• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.3
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• pp.180-190
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• 2014

It has been customary to exclude top 10-20% of velocity profiles in the Acoustic Doppler Current Profiler (ADCP) measurement due to side lobe effects at the boundary. To better understand the mixing in the Yeongsan estuary, the freshwater advection speed (FAS) was recovered from highly contaminated ADCP data near the surface. The velocity profiles were measured by using ADCP at two stations in the Yeongsan estuary during August 2011: one was located in front of the Yeongsan estuarine dam and the other was deployed near Goha Island. The FAS was recovered from the ADCP data set by applying rigorous post-processing methods and compared with the sediment advection speed (SAS). The SAS was determined by the peak time difference of suspended sediment concentration between two stations in the channel, divided by the distance of two stations. The FAS and the SAS showed very similar value when the freshwater discharge was greater than $2.0{\times}10^7$ ton and the SAS was a bit greater when the freshwater discharge was smaller. Since the FAS was on average about 0.8 m/s greater than the velocity at 0.8 of water depth from the bottom, the net discharge, estimated with recovered FAS and integrated over water depth and tidal cycle, was directed seaward during the high discharge contrary to the onshore direction of the net discharge estimated with 0.8 of water depth from the bottom. Moreover, the velocity shear and Richardson number changed when the FAS was used. Thus, the importance of the true FAS is appreciated in the investigation of the surface layer stability. If currents, temperature and salinity were observed for longer time in the future, it could be possible to more accurately understand the formation and decay of stratification as well as the suspended sediment transport processes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.12 no.4 s.27
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• pp.301-306
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• 2006

In order to estimate the characteristics of water movements around artificial upwelling structure, current measurements were carried out along lines E-W and S-N on May 4th(neap tide} and May 30th(spring tide), 2006. In the study area, southeastward flow was dominant during the field observations, and the pattern of water movement in the upper layer above 30m depth was different from that in the lower layer below 30m depth Vertical flow(w-component} around the artificial structure area and western area was shown to be upward flow, but downward flow occurred in the southern, northern and eastern parts at the neap tide. At the spring tide, the ebb current along E-W line showed upwelling flow in the eastern part and western area and showed upwelling flow near the artificial structure area and downwelling flow far away that one. At the spring tide, upward flow was dominant along S-N line during the flood current Volume transport by upward flow was higher than that by downward flow. Volume transport by upward flow during ebb of neap tide was greater than during flood current of neap tide, but was reverse at the spring tide.

• Journal of the Korean Association of Geographic Information Studies
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• v.25 no.4
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• pp.136-150
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• 2022

In this study, a comparative review was conducted on how to use RGB images to obtain river topographic information, which is one of the most essential data for eco-friendly river management and flood level analysis. In terms of the topographic information of river zone, to obtain the topographic information of flow section is one of the difficult topic, therefore, this study focused on estimating the river topographic information of flow section through RGB images. For this study, the river topography surveying was directly conducted using ADCP and RTK-GPS, and at the same time, and orthomosiac image were created using high-resolution images obtained by drone photography. And then, the existing developed regression equations were applied to the result of channel topography surveying by ADCP and the band values of the RGB images, and the channel bathymetry in the study area was estimated using the regression equation that showed the best predictability. In addition, CCHE2D flow modeling was simulated to perform comparative verification of the topographical informations. The modeling result with the image-based topographical information provided better water depth and current velocity simulation results, when it compared to the directly measured topographical information for which measurement of the sub-section was not performed. It is concluded that river topographic information could be obtained from RGB images, and if additional research was conducted, it could be used as a method of obtaining efficient river topographic information for river management.

• Journal of Korea Water Resources Association
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• v.40 no.12
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• pp.957-968
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• 2007

