Účinnost větrolamů na základě měření větrného pole a optické porozity

Abstract

Windbreaks have been used for many years to reduce wind speed as a wind-erosion control mea­su­re. To assessment of windbreak efficiency two main parameters are using: height of windbreak (H) and aerodynamic porosity. In South Moravian Region the total area of windbreaks is approximately 1200 ha. For purposes of horizontal profile measurement of wind speed and wind direction windbreaks with various spices composition, age and construction in cadastral territory Suchá Loz and Micmanice were chosen. Windbreak influence on horizontal wind profile was found out in distance of 50, 100, 150 and 200 m in front and behind windbreak in two-meter height above surface. For the optical porosity measurement the ImageTool program was used. The wind field measurement results of windbreak in Suchá Loz cadastral shows limited effect of windbreak on wind speed. The windbreak is created mainly by Canadian poplars (Populus × canadensis). In dependence on main species foliage stage the effect of windbreak was obvious on leeward side to distance of 100–150 m (c. 5–7 H). Average optical porosity of windbreak in Suchá Loz was 50% (April). Reduction of average wind speed was about 17% maximally in this stage. Optical porosity was 20% and wind speed reduction was about 37% during second measurement (October). The second monitored windbreak (Micmanice) had a significant influence on wind speed even to the maximal measured distance (200 m, c. 14 H). This windbreak crea­ted mainly by Acer sp. and Fraxinus excelsior reduced the wind speed about 64%. During first measurement (May) the optical porosity of 20% and maximal wind speed reduction of 64% were assessed. For optical porosity of 21% (October) the wind speed reduction was about 55%. Close relation between optical porosity and wind speed reduction was found out by statistical evaluation. Correlation coefficient regardless locality for distance of 50 m was −0.80, 100 m −0.92, 150 m −0.76 and for distance of 200 m −0.63.