• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.207-211
• /
• 2011

하천공사의 매립 및 준설 시 뿐만 아니라 최근에는 호우 시에도 발생하는 고농도 오탁수의 유출 확산으로 인하여 주변 수역의 수산자원 및 자연환경에 심각한 영향을 미치고 있다. 특히 유사는 하천과 호소에 유입되어 탁도를 증가시켜 수자원의 이용가치를 저하시키며, 박테리아나 각종 미생물의 이동 매개체가 되고 있다. 또한 퇴적된 유사는 유량이 증가하면 다시 침식되어 부유상태가 되며 이때에 영양염류나 독성물질이 재용출 되기도 하는 등 하천의 물리 및 토양환경의 장 단기적인 변화를 유발하는 원인이 된다. 결국 유사는 다양한 방식으로 하천과 호소의 생태환경에 큰 변화를 초래한다. 부유토사의 발생 가능한 피해의 범위와 정도는 유역의 부유토사 발생율과 하천, 호소 퇴적물의 성분종류와 입도분포, 그리고 유속에 따라 결정된다. 따라서 탁수의 영향범위를 예측하고, 악영향이 예측될 경우에는 탁도를 저하시킬 수 있는 오탁물질의 저하기법을 적용하여 그 대책을 수립하여야 한다. 현재 정부가 역점을 두고 있는 4대강 살리기 사업 중 하나인 하천 준설 사업 시 발생되는 고농도 오탁수는 주변 수역의 수자원 및 자연환경에 심각한 영향을 미치므로 자연환경의 보존, 해양자원을 보호하기 위하여 오탁물질의 제어가 반드시 필요한 실정이다. 기존의 오탁 저감시설이나 방법의 경우 오탁물질의 확산을 제어하는데 한계가 있고 오탁물질의 종류와 관계없이 일률적으로 시공함으로서 오탁제어 효과가 의문 시 되고 있다. 이러한 문제점을 개선하기 위하여 오탁물질의 확산 범위를 줄이고 침강효율을 높이는 방법을 찾아 오탁확산 제어 효율을 개선할 필요가 있다. 본 연구에서는 오탁물질 제어 시 2차 응집물로 인한 오염이 발생하는 않는 천연광물 제올라이트를 이용한 실내실험을 통하여 고농도 탁수의 탁도 저감효율을 파악하여 고농도 탁수의 탁도 저감에 대한 제올라이트의 적용 가능성을 살펴보았다. 4대강 살리기 사업 중인 OO강 OO공구의 OO보 현장에서 하천 준설 시 발생하는 고농도 탁수를 이온을 첨가한 제올라이트를 이용하여 확산제어에 관한 효과를 검토한 결과 2,000NTU 정도의 고농도로 유하하는 탁수에 대하여 제올라이트 혼합 후 20분이 경과한 시점에 제거효율이 90%이상으로 제올라이트의 탁수저감 효과가 대단히 크다는 것을 알 수 있었다.

• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.1
• /
• pp.1-10
• /
• 2000

An experimental study regarding the effect of emulsions on RO is presented. Heavy oil was added to the sea water and the distilled water separately and treated for 30 minutes by a homogenizer to make emulsions. For the case of the sea water without heavy oil the permeate decreased from the beginning of the experiment. Chloride and conductivity increased with time, due to the fouling occurring as the suspended solids in the sea water accumulated on the membrane surface. Rejection rate of salt was 99.6~99.7%. As for the sea water containing heavy oil, the permeate decreased slowly from the beginning of the experiment. This result was the same for the case of the sea water only. However. chloride and conductivity increased significantly when heavy oil was added. In the second experiment with sea water containing heavy oil, the operation time of RO was reduced considerably. With addition of oil, the chloride increased greatly, while the permeate reduced comparatively. In the experiment where emulsion of $0.3{\sim}0.8mg/{\ell}$ was supplied to RO. oil concentration was about 10ppb in the permeate at the end of the experiment. In case of the distilled water containing heavy oil. the conductivity increased. However. the permeate reduced to 30% compared to the case of the sea water containing heavy oil. The case of sea water containing heavy oil showed an opposite result, but the effect of the addition of oil on RO was significant. Oil caused fouling of the RO and the contamination of the whole system, and as the result the system could not be operated properly. As a result the membrane capacity, the amount and water quality of permeate deteriorated significantly.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.2B
• /
• pp.113-121
• /
• 2012

