WIND PROFILES IN AN ORCHARD PLANTATION

Wind velocity measurements were made in an orchard with trees of crown diameter 13 ft., height 12 ft. and spacing 24 ft. The horizontal attenuation at 7 ft. height as the orchard is entered is large for the first 3-4 tree rows beyond which an approximately linear decrease of velocity is observed. This is dependent on the velocity at which the wind approaches the orchard and is about 0.44 ft./sec per tree row at 30 ft./sec and 0.15 ft./sec per tree row at 5 ft./sec. Vertical profiles of wind speed between 6 and 40 ft. height were obtained and fitted to a logarithmic profile law. In leafless conditions the profile is predominated by the ground cover of grass. In full foliage profiles depend on the incident wind direction. No significant relationships between profile parameters and atmospheric stability were observed. Roughness lengths of 0.75 ft. in leafless and 4 ft. in full leaf conditions were obtained. Horizontal gustiness coefficients mainly lie between 0.10 and 0.25 and the variation of gustiness with height shows a discontinuity at tree top level which is most marked in full leaf conditions. © 1969.