Flow Patterns and Vegetation Interactions in A Straight Channel: An Experimental Study

Abstract

The presence of natural vegetation in a river or canal can have various effects on different aspects of flow structures, including conveyance capacity, turbulent properties, sediment transportation and deposition, pollutant transportation, water quality improvement, and the provision of food and shelter for aquatic life. The focus of the present study is on the turbulent flow structure in a partially vegetated straight channel. Experimental work was carried out in a straight tilting flume measuring 12 meters in length, 0.6 meters in width, and 0.9 meters in depth. In this study, natural Vetiver grass (Chrysopogon zizanioides) was used in the half width of the channel and placed in a staggered pattern on the sand bed under emergent conditions. The experiment involved the use of natural flexible vegetation in the emergent condition on one side of the channel under mobile bed conditions to investigate turbulent flow properties, including three-dimensional velocity, three-dimensional turbulent intensity, and turbulent kinetic energy. Instantaneous velocities were recorded using a 3-D micro ADV with a 5 cm down-looking sensor operating at 50 Hz to analyze the time-averaged velocity and turbulence properties under steady flow conditions. The turbulent flow properties were examined in the vegetated side, interface of vegetation, and nonvegetated side, and comparisons were made between these regions. The experimental results revealed that longitudinal velocity increases in the non-vegetated side while decreasing in the vegetated side and S-shape profile is observed at the interface of the vegetation in the channel. The distribution of vertical velocity decreases in the non-vegetated side, increases in the interface of vegetation, and further increases in the vegetated side of the channel. Three-dimensional turbulent intensity and turbulent kinetic energy are also discussed in this study. This study provides valuable insights into understanding the flow characteristics in the non-vegetated, interface, and vegetated side of the channel.