Turbid Density Current Venting through Reservoir Outlets

Fong-Zuo Lee,Jihn-Sung Lai,Yih-Chi Tan,Chia-Chi Sung 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.2

The planning and design of an outlet operation by releasing a turbid density current from a reservoir requires accurate prediction ofoutflow concentration for sluicing sediment through outlet structures. This study investigates outflow concentration and ventingefficiency through reservoir outlets in a reservoir sluicing operation related to turbid density current. A 3D numerical model isemployed to simulate a venting operation for a turbid density current in typhoon-induced flood events. A simple and efficientformula derived from theoretical analysis with experimental data is proposed for estimating outflow concentration and ventingefficiency. By adopting the proposed formula to avoid time-consuming calculation using the 3D numerical model, the estimatedoutflow concentration and venting efficiency through reservoir outlets have shown good agreement with the measured and simulatedresults in typhoon flood events. This demonstrates that the formula provides an efficient approach for engineering practice in realtimereservoir venting operations.

인공호에서 몬순과 태풍 강우에 의한 고탁수층의 이동과 소멸특성

박재충,박정원,신재기,이희무 한국육수학회 2005 생태와 환경 Vol.38 No.1

낙동강 수계의 최대 인공호인 안동댐 저수지에서 2002~2004년 동안 홍수기의 수온성층 구조에 따른 고탁수의 유입특성과 시·공간적 변동을 조사하였다. 6월부터 수온성층이 형성되었으며 성층구조에 따라 유입 수괴의 이동경로가 결정되었고 고탁수의 유입에 의해 성층 구조가 변하였다. 고탁수는 유입 시기와 수량에 관계없이 저수지 상류부에서는 심층류로 유입되었고 중류부에서 바닥으로부터 분리되어 중층 밀도류의 형태로 하류까지 이동하였다 또한 중층 밀도류의 형성지점은 유입량과 시기에 따라 공간적으로 다소 차이가 있었다. 유입량에 의해 수온성층과 BO분포가 변하였고, 시기에 따라 변수층에는 2개의 수온 급감층과 저산소층이 각각 존재하였다. 최하류까지 이동한 홍수량의 고탁수층은 상승류를 형성하여 수심 15 m 아래에서 최대 20m 두께로 고탁수층을 형성하였다. 고탁수층은 저수지 바닥으로 침전되지 않았고 중층의 취수구를 통해 하류로 배출되었으며 가을 순환시기 이후 완전 소멸되었다. During the period of heavy rain from 2002 to 2004, the characteristics of the inflow, temporal and spatial fluctuations of high turbid water according to thermal stratification were studied on the Andong Reservoir which is the largest artificial lake in the Nakdong River basin, Korea. Thermal stratification was formed in June. Its structure determined to the pathway of inflowing turbid water and has affected by the transportation of high turbid water. Regardless of the time and amount of inflow, the high turbid water showed the shape of underflow at the riverine zone, separated from the bottom at the transition zone and moved to the lacustrine zone with the shape of density current. The plunging point depended on the time and amount of inflow. The distributions of thermal stratification and DO concentrations were changed by inflowing discharge. Two thermoclines and minimum DO layers were found out existing at metalimnion in a specific time, respectively. The layer of high turbid water which formed with the thickness of 20 m at the maximum below the depth of 15 m moved toward dam. Not settled to the bottom, the newly formed layer was discharged through the intake-outlet and dispersed into all layers by the circulation in the fall.

