Porosity and Drag Determination of a Single-Row Vegetative Barrier (Maclura pomifera)

Abstract

Abstract. Deciduous trees of the species (Osage orange) are commonly established as vegetative barriers for wind erosion control throughout the U.S. Great Plains. Because there is no previous research on the aerodynamic effectiveness of these vegetative barriers during different seasons (leaf-on and leaf-off conditions), this study focused on determining the porosity and drag characteristics of this tree species. Digital image analyses were used to determine optical porosities that were then correlated with barrier drag coefficients. Images were taken in the field during calm wind conditions when the sunlight was suitable for digital imaging. Wind speeds were measured at different heights for a single-row Osage orange barrier using cup anemometers. Two anemometer towers were positioned relative to the barrier. One was located windward at 10H distance from the barrier; the other was located leeward and was movable to distances of 1H, 2H, 4H, 7H, 10H, 12H, 15H, and 20H from the barrier, where H is the average barrier height. The wind speeds measured in the field ranged from 4 to 7 m s-1, with lower wind speeds encountered during the leaf-off condition. As expected, wind speed reductions were greater for the leaf-on condition and ranged from 40% to 80% at 1H from the barrier, while the reduction was 20% to 38% for the leaf-off condition. The crown portion of the barrier was found to be responsible for much of the reduction. Mean values of the drag coefficient were 1.3 for the leaf-on condition, decreasing to 0.9 for the leaf-off condition of the Osage orange barrier, which corresponded to mean optical porosities of 20% and 61%, respectively Keywords: Drag coefficient, Image analysis, Osage orange, Porosity, Vegetative barrier, Wind erosion.

Drones and windbreaks

“…The importance of vegetal barriers is also highlighted in the case of the protection of communication ways, [5]. We followed the path described by the authors [3] until to the method of obtaining the experimental data. Vegetative barrier effectiveness is commonly measured by its sheltering efficiency leeward of the barrier via reduced wind speed, [3].The aerodynamic ( ) and the optical ( ) porosities of the vegetative barrier are defined in [3].…”

“…where is the height of the barrier, in m, ̅ is the leeward wind speed (bleed wind speed), in m s -1 , and is the mean windward wind speed, in m s -1 . The optical porosity is defined by the formula, [3]:…”

“…According to [3], the background area (representing gaps outside the area occupied by the tree including leaves, branches, stems, and trunk), is obtained from image analysis of digitized photographs. Although βp is convenient to use because it does not require wind measurement, a relationship between αp and βp is necessary, especially for deciduous trees that experience porosity variations throughout the year, as it is specified in [3].…”

“…According to [3], the background area (representing gaps outside the area occupied by the tree including leaves, branches, stems, and trunk), is obtained from image analysis of digitized photographs. Although βp is convenient to use because it does not require wind measurement, a relationship between αp and βp is necessary, especially for deciduous trees that experience porosity variations throughout the year, as it is specified in [3]. Specific objectives of the study from article [3], were to: determine optical porosity using image analysis, determine aerodynamic porosity and drag coefficients during leaf-on and leaf-off conditions using wind profile measurements, and measure the effects of vegetative barrier leaf condition on wind speed reduction.…”

“…Although βp is convenient to use because it does not require wind measurement, a relationship between αp and βp is necessary, especially for deciduous trees that experience porosity variations throughout the year, as it is specified in [3]. Specific objectives of the study from article [3], were to: determine optical porosity using image analysis, determine aerodynamic porosity and drag coefficients during leaf-on and leaf-off conditions using wind profile measurements, and measure the effects of vegetative barrier leaf condition on wind speed reduction. This article proposes a new approach, with new tools and concepts, for the same problem of forest curtains.…”