scholarly journals Influence of floodplain and riparian vegetation in the conveyance and structure of turbulent flow in compound channels

2018 ◽  
Vol 40 ◽  
pp. 06035 ◽  
Author(s):  
João N. Fernandes ◽  
João B. Leal ◽  
António H. Cardoso
Keyword(s):  
Turbulent Flow ◽  
Riparian Vegetation ◽  
Main Channel ◽  
Submerged Vegetation ◽  
Doppler Velocimetry ◽  
Compound Channels ◽  
Turbulence Structures ◽  
Experimental Campaign ◽  
Turbulent Flow Structure ◽  
Acoustic Doppler Velocimetry

The present study aims at understanding the changes in the channel conveyance and in the turbulent flow structure due to the presence of both submerged vegetation in the floodplains and riparian vegetation. An experimental campaign was carried out comprising uniform compound channels flows (i) without any kind of vegetation, (ii) with synthetic grass in the floodplains, (iii) with synthetic grass in the floodplains and rods in the interface between main channel and the floodplain and (iv) with synthetic grass in the floodplains and artificial shrubs in the interface between main channel and the floodplain. For comparison, the water depth in all flow cases was kept constant. Accurate acoustic Doppler velocimetry was used to evaluate the 3d velocity field and the turbulence structures characteristics.

scholarly journals Turbulent Flow Structure in a Confluence: Influence of Tributaries Width and Discharge Ratios

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 465
Author(s):  
Leila Alizadeh ◽  
João Fernandes
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Flow Structure ◽  
Transport Processes ◽  
Momentum Ratio ◽  
Experimental Campaign ◽  
Flow Mechanisms ◽  
Turbulent Flow Structure ◽  
Physical Mixing ◽  
The Difference

River channel confluences are rather important interfaces where intense changes in physical, mixing and sediment transport processes occur. Following an experimental campaign, the main flow mechanisms in confluences and the development of the shear layer formed between the two tributary flows are presented. As the experimental flow cases comprised changes in the flow discharge and channel widths of the tributaries, the influence of width and discharge ratios on the turbulent flow structure and shear layer is also evaluated. Main findings indicate that changes in the difference between momentum ratio in the tributaries have a significant effect on the magnitude and location of flow mechanisms.

scholarly journals Experimental study of open-channel flow with partial double-layered vegetation

2019 ◽  
Vol 81 ◽  
pp. 01010 ◽  
Author(s):  
Xiaonan Tang ◽  
Hamidrez Rahimi ◽  
Prateek Singh ◽  
Zishun Wei ◽  
Yuxuan Wang ◽  
...  
Keyword(s):  
Experimental Study ◽  
Riparian Vegetation ◽  
Open Channel ◽  
Open Channel Flow ◽  
Doppler Velocimetry ◽  
Flume Experiments ◽  
Flow Process ◽  
River Flood ◽  
Acoustic Doppler Velocimetry ◽  
Natural Rivers

Many rivers and wetlands have vegetation. The effect of riparian vegetation on ecological and flow process in channels has become increasingly important in river flood risk and aquatic environmental management. Most previous studies have been done on the flow structure of vegetation of the same height which is not realistic in natural rivers. There are only a few studies on flows with a mixing array of short and tall vegetation under either submerged or emergent flow condition. This paper is to undertake a novel experimental study on a flow with double-layered vegetation under submerged and emergent conditions, which often occur in most rivers. Two different heights of dowels, 10 cm and 20 cm, were used in the water flume to represent the short and tall vegetation respectively, and they were allocated on one side of the flume. Experiments in two flow depths were undertaken to represent different submergence ratios of vegetation, and velocities at various locations were measured by Acoustic Doppler Velocimetry (ADV) and propeller velocimetry. Experimental results show that the velocity profile is almost uniform within the depth of short vegetation in different configurations. The velocity starts to increase in the region near the edge of short vegetation, and then followed by a rapid increase through the height of tall vegetation to the free surface. Meanwhile, a strange shear layer exists laterally between vegetation and non-vegetation, showing that the vegetation significantly reduces the velocity of flow.

