Influence of riparian vegetation on flow resistance in mobile bed straight compound channels

Design guidelines were developed for a number of in-stream structures; however, the knowledge about their morphological and hydraulic function is still incomplete. A variant is submerged groynes, which aim to be applicable for bank protection especially in areas with restricted flood water levels due to their shallow height. Laboratory experiments were conducted to investigate the backwater effect and the flow resistance of submerged groyne fields with varying and constant field length and groyne distance. The effect of the shape of a groyne model was investigated using two types of groynes. The validity of different flow types, from “isolated roughness” to “quasi smooth”, was analyzed in relation to the roughness density of the groyne fields. The results show a higher backwater effect for simplified groynes made of multiplex plates, compared to groynes made of gravel. The relative increase of the upstream water level was lower at high initial water levels, for short length of the groyne field, and for larger distance between the single groynes. The highest roughness of the groyne fields was found at roughness densities, which indicated wake interference flow. Considering a mobile bed, the flow resistance was reduced significantly.

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Hydro-morphodynamic modelling of floodplains: the role of vegetation in suspended sediment transport

10.5194/egusphere-egu2020-22003 ◽

2020 ◽

Author(s):

Daniel A. S. Conde ◽

Robert M. Boes ◽

David F. Vetsch

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Flow Resistance ◽

Laboratory Data ◽

Anthropogenic Factors ◽

Future Research ◽

Suspended Sediment Transport ◽

Compound Channels ◽

Closure Models

Riverine environments are amongst the most complex ecosystems on the planet. As several anthropogenic factors have increasingly disrupted the natural dynamics of rivers, namely through stream regulation, the need for re-establishing the ecological role of these systems has gained relevance.Of particular interest are floodplains in compound channels, primarily regarded for safety against floods, but which also comprise an extensive realm for ecological functions and establishment of various species. Floodplain vegetation affects flow resistance and dispersion, playing a fundamental role in erosion and deposition of suspended sediment.The present work aims at quantifying the interaction between vegetation and suspended sediment transport on floodplains in compound channels by numerical simulations. The employed numerical tool is BASEMENT v3, a GPU-accelerated hydro-morphodynamic 2D model developed at the Laboratory of Hydraulics, Hydrology and Glaciology of ETH Zurich. In the context of the present study, the model is extended with turbulence and suspended sediment transport capabilities. The implemented closure models for turbulence pertain to three major groups, namely (i) mixing-length, (ii) production-dissipation and (iii) algebraic stress models. For suspended sediment transport, the main classical formulations from fluvial hydraulics were implemented in the numerical model.Laboratory data from flume experiments featuring suspended sediment load and vegetation-like proxies are used for model validation. The numerical results are compared with the observed water depths, velocities and sediment concentrations for different sets of experiments with varying properties, such as density and submergence. The implemented closure models for flow resistance, turbulence and suspended sediment are then combined, calibrated and classified in terms of numerical output quality.The obtained results from this modelling effort mainly contribute to understanding the applicability of 2D (depth-averaged) models to complex eco-morphodynamics scenarios. The calibration and rating of well-known closure models for turbulence and sediment transport provides relevant guidelines for both future research and practice in fluvial modelling.

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A comparison of one-dimensional methods for estimating discharge capacity of straight compound channels

Canadian Journal of Civil Engineering ◽

10.1139/l04-053 ◽

2004 ◽

Vol 31 (4) ◽

pp. 619-631 ◽

Cited By ~ 36

Author(s):

Galip Seckin

Keyword(s):

Discharge Capacity ◽

Single Channel ◽

Scale Effects ◽

Compound Channels ◽

One Dimensional ◽

Mobile Bed ◽

Series Of Experiments ◽

And Performance ◽

Discharge Estimation ◽

Fixed Boundaries

A series of experiments was carried out in a two-stage flume having a smooth main channel and smooth or rough floodplains to investigate the reliability and performance of four different one-dimensional methods for computing the discharge capacity of compound channels, namely, the single-channel method (SCM), the divided-channel method (DCM), the exchange discharge method (EDM), and the Ackers method (AM). Additional data from fixed- and mobile-bed compound laboratory channels with smooth and roughened floodplains and of a prototype compound river channel were also used in the computations. The boundary roughness and scale effects associated with the performance of the four methods are also examined. The results show that the EDM and the AM are able to simulate the measured discharge values more accurately than those of the traditional methods, namely, the DCM and the SCM. Although the error in discharge estimation produced by both the AM and the EDM was generally lower than 10% for both smooth and fixed boundaries, it increased up to 20% for mobile boundaries. Overall, the average relative error in discharge estimations using the AM and the EDM was about 5.4% and 7.1%, respectively, with a standard deviation of 6.7% and 6.8%, respectively. Key words: compound channel flow, stage-discharge relationship, one-dimensional methods.

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Effect of Riparian Vegetation on Flow Resistance and Flood Potential

Journal of Hydraulic Engineering ◽

10.1061/(asce)0733-9429(2000)126:12(954) ◽

2000 ◽

Vol 126 (12) ◽

pp. 954-954 ◽

Cited By ~ 9

Author(s):

N. Kouwen

Keyword(s):

Riparian Vegetation ◽

Flow Resistance

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

E3S Web of Conferences ◽

10.1051/e3sconf/20184006035 ◽

2018 ◽

Vol 40 ◽

pp. 06035 ◽

Cited By ~ 1

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.

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