Boundary-Layer Meteorology

, Volume 22, Issue 1, pp 79-90

First online:

Averaging procedures for flow within vegetation canopies

  • M. R. RaupachAffiliated withCSIRO Division of Environmental Mechanics
  • , R. H. ShawAffiliated withDepartment of Land, Air and Water Resources, University of California

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


Most one-dimensional models of flow within vegetation canopies are based on horizontally averaged flow variables. This paper formalizes the horizontal averaging operation. Two averaging schemes are considered: pure horizontal averaging at a single instant, and time averaging followed by horizontal averaging. These schemes produce different forms for the mean and turbulent kinetic energy balances, and especially for the ‘wake production’ term describing the transfer of energy from large-scale motion to wake turbulence by form drag. The differences are primarily due to the appearance, in the covariances produced by the second scheme, of dispersive components arising from the spatial correlation of time-averaged flow variables. The two schemes are shown to coincide if these dispersive fluxes vanish.