scholarly journals Turbulent flow structure at a 90-degree open channel confluence: Accounting for the distortion of the shear layer

2016 ◽  
Vol 12 ◽  
pp. 130-147 ◽  
Author(s):  
Saiyu Yuan ◽  
Hongwu Tang ◽  
Yang Xiao ◽  
Xuehan Qiu ◽  
Huiming Zhang ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Flow Structure ◽  
Open Channel ◽  
Turbulent Flow Structure ◽  
Channel Confluence

Turbulent flow structure at a discordant river confluence: Asymmetric jet dynamics with implications for channel morphology

2017 ◽  
Vol 122 (6) ◽  
pp. 1278-1293 ◽  
Author(s):  
Alexander N. Sukhodolov ◽  
Julian Krick ◽  
Tatiana A. Sukhodolova ◽  
Zhengyang Cheng ◽  
Bruce L. Rhoads ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Flow Structure ◽  
Channel Morphology ◽  
River Confluence ◽  
Turbulent Flow Structure

scholarly journals Role of Transient Characteristics in Fish Trajectory Modeling

2020 ◽  
Author(s):  
zhu gao ◽  
zu hao zhou ◽  
Helge I Andersson
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Turbulent Flow ◽  
Transient Flow ◽  
Simultaneous Recording ◽  
Fish Locomotion ◽  
Vertical Slot ◽  
Turbulent Flow Structure ◽  
General Method

In this paper, we analyzed the live fish trajectory recorded from an experiment in an experimental vertical slot fishway. Combined with a numerical simulation, we demonstrated that randomness shown in fish trajectory might not merely be attributed to fish's random choices in its swimming, also could be an adaption consequence to the bulk unsteady turbulent flow structure. Simple superposing the fish trajectory on the time-averaged flow field obtained either by interpolating on discrete point measurements or numerical simulation is not an ideal method for fish movement description in fishway engineering. How to model the fish paths in transient flow and the necessity of simultaneous recording of the flow field and the fish locomotion are challenging topics. The suggested spectrum analysis of the flow field may provide a new general method to reproduce the fish trajectory in a complex turbulent flow.

scholarly journals Riparian Vegetation Density Mapping of an Extremely Densely Vegetated Confined Floodplain

Hydrology ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 176
Author(s):  
István Fehérváry ◽  
Tímea Kiss
Keyword(s):  
Riparian Vegetation ◽  
Woody Species ◽  
Submerged Vegetation ◽  
Vegetation Types ◽  
Vegetation Density ◽  
Vegetation Zone ◽  
Density Mapping ◽  
Vegetation Zones ◽  
Branch Density ◽  
Vegetation Patches

The most crucial function of lowland-confined floodplains with low slopes is to support flood conveyance and fasten floods; however, obstacles can hinder it. The management of riparian vegetation is often neglected, though woody species increase the vegetation roughness of floodplains and increase flood levels. The aims are (1) to determine the branch density of various riparian vegetation types in the flood conveyance zone up to the level of artificial levees (up to 5 m), and (2) to assess the spatial distribution of densely vegetated patches. Applying a decision tree and machine learning, six vegetation types were identified with an accuracy of 83%. The vegetation density was determined within each type by applying the normalized relative point density (NRD) method. Besides, vegetation density was calculated in each submerged vegetation zone (1–2 m, 2–3 m, etc.). Thus, the obstacles for floods with various frequencies were mapped. In the study area, young poplar plantations offer the most favorable flood conveyance conditions, whereas invasive Amorpha thickets and the dense stands of native willow forests provide the worst conditions for flood conveyance. Dense and very dense vegetation patches are common in all submerged vegetation zones; thus, vegetation could heavily influence floods.

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