• Journal of Korean Society of Environmental Engineers
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• v.38 no.4
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• pp.210-218
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• 2016

The pollutant removal efficiencies of stormwater runoff by settling were analyzed using field samples collected in 4 different raining events in a test bed installed in the Gwanpyung-Cheon stream in Daejeon. A 1.8 m high with 30 cm diameter cylindrical settling device was used for the settling test by measuring concentration of TSS, TP and TN for time and height. The pollutants removal rate was relatively high in the first 4 hours while 24 hours seem to be necessary to reach steady state in pollutant concentrations. However, there were no considerable differences in concentrations for height at a given time. This indicates most of particulate pollutant in the test seems to show independent settling with no interference to each other. Much part of particle sizes were distributed in the range of $10{\sim}100{\mu}m$. Average particulate fractions of TP and TN were estimated as 52.4% and 23.5%, respectively. This results explain why TN is difficult to remove by simple settling. This study indicates that a simple settling can provide effective method to remove significant amount of TSS and TP effectively and this can be used to protect urban river water quality.

• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.715-721
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• 2017

Tree box filters, an example of bioretention systems, were compacted and versatile urban stormwater low impact development technique which allowed volume and water quality treatment performance to be adjusted based on the hydrologic, runoff quality and catchment characteristics. In this study, the overall performance of a 6 year-old tree box filter receiving parking lot stormwater runoff was evaluated. Hydrologic and hydraulic factors affecting the treatment performance of the tree box filter were also identified and investigated. Based on the results, the increase in rainfall depth caused a decrease in hydrologic and hydraulic performance of the tree box filter including volume, average flow, and peak flow reduction (r = -0.53 to -0.59; p<0.01). TSS, organics, nutrients, and total and soluble heavy metals constituents were significantly reduced by the system through media filtration, adsorption, infiltration, and evapotranspiration mechanisms employed in the tree box filter (p<0.001). This significant pollutant reduction by the tree box filter was also found to have been caused by hydrologic and hydraulic factors including volume, average flow, peak flow, hydraulic retention time (HRT) and runoff duration. These findings were especially useful in applying similarly designed tree box filter by considering tree box filter surface area to catchment area of less than 1 %.

• Journal of Wetlands Research
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• v.15 no.3
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• pp.407-412
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• 2013

The aim of this study was to develop a tree box filter system, an example of Low Impact Development technology, for treating stormwater runoff from road. Monitoring of storm events was performed between June 2011 and November 2012 to evaluate the system performance during wet day. Based on the results, all runoff volume generated by rainfall less than 2 mm was stored in the system. The minimum volume reduction of 20% was observed in the system for rainfall greater than 20 mm. The greatest removal efficiency was exhibited by the system for total heavy metals ranging from 70 to 73% while satisfactory removal efficiency was exhibited by the system for particulate matters, organic matters and nutrients ranging from 60 to 68%. The system showed greater pollutant removal efficiency of 67 to 83% for rainfall less than 10 mm compared to rainfall greater than 10 mm which has 39 to 75% pollutant removal efficiency. The system exhibited less pollutant reduction for rainfall greater than 10 mm due to the decreased retention capacity of the system for increased rainfall. Overall, the system has proved to be an option for stormwater management that can be recommended for on-site application. Similar system may be designed based on several factors such as rainfall depth, facility size and pollutant removal efficiency.

• Journal of Wetlands Research
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• v.20 no.1
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• pp.63-71
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• 2018

The particle filtration mechanisms in an infiltration trench should be varying due to the different hydraulic conditions during stormwater runoff. The understanding of these variations associated with different filtration mechanisms and their effect on the particle removal efficiency is of vital importance. Therefore, a LID (Low Impact Development) system comprising of an infiltration trench packed with gravel and woodchip was investigated during the monitoring of several independent rainfall events. A typical rainfall event was divided into separate regimes and their corresponding flow conditions as well as filtration mechanisms in the trench were analyzed. According to hydraulic conditions, it was found out that filtration changes between vertical and horizontal flows as well as between unsaturated, saturated, and partially-saturated flows. Particle separation efficiency was high (55-76%) and was mainly governed by physical straining during the unsaturated period. It was then enhanced by diffusion during the saturated period (75-95%). When the trench became partially saturated at the end of the rainfall event, the efficiency decreased which was believed to be due to the existence of a negatively charged air-water interface which limited the removal to positively charged particles.

• Journal of Environmental Impact Assessment
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• v.31 no.1
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• pp.1-10
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• 2022

This study was carried out to understand the water quality characteristics of the initial stormwater runoff and the origin of soluble pollutants according to various rainfall conditions from a non-point source reducing facility. The water sample from this study was collected among 10 collection facilities in the G-drainage area. Specifically, five of the collection points including #1, #5, #8, #9, and #10 were reported with unknown water inflow even during non-rain conditions. The leakage characteristics of non-point pollutants from the collection facilities were then able to identify accordingly. The water quality characteristics of the stormwater runoff from the collection facilities were strongly affected by the amounts of rainfalls. The average concentrations of EC, BOD, TOC, and TN during non-rain were found to be higher than their concentrations during rain; on the other hand, the average concentrations of DO were found to be lower than its concentrations during rain. In addition, the distribution of organic components existing in the effluent of collection facilities were identified based on the dissolved organic matter analysis. In summary, the stormwater runoff was highly affected by pollutants flowing from the surrounding environment, and the amounts of hard-to-decompose humic substances were greatly increased in the collection facilities due to rain.