It is essential to obtain accurate and highly reliable streamflow data for quantitative management for water resources. Thereafter such real-time streamflow gauging methods as ultrasonic flowmeter and index-velocity are introduced recently. Since these methods calculate flowrate through entire cross-section by measuring partial velocities of it, rational and theoretical basis are necessary for accurate estimation of discharge. The purpose of the present study lies in analysis on the applicability of Chiu#s(1987, 1988) two dimensional velocity distribution equations by applying them to natural rivers and by comparing simulated velocity distributions with observed ones obtained with ADCP. Maximum and mean velocities are calculated from observed data to estimate entropy parameter M. Such isovel shape parameters as h and $\beta_i$ are estimated by object function based on least squares criterion. In case optimized parameters are applied, Chiu#s velocity distributions fairly well simulate observed ones. By using 14 simulated data sets which have relatively high correlation coefficients, properties of parameters are analyzed and h, $\beta_i$ are estimated for velocity-unknown river sections. When estimated parameters are adopted for verification, simulated velocity distributions well reproduce real ones. Finally, calculated discharges display rough agreement with measured data. The results of the present study mean that if parameters related are properly estimated, Chiu#s velocity distribution is likely to reproduce the real one of natural rivers.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.308-308
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• 2011

하천에서 유량을 산정하기 위해서 전자파표면유속계를 이용하여 표면유속을 측정하고 수심평균유속환산계수 0.85를 일률적으로 적용하여 수심평균유속을 산정하고 있다. 이 수심평균유속환산계수 0.85의 적절성에 대한 논의가 지속되어져 왔으나 그 동안에는 이에 대한 현장검증을 할 수 있는 방법이 없었던 실정이다. 하지만 최근 들어서는 ADCP(Acoustic Doppler Current Profiler)의 하천용 Application인 StreamPro ADCP가 개발되어 이를 이용하면 홍수기에 수심별 유속을 측정할 수 있다. 다만 홍수기에 StreamPro ADCP의 적용시에는 여러 가지 높은 위험성이 상존하는 것은 인지의 사실이지만, 그 외의 별다른 방법이 없는 실정이다. 따라서 홍수기에 StreamPro ADCP를 이용하여 수심별 유속을 측정하고 이와 동시에 측정한 표면유속을 이용하여 수심평균유속환산계수를 산정하여 기존에 환산계수로 적용하고 있는 0.85의 적절성을 파악하고자 하였다. 흐름조건별 수심평균유속환산계수 산정을 위하여 평수기 용담 수자원시험유역의 동향지점에서 수심평균유속환산계수를 산정한 결과 0.632~1.352로 넓게 분포하고 있음을 파악하였다. 이렇게 계수가 실제 적용하는 0.85와는 크게 차이가 나는 이유로는 수심이 얕아서 바닥마찰의 영향이 크기 때문인 것으로 판단되었다. 이에 본 연구에서는 여러 지점에서 홍수기 수심별 유속의 실측을 통하여 수심평균유속환산계수 분포정도를 산정하고자 하였다. 대청댐 상류의 수통수위표가 위치해 있는 적벽대교지점에서 StreamPro ADCP를 이용하여 수심평균유속환산계수를 산정한 결과 0.735~0.986 사이에 분포하고 있다. 측정한 결과의 수심평균유속환산계수의 평균값은 0.853으로 기존에 수심평균유속의 산정을 위하여 적용하고 있는 0.85와 거의 일치함을 보이고 있다. 측정당시 수심이 3.6 m에 이르고 있고 유속 또한 1.55 m/s에 이르고 있어 홍수시 일반하천에서 발생하는 수위와 유속임을 감안할 때, 0.735~0.986의 수심평균유속환산계수는 홍수시 순간적인 변화의 폭이 큼을 알 수 있다. 이렇게 순간적인 변화가 큰 이유로는 난류의 성분이 강해서 나타나는 것으로 이를 평균하면 0.853으로 나타나고 있어 홍수시에 수심평균유속환산계수를 0.85를 사용하여도 무방함을 알 수 있다. 동향지점에서 홍수기에 수심별 유속의 실측을 통하여 수심평균유속환산계수를 산정하고자 하였다. 그러나 이 지점은 강한 와류로 인하여 ADCP가 심하게 흔들림으로 인하여 순간적인 유속의 차이가 최대 4배까지 보임을 알 수 있다. 이로 인하여 수심평균유속환산계수의 범위는 0.233~0.983에 이른다. 측정당시 표면유속이 2.07 m/s 인 것을 감안하여 이 표면유속에 상응하는 수심별 유속 자료만을 이용하여 산정시, 수심평균유속환산계수는 0.876이다. 하천의 하류지점에서 수심별 유속을 측정하여 수심평균유속환산계수를 산정하고자 한강하류로 유입하는 굴포천의 구교 및 박촌1교 지점에서 유속측정을 실시하였다. 이들 두 지점은 홍수기에 조차도 유속이 1 m/s 에 이르지 못하는 지점으로, 수심평균유속환산계수를 산정한 결과 각각 0.826, 0.833을 나타내고 있어, 수심평균유속환산계수 0.85가 홍수기뿐만 아니라 평 갈수기에도 적용할 수 있는 가능성을 확인하였다.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.181-190
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• 2021