When a heavy rain brings flooding, a high turbid water is flowing into a reservoir. In this study, the effectiveness of the intake structures for the selective withdrawal from the various levels of a stratified reservoir was evaluated by the field experiments and the numerical modeling of the three-dimensional approaching flows. The temperature, the turbidity, and the velocity fields for the selective withdrawal were measured using both YSI6600EDS and YSI6600ADV, respectively. A threedimensional model, FLOW-3D, was used to predict the performance of the intake tower in Imha reservoir. The comparisons of the vertical velocity field showed a good agreement with the field measurements. The efficiency of the turbid-water elimination of the selective withdrawal method from low levels was higher up to 46% than that of the surface withdrawal. From the analysis of the numerical simulation, the efficiency of turbidity elimination increased by 10% for the selective withdrawal from middle levels, and by 30% from low levels. These results showed that the selective withdrawals from middle and low levels are more effective than the surface-water intake. The similar results were obtained by the one-dimensional model, SELECT, which is much more computationally time-efficient.

• Journal of Korea Water Resources Association
• /
• v.40 no.8
• /
• pp.601-615
• /
• 2007

A selective withdrawal method has been widely used to control the quality of water released from a stratified reservoir and to improve downstream ecosystem habitats. Recently, several existing reservoir withdrawal facilities have been modified to accommodate multi-level water intake capabilities in order to adapt the impact of long-term discharge of high turbidity flow. The purpose of this study was to assess the effect of selective withdrawal method on the control of downstream turbidity and its impact on water quality in Daecheong Reservoir. A laterally integrated two-dimensional hydrodynamic and eutrophication model, which was calibrated and validated in the previous studies, was applied to simulate the temporal variations of outflow turbidity with various hypothetical selective withdrawal scenarios. In addition, their impacts on the algal growth as well as water quality constituents were analyzed in three different spatial domains of the reservoir The results showed that the costly selective withdrawal method would provide very limited benefits for downstream turbidity control during two years of consecutive simulations for 2004-2005. In particular, an excessive withdrawal from the epilimnion zone for supplying upper layer clean water resulted in movement of turbidity plume that contained high phosphorus concentrations upward photic zone, and in turn increased algal growth in the lacustrine zone.

• Journal of Environmental Impact Assessment
• /
• v.19 no.3
• /
• pp.247-257
• /
• 2010

Watershed runoff and turbid water dynamics were simulated in the Youngju Dam, being constructed. The runoff flow and suspended solids were simulated and then thermal stratification and turbid water current in the reservoir were predicted by HSPF and CE-QUAL-W2 model, respectively. Considering selective withdrawal, we hypothesized 3 withdrawal types from the dam, i.e. surface layer, middle layer and the lowest layer. The maximum concentration of SS was 400mg/L in reservoir and it was decreased by the withdrawal. The inflowed turbid water fell to 30 NTU after 12 days regardless of the withdrawal types, but the surface layer withdrawal was a better type at turbid water discharge than the others. In current environmental impact assessment(EIA), we concluded that runoff and reservoir water quality predicted by HSPF and CE-QUAL-W2 was desirable, and appropriate parameters were selected by continous monitoring after EIA.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6B
• /
• pp.499-505
• /
• 2011

The mixing behavior of turbidity currents in a reservoir is closely related with the annual temperature change of the reservoir. In the summer, the reservoir has a well defined structure: one or two thermoclines and some layers of different densities. This density stratification inhibits vertical mixing and affects various hydrodynamic processes within the reservoir. Therefore, many reservoirs can be operated to release water of the specific quality with the selective withdrawal. In this study, the hydraulic experiments were performed to analyze the efficiency of selective withdrawal. The velocity distributions are measured with PIV in the stratified tank with the "two-tank" method. The relationship between the Richardson number and the selective withdrawal efficiency are provided using the measured velocity distributions.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.482-486
• /
• 2005