• Journal of Wetlands Research
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• v.15 no.1
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• pp.79-90
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• 2013

Stormwater wetland targeted to treat the rainfall runoff from cow feeding-lot basin has been monitored from May 2010 to November 2011. Reduction efficiency estimated based on 20 rainfall event monitoring was 88%, 54%, 70%, 31%, and 64% for TSS, BOD, $COD_{Cr}$, TN, and TP, respectively. Theoretically, as rainfall depth increases, hydraulic exchange ratio has to be increased. When the exchange ratio approaches to 1 (usually design goal), TSS reduction efficiency was estimated about 55%. Uncertainty in reduction efficiency of the stormwater wetland is normally very high due to the continuous rainfall activity, its magnitude and intensity, antecedent dry days, and other natural variables which can not be controlled by experiment conductors. In this study, predominant affecting variables was found to be hydraulics caused by consecutive rainfall events having different intensity and algal growth during dry days.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.10
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• pp.684-693
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• 2012

The stormwater runoff from the increasing paved roads and vehicles resulted in the increase in the pollutants load to adjacent water bodies. The granular media filtration facilities are the most widely adopted to minimize the non-point source pollution from motorways. It is essential to consider the severe variation of hydraulic condition, suspended solid (SS) characteristics, and the medium characteristics for stormwater management filter. In this study, different types of media, including sand, were tested and the performance of downflow sand filters was investigated under various linear velocity and influent solid particle size. Results showed that the best medium is the coarse sand with large grain size, which showed the specific SS removal before clogging of more than $8.498kg/m^2$, the SS removal of higher than 95%, and minimum head loss. Linear velocity did not affect the total solid removal, while the performance was improved when fine solid was introduced. It is suggested that the life of a downflow sand filter bed can be extended by deep bed filtration when influent particles are fine. However, the captured particles can be washed out after a long period of operation.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.1
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• pp.159-167
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• 2000

In recent years, combined and separated sewer overflows (CSOs, SSOs) have been recognized as a significant pollution problem. To solve this problem a series of experiments were performed in a small scale Rapid Floc Settler (RFS) device to determine its ability in removing micro particles and dissolved materials from polluted waters. The RFS device is a compact physico-chemical wasterwater treatment system. Polyacrylamide (PAM) is used as a coagulant for treating stormwater in the RFS. The results of Jar test showed that PAM could be an excellent coagulant as compared with aluminum sulfate. and ferric chloride. In several experimental conditions, the influence of different variation parameters was tested to measure the efficiency of the RFS. Tests have been carried out with typical CSOs concentrations (50~1.000mg SS/L). The treatment efficiency with regard to SS and COD, which can be obtained at an overflow rate of $130m^3/m^2/day$, are 90% and 80%, respectively. Comparing other sedimentation technologies with RFS, the overflows rate of RFS is ten times faster. The distribution of particle size and number were analyzed. The RFS is suitable for the treatment of CSOs and also the removal of settleable and dissolved materials in urban stormwater runoff.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.6
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• pp.567-575
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• 2017

It is not cost effective to raise the density of catch basins in preparation for heavy rainfall in terms of construction and maintenance. Our researchers have developed the new catch basin for increasing interception capacity of runoff with internal filtration structure. To compare interception capacity of an existing catch basin with the invented catch basin, a hydraulic experiment device with 4% of road gradients and 0.2% of road gradients was constructed. For runoff conditions of 4.4 l/s, 6.7 l/s and 10.4 l/s, capability of runoff and separation capability of debris (sand and leaves) were evaluated. As the main experimental results, the effectiveness of the developed catch basin has been verified with an increase in interception rate of approximately 22% for the runoff of 6.7 l/s as heavy rainfall. However, the results of invented catch basin showed only 4.5% of settlement rate of debris regarding sand. Therefore, the authors proposed an improved tilted screen structure additionally. After reviewing the performance of improved catch basin, application of the invented catch basin is expected to drain runoff effectively when it is applied to the faulty road drainage section.

• Proceedings of the KSRS Conference
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• 2006.03a
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• pp.228-231
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• 2006

유출계수(Runoff Curve Number, CN)란 강수량으로부터 대상유역의 유출량과 우수 잠재능(stormwater potential) 평가에 이용하는 수문학 변수로, 미국 자연자원 보존국(Natural Resources Conservation Service; NRCS)이 제안한 방법이다. 유출계수를 평가하기 위해서는 토지피복, 토양형, 토양 습윤 조건에 대한 정보를 조합하여 분석해야 한다. 본 연구의 목적은 미국 North Carolina의 Raleigh와 Cary시를 관통하는 Walnut Creek 유역 서부지역의 토지 피복도를 제작하여, 이 유역의 유출계수를 산정하는 것이다. 이를 위해서, 첫째 위의 불투수면 레이어와 정사항공사진을 기초자료로, ArcGIS와 Feature Analyst를 이용하여 서부 Walnut Creek 유역의 토지피복도를 제작하였다. 둘째, 제작된 토지 피복도와 본 유역의 수문학적 토양 분류체계도(Hydrologic Soil Group Map)를 중첩하여 이 유역의 유출계수도를 제작하였다.