A method for categorizing shelterbelt porosity

States that porosity is the most important single parameter describing shelterbelts but is very difficult to measure or define. Describes a method for categorizing wind breaks in terms of porosity using only measured minimum leeward-wind velocity. Gives theoretical expressions for the flow through a porous shelterbelt. Describes experiment to measure wind velocities around shelterbelts of low, medium and high porosity. Shows that wind measurements could be made any height without affecting relative reduction in velocity. Finds that tree-stand porosityis the dominant parameter governing the wind reduction obtained, while the range of sheltering is controlled by the amount of local turbulence and the turbulence present in the atmosphere beforehand.