Document Type : Research Article
Authors
1 Zabol University
2 University of Zabol
Abstract
Introduction: Wind erosion is one of the most important factors in desert environments. Prevailing winds can shift sand dunes and affect their accumulation and morphology. Also, wind regime determines the direction of sand dune mobility in different ways. Therefore, the wind regime, frequency, direction and velocity are supposed to be the most important factors to form the morphology of sand dunes. Wind energy and changes in different directions (wind regime) have large impacts on the morphology, maintenance and transformation of wind features. Having a global knowledge of the magnitude of aeolian processes, we can assess the powerful impact of sand dune mobility on residential areas and infrastructures. The most important factors including the frequency, magnitude and directional mobility of aeolian processes have a very important effect on the entrainment and form of sand dunes.
Materials and Methods: To understand and identify the wind erosion regions, wind regime is a useful way since there is a strong correlation between wind regimes and sand dune morphology and structure. Sand rose and wind rose are assumed to be easy, fast and most accurate methods for the identification of wind erosion. Wind regimes processes have been studied by many researchers who believed that investigating wind regimes and sand dune mobility gives a measure of drift potential. Drift potential is a measure of the sand-moving capability by wind; derived from reduction of surface-wind data through a weighting equation. To predict drift potential, wind velocity and direction data from meteorological synoptic stations were used. Regarding the estimation of sand transport rate by wind, many formulas exist such as Bagnold, Kawamura, and Lattau. Also, many software applications have been suggested. However, among these formulas, Fryberger’s is the best and has been widely used since 1979.
Results and Discussion: The aim of this study was to analyze wind velocities and directions from 1992 to 2003 in order to predict the volume of sand transportation and its direction using sand-rose and wind-rose softwares. As described earlier, in this research, the drift potential (DP) is estimated for all possible wind speed categories, summed up for all categories of each direction sector using Fryberger’s Equation. The sand drift potential in Shileh was estimated about 3439 vector units with a resultant drift direction along the Southeast, which places it in the high class of wind erosive power based on the Fryberger and Dean (1979) classification method. The sand drift potential values show that the resultant drift direction is from the Northwest towards the Southeast. It was also found that the most powerful winds (the prevailing winds) blow in the summer and the spring seasons, respectively. In contrast, the percentage of calm winds increases during autumn and winter times. The sand transport discharge was predicted to be 20.422 t m-1 year-1 using Lattau and Lattau Equation. With regard to the monthly sand rose, it was seen that the resultant drift potential was low in December and January and high in June and July. The prevailing wind direction ranged from North to Northwest in all seasons. The winds with the highest velocities were observed in the summer, while the winds with lower velocities were observed during the winter. Wind velocities higher than 11 m s-1 had the largest frequencies in the summer and the lowest frequencies in the winter. Wind unidirectional index (UDI) is estimated to be 0.95, implying that the index provides a suitable condition for the creation of transverse (barchanoid) dunes.
Conclusion: The Sistan plain is one of the windiest places in the world that is exposed to wind erosion and dust storms. The result of this study is very important due to the construction of an international roadway that connects Chabahar port to Sistan plain and continues towards the Afghanistan border. Therefore, the practical result of this research could be used to protect this highway from sand dune migration. The residential areas and the infrastructure can be damaged by the migration of sand dunes since the sand dunes can move both spatially and temporally. For example, we can even notify the highway passengers about the rate of monthly and seasonal migration of sand dunes so that they avoid travelling during high-storm seasons. The results of this study are also important regarding wind-break design to protect the infrastructure such as highways and agricultural fields. Therefore, sand encroachment hazards affect man-made infrastructures due to wind speed and direction. Sand drift potential is a serious hazard to settlements and other lands as well. This problem is accelerated by the extreme arid conditions (such as the case of Shileh) that may occur in different months of summer.
Keywords: Resultant Drift Direction, Sand Drift Potential, Sand Dune, Wind Erosion, Wind Regime
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