تحلیل فرسایندگی باد و پتانسیل حمل ماسه‌های روان واقع در قلمرو بیابان لوت

در این تحقیق به منظور بررسی جهت باد و پتانسیل حمل ماسه در سطح بیابان لوت، از آمار 20 ساله ی چهار ایستگاه سینوپتیک بم، شهداد، نهبندان و نصرت آباد استفاده شد. تحلیل این داده ‌ها، در نرم ‌افزارهای ویندروز و سندروز انجام شد. نتایج بر این دلالت داشت که غالب بادها در ایستگا ه ‌های شهداد و نهبندان از جهات شمالی می وزند، اما در ایستگاه ‌های بم و نصرت‌ آباد به سمت لوت متمرکز می ‌شوند. تطبیق نتایج گل ‌طوفان و گل ‌ماسه‌ ها نشان می ‌دهد که جهت بادهای ایستگاه ‌های شهداد و بم با جهت شمال غربی جنوب شرقی کلوتک ‌های واقع در غرب بیابان لوت انطباق کامل دارد و در شرق لوت جایی که ریگ وسیع یلان قرار دارد، بادهای دو ایستگاه نهبندان و نصرت‌ آباد کاملاً مخالف هم هستند که شرایط لازم را برای تشکیل هرم‌ های ماس‌ه ای در مرکز این ریگ فراهم می ‌کند. در ایستگاه‌ های بم و شهداد، بالاترین پتانسیل حمل ماسه (dp) مربوط به جهات شمال و شمال شرقی و در ایستگاه شهداد، جهات مابین غرب تا شمال شرقی است؛ در حالی که در ایستگاه نصرت آباد، جهت آن کاملاً نسبت به سایر ایستگاه‌ ها متفاوت و بالاترین مقدار آن مربوط به جهات جنوب و جنوب غربی است. مجموع توان حمل ماسه (dpt) نیز به ترتیب به ایستگاه ‌های شهداد، نهبندان، نصرت آباد و بم اختصاص دارد. بالاترین مقدار بردار برآیند توان حمل ماسه (rdp)، مربوط به ایستگاه شهداد است و بعد از آن به ترتیب ایستگاه ‌های نهبندان، نصرت آباد و بم قرار دارند. بررسی شاخص همگنی جهت حمل ماسه (udi)، بیانگر بادهای یک جهته در ایستگاه نهبندان و بادهای دو جهته با زاویه ی منفرجه در ایستگاه‌ های بم، شهداد و نصرت ‌آباد است. بیشترین مقدار دبی حمل ماسه مربوط به ایستگاه شهداد و کمترین میزان آن مربوط به ایستگاه نصرت آباد است. بیشترین مقدار کل ماسه ‌ی حمل شده (tsf) به ‌ترتیب به ایستگاه شهداد، نهبندان، نصرت‌ آباد و بم تعلق دارد. بیشترین مقدار برآیند حمل ماسه (dsf) نیز به ‌ترتیب به ایستگاه شهداد، نهبندان، بم و نصرت‌ آباد بازمی ‌گردد.

Analysis of wind erosion and transport potential of quick sands located in the territory of Lut desert

