• The Korean Journal of Quaternary Research
• /
• v.20 no.2
• /
• pp.11-29
• /
• 2006

A bedrock river is a channel in which bedrock is exposed along the channel bed or walls for at least approximately half of its length. In some case, a continuous alluvial veneer may be present, but this is completely mobilized during floods. From the point of long term landscape evolution during the Quaternary, the bedrock channel determines local base level and the lowering rate of bedrock channels controls the rate of erosion and transport processes and forms on the adjacent hillslopes. In this review, various erosional processes in bedrock river channels are classified and discussed. Especially, theoretical and numerical models on channel bed abrasion with bed load sediment particles are introduced and discussed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2018.11a
• /
• pp.32-33
• /
• 2018

낙동강 하구의 지형변화를 포함한 제 해양환경은 낙동강 하굿둑이 건설된 1987년 7월 이후로 분기된다. 즉, 낙동강 하굿둑이 건설되기 전에는 낙동강의 작은 하상구배로 담수와 해수가 혼합되는 구역이 현재의 하굿둑 보다 상류에 위치하였으나 하굿둑 건설 이후에는 하굿둑 수문 조작에 따라 방류되는 유출수에 의해 유동 양상이 변화되기에, 낙동강 하굿둑의 방류량을 파악하는 것은 매우 중요하다 하겠다. 이에 본 연구에서는 낙동강 하굿둑 제원, 방류패턴, 하굿둑 주변 강수량, 하굿둑 방류량을 분석하였다. 또한, 낙동강 하굿둑 방류량에 의한 유사량 분석을 수행하여, 낙동강 하류역의 지형변동의 기초자료를 제공하였다. 연구결과, 낙동강 하굿둑 방류량은 최근 13년 동안의 연평균방류량은 $19,274.56{\times}106m^3$이고 일평균 방류량은 $52.81{\times}106m^3$이고 초당평균 방류량은 $611.19m^3$으로 산정되었다. 낙동강 하굿둑 건설 이후 퇴사량과 준설량을 근거하여 계산된 연간 평균 총유사량은 $3,184,405m^3/yr$이고, 낙동강 하굿둑의 경우 연평균 부유사량이 $3,153,995m^3/yr$, 소류사량이 $30,410m^3/yr$이며 소유사량이 부유사량의 약 1.0%로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.493-493
• /
• 2017

부유사 수리실험에서 부유사의 농도를 측정하는 것은 불확실성이 매우 크다. Einstein(1950)은 유사의 pickup function 결정에서 이러한 불확실성 때문에 유사입자의 거동을 발생시키는 양력의 확률을 적용하기도 하였다. 일반적으로 부유사의 측정은 부유사 채집기를 통해 수행하지만, 시간적으로 비효율 적이며, 채집 시 채집기의 부피로 인한 난류 발생으로 채집 후 흐름 변화가 발생할 수 있다. 수리실험의 규모라면 이 문제는 더욱 부각될 수 있다. 연속적인 부유사의 농도 측정을 위해 이러한 점은 개선되어야 하는 문제이다. 본 연구에서는 유사 실험의 이러한 단점을 극복하고자 image processing 기법을 적용하였다. Image processing은 부유사의 농도가 증가할수록 탁도가 증가하는 특성을 이용하여, 부유사 농도를 추정하는 방법이다. 이 과정에서 RGB(Red-Green-Blue)로 색을 표시하는 방식에서 image를 변환하여 gray scale로 전환해야 하며, 파(wave)의 전파에 의한 image 결과의 변형은 없다고 가정하였다. Gray scale과 탁도와의 관계를 도출하기 위해 하상에 유사를 포설하고, 단파(surge)를 발생 시켰다. 실험은 길이 12.0m, 폭 0.8m, 높이 0.75m의 개수로에서 수행하였으며, 수로 상류에 sluice형 gate를 급격하게 개방하는 것으로 단파를 재현하였다. 탁도 측정을 위해 유사 채집기를 이용하였으며, 상기에서 제시한 흐름 교란문제로, 1지점에서 1개의 시간동안만 채집을 수행하였으며, image의 촬영을 병행하였다. 또한 data의 정확도를 높이기 위해 3번의 반복실험을 수행하였다. 실험결과 gray scale과 탁도와는 일정한 관계가 나타났으며, 이를 토대로 gray scale-SSC(suspended sediment concentration)와의 관계를 도출하였다. Bayesian 분석을 이용하여 image processing의 보정(확률적 보정)을 추가적으로 수행하였다. 최종적으로 실측한 값과 image processing을 통한 값을 1:1 curve를 통해 비교하였으며, 약 9%의 평균 오차가 발생하여, image processing과 bayesian 적용을 통한 부유사 농도 측정은 신뢰할 만한 결과를 도출하는 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.25-25
• /
• 2022

