[논문]부유사 지표로 초음파산란도를 활용한 합류부 3차원 수체혼합 특성 도출

손근수; 김동수; 곽성현; 김영도; 류시완

doi:10.3741/jkwra.2021.54.3.167

부유사 지표로 초음파산란도를 활용한 합류부 3차원 수체혼합 특성 도출
Characterizing three-dimensional mixing process in river confluence using acoustical backscatter as surrogate of suspended sediment 원문보기

Journal of Korea Water Resources Association = 한국수자원학회논문집, v.54 no.3, 2021년, pp.167 - 179

손근수 (단국대학교 토목환경공학과) , 김동수 (단국대학교 토목환경공학과) , 곽성현 (환경부 물관리위원회 지원단) , 김영도 (명지대학교 토목환경공학과) , 류시완 (창원대학교 토목환경화공융합공학부)

초록
AI-Helper

하천 합류부는 두 하천이 만나 형성되는 지역으로 합류부 구간의 혼합 매커니즘을 이해하기 위해서는 지류의 다양한 유입조건에 따른 본류와의 수체혼합의 공간적인 패턴을 분석하는 것이 중요하다. 그러나, 대부분의 합류부 연구들은 실측을 통한 현장데이터를 획득하기 어렵기 때문에 수리 및 수질 수치모형을 통한 연구가 주로 수행되어 왔다. 본 연구에서는 지류와 본류의 합류의 혼합 현상을 규명하는 인자로 유속과 수심 등 기본적인 수리학적 인자들 외에 최근 하천 유사측정을 위해 부유사농도의 지표로 연구되고 있는 ADCP의 초음파산란도를 활용하여 합류부에서 상이한 유사특성을 가진 두 수체가 혼합되는 양상을 측정하여 합류부의 혼합 특성을 해석하고자 하였다. 초음파산란도는 부유사와 관련되는 인자로 SonTek ADCP 이동식으로 측정된 초음파산란도(SNR)자료를 빔퍼짐에 대한 보정, 물에 의한 흡수를 고려하여 보정한 후 3차원 혼합거동의 공간적인 분포를 도출하였다. 그리고 측정기간 중 드론(UAV), LISST를 이용하여 합류부의 혼합양상을 모니터링하여 초음파산란도를 이용한 분석결과와 비교하였다. 분석결과, ADCP로부터 제공되는 초음파산란도를 보정한 결과 합류부의 3차원적인 유사 혼합의 공간적 특성을 규명하는 데 적합한 인자라고 할 수 있었고, 상이한 본류와 지류의 유입을 고려하였을 때 다양한 혼합 거동을 분석하는데 지표로 사용이 가능함을 확인할 수 있었다. 따라서 본 연구에서는 남강과 낙동강의 합류부에 대해 초음파산란도를 활용하여 합류부의 혼합 특성을 분석하였다.

Abstract ▼ AI-Helper

In order to characterize the mixing process of confluence for understanding the impacts of a river on the other river, it has been crucial to analyze the spatial mixing patterns for main streams depending on various inflow conditions of tributaries. However, most conventional studies have mostly relied upon hydraulic or water quality numerical models for understanding mixing pattern analysis of confluences, due to the difficulties to acquire a wide spatial range of in-situ data for characterizing mixing process. In this study, backscatters (or SNR) measured from ADCPs were particularly used to track sediment mixing assuming that it could be a surrogate to estimate the suspended sediment concentration. Raw backscatter data were corrected by considering the beam spreading and absorption by water. Also, an optical Laser diffraction instrument (LISST) was used to verify the method of acoustic backscatter and to collect the particle size distribution of main stream and tributary. In addition, image-based spatial distributions of sediment mixture in the confluence were monitored in various flow conditions by using an unmanned aerial vehicle (UAV), which were compared with the spatial distribution of acoustic backscatter. As results, we found that when acoustic backscatter by ADCPs were well processed, they could be proper indicators to identify the spatial patterns of the three-dimensional mixing process between two rivers. For this study, flow and sediment mixing characteristics were investigated in the confluence between Nakdong and Nam river.

주제어

표/그림 (9)

그림 Fig. 1. Typical flow regimes and their characteristics in river confluence (Best, 1987)
그림 Fig. 2. Study area where the confluence of Nam and Nakdong river is location and its various spatial scales: a) Nakdong River basin; b) regional location; c) the shape of the confluence in the higher spatial resolution
그림 Fig. 3. Morphological representation of the confluence between Nam and Nakdong River where bathymetric maps are interpolated based on ADCP measurements collected in: (a) April 28 ~ 29; (b) June 16
표 Table 1. Hydraulic and geometric conditions for each measurement campaign
그림 Fig. 4. Hydrodynamic velocity distribution in the vicinity of the confluence between Nam and Nakdong river, which were measured and depth-averaged by using ADCP moving boat measurements at: (a) April 28; (b) April 29; (c) June 16
그림 Fig. 5. Comparative analysis in terms of visual inspection between ADCP backscatter near the water surface and UAV-based aerial mixing pattern monitored in the downstream vicinity of the confluence at a concurrent day of April 28: (a)derived spatial mapping of acoustical backscatter corrected for beam spreading and water absorption based on interpolation ADCP moving boat measurements; (b) visual monitoring of two water bodies and their scale in the middle of the mixing captured by DJI Drone
그림 Fig. 6. Comparative analysis in terms of visual inspection between ADCP backscatter near the water surface and UAV-based aerial mixing pattern monitored in the downstream vicinity of the confluence at a concurrent day of April 29: Captions for (a) and (b) are identical denoted in Fig. 5
그림 Fig. 7. Comparative analysis in terms of visual inspection between ADCP backscatter near the water surface, UAV-based aerial mixing pattern, and actual suspended sediment distribution monitored in the downstream vicinity of the confluence at a concurrent day of April 29: captions for (a) and (b) are identical denoted in Fig.5, and (c) suspended sediment distribution measured near water surface interpolated by LISST, which was spatially dragged mounted on a boat
그림 Fig. 8. Three-dimensional distribution of corrected acoustical backscatter as a surrogate of suspended sediment concentration for various flow regimes at the confluence of Nam and Nakdong river: (a) processed by ADCP measurements collected at April 28; (b)April 29, and (c) June 16

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