In this study, a large-scale levee breach experiment from lateral overflow was conducted to verify the effect of the new reinforcement method applied to the levee's surface. The new method could prevent levee failure and minimize damage caused by overflow in rivers. The levee was designed at the height of 2.5 m, a length of 12 m, and a slope of 1:2. A new material mixed with biopolymer powder, water, weathered granite, and loess in an appropriate ratio was sprayed on the levee body's surface at a thickness of about 5 cm, and vegetation recruitment was also monitored. At the Andong River Experiment Center, a flow (4 ㎥/s) was introduced from the upstream of the A3 channel to induce the lateral overflow. The change of lateral overflow was measured using an acoustic doppler current profiler in the upstream and downstream. Additionally, cameras and drones were used to analyze the process of the levee breach. Also, a new method using 3D point cloud for calculating the surface loss rate of the levee over time was suggested to evaluate the performance of the levee reinforcement method. It was compared to existing method based on image analysis and the result was reasonable. The proposed 3D point cloud methodology could be a solution for evaluating the performance of levee reinforcement methods.

• Journal of Korea Water Resources Association
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• v.55 no.1
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• pp.43-57
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• 2022

Advances in measurement techniques have reduced measurement costs and enhanced safety resulting in less uncertainty. For example, an acoustic doppler current profiler (ADCP) based suspended sediment concentration (SSC) measurement technique is being accepted as an alternative to the conventional data collection method. In Korean rivers, horizontal ADCPs (H-ADCPs) are mounted on the automatic discharge monitoring stations, where SSC can be measured using the backscatter of ADCPs. However, automatic discharge monitoring stations and sediment monitoring stations do not always coincide which hinders the application of the new techniques that are not feasible to some stations. This work presents and analyzes H-ADCP-SSC models for 9 discharge monitoring stations in Korean rivers. In application of the Gaussian mixture model (GMM) to sediment-related variables (catchment area, particle size distributions of suspended sediment and bed material, water discharge-sediment discharge curves) from 44 sediment monitoring stations, it is revealed that those characteristics can distinguish sediment monitoring stations regionally. Linking the two results, we propose a protocol determining the H-ADCP-SSC model where no H-ADCP-SSC model is available.

• Journal of Korea Water Resources Association
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• v.55 no.5
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• pp.383-392
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• 2022

The restoration of the Nakdong River estuary is one of the most important projects of the Ministry of Environment, Republic of Korea. A real-scale experiment of gate operation was executed from 2019 to 2020, and a pilot operation was performed in 2021. The gate of Nakdong River Estuary Barrier (NEB) is supposed to be continuously opened based on the experiment results. Many critical decisions should be made immediately during the experiment based on the real-time measured data and numerical analysis considering the seawater inflows. The decision-making sequence was made systematically with the accurate estimation of seawater inflow. The estimation of seawater inflow is the main research objective and the equations of seawater inflow were developed, reflecting the structural characteristics of NEB. The inflow equations were developed in two forms, overflow and underflow. ADCP (Acoustic Doppler Current Profiler) was used to measure seawater inflow, check the accuracy of the developed equations, and derive the flow coefficient. The comparison error of the developed equations was about 3% compared to the measured data.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.305-305
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• 2023

