Abstract
During floods, the riparian vegetation in a watercourse significantly changes the velocity distribution and the turbulence structures of the flow. However, a certain influence on them is always exerted by the bed sediments. The aim of the present work is to study the bed roughness effects on the turbulence characteristics in an open-channel flow with rigid and emergent vegetation. Toward this end, an experimental campaign was conducted and consisted of three runs with different bed roughness conditions. The study is based on the analysis of the velocity, Reynolds shear stress, and viscous stress distributions. The results show that, in the region below the free surface region, the flow is strongly influenced by the vegetation. However, moving toward the bed, the flow is affected by a combined effect of vegetation, firstly, and bed roughness, secondly. This flow zone becomes more extended, as the size of the bed sediments increases. The shear stress distributions confirm the distinction between the two flow regions. In fact, the shear stresses are practically negligible in the upper zone of the water depth influenced by vegetation, whereas, owing to the bed roughness, they reach the maximum value near the bed surface. Finally, the analysis of the turbulent kinetic energy (TKE) revealed high values below the crest level and in the near-bed flow zone in the streamwise direction, whereas a strong lateral variation of TKE from the flume centerline to the cylinder occurred in the intermediate region.
Highlights
Vegetation on river banks and floodplains plays an extremely important role in mitigating the adverse anthropogenic effects on the environment [1,2,3,4,5], especially in the areas most affected by human alterations [6,7,8]
Concluding Remarks that the turbulent kinetic energy (TKE) results are affected by both vegetation and bed roughness, causing an increase in the velocity fluctuations
This study effects on onthe theturbulence turbulencecharacteristics characteristics flows through emergent rigid vegetation, performing three experimental runs with relatively uniform bed emergent rigid vegetation, performing three experimental runs with relatively uniform bed sediments sedimentsthe and under the sameconditions
Summary
Vegetation on river banks and floodplains plays an extremely important role in mitigating the adverse anthropogenic effects on the environment [1,2,3,4,5], especially in the areas most affected by human alterations (presence of bridge piers and abutments, pipelines, etc.) [6,7,8]. Vegetation can have a significant impact on the flow hydrodynamics, influencing the exchange of mass and momentum across the river section [4,9,10,11], as well as on fluvial geomorphology, water quality, and biodiversity (e.g., [12,13]). Vegetation is an important issue for bank stability of rivers and natural channels [14], since plant roots reinforce bank soil and increase its strength for the stability [15]. Flow deceleration promotes local sediment deposits [18], with a further decrease of flow conveyance and increase of river flooding [13].
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