بررسی سرعت آستانه‌ی فرسایش بادی و تاثیرپذیری آن از خصوصیات خاک در کانون‌های تولید گردوغبار استان البرز

گردوغبار یکی از مخاطرات طبیعی است که عمدتاً در مناطق خشک و نیمه‌خشک جهان رخ می‌دهد و به همین دلیل یکی از معضلات اصلی کشور ایران نیز به شمار می‌رود. استان البرز ازجمله مناطقی است که به دلیل شرایط آب و هوایی، کاهش بارندگی و وجود منشاهای داخلی تولید گردوغبار در سال‌های اخیر به‌شدت در معرض طوفان‌های محلی گردوغبار قرار گرفته است. در این پژوهش به بررسی خصوصیات خاک و تاثیر آن بر فرسایش بادی و سرعت آستانه در کانون‌های تولید گردوغبار استان البرز پرداخته شده است. در منطقه‌ی مطالعاتی، 27 نمونه خاک تا عمق 5 سانتی‌‌متری جمع‌آوری و به آزمایشگاه منتقل گردید. همچنین از دستگاه تونل باد جهت اندازه‌گیری سرعت آستانه استفاده شد. مطالعات حاصل از تحلیل گلباد و گل طوفان در منطقه نشان داد که جهت باد غالب در منطقه، از شمال غرب است و بیش از نیمی از بادهای منطقه دارای توان فرسایشی می‌باشند و توانایی جابجایی ذرات خاک و تولید گردوغبار را دارند. به منظور بررسی رابطه ی خصوصیات خاک و سرعت آستانه، از آزمون رگرسیون و روش حذف پس‌رو استفاده شد. نتایج نشان داد رطوبت خاک، اندازه‌ی ذرات، میزان آهک و مقاومت برشی و فشاری خاک، تاثیرگذارترین پارامترهای موثر بر سرعت آستانه هستند. هرچه میزان آهک در خاک بیش‌تر باشد، با ایجاد چسبندگی بیش‌تر ذرات، مقاومت فشاری و برشی خاک و همچنین سرعت آستانه افزایش می‌یابد؛ از جهتی با افزایش درصد ذرات با قطر بین 0.1 تا 0.5 میلی‌متر در خاک، سرعت آستانه کاهش می‌یابد. میزان درصد سدیم در خاک‌های نمونه‌برداری شده بسیار بالاست و همین عامل باعث ازهم‌پاشیدگی ذرات خاک و کاهش سرعت آستانه‌ی فرسایش بادی در منطقه‌ی موردمطالعه می‌شود. نتایج پژوهش نشان داد که رطوبت، مهم‌ترین و بارزترین پارامتر موثر بر سرعت آستانه‌ی فرسایش بادی در کانون گردوغبار است.

Investigating wind erosion threshold velocity and the effect of soil characteristics in dust production centers in Alborz province

Dust phenomenon is one of the most common and destructive phenomena in the dry and desert regions of the world and Iran, which can have harmful effects on human life and the environment. Wind erosion and the removal and transport of soil particles by wind create dust. Controlling wind erosion will be effective when enough information is available on the factors affecting it.  The results of the related studies show that wind erosion phenomenon is very complex and controls many factors. Soil characteristics influence the severity of wind erosion through its impact on its erosion. However, in most researches conducted on wind erosion throughout the world, the role of soil characteristics has been confirmed in wind erosion, but few studies have been conducted in Iran, and the Alborz province, which has been exposed to wind erosion and dust storms in recent years, has not been investigated in these studies. Considering the importance of the issue in this area, the present study was conducted to investigate the role and effect of soil characteristics on the wind erosion threshold velocity and the occurrence of dust phenomenon. In this study, the wind erosion threshold velocity was measured in normal conditions using desert wind tunnel device, and the physical, chemical and mechanical characteristics of the soil were also obtained after sampling in the laboratory and compared with the estimated threshold velocity. Also, using wind velocity data and velocity thresholds, wind rose and storm rose area of the area were drawn and examined. The characteristics of the soil samples examined with  high-precision included limestone, sodium, phosphorus, calcium, magnesium, organic matter, nitrogen, humidity content, shear strength, compressive strength, EC, pH, and d.( In this study, using grading of the soil samples , a variable called d has been measured. This variable indicates the percentage of particles with diameters between 0.1 to 0.5 mm as the most sensitive particles for wind erosion in the collected samples.) The results of measuring the threshold velocity using a wind tunnel device showed that the minimum and maximum wind speed thresholds in the area were 7.5 m / s, and 9 m / s, respectively. The range of 7.5 to 9 m / s indicates the high sensitivity of the region to the wind erosion; this is while the width of these areas is also high and this could be a serious threat to the province of Alborz   and its neighboring provinces. Studies of the wind rose and storm rose in the region showed that the dominant winds in the region are from the northwest. And more than half of the winds erupted in the area are erosive and have the ability to move particles of soil and create dust. The relationship between soil characteristics and threshold velocity was investigated using the stepwise regression test. The results showed that the most effective parameters on soil moisture threshold velocity included particle size, lime content and shear and pressure strength of the soil. That is, as the amount of lime in the soil increases, the adhesion of the particles and consequently the pressure and shear strength of the soil increase. Moreover, when the percentage of particles with a diameter of 0.1 to 0.5 mm in the soil increases, threshold velocity decreases.In this study, soil moisture has the highest effect on the threshold velocity and has a direct relation with the velocity of wind erosion. The percentage of sodium in the sampled soils was very high, and this caused the disintegration of soil particles and reduction in the wind erosion threshold velocity. The study showed that the risk of wind erosion and dust-fogging greatly threatens the Alborz province. The actual focal points for the production of dust constitute a vast area of the province. These areas, integrated into the central part of the Eshtehard plain and being bordered by the deserts of the Buinzahra plain in Qazvin province, have placed a wider field of dust in front of the wind and are regarded as a serious threat and would have harmful consequences in the provinces of Alborz, Tehran and other neighboring provinces.  Therefore, it is necessary to take a special look at these areas in order to prevent the risks of this problem from being exacerbated in the first stage and to reduce the risks in the next stage.