불투수지역의 증가에 따른 도시지역의 비점오염원 해석 및 예측은 수자원 관리측면에서 중요성이 증가하고 있다. 그러나, 실측자료의 부족, 오염물질 발생경로의 불명확, 간헐성, 강우 및 유역특성에 따라 오염부하량 및 첨두농도 등의 변화가 심하므로 인하여 연구에 어려움이 많은 실정이다. 이를 극복하기 위해서는 장기적인 자료수집과 국내실정에 맞는 모형개발이 이루어져야 할 것이다. 따라서, 본 연구에서는 초기강우에 의한 수질항목별 오염부하량 및 농도계산이 가능한 ILLUDAS-NPS 모형을 개발하였다. 본 모형은 국내의 도시지역 유출해석에 주로 사용되는 ILLUDAS 모형에 건기 및 우기시의 수질해석 과정들을 추가하여 해석되어 진다. 건기시의 경우 유량 및 수질 계산은 계수지정법을 사용하였으며, 우기시의 경우 유량계산은 기존 ILLUDAS 모형의 알고리즘을 이용하였고, 수질 계산은 일일 오염물 축적법과 쓸림방정식을 적용하여 계산시간별 오염물질 부하량 및 농도 등을 계산하였다. 모형의 검정을 위하여 홍제천 시험유역의 총 3가지 강우사상을 대상으로 검토한 결과 총부하량, 첨두농도, 첨두농도 발생시간 등에서 전반적으로 실측치와 유사한 결과를 얻을 수 있었다. 또한, ILLUDAS-NPS 모형과 SWMM, STORM 등의 기존 도시유출$\cdot$수질 모형들에 의한 결과들의 비교에서 SWMM 모형과 다소의 차이는 있으나 대부분 잘 일치함을 확인할 수 있었다. 추후, 합리적이고 보다 정확한 비점오염 해석을 위하여 도시지역의 건거시 오염물질의 축적율 및 초기강우에 의한 오염물질 쓸림량 등에 관한 실험 및 현장자료 축적이 필요하다.월이 긴 것으로 나타났다. 이러한 현상은 유입수가 저수지로 유입되면서 초기수위가 높은 경우에 운동량이 상대적으로 많이 소멸되기 때문으로 판단된다. 또한 탁수층의 두께도 8월 성층의 경우가 상대적으로 큰 것으로 나타났다. 이는 중층의 8월 수온분포 또는 밀도분포가 상대적으로 균일하기 때문에 연직방향 이송$\cdot$확산이 많이 이루어졌기 때문으로 판단된다.이는 토성간의 침투속도 및 투수속도의 경향이 반영된 것이다. 경사에 따라서는 경사도가 증가할수록 지수적으로 감소하였으며 $10\% 경사일 때를 기준으로 $I(mm)=I_{10}{\times}1.17{\times}e^{-0.0164s(\%)}$로 나타났다. 같은 조건에서 강우량과 유거수의 관계는 $Ro_{10}(mm)=5.32e^{0.11R(mm)}(r^2=0.69)$로 나타났다. 이는 토양의 투수특성에 따라 강우량 증가에 비례하여 점증하는 침투수와 구분되는 현상이었다. 경사와 토양이 같은 조건에서 나지의 경우 역시 $Ro_{B10}(mm)=20.3e^{0.08R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10

• Pediatric Infection and Vaccine
• /
• v.3 no.2
• /
• pp.168-174
• /
• 1996

Purpose : Aseptic meningitis is relatively frequent in children and caused mostly by enterovirus. The aim of the present study was to determine the effect of early diagnosis (spinal tapping) on symptom duration of childhood aseptic meningitis. Methods : One hundred fifty-three children who were hospitalized due to aseptic menigitis in the Department of Pediatrics St. Benedict Hospital from July 1996 through October 1996 were included in this study. Patients were divided to two groups according to the duration from first symptom onset to diagnosis. Early diagnosis group is diagnosed within 3 days from first symptom onset. Later diagnosis group is diagnosed after 4 days from first symptom onset. Results : 1) The average age of these patients was 4.3 years old in early diagnosis group and 4.1 years old in later diagnosis group. The sex ratio(male: female) was 2.04:1 in early diagnosis group and 2.5:1 in later diagnosis group. 2) The mean duration of diagnosis of this study was 2.04 day in early diagnosis group and 5.12 day in later diagnosis group. 3) The percentage of symptom and sign of the early diagnosis group were fever(100%), headache(88.4%), vomiting(86.9%), abdominal pain(39%), neck stiffness(36.2%), skin rash(18.8%), diarrhea(16.9%) and that of later diagosis group were fever(100%), headache(83.3), vomiting(80.9%), abdominal pain(47.6%), neck stiffness(41.6%), skin rash(29.7%), diarrhea(16.6%). 4) Initial CSF findings revealed leukocyte $146.8{\pm}386.3/mm^3$ with PMNL 38%, protein 32.47mg/dl, sugar 66.23mg/dl in early diagnosis group and leukocyte $458.1{\pm}663.2/mm^3$, protein 31.22mg/dl, sugar 64.21 mg/dl in later diagnosis group. 5) There was no statistically significant differance in the peripheral blood findings between early diagnosis group and later diagnosis group. 6) The duration of disappearance of symptom after spinal tap were 2.3 days in early diagnosis group and 2.24 days in later diagnosis group. Total symptom duration was 4.34 days in early diagnosis group and 7.36 days in later diagnosis group. Conclusions : Our results demonstrate that early diagnosis(early spinal tap) shortened duration of clinical symptoms.