, non-point source(NPS) contribution was investigated based on flow rates and water qualities of streams into the lake during rainfall events. Event mean concentration(EMC) and the pollution loads were calculated to establish a database for NPS control measurement in the survey area, and so on. The runoff characteristics of NPS were investigated and estimated on the basis of the ratio of an agricultural to forest area in the stream of sub-catch basin during rainfall events. Non-point source pollution loads were also calculated to establish a database for NPS control measure in the upstream lake Chinyang. At a rainfall event, BOD concentrations rise sharply at the early peak time of runoff, however, peaks of TSS concentration were observed at the similar time of peak flow. This was a phenomenon shown at the watersheds caused by forest and geological types. The discharged EMC range was 2.9-4.8 mg/L in terms of BOD. The discharged EMC range was 6.2-8.2 mg/L in terms of SS. The discharged EMCs of T-N and T-P were 1.4-2.5 mg/L and 0.059-0.233 mg/L, respectively. Total BOD loading rate through the 3 tributaries to the lake Chinyang was 1,136 kg/d during dry weather. The upper watershed area of the Nam-river dam in this study was divided into 14 catchment basins based on the Korean guideline for total maximum daily load(TMDL) of water quality pollutants. The higher the agricultural land-use ratio, the more NPS loading rate discharged, but the more occupied a forest area, the lower more NPS loading rate discharged. In an agricultural land-use area more than 20%, the increase of NPS loadings might be dramatically diffused by increasing the integrated complex-use like vinyl-house facilities and fertilizer use etc. according to the effective land-use utilization. The NPS loading rates were BOD 0.3 $kg/ha{\cdot}day$, SS 0.21 $kg/ha{\cdot}day$, TN 0.02 $kg/ha{\cdot}day$, TP 0.005 $kg/ha{\cdot}day$ under less than 10% agricultural land-use. In agricultural land-use of 20%-50%, these values were investigated in the range of 0.32 $kg/ha{\cdot}day$-0.73 $kg/ha{\cdot}day$ for BOD, 0.92 $kg/ha{\cdot}day$-3.32 $kg/ha{\cdot}day$ for SS, 0.70 $kg/ha{\cdot}day$-0.90 $kg/ha{\cdot}day$ TN, 0.03 $kg/ha{\cdot}day$-0.044 $kg/ha{\cdot}day$ for TP.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4B
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• pp.375-381
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• 2008

In this research, a physics based grid-multi layer distributed flood runoff model was developed to analyze discharge for the Namgang Dam Watershed ($2,293km^2$) and applied for sensitivity analysis for estimation of parameters, mainly initial soil moisture condition and saturate infiltration coefficient, which have a strong influence on discharge. Capability of the model was evaluated using VER and QER from the results of rainfall-runoff analysis and showed enhanced results of 6% compared to parameters before calibration. As the result with the sensitivity analysis of parameters, the part of the most influence on the runoff was the infiltration coefficient and ratio of layer partition. The total discharge and peak time showed comparatively precise runoff results without the initial calibration of the parameters.

• Journal of The Geomorphological Association of Korea
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• v.18 no.4
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• pp.271-282
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• 2011

The purpose of this study is to clarify the discharge patterns of Yongnup, Daeam-san. Many hydrographs were analyzed by the types of rising and falling stages, and the slope of those stages with the semi-log graph paper was a key point to distinguish the discharge patterns during rainstorms. The correlation between rainfall intensity and slopes of the second or third rising stage was higher than that between slopes of the first rising stage and rainfall intensity. Also, the coefficient of correlation between discharge decrement and the lapsed time from the peak to inflection point of hydrograph, during high water stages, was better than that during low water stages. The annual average discharge rate of Yongnup was 0.54 and the average direct runoff ratio was 0.14. The total discharge amount from Yongnup was about 410,000 tons for a water year, the monthly maximum amount emerged in September and the minimum amount was occurred in March. In summer, 37.7% was a seasonal maximum runoff ratio; on the other hand, 9.4% was a seasonal minimum runoff ratio in winter.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.15-27
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• 2012

SWMM (Storm Water Management Model) has been widely used in the world as a typical model for flood runoff analysis of urban areas. However, the calibration of the model is difficult, which is an obstacle to easy application. The purpose of the study is to develop an automatic calibration module of the SWMM linked with SCE-UA (Shuffled Complex Evolution-University of Arizona) algorithm. Generally, various objective functions may produce different optimization results for an optimization problem. Thus, five single objective functions were applied and the most appropriate one was selected. In addition to the objective function, another objective function was used to reduce peak flow error in flood simulation. They form a multiple objective function, and the optimization problem was solved by determination of Pareto optima. The automatic calibration module was applied to the flood simulation on the catchment of the Guro 1 detention reservoir and pump station. The automatic calibration results by the multiple objective function were more excellent than the results by the single objective function for model assessment criteria including error of peak flow and ratio of volume between observed and calculated flow. Also, the verification results of the model calibrated by the multiple objective function were reliable. The program could be used in various flood runoff analysis in urban areas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.930-934
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• 2006

In this study, we conducted water-quality analysis of wastewater and in-situ flow measurement using automatic flow rate measuring instrument to identify characteristics of wastewater in urban areas, and collected samples in gutter fur storm water drain, rainfall bucket, and aqueduct of pipe from roof, and outfalls of basins to examine the contribution by pollution origins such as base wastewater, atmospheric washing, runoff by roof surface, runoff by road surface, erosion of sewer sediment. In the result, the concentration of pollutants reached peak in the beginning of rainfall due to first flush, was 3 to 10 times higher than average concentration of dry period, and was lower than that of dry period due to dilution of storm water. In the analysis of the contribution by pollution origins, the ratio of load by sewer sediment resuspension to the total pollution load was 54.6% fer COD, and 73.3% fur SS. Accordingly, we can reduce the total pollutant load by periodical dredging and washing of sewer sediment, and control the loadings by overflow of combined sewer overflows.

• Journal of Korea Water Resources Association
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• v.38 no.6 s.155
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• pp.449-460
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• 2005

In this study, a WEP (Water and Energy transfer Processes) model was used to simulate the water cycle of the Dorimcheon catchment which suffers from the distorted water cycle as a typical urban catchment. Two different land uses in the past (i.e. 1975) and at present (i.e. 2000) were incorporated into the simulation to investigate the runoff characteristics resulting from the increase of the impervious ratio due to urbanization. The simulation results show that the concentration time is decreased and the peak discharge and the total runoff are increased by urbanization while the infiltration and baseflow are reduced. In addition, the effects of infiltration trenches and permeable pavements were also simulated to search for alternatives that can restore the distorted water cycle. The simulation results prove that the installation of both alternatives can restore the runoff characteristics to that prior to urbanization.