Flow and sediment transport in vegetated waterways: a review

Montakhab, Amir; Yusuf, Badronnisa; Ghazali, Abdul Halim; Mohamed, Thamer Ahmed

doi:10.1007/s11157-012-9266-y

Cited by 39 publications

(27 citation statements)

References 68 publications

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“…Macrophytes also influence the geomorphology of the river bed [9,75], higher velocities adjacent to patch might lead to scouring or grain sorting. Firstly, the maximum values for the bed shear stress are 0.37 and 0.73 N m -2 (Table 4), respectively, with and without the inclusion of macrophyte reconfiguration.…”

Section: Discussionmentioning

confidence: 99%

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

et al. 2015

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In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters.& Veerle Verschoren

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Section: Discussionmentioning

confidence: 99%

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

et al. 2015

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“…When turbidity currents encounter arrays of obstacles, such as vegetation canopies in salt marshes, lake littoral zones and seagrass meadows, the drag forces of the obstacles act to reduce the current speed, as well as causing decreases in bed shear stress, which lead to reduced erosion and transport of bed sediment (Zong & Nepf, ; Montakhab et al ., ). However, work on turbidity current interactions with vegetated canopies and other arrays of obstacles has so far been restricted to understanding their hydrodynamics.…”

Section: Introductionmentioning

confidence: 99%

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

et al. 2017

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A laboratory flume experiment was carried out in which the hydrodynamic and sedimentary behaviour of a turbidity current was measured as it passed through an array of vertical rigid cylinders. The cylinders were intended primarily to simulate aquatic vegetation canopies, but could equally be taken to represent other arrays of obstacles, for example forests or offshore wind turbines. The turbidity currents were generated by mixing naturally sourced, poly‐disperse sediment into a reservoir of water at concentrations from 1·0 to 10·0 g l−1, which was then released into the experimental section of the flume by removing a lock gate. For each initial sediment concentration, runs with obstacle arrays with solid plant fractions of 1·0% and 2·5%, and control cases with no obstacles, were carried out. The progress of the current along the flume was characterized by the array drag term, CDaxc (where CD is the array drag coefficient, at the frontal area of cylinders per unit volume, and xc is the position of the leading edge of the current along the flume). The downward depositional flux of sediment out of the current as it proceeded was measured at 13 traps along the flume. Analysis of these deposits divided them into fine (2·2 to 6·2 μm) and coarse (6·2 to 104 μm) fractions. At the beginning of their development, the gravity currents proceeded in an inertia‐dominated regime until CDaxc = 5. For CDaxc > 5, the current transitioned into a drag‐dominated regime. For both fine and coarse sediment fractions, the rate of sediment deposition tended to decrease gradually with distance from the source in the inertial regime, remained approximately constant at the early drag‐dominated regime, and then rose and peaked at the end of the drag‐dominated stage. This implies that, when passing through arrays of obstacles, the turbidity currents were able to retain sufficient sediment in suspension to maintain their flow until they became significantly influenced by the drag exerted by the obstacles.

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“…McLoughlin et al 2014). Although flows through vegetation have been studied extensively both in open channels and adjacent wetlands (e.g., Folkard 2011;Montakhab et al 2012;Nepf 2012a, b), a majority of studies were focused on unidirectional flows through freshwater vegetation. Even though, recently, more attention has been paid to oscillatory flows in coastal vegetated areas, where both waves and currents coexist (e.g., Luhar et al 2010;Callaghan et al 2010;Manca et al 2012), most of the existing studies focused on wave energy dissipation caused by vegetation (e.g., Paul and Amos 2011;Chen and Zhao 2012;Ozeren et al 2013;Anderson and Smith 2014;Blackmar et al 2014;Möller et al 2014).…”

Section: Introductionmentioning

confidence: 99%

A Field Study of How Wind Waves and Currents May Contribute to the Deterioration of Saltmarsh Fringe

Karimpour

Chen

Twilley

2015

Estuaries and Coasts

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Deltaic landscapes, such as the Mississippi River Delta, are sites of extensive conversion of wetlands to open water, where increased fetch may contribute to erosion of marsh edges, increasing wetland loss. A field experiment conducted during a storm passage tested this process through the observations of wave orbital and current velocities in the fringe zone of a deteriorating saltmarsh in Terrebonne Bay, Louisiana. Incident waves seaward of the marsh edge and wave orbital and current velocities immediate landward of the marsh edge were measured. Through a dimensional analysis, it shows that the current and orbital velocities in the marsh fringe were controlled by the incident waves, inundation depth, submergence ratio, and vegetation density. Similarly, it is shown that the longshore currents in the inundated saltmarsh fringe depended on the local wave-induced momentum flux, vegetation submergence, and vegetation density in the fringe zone. The cross-shore current showed the presence of a return flow in the lower region of the velocity profile. A high correlation between the current direction and the local flow-wave energy ratio as well as the vegetation submergence and density is found, indicating the important role of surface waves in the fringe flow landward of an inundated wetland under storm conditions. The field observations shed light on the potential ecological consequences of increased wave activities in coastal saltmarsh wetlands owing to subsidence, sea level rise, limited sediment supply, increases in wind fetch, and storm intensity.

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Flow and sediment transport in vegetated waterways: a review

Cited by 39 publications

References 68 publications

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

A Field Study of How Wind Waves and Currents May Contribute to the Deterioration of Saltmarsh Fringe

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