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http://dx.doi.org/10.3741/JKWRA.2021.54.3.167

Characterizing three-dimensional mixing process in river confluence using acoustical backscatter as surrogate of suspended sediment  

Son, Geunsoo (Department of Civil & Environmental Engineering, Dankook University)
Kim, Dongsu (Department of Civil & Environmental Engineering, Dankook University)
Kwak, Sunghyun (Water Commission Support Department, Ministry of Environment)
Kim, Young Do (Department of Civil and Environmental Engineering, Myongji University)
Lyu, Siwan (Department of Civil Engineering, Changwon National University)
Publication Information
Journal of Korea Water Resources Association / v.54, no.3, 2021 , pp. 167-179 More about this Journal
Abstract
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.
Keywords
ADCP; UAV; LISST; Confluence; Mixing;
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