하천의 개발 및 보전 계획을 수립하는 데에 있어 자연하천의 부유사량 및 총유사량을 계측하는 것은 매우 중요하다. 우리나라에서는 매년 국내 자연하천을 대상으로 부유사량을 실측하고 실측 부유사량을 바탕으로 수정 아인슈타인 방법을 적용해 총유사량을 산정하고 있으나 이 또한 홍수기에 국한되어 있다. 가장 일반적인 유사량 계측 방법인 시료 채집에 의한 방법은 많은 노력과 비용을 수반하기 때문에 유사량 관측소와 관측 빈도를 늘릴 수 없는 실정이다. 최근에는 ADCP 음파 신호의 후방산란도가 부유사 농도에 따라 증가한다는 성질을 이용해 부유사 농도 계측에 ADCP를 이용하고자 하는 노력이 계속되고 있다. 이러한 특성을 이용해 본 연구에서는 전라남도 나주시에 위치한 남평교 자동유량관측소에 설치된 횡방향 ADCP (H-ADCP)를 대상으로 서포트 벡터 회귀(SVR)를 적용한 실시간 유사량 모니터링 모형을 제안하였다. 여기서 제시하는 유사량산정 모형은 크게 유량과 초음파 산란도를 입력 변수로 해 부유사 농도를 산정하는 서포트 벡터 회귀 모형과 첫 번째 모형으로부터 산정된 부유사 농도와 흐름 정보를 이용해 총유사량을 산정하는 모형으로 구성되어 있다. 개발된 SVR 부유사량 및 총유사량 산정 모형의 정확도가 결정계수(R²) 기준으로 각각 0.82, 0.90 으로 나타났다. 주목할 점은, 본 연구에서 제시하는 SVR 모형을 이용해 멱함수 기반 유사량 관계식으로는 예측할 수 없는 유사량의 이력현상을 재현해낼 수 있다는 것이다. 본 연구에서 제시하는 H-ADCP 기반 총유사량 모니터링 방법은 기존 자동 유량 관측소 시설을 그대로 이용할 수 있다는 장점이 있다. 따라서 실무 적용 시 낮은 추가비용으로 양질의 유사량 모니터링이 가능할 것으로 기대된다.

• Journal of the Korean association of regional geographers
• /
• v.13 no.4
• /
• pp.409-421
• /
• 2007

The purpose of this paper is to consider the formation processes and depositional conditions of bars formed at the upper-stream part of Sayeon Dam since Sayeon Dam construction in 1964. Results of analyzing the shape characteristics of bars and their sediment grain size distribution are as follow: Firstly, bars are able to categorized as subaqueous bars (A, B), mid-channel bars(C, D), and tributary side-bars(E). Secondly, the outline of bars has longish along the flow path, and their height lowers more and more going towards downstream. Also the height of bar surface tend to heighten from flow path to mountain slope. However, the near part of A is comparatively higher than its distant part, A is defined as a subaqueous natural levee and back swamp. Thirdly, the average particle size of A and B become smaller toward mountain slope. In transportation style, ratio of suspended load become higher toward mountain slope. Fourthly, sorting is worse to very worse according with lake's random changable water level. Fifthly, bar A and B were formed by vertical sedimentation of sediments according as sediments transported along flow path in the subaqueous conditions were spreaded out of flow path. C and D were formed by bed load as flood level lowered. And E was formed by vertical sedimentation while stream flow stopped in tributary's mouth areas with the water level heightening.

• Journal of Korea Water Resources Association
• /
• v.38 no.10 s.159
• /
• pp.871-883
• /
• 2005

This paper investigates the impacts of turbulent anisotropy on the mean flow and turbulence structures in vegetated open-channel flows. The Reynolds stress model, which is an anisotropic turbulence model, is used for the turbulence closure. Plain open-channel flows and vegetated flows with emergent and submerged plants are simulated. Computed profiles of the mean velocity and turbulence structures are compared with measured data available in the literature. Comparisons are also made with the predictions by the k-$\epsilon$ model and by the algebraic stress model. For plain open-channel flows and open-channel flows with emergent vegetation, the mean velocity and Reynolds stress profiles by isotropic and anisotropic turbulence models were hardly distinguished and they agreed well with measured data. This means that the mean flow and Reynolds stress is hardly affected by anisotropy of turbulence. However, anisotropy of turbulence due to the damping effect near the bottom and free surface is successfully simulated only by the Reynolds stress model. In open-channel flows with submerged vegetation, anisotropy of turbulence is strengthenednear the vegetation height. The Reynolds stress model predicts the mean velocity and turbulence intensity better than the algebraic stress model or the k-$\epsilon$ model. However, above the vegetation height, the k-$\epsilon$ model overestimates the mean velocity and underestimates turbulence intensity Sediment transport capacity of vegetated open-channel flows is also investigated by using the computed profiles. It is shown that the isotropic turbulence model underestimates seriously suspended load.

