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André Vézina, ITA, La Pocatière Campus
Shelterbelt Efficiency Criteria
April 2006
André Vézina, ITA, La Pocatière Campus
Criteria affecting shelterbelt efficiency
Porosity
Height
Length and width
Orientation
Cross profile shape
Environment
André Vézina, ITA, La Pocatière Campus
Porosity () = Perforated area x 100% Total surface area exposed to the wind
André Vézina, ITA, La Pocatière Campus
Low porosity (very dense)
André Vézina, ITA, La Pocatière Campus
Medium porosity
André Vézina, ITA, La Pocatière Campus
Wind speed reduction (% of wind measured in open area) at various distances from a windbreak made of very dense and moderately dense common reed screens (adapted from Nägeli, as used in Guyot, 1977)
Wind
Windbreak
Very denseModerately dense
Average reduction on 20H
André Vézina, ITA, La Pocatière Campus
Windbreak
10 H 20 H
Average windspeed reduction of 50 %
Wind Average windspeed reduction of 25 %
Average windspeed reduction in the lee of a windbreak (porosity=50%, wind measured at 0,5 H above the ground surface)
André Vézina, ITA, La Pocatière Campus
Windbreak Quiet zone
Turbulent zone (plume dilution)
Distance from the windbreak (H)
From Raine (1974) in McNaughton, (1988)
André Vézina, ITA, La Pocatière Campus
André Vézina, ITA, La Pocatière Campus
André Vézina, ITA, La Pocatière Campus
Wind speed reduction (%) obtained from a hedge of hybrid poplars spaced at 1 metre (adapted from Vézina, 1985)
André Vézina, ITA, La Pocatière Campus
André Vézina, ITA, La Pocatière Campus
Siberian elm spaced at 3 m
André Vézina, ITA, La Pocatière Campus
Snow dispersion profile produced by Siberian elm
André Vézina, ITA, La Pocatière Campus
Red ash spaced at 3 m
André Vézina, ITA, La Pocatière Campus
Snow dispersion profile produced by red ash
André Vézina, ITA, La Pocatière Campus
Height impact (from Nägeli 1953, in Guyot, 1989)
Relative heigth
Rel
ativ
e w
ind
spee
d (u
/u0)
Distance (H)
André Vézina, ITA, La Pocatière Campus
André Vézina, ITA, La Pocatière Campus
Odour reduction at W/H
W/H = 0.6 92% reduction
W/H = 8 26% reduction
Odour source
André Vézina, ITA, La Pocatière Campus
Lateral air circulation around the shelterbelt
Protected zone
Wind
André Vézina, ITA, La Pocatière Campus
Several American researchers (Hintz, 1986; Smith and Scholten, 1980) recommend planting very large windbreaks (up to 10 rows of trees and shrubs). However, Read (1964) has demonstrated that narrower, denser hedges are just as effective as very large ones.
André Vézina, ITA, La Pocatière Campus
Orientation
Prevailing winds
André Vézina, ITA, La Pocatière Campus
Perpendicular
Oblique
André Vézina, ITA, La Pocatière Campus
Protected zone
No slope
Downward slope
Upward slope
Protected zone
Protected zone
Prevailing winds
Prevailing winds
Prevailing winds
André Vézina, ITA, La Pocatière Campus
André Vézina, ITA, La Pocatière Campus
Hedge spacing
(Nägeli, 1969, as used in Guyot,1989)Spacing
20 X H
Spacing15 X H
Spacing10 X H
André Vézina, ITA, La Pocatière Campus
Relative spacing (D/H)
Tem
pera
ture
var
iatio
n at
gro
und
leve
l (ºC
)
