### Abstract

Original language | English |
---|---|

Pages (from-to) | 3179-3196 |

Number of pages | 18 |

Journal | Water Resources Research |

Volume | 53 |

Issue number | 4 |

DOIs | |

Publication status | Published - 18 May 2017 |

### Fingerprint

### Cite this

}

*Water Resources Research*, vol. 53, no. 4, pp. 3179-3196. https://doi.org/10.1002/2016WR020090

**A new model for predicting the drag exerted by vegetation canopies.** / Etminan Farooji, Vahid; Lowe, Ryan; Ghisalberti, Marco.

Research output: Contribution to journal › Article

TY - JOUR

T1 - A new model for predicting the drag exerted by vegetation canopies

AU - Etminan Farooji, Vahid

AU - Lowe, Ryan

AU - Ghisalberti, Marco

PY - 2017/5/18

Y1 - 2017/5/18

N2 - The influence of vegetation canopies on the flow structure in streams, rivers, and floodplains is heavily dependent on the cumulative drag forces exerted by the vegetation. The drag coefficients of vegetation elements within a canopy have been shown to be significantly different from the well-established value for a single element in isolation. This study investigates the mechanisms that determine canopy flow resistance and proposes a new model for predicting canopy drag coefficients. Large Eddy Simulations were used to investigate the fine-scale hydrodynamics within emergent canopies with solid area fractions ( math formula) ranging from 0.016 to 0.25. The influences of three mechanisms in modifying canopy drag, namely, blockage, sheltering, and delayed separation, were investigated. While the effects of sheltering and delayed separation were found to slightly reduce the drag of very sparse canopies, the blockage effect significantly increased the drag of denser canopies ( math formula). An analogy between canopy flow and wall-confined flow around bluff bodies is used to identify an alternative reference velocity in the definition of the canopy drag coefficient; namely, the constricted cross-section velocity (Uc). Through comparison with both prior experimental data and the present numerical simulations, typical formulations for the drag coefficient of a single cylinder are shown to accurately predict the drag coefficient of staggered emergent canopies when math formula is used as the reference velocity. Finally, it is shown that this new model can be extended to predict the bulk drag coefficient of randomly arranged vegetation canopies.

AB - The influence of vegetation canopies on the flow structure in streams, rivers, and floodplains is heavily dependent on the cumulative drag forces exerted by the vegetation. The drag coefficients of vegetation elements within a canopy have been shown to be significantly different from the well-established value for a single element in isolation. This study investigates the mechanisms that determine canopy flow resistance and proposes a new model for predicting canopy drag coefficients. Large Eddy Simulations were used to investigate the fine-scale hydrodynamics within emergent canopies with solid area fractions ( math formula) ranging from 0.016 to 0.25. The influences of three mechanisms in modifying canopy drag, namely, blockage, sheltering, and delayed separation, were investigated. While the effects of sheltering and delayed separation were found to slightly reduce the drag of very sparse canopies, the blockage effect significantly increased the drag of denser canopies ( math formula). An analogy between canopy flow and wall-confined flow around bluff bodies is used to identify an alternative reference velocity in the definition of the canopy drag coefficient; namely, the constricted cross-section velocity (Uc). Through comparison with both prior experimental data and the present numerical simulations, typical formulations for the drag coefficient of a single cylinder are shown to accurately predict the drag coefficient of staggered emergent canopies when math formula is used as the reference velocity. Finally, it is shown that this new model can be extended to predict the bulk drag coefficient of randomly arranged vegetation canopies.

U2 - 10.1002/2016WR020090

DO - 10.1002/2016WR020090

M3 - Article

VL - 53

SP - 3179

EP - 3196

JO - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 4

ER -