Flow characteristics of meandering streams at various sinuosities.

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Sung-Uk Choi, Chaewoong Ban, Donsu Kim

Tuesday 30 june 2015

12:15 - 12:30h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 5F. Engineering - Instrumentation

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Natural streams show various levels of sinuosity depending on the flow regime, sediment particles, and geometry of the adjacent area. In the past, to investigate the flow characteristics of the meandering stream, a lot of laboratory experiments have been carried out. However, most previous experiments were done with an indoor small-scale channel in the laboratory (Jamieson et al., 2010;Kashyap et al., 2010; Blanckaert, 2010, 2011). Furthermore, laboratory experiments used simple cross sections such as a rectangular channel (Tominaga et al., 1999; da Silva et al., 2006; Blanckaert, 2009; Abad and Garcia, 2009a, 2009b). Thus, in order to understand better the flow characteristics of the curved stream, large-scale experiments are needed with a realistic bathymetry. This study presents experimental investigations of meandering streams at various values of sinuosity. Experiments were performed in an outdoor real-scale meandering stream in River Experiment Center in KICT.The outdoor stream has cross sections of natural bathymetry at three values of sinuosity, namely 1.2, 1.5, and 1.7, and the top width is about 11 m. The total length of the curved stream is 680 m, and three different curved streams at a constant sinuosity are connected by about 30 m long transitions. The average slope of the stream is 1/800. Size of sediment particles at the stream bed ranges between 0.25 – 0.5 mm. The boat-mounted Acoustic Doppler Current Profiler was used to measure the velocity at 80 cross sections in the meandering stream. Using the measured data, the impact of sinuosity on the flow was investigated in the meandering stream. Based on the relative location of the streamline that halves the discharge and the centerline, the accelerating and decelerating zones were identified. The sinuosity was found to affect greatly the location and partition of the accelerating and decelerating zones in the meandering stream. The results also indicated that the maximum velocity, located along the outer part near the apex, moves upstream as the sinuosity increases. This is consistent with previous findings from laboratory experiments of da Silva et al. (2006). In addition, it was revealed that the convergence flow is made from one apex to another at a small sinuosity and the convergence zone migrates upstream as the sinuosity increases.