ULTIMATE 기법을 이용한 부유사 밀도류 전파 수치모의

최성욱,최성욱 한국수자원학회 2017 한국수자원학회논문집 Vol.50 No.1

This study presents a numerical model for simulating turbidity currents using the ULTIMATE scheme. For this, the layer-averaged model is used. The model is applied to laboratory experiments, where the flume is composed of sloping and flat parts, and the characteristics of propagating turbidity currents are investigated. Due to the universal limiter of the ULTIMATE scheme, the frontal part of the turbidity currents at a sharp gradient without numerical oscillations is computed. Simulated turbidity currents propagate super-critically to the end of the flume, and internal hydraulic jumps occur at the break-in-slope after being affected by the downstream boundary. It is found that the hydraulic jumps are computed without numerical oscillations if Courant number is less than 1. In addition, factors that affect propagation velocity of turbidity currents is studied. The particle size less than 9 μm does not affect propagation velocity but the buoyancy flux affects clearly. Finally, it is found that the numerical model computes the bed elevation change due to turbidity currents properly. Specifically, a discontinuity in the bed elevation, arisen from the hydraulic jumps and resulting difference in sediment entrainment, is observed. 본 연구에서는 ULTIMATE 기법을 이용하여 밀도류 층적분 모형의 해석을 위한 수치모형을 제시하였다. 개발된 모형을 경사부와 평탄부로 이루어진 실내 실험에 적용하여 경사부에 유입된 부유사 밀도류의 전파 특성에 대해 분석하였다. ULTIMATE 기법의 범용제한자로 인하여 밀도류의 선단부가 수치진동 없이 비교적 급한 형태로 전파되는 것을 모의하였다. 그리고 사류로 전파되고 수로 끝에서부터 상류로 변화되는 밀도류의 내부 도수 발생 과정을 재현하였다. 이러한 내부 도수는 ULTIMATE 제한자를 사용하면 Courant 수가 1 미만일 때 안정적으로 모의되는 것을 확인하였다. 또한 밀도류의 전파 속도에 영향을 주는 인자에 대하여 분석하였다. 입자의 크기는 9 μm 이하일 때 밀도류의 전파 속도에 큰 영향을 주지 않는 반면, 부력 흐름률은 확연한 영향을 주는 것을 확인하였다. 마지막으로 부유사 밀도류에 의한 하상변동에 대해 검토하였다. 수치모형으로 부유사 밀도류의 전파에 의한 하상변동을 정량적으로 적절히 모의하였으며, 도수로 인한 부유사 연행의 차이와 이로 인한 하상의 불연속적인 형태를 관찰할 수 있었다.

단기간 탁수와 유속 변동이 부착돌말류 성장에 미치는 영향

김백호 ( Baik Ho Kim ),박혜진 ( Hye Jin Park ),민한나 ( Han Na Min ),공동수 ( Dong Su Kong ),황순진 ( Soon Jin Hwang ) 한국물환경학회 2011 한국물환경학회지 Vol.27 No.6

Short-term effects of current velocity and turbid water on the benthic diatom community and water quality were examined in artificial channel (20×200×10 cm) with two different experiments. The first and second experiments were consisted of different current velocities such as 1 L/min., and 1, 3, and 6 L/min., respectively. The concentration of turbid water is prepared with loess and fixed at 10 and 20 times of the turbidity of control inflow (10 NTU, LTW), respectively. At experiment 1 (EXP-1), introduction of turbid water increased dissolved oxygen, electric conductivity, pH and turbidity, but there were no differences between low- (100 NTU, MTW) and high-turbid water (200 NTU, HTW). However, experiment 2 (EXP-2) did not change any environmental parameters except dissolved total and inorganic nitrogen like EXP-1. MTW in EXP-1 strongly stimulated the growth of benthic diatom, while both MTW (150 NTU) and HTW (300 NTU) in EXP-2 did not increase or decrease the diatom abundance. Over the study, the dominant species was four, Aulacoseira ambigua, Cyclotella stelligera, Aulacoseira granulata and Achnanthes minutissima. In EXP-1, two highest species in abundance, A. ambigua and A. granulata were highly grown in MTW, while Achnanthes minutissima high in HTW adversely. These results indicate that the introduction of turbid water can play an important role in the shift of water quality and benthic diatom community in stream ecosystem, especially inflow of soil water in low current velocity.

