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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Flow characteristics of meandering streams at various sinuosities
Flow characteristics of meandering streams at various sinuosities
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 (Kashyap et al., 2012; Blanckaert, 2010, 2011; Jamieson et al., 2010). Furthermore, laboratory experiments
used simple cross sections such as a rectangular channel (Abad and Garcia, 2009a, 2009b; Blanckaert, 2009; da Silva et
al., 2006; Tominaga et al., 1989). Thus, in order to understand better the flow characteristics of the curved stream, largescale
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 Korea Institute of Civil Engineering
and Building Technology (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 ĘC 0.5 mm. The boat-mounted Acoustic
Doppler Current Profiler (ADCP) was used to measure the velocity components 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.
Figure 1 shows the locations of the centerline, half-discharge line, and maximum velocity line along the streamwise
direction. Here, the centerline and half-discharge lines are defined by the lines that halve the flow area and total discharge,
respectively. In the figure, the vertical axis is the lateral distance from the side normalized by the width. The relative
gradient of the lines in the streamwise direction determines the accelerating or decelerating zone (da Silva et al., 2006).
That is, the flow is accelerating if the gradient of the half-discharge line (red line) is larger than that of the centerline (blue
line), and the flow is decelerating under the opposite condition. At the origin of the figure, the flow is accelerating and
decelerating at the outer and inner parts, respectively, and the flow undergoes the transition at about s = 68 m. It can be
seen that the maximum velocity line is located most closely to the side where the flow transition is made.
The maximum velocity lines for two sinuosities are shown in Figure 2. The location of the maximum velocity that is most
close to the side is referred to as the location of the near-side maximum velocity. It can be seen that the location of the
near-side maximum velocity changes with sinuosity, which is clearly related to the change of the location of the flow
transition. In the figure, the location of the flow transition changes from the crossover to the apex as the sinuosity changes
from 1.2 to 1.5. This indicates that the location of the near-side maximum velocity moves in the upstream direction with
increasing sinuosity.
File Size : 216,782 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 17/08/2015
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