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 dense Moderately 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 WindbreakQuiet zone Turbulent zone (plume dilution) Distance from the windbreak (H) From Raine (1974) in McNaughton, (1988)

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

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 Relative wind speed (u/u 0 ) Distance (H)

André Vézina, ITA, La Pocatière Campus

Odour reduction at W/H W/H = % 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 Prevailing winds

André Vézina, ITA, La Pocatière Campus

Hedge spacing (Nägeli, 1969, as used in Guyot,1989) Spacing 20 X H Spacing 15 X H Spacing 10 X H

André Vézina, ITA, La Pocatière Campus Relative spacing (D/H) Temperature variation at ground level (ºC)