저수지로 유입되는 부유사 밀도류의 수치모의

최성욱,반채웅,최성욱 한국수자원학회 2017 한국수자원학회논문집 Vol.50 No.3

본 연구에서는 저수지에 유입된 부유사 밀도류에 의해 유사가 포집되는 현상을 모의하기 위한 수치모형을 제시하였다. 개발된 모형을 Toniolo and Schultz (2005)의 실내 실험에 적용하여, 부유사 밀도류의 전파, 하도형태의 변화, 그리고 댐에 의한 유사의 포집현상을 모의하였다. 삼각주 의 전면층에서 침강된 밀도류가 빠르게 댐까지 전파된 후, 댐에 의해 차단되고 두께가 증가되어 상류로 영향을 전파하는 일련의 과정을 모의하였 다. 또한, 소류사와 부유사에 의해 저수지 삼각주에서 전면층이 전진하고, 부유사에 의해 기저층의 두께가 상승하는 현상을 잘 모의하였다. 댐 취수 구의 높이에 따른 밀도류의 최대 두께와 내부 도수 발생 위치를 확인하였다. 유사 포집 효율은 수치모형으로 실측 결과의 값을 적절히 모의하였으 나, 실험의 한계로 인해 댐 취수구의 높이와 포집 효율과의 관계는 찾아볼 수 없었다. 수치모의 결과를 이용하여 유사 포집 효율의 민감도 분석을 수 행한 결과 부유사의 입자 크기가 포집 효율에 가장 민감하게 작용하는 것을 확인할 수 있었다. This study proposes a numerical model which is able to simulate turbidity currents intruding into a reservoir and resulting sediment depositions. The proposed model is applied to laboratory experiments by Toniolo and Schultz (2005), and propagation of turbidity currents, morphological change, and trap of suspended sediment are simulated. It is simulated that the turbidity current after plunging at the foreset of the model delta, propagates along the bottom. The thickness of the turbidity current increases significantly after being blocked by the dam, and this effect is propagated in the upstream direction. In addition, it is simulated that the foreset moves in the downstream direction due to both the bedload and suspended load and the thickness of the bottom set increases due to the suspended load. It is found that the height of the intake affects the thickness of the turbidity current and the location of the internal hydraulic jump. The impact of the height of the intake on the trap efficiency is not clear in the experimental results, however, overall trap efficiency is predicted quite successfully by the model. Also, sensitivity analysis is carried out, and the results indicates that the particle size affects the trap efficiency most.

Syneruptive and intereruptive lithofacies in lacustrine environments: The Cretaceous Beolkeum Member, Wido Island, Korea

Gihm, Y.S.,Hwang, I.G. Elsevier Scientific Pub. Co 2014 Journal of volcanology and geothermal research Vol.273 No.-

The Cretaceous Beolkeum Member was deposited in a lacustrine environment affected by explosive volcanism, and a number of syneruptive lithofacies are intercalated with lacustrine mudstones. The syneruptive lithofacies were formed by primary volcanic processes and resedimented depositional processes during and after eruptions and exhibit unique depositional features, which can be grouped into four syneruptive lithofacies assemblages (SLA-1-to SLA-4, from bottom to top). Primary syneruptive lithofacies are represented by welded massive lapilli tuff in SLA-1 and a normally graded lapilli tuff in SLA-2. In SLA-1, sustained pyroclastic density currents were able to displace lake water and rarely interacted with lake water, resulting in the formation of a welded texture and columnar joints. In SLA-2, unsteady pyroclastic density currents rapidly disintegrated, mixed with ambient water, and transformed into high-density turbidity currents, depositing thick normally graded lapilli tuff. Resedimented syneruptive lithofacies were primarily controlled by volcaniclastic sediment supply after eruptions. When volcaniclastic sediments were continuously supplied into the lake by debris flows, a volcaniclastic fan can be formed (SLA-1), resulting in a coarsening-upward trend and progradational geometry. In case of relatively small amounts of volcaniclastic sediment supply, turbidity currents would be a main depositional process, depositing a series of normally graded tuff on the primary syneruptive lithofacies (SLA-2), showing a fining-upward trend. In SLA-3 and SLA-4, there are only a few cm thick, normally graded tuff, reflecting minor volcaniclastic sediment supply. However, overlying normally graded sandstones in SLA-3, showing a coarsening-upward trend, and a thick normally graded sandstone in SLA-4 suggest favorable conditions for the generation of the sediment gravity flows, probably due to an increase in volcaniclastic sediment supply after eruptions.