수문조사기기 검정은 강수량, 수위, 유량 등과 같은 수문자료를 관측하는 수문조사기기가 대상지역의 수문상황을 정확하게 관측하는지를 검사하는 일련의 과정으로 「수자원의 조사 계획 및 관리에 관한 법률」 제12조에 법적 기반을 두고 있다. 검정 대상은 강수량, 수위, 유속, 유사량, 토양수분량, 증발산량, 증발량 측정기기 총 7종이며, 환경부장관으로부터 한강홍수통제소가 검정업무를 위임받고, 한국건설기술연구원과 한국수자원조사기술원이 위탁받아 운영중에 있다. 최근에는 증발산량, 토양수분량 및 유량 측정기기기 등이 첨단화되어 기존 검정 방식에 대한보완 및 신설에 대한 요구가 증가하고 있다. 특히, 유량 측정시 기존에 사용하였던 회전식 유속계는 ADCP(Acoustic Doppler Current Profiler) 유량측정기기로 대체되어 활용률이 2013년 24%에서2021년 67%로 약 2.8배 급격히 증가하였다. 하지만 수문조사기기 검정 관련 고시 내 ADCP에 대한검사방법 및 허용오차 등의 규정이 부재하여 수문조사기기의 검정 공백이 발생하는 등의 문제가 존재하고 있다. 이에 본 연구에서는 ADCP 운영 및 기술 현황, 현행 법령, 국외 사례 등을 검토하여 ADCP 유량측정기기의 검사방법 및 허용오차에 대한 방안을 제시하고자 한다. ADCP 검사방법은 총 5단계로 외관검사, 자가진단 검사, 온도센서 검사, 수심측정 검사, 유량비교측정 검사에 따라 검정을 실시한다. 첫 번째 외관검사시에는 기기 외관과 센서 등 물리적 손상을 점검하고, 두 번째 자가진단 검사에서는 센서 변환 매트릭스 값, 수신부 센서 테스트, RAM/ROM 테스트, 통신 테스트 등에 관한 정상값 산출 여부를 확인한다. 세 번째 온도센서 검사에서는 검증용 온도센서를 이용한 값과 ADCP에 부착된 온도센서 값과 차이를 확인하고 ±2℃초과시 재검사 또는 적절한 조치를 취한 후 다음 단계의 검사를 진행한다. 네 번째 수심측정 검사에서는 수조 내 수심 측정을 확인하여 실제 수심과의 오차를 확인하고 ±1% 초과시 재검사 또는 적절한 조치 후 다음 검사를 실시한다. 유량비교 측정검사에서는 각 기기 간의 평균유량의 상대오차를 평가하는 것으로 ±5%미만에는 합격, ±5이상 ±10%미만에서는 재검사, ±10%이상에서는 공장수리를 권고하도록 하고, 1~5 단계의 검사를 통과한 기기를 대상으로 인증서를 발급하도록 한다. 유량비교 측정검사시에는 매년 ADCP를 사용하는 일반기업 및 공공기관 등이 모여 ADCP의 성능을 상호간 비교하는 'ADCP 기술협력 워크숍'을 확장하여 실시할 수 있다. 각 검사 단계의 허용오차는 USGS 또는 제조사 기준과 2022년 ADCP 기술협력 워크숍 성능검사 분석 결과를 토대로 하였다. 본 ADCP 검정 방안은 향후 ADCP 모델별로 단계별 시범 검토를 통해 세부사항에 대한 제시가 필요하며, 온도센서 검사, 수심측정 검사, 유량 비교측정검사에 대한 허용오차에 대한 타당성에대한 검증 및 검토가 이루어져야 할 것으로 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.3
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• pp.321-335
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• 2023

Monitoring sediment loads in natural rivers is the key process in river engineering, but it is costly and dangerous. In practice, suspended loads are directly measured, and total loads, which is a summation of suspended loads and bed loads, are estimated. This study proposes a real-time sediment discharge monitoring system using the horizontal acoustic Doppler current profiler (H-ADCP) and support vector regression (SVR). The proposed system is comprised of the SVR model for suspended sediment concentration (SVR-SSC) and for total loads (SVR-Q_TL), respectively. SVR-SSC estimates SSC and SVR-Q_TL mimics the modified Einstein procedure. The grid search with K-fold cross validation (Grid-CV) and the recursive feature elimination (RFE) were employed to determine SVR's hyperparameters and input variables. The two SVR models showed reasonable cross-validation scores (R²) with 0.885 (SVR-SSC) and 0.860 (SVR-Q_TL). During the time-series sediment load monitoring period, we successfully detected various sediment transport phenomena in natural streams, such as hysteresis loops and sensitive sediment fluctuations. The newly proposed sediment monitoring system depends only on the gauged features by H-ADCP without additional assumptions in hydraulic variables (e.g., friction slope and suspended sediment size distribution). This method can be applied to any ADCP-installed discharge monitoring station economically and is expected to enhance temporal resolution in sediment monitoring.