Flow resistance of in-line vegetation in open channel flow

ABSTRACT

Open channel flow through a line of vertically oriented circular rods, designed to represent idealized bankline vegetation, is studied. Bankline vegetation is a common feature in rivers and streams and yet has not received as much attention as fully vegetated flows. Particular focus is placed on the effect of vegetation diameter on the flow resistance which is quantified via a drag coefficient. A large number of laboratory experiments of uniform flow through one-line of vegetation were carried out and drag coefficients were calculated via a momentum balance. Experimentally obtained drag coefficients are then compared to those calculated using a number of empirical expressions that have been proposed in the literature. Good agreement is generally observed. The results show that varying the diameter of the rigid emergent vegetation affects flow resistance, and that the drag coefficient of in-line vegetation exhibits limited sensitivity to the stem Reynolds number.

KEYWORDS:

• Vegetation roughness
• emergent vegetation
• drag coefficient
• blockage

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The first author has been sponsored by the Iraqi government since 1st July 2012.