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Comparison of thermal, salt and dye tracing to estimate shallow flow velocities: Novel triple-tracer approach
Journal of Hydrology ( IF 6.4 ) Pub Date : 2018-02-01 , DOI: 10.1016/j.jhydrol.2017.12.048
João R.C.B. Abrantes , Rodrigo B. Moruzzi , Alexandre Silveira , João L.M.P. de Lima

Abstract The accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow. In this study, a novel triple-tracer approach was used to re-evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities. For this purpose a triple tracer (i.e. dyed-salted-heated water) was used. Optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow. Leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated. Experiments were carried out for different flow discharges (32–1813 ml s −1 ) on smooth acrylic, sand, stones and synthetic grass bed surfaces with 0.8, 4.4 and 13.2% slopes. The results showed that thermal tracers can be used to estimate shallow flow velocities, since the three techniques yielded very similar results without significant differences between them. The main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space-averaged flow velocities instead of only one velocity value, with the salt tracer. The correction factors used to determine the actual mean velocity of overland flow varied directly with Reynolds and Froude numbers, flow velocity and slope and inversely with flow depth and bed roughness. In shallow flows, velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements, especially in field studies where these variables vary appreciably in space and time.

中文翻译:

比较热、盐和染料示踪以估计浅层流速:新型三重示踪方法

摘要 浅层流速的准确测量对于理解和模拟地表流对沉积物和污染物输送的动力学至关重要。在这项研究中,一种新的三重示踪方法被用于重新评估和比较传统和完善的染料和盐示踪技术与较新的热示踪技术在估计浅层流速方面。为此,使用了三重示踪剂(即染色的盐水)。光学和红外摄像机以及电导率传感器用于检测流中的示踪剂。测量示踪剂的前沿和质心速度,并比较和研究用于根据示踪剂测量速度确定实际平均流速的校正因子。在坡度为 0.8%、4.4% 和 13.2% 的光滑丙烯酸、沙子、石头和合成草床表面上进行了不同流量排放(32-1813 ml s -1 )的实验。结果表明,热示踪剂可用于估计浅层流速,因为这三种技术产生了非常相似的结果,而它们之间没有显着差异。热示踪剂的主要优点是沿测量部分的示踪剂移动比在真实图像视频中更容易看到,并且可以测量空间平均流速而不是仅测量一个速度值,与盐示踪剂。用于确定地表径流实际平均速度的校正因子直接随雷诺数和弗劳德数变化,流速和坡度,与流动深度和床层粗糙度成反比。在浅层流中,使用示踪剂进行速度估计会带来相当大的不确定性,因此必须谨慎进行这些测量,尤其是在这些变量在空间和时间上有明显变化的现场研究中。
更新日期:2018-02-01
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