• Korean Journal of Soil Science and Fertilizer
• /
• v.31 no.3
• /
• pp.211-215
• /
• 1998

Soil loss and runoff were investigated in a small watershed located in Sangeo-ri, Yeoju-eup, Yeoju-gun, Kyonggi-do. The watershed with the area of 35 ha consists of forest, grassland, uplands and mulberry. V-notch type water tank. flow-meter, automatic water sampler and rain gauge were installed at the main outlet stream. Out of $1.037.9Mg\;35ha^{-1}$ of total annual rainfall. 17.9% was lost via run-off. The total amount of soil eroded was $152.2Mg\;35ha^{-1}$, of which $78.6Mg\;35ha^{-1}$ was suspended load and $73.6Mg\;35ha^{-1}$ ha was sediment load. The soil losses under different land uses were $16.02Mg\;ha^{-1}$ for upland annual Crops. $2.69Mg\;ha^{-1}$ for mulberry field, $0.58Mg\;ha^{-1}$ for grassland and $0.55Mg\;ha^{-1}$ for forest. The predicted soil loss by Universal Soil Loss Equation was approximately 20% underestimated in forest, grassland and uplands, and 32% underestimated in mulberry field.

• Journal of Korea Water Resources Association
• /
• v.44 no.12
• /
• pp.991-1000
• /
• 2011

The relationship between discharge (Q) and suspended sediment (SS) concentration often is used for the estimation of inflow SS concentration in reservoir turbidity modeling in the absence of actual measurements. The power function, SS=aQb, is the most commonly used empirical relation to determine the SS load assuming the SS flux is controlled by variations of discharge. However, Q-SS relation typically is site specific and can vary depending on the season of the year. In addition, the relation sometimes shows hysteresis during rising limb and falling limb for an event hydrograph. The objective of this study was to examine the hysteresis of Q-SS relationships through continuous field measurements during flood events at inflow rivers of Yongdam Reservoir and Soyang Reservoir, and to analyze its effect on the bias of SS load estimation. The results confirmed that Q-SS relations display a high degree of scatter and clock-wise hysteresis during flood events, and higher SS concentrations were observed during rising limb than falling limb at the same discharge. The hysteresis caused significant bias and underestimation of SS loading to the reservoirs when the power function is used, which is important consideration in turbidity modeling for the reservoirs. As an alternative of Q-SS relation, turbidity-SS relation is suggested. The turbidity-SS relations showed less variations and dramatically reduced the bias with observed SS loading. Therefore, a real-time monitoring of inflow turbidity is necessary to better estimate of SS influx to the reservoirs and enhance the reliability of reservoir turbidity modeling.

• Journal of Environmental Science International
• /
• v.16 no.5
• /
• pp.571-581
• /
• 2007

The mechanism of water pollution in Lake Shihwa, one of highly eutrophicated artificial lakes in Korea, has been studied using a numerical 3D physical-biochemical coupled model. In this study, the model was applied to estimate the contribution of land-based pollutant load to water quality of heavily polluted Lake Shihwa. The chemical oxygen demand(COD) was adopted as an index of the lake water quality, and the spatial distribution of an average COD concentration during the summer from 1999 to 2000 was simulated by the model. The simulated COD showed a good agreement with the observed data. According to reproducibility of COD, the high-est levels between 8 and 9 mg/L were shown at the inner site of the lake with inflow of many rivers and ditches, while the lowest was found to be about 5 mg/L at the southwestern site near to dike gate. In the pre-diction of water quality of Lake Shihwa, COD showed still higher levels than 3 mg/L in case of reduction of 95% for land-based pollutant load. This suggests that the curtailment of land-based pollutant load is not only sufficient but the improvement of sediment quality or the increase of seawater exchange should be considered together to improve a water quality in Lake Shihwa.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.24 no.4
• /
• pp.535-547
• /
• 2019

In this study, the heavy metal analysis in sediments (surface sediments, sediments cores and settling particles) from Shihwa Lake has been carried out to evaluate the changes of metal pollution levels in sediments after the operation of Tidal Power Plant (TPP). The average concentrations of metals in surface sediments sampled in 2015 were 8% (Cd)~31% (Zn, Hg) lower than in 2009 before TPP operation. Results of calculating the pollution load index (PLI) with 8 metals, the PLI value in 2015 showed a 18% decrease compared to 2009. However, Cu, Zn, Pb concentrations of surface sediments in 2015 at the upper region around industrial complex still exceeded the TEL (threshold effect level) values for sediment quality guideline in Korea. After the operation of TPP, the metal contaminated depths were increasing from 15 cm to 30 cm at S6 site and from 8 cm to 20 cm at S7 site, respectively. Our data showed that the mean concentration of heavy metals in core samples decreased but the contaminated depth increased. The average of the total sedimentation flux for particulate matter increased by 3.2 times from 32.5 g/㎡/d in 2009 to 103.5 g/㎡/d in 2015. This showed that the bottom sediments were resuspended by the operation of TPP, resulting in an increase of particulate matter in the water column. These results suggest that the sediments contaminated with heavy metals seem to be resuspended and relocated due to the water current caused by the operation of TPP. Cr, Cu, Zn, Pb and Cd were highly exceeding the TEL values in the upstream region and accumulated more than 40 cm of sediment depth, indicating that heavy metal contamination through industrial activity were still a serious environmental problem of Shihwa Lake. Although the metal pollution of Shihwa Lake has been slightly reduced, the contaminated sediments with heavy metals inside of Shihwa Lake might be discharged to outer sea after the resuspension by TPP operation. It is necessary for the advanced scientific approach and political decision to drastically reduce the heavy metal pollution of the study region.