Vegetation is a common feature in natural coastal and riverine waters, interacting with both wate... more Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation reduced the bedload transport. Thanks to the partitioning of shear stress, it was possible to predict the bedload transport using standard formulas with a reasonable accuracy.
The development of vegetation in the river bed and in the banks can affect the hydrodynamic condi... more The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.
Les rivières forment un système dynamique complexe soumis à des variations de grande ampleur, en ... more Les rivières forment un système dynamique complexe soumis à des variations de grande ampleur, en effet les précipitations sont jugées comme la cause fondamentale de ces fluctuations. Au cours du temps, la morphologie des rivières évolue sous l’influence de plusieurs paramètres, en particulier les crues, les ouvrages hydrauliques, le transport sédimentaire. Le développement de la végétation dans le lit de la rivière et sur les berges peut affecter les conditions hydrodynamiques et le comportement des cours d'eau, ainsi l'impact de la végétation est une question cruciale pour la gestion des réseaux d'irrigation et des flux naturels. En réduisant la vitesse, la présence de végétation peut augmenter les dépôts de sédiments et modifier le risque d'inondation du fait des effets combinés de l'augmentation de la rugosité et de la diminution de la zone d'écoulement du chenal principal du fleuve. Ces aspects sont mis en avant par l’application de simulations numériques...
The flow velocity above large scale roughness is investigated for low and steep slope between 0 a... more The flow velocity above large scale roughness is investigated for low and steep slope between 0 and 4 %. The experiments were conducted in the laboratory of Fluid Mechanics Institute of Toulouse -IMFT. For the velocity measurement, the channel is equipped with a fast camera and a lightening system. The originality of the study lies in the application of a particle tracking technique (Particle Tracking Velocimetry). It is a non-intrusive measurement technique to measure instantaneous velocity in two-dimensional fields in stationary and unsteady flows. Analysis of the results is performed by processing images taken by the camera using a developed detection algorithm. A logarithmic distribution has been found for The velocity profiles which are influenced by roughness and slope. The obtained results show a depression of the maximum speed below the free surface. This behavior indicates a delay of the flow in the vicinity of the free surface and this is a direct consequence of the presen...
Les rivieres forment un systeme dynamique complexe soumis a des variations de grande ampleur, en ... more Les rivieres forment un systeme dynamique complexe soumis a des variations de grande ampleur, en effet les precipitations sont jugees comme la cause fondamentale de ces fluctuations. Au cours du temps, la morphologie des rivieres evolue sous l’influence de plusieurs parametres, en particulier les crues, les ouvrages hydrauliques, le transport sedimentaire. Le developpement de la vegetation dans le lit de la riviere et sur les berges peut affecter les conditions hydrodynamiques et le comportement des cours d'eau, ainsi l'impact de la vegetation est une question cruciale pour la gestion des reseaux d'irrigation et des flux naturels. En reduisant la vitesse, la presence de vegetation peut augmenter les depots de sediments et modifier le risque d'inondation du fait des effets combines de l'augmentation de la rugosite et de la diminution de la zone d'ecoulement du chenal principal du fleuve. Ces aspects sont mis en avant par l’application de simulations numeriques...
Vegetation is a common feature in natural coastal and riverine waters, interacting with both wate... more Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation...
Fluid Mechanics research International Journal, 2018
Nomenclature a x : Distance between 2 roughness in the transverse direction (m) a y : Distance be... more Nomenclature a x : Distance between 2 roughness in the transverse direction (m) a y : Distance between 2 roughness in the longitudinal direction (m) B: Width of the channel (m) C: Roughness function d: Displacement height of the velocity logarithmic profile (m) D: Averaged diameter of the large-scale roughness (m) g: the gravitational constant (m/s-2
The development of vegetation in the river bed and in the banks can affect the hydrodynamic condi... more The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.
Vegetation is a common feature in natural coastal and riverine waters, interacting with both wate... more Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation reduced the bedload transport. Thanks to the partitioning of shear stress, it was possible to predict the bedload transport using standard formulas with a reasonable accuracy.
The development of vegetation in the river bed and in the banks can affect the hydrodynamic condi... more The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.
Les rivières forment un système dynamique complexe soumis à des variations de grande ampleur, en ... more Les rivières forment un système dynamique complexe soumis à des variations de grande ampleur, en effet les précipitations sont jugées comme la cause fondamentale de ces fluctuations. Au cours du temps, la morphologie des rivières évolue sous l’influence de plusieurs paramètres, en particulier les crues, les ouvrages hydrauliques, le transport sédimentaire. Le développement de la végétation dans le lit de la rivière et sur les berges peut affecter les conditions hydrodynamiques et le comportement des cours d'eau, ainsi l'impact de la végétation est une question cruciale pour la gestion des réseaux d'irrigation et des flux naturels. En réduisant la vitesse, la présence de végétation peut augmenter les dépôts de sédiments et modifier le risque d'inondation du fait des effets combinés de l'augmentation de la rugosité et de la diminution de la zone d'écoulement du chenal principal du fleuve. Ces aspects sont mis en avant par l’application de simulations numériques...
The flow velocity above large scale roughness is investigated for low and steep slope between 0 a... more The flow velocity above large scale roughness is investigated for low and steep slope between 0 and 4 %. The experiments were conducted in the laboratory of Fluid Mechanics Institute of Toulouse -IMFT. For the velocity measurement, the channel is equipped with a fast camera and a lightening system. The originality of the study lies in the application of a particle tracking technique (Particle Tracking Velocimetry). It is a non-intrusive measurement technique to measure instantaneous velocity in two-dimensional fields in stationary and unsteady flows. Analysis of the results is performed by processing images taken by the camera using a developed detection algorithm. A logarithmic distribution has been found for The velocity profiles which are influenced by roughness and slope. The obtained results show a depression of the maximum speed below the free surface. This behavior indicates a delay of the flow in the vicinity of the free surface and this is a direct consequence of the presen...
Les rivieres forment un systeme dynamique complexe soumis a des variations de grande ampleur, en ... more Les rivieres forment un systeme dynamique complexe soumis a des variations de grande ampleur, en effet les precipitations sont jugees comme la cause fondamentale de ces fluctuations. Au cours du temps, la morphologie des rivieres evolue sous l’influence de plusieurs parametres, en particulier les crues, les ouvrages hydrauliques, le transport sedimentaire. Le developpement de la vegetation dans le lit de la riviere et sur les berges peut affecter les conditions hydrodynamiques et le comportement des cours d'eau, ainsi l'impact de la vegetation est une question cruciale pour la gestion des reseaux d'irrigation et des flux naturels. En reduisant la vitesse, la presence de vegetation peut augmenter les depots de sediments et modifier le risque d'inondation du fait des effets combines de l'augmentation de la rugosite et de la diminution de la zone d'ecoulement du chenal principal du fleuve. Ces aspects sont mis en avant par l’application de simulations numeriques...
Vegetation is a common feature in natural coastal and riverine waters, interacting with both wate... more Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation...
Fluid Mechanics research International Journal, 2018
Nomenclature a x : Distance between 2 roughness in the transverse direction (m) a y : Distance be... more Nomenclature a x : Distance between 2 roughness in the transverse direction (m) a y : Distance between 2 roughness in the longitudinal direction (m) B: Width of the channel (m) C: Roughness function d: Displacement height of the velocity logarithmic profile (m) D: Averaged diameter of the large-scale roughness (m) g: the gravitational constant (m/s-2
The development of vegetation in the river bed and in the banks can affect the hydrodynamic condi... more The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.
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Papers by Hela ROMDHANE