بررسي سرعت آستانه‌ي فرسايش بادي و تأثيرپذيري آن از خصوصيات خاك در كانون‌هاي توليد گردوغبار استان البرز

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

گردوغبار يكي از مخاطرات طبيعي است كه عمدتاً در مناطق خشك و نيمه‌خشك جهان رخ مي‌دهد و به همين دليل يكي از معضلات اصلي كشور ايران نيز به شمار مي‌رود. استان البرز ازجمله مناطقي است كه به دليل شرايط آب و هوايي، كاهش بارندگي و وجود منشأهاي داخلي توليد گردوغبار در سال‌هاي اخير به‌شدت در معرض طوفان‌هاي محلي گردوغبار قرار گرفته است. در اين پژوهش به بررسي خصوصيات خاك و تأثير آن بر فرسايش بادي و سرعت آستانه در كانون‌هاي توليد گردوغبار استان البرز پرداخته شده است. در منطقه‌ي مطالعاتي، 27 نمونه خاك تا عمق 5 سانتي‌‌متري جمع‌آوري و به آزمايشگاه منتقل گرديد. همچنين از دستگاه تونل باد جهت اندازه‌گيري سرعت آستانه استفاده شد. مطالعات حاصل از تحليل گلباد و گل­طوفان در منطقه نشان داد كه جهت باد غالب در منطقه، از شمال غرب است و بيش از نيمي از بادهاي منطقه داراي توان فرسايشي مي‌باشند و توانايي جابجايي ذرات خاك و توليد گردوغبار را دارند. به منظور بررسي رابطه­ي خصوصيات خاك و سرعت آستانه، از آزمون رگرسيون و روش حذف پس‌رو استفاده شد. نتايج نشان داد رطوبت خاك، اندازه‌ي ذرات، ميزان آهك و مقاومت برشي و فشاري خاك، تأثيرگذارترين پارامترهاي مؤثر بر سرعت آستانه هستند. هرچه ميزان آهك در خاك بيش‌تر باشد، با ايجاد چسبندگي بيش‌تر ذرات، مقاومت فشاري و برشي خاك و همچنين سرعت آستانه افزايش مي‌يابد؛ از جهتي با افزايش درصد ذرات با قطر بين 0/1 تا 0/5 ميلي‌متر در خاك، سرعت آستانه كاهش مي‌يابد. ميزان درصد سديم در خاك‌هاي نمونه‌برداري شده بسيار بالاست و همين عامل باعث ازهم‌پاشيدگي ذرات خاك و كاