Modeling the flow resistance of woody vegetation using physically based properties of the foliage and stem

Kaisa Västilä*, Juha Järvelä

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

51 Citations (Scopus)


Both the foliage and stem essentially influence the flow resistance of woody plants, but their different biomechanical properties complicate the parameterization of foliated vegetation for modeling. This paper investigates whether modeling of flow resistance caused by natural woody vegetation can be improved using explicit description of both the foliage and stem. For this purpose, we directly measured the drag forces of Alnus glutinosa, Betula pendula, Salix viminalis, and Salix x rubens twigs in a laboratory flume at four foliation levels, parameterized with the leaf-area-to-stem-area ratio A L/AS. The species differed in the foliage drag but had approximately equal stem drag. For the foliated twigs, increasing A L/AS was found to increase the reconfiguration and the share of the foliage drag to the total drag. The experiments provided new insight into the factors governing the flow resistance of natural woody vegetation and allowed us to develop a model for estimating the vegetative friction factor using the linear superposition of the foliage and stem drag. The model is novel in that the foliage and stem are separately described with physically based parameters: drag coefficients, reconfiguration parameters, and leaf area and frontal-projected stem area per ground area. The model could satisfactorily predict the flow resistance of twig to sapling-sized specimens of the investigated species at velocities of 0.05-1 m/s. As a further benefit, the model allows exploring the variability in drag and reconfiguration associated with differing abundance of the foliage in relation to the stem. Key Points Leaf-area-to-stem-area ratio-controlled flow resistance of foliated vegetation Separate parameterization of foliage and stem improved description of drag New flow resistance model based on the superposition principle was proposed

Original languageEnglish
Pages (from-to)229-245
Number of pages17
JournalWater Resources Research
Issue number1
Publication statusPublished - Jan 2014
MoE publication typeA1 Journal article-refereed


  • drag
  • flow resistance
  • modeling
  • parameterization
  • reconfiguration
  • vegetation


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