As density decreases, the amount of air passing through the windbreak increases, moderating the low pressure and turbulence, and increasing the length of the downwind protected area. While this protected area is larger, the wind speed reductions are not as great. By adjusting windbreak density, different flow patterns and areas of protection are established. A windbreak density of 40 to 60 percent provides the greatest downwind area of protection and provides excellent soil erosion control. To get even distribution of snow across a field, densities of 25 to 35 percent are most effective but may not provide sufficient control of soil erosion.
Windbreaks are most effective when oriented at right angles to prevailing winds.
Although the height of a windbreak determines the extent of the protected area downwind, the length of a windbreak determines the total area receiving protection. This ratio reduces the influence of end-turbulence on the total protected area. The continuity of a windbreak also influences its efficiency. Gaps in a windbreak become funnels that concentrate wind flow, creating areas on the downwind side of the gap in which wind speeds often exceed openfield wind velocities. Where there are gaps, the effectiveness of the windbreak is diminished.