2차원 수리 수질모델(CE-QUAL-W2)을 이용한 소양호 수온 성층현상과 홍수기 밀도류 이동 현상의 모델링

김윤희,김범철,최광순,서동일 江原大學校 附設 環境硏究所 2001 環境硏究 Vol.18 No.-

The temporal and spatial distribution of water temperature was surveyed and simulated in a deep warm monomitic Reservoir. The great depth (maximum depth of 100 m) and wind-sheltered dendritic shape caused strong summer stratification, Turbid storm runoff during the summer monsoon formed a metalimnion of 20~40m thickness which was distinct from the clearer epilimnion and hypolimnion. The temperature distribution and the movement of density current were simulated by using the 2-dimensional hydrologic model CE-QUAL-W2. Model was calibrated with 1996 date and verified data from 1995-1999 by applying the same set of parameters and constants as in calibration. The model could simulate temperature profiles with excellent agreement. Simulation results of movement of the intermediate density current also satisfactory. It can be concluded that the CE-QUAL-W2 model is useful in the prediction of the temperature distribution and movement of density current in reservoirs, which implies merits for further employment in water quality simulation.

ELCOM-CAEDYM을 이용한 대청댐 유입탁수의 3차원 모델링

정세웅,이흥수,류재일,류인구,오동근 한국수자원학회 2008 한국수자원학회논문집 Vol.41 No.12

국내 많은 저수지들과 그 하류하천은 높은 탁도를 가진 물의 장기적인 방류로 인해 수자원 이용과 수생태계 관리에 많은 어려움을 겪고 있다. 탁도()는 물의 탁한 정도를 나타내는 척도로써, 수질과 수환경의 건강을 평가하는 매우 중요한 지표로써 광범위하게 사용되어 왔지만, 모형의 검증에 필요한 실험 자료의 부족으로 인해 탁도 모델링에 대한 연구는 지금까지 매우 부족하였다. 본 연구의 목적은 광범위한 현장 실측자료를 이용하여 성층화된 대청호로 유입한 탁수의 밀 Many reservoirs in Korea and their downstream environments are under increased pressure for water utilization and ecosystem management from longer discharge of turbid flood runoff compared to a natural river system. Turbidity() is an indirect measurement

홍수 규모별 대청호에 유입하는 하천 밀도류의 특성 변화

윤성완,정세웅,최정규 한국수자원학회 2008 한국수자원학회논문집 Vol.41 No.12

여름철 홍수시 성층화된 저수지로 유입하는 하천수는 저수지 표층수에 비해 낮은 수온과 높은 부유고형물질(SS) 농도를 가지므로 주변수에 비해 상대적으로 높은 밀도를 가지게 된다. 이러한 밀도차로 인해 형성된 밀도류의 저수지 내 진행과정은 수질과 수생태계에 큰 영향을 주게 된다. 따라서 하천수 밀도류의 거동분석은 저수지 수질관리를 위한 현장조사의 최적화, SS와 영양염류 등 오염물질의 이송 확산 해석에 중요한 요소이다. 본 연구의 목적은 기존 연구를 통해 Stream inflows induced by flood runoffs have a higher density than the ambient reservoir water because of a lower water temperature and elevated suspended sediment(SS) concentration. As the propagation of density currents that formed by density difference

댐 재개발이 호수 수온 및 탁수 거동 변화에 미치는 영향 예측을 위한 모델 연구

정선아(Seon A Jeong),박석순(Seok Soon Park) 大韓環境工學會 2005 대한환경공학회지 Vol.27 No.8