Extended abstract1 IntroductionArid and semiarid regions of the world cover more than 30% of the earthchr('39')s surface. Wind, as one of the erosive agents of the earthchr('39')s surface, causes the transport of sand and deformation in arid areas. Wind erosion is directly related to wind speed. The higher the wind speed is above the threshold value, the more increase in wind speed. This issue increases wind erosion and thus, it intensifies wind erosion. The Iranian plateau is one of the most sensitive areas of the world to wind erosion due to its location on the arid belt of the northern hemisphere. The Lut Desert is one of the most active places for changes in wind speed and direction with its huge volume of sand masses. The eastern part of this region, which includes the largest sand mass in Iran, namely Yalan sand, is dominated by 120day winds, which doubles the importance of studying winds and its shaping role in the wind season. The main purpose and assumption of this study is to analyze the frequency of erosive winds and estimate the potential and final direction of sand transport flow in the Lut plain and to investigate its relationship with the geomorphology of existing wind forms using time series data of wind direction and speed recorded in Synoptic stations are located around this plain.2 MethodologyIn this study, in order to analyze the wind situation and study the erosive winds in the Lut plain, the available meteorological data for 4 synoptic stations around this plain were used. WRPLOT view 7 software was used for statistical calculations of wind and drawing of wind rose. Sand Rose Graph 3 software was also used to draw the sand rose of the stations around Lut plain due to the high volume of calculations. To calculate the values of sand transport potential (DP) in different geographical directions, the FreibergerDean relationship based on the basic equations of Begnold and LetoLeto was used. From the sum of DP values in different directions, the total sand carrying capacity (DPt) is obtained and in fact it is an indicator that represents the total wind energy to carry sand to the desired station. RDP stands for the amount or size of the output vector (resulting vector) of sand carrying capacity, which is obtained by summing the DP values in 8 or 16 different directions and shows the final status of sand transport in the study area. RDD indicates the net direction of sand movement (result vector direction) during the year, month or season. In order to determine the amount of sand transferred per unit time, a unit of width is used from the equations presented by Begnold, Xing, 1953, Kawamura, 1964, Hesu, 1973 and LetoLeto, 1978.3 Results At Shahdad station, about 40% of the winds blow from the north, northnorthwest and northnortheast, and the rest of the winds often blow from the east and west. At Nehbandan station, about 20% of the winds blow from the north and northeast, and the rest of the winds have a great variety in the directions. At Bam station, about 36% of the winds blow from the west and westnorthwest and the rest of the wind blows from the north and its surroundings. At Nusratabad station, about 31% of the winds blow from the east and southeast, about 27% of the winds from the west and northwest, and the rest of the winds from other directions with great variety. The results of annual hurricanes indicate that winds with north, northnorthwest and northnortheast are the dominant winds in Nehbandan and Shahdad stations. At Bam station, in addition to the north directions, these winds also blow from the west and westnorthwest directions. At Nusratabad station, there is a great variety of wind directions, but unlike other stations, the wind does not blow from the north. Analysis of net direction of sand movement (RDD) of the studied stations shows that the direction of sand movement in Bam and Shahdad stations is southsoutheast, in Nehbandan station to the south and in Nusratabad station is to northnortheast. The analysis of the direction of movement of the sandrose shows the complete correspondence with the hurricane rose of the studied stations. Total sand carrying capacity (DPt) indicates moderate erosion power for Bam and Nusratabad stations and high erosion power for Shahdad and Nehbandan stations. The highest value of vector output of sand carrying capacity (RDP) is related to Shahdad station, followed by Nehbandan, Nusratabad and Bam stations, respectively. For Shahdad, Bam and Nehbandan stations, the maximum amount of oneway winds occurs in autumn and in Nusratabad station in late winter and spring. The maximum amount of sand flow for Bam, Shahdad, Nehbandan and Nusrat Abad stations is 165, 320, 233 and 202 kg/m/s, respectively.4 Discussion ConclusionsThe results indicated that in Shahdad and Nehbandan stations located in the northern half of Lut plain, most of the winds blow from the north, but in Bam and Nusratabad stations located in the southern half of Lut plain, most of the winds are concentrated towards Lut. The highest percentage of occurrence of winds above the threshold speed for Shahdad, Nehbandan and Bam stations occur in summer and the highest percentage of occurrence in Nusratabad station is related to spring. Analysis of net direction of sand movement (RDD) shows that the direction of sand movement in Bam and Shahdad stations is to the southsoutheast, in Nehbandan station is to the south and in Nusratabad station is to the northnortheast. Total sand carrying capacity (DPt) indicates moderate erosion power for Bam and Nusratabad stations and high erosion power for Shahdad and Nehbandan stations. The highest value of vector output of sand carrying capacity (RDP) is related to Shahdad station, followed by Nehbandan, Nusratabad and Bam stations, respectively. The study of sand homogeneity index (UDI) indicates oneway winds for Nehbandan station and twoway winds with aperture angle for Bam, Shahdad and Nusratabad stations. The highest flow rate of sand is related to Shahdad station with 320 kg/m/s and the lowest is related to Nusratabad station with 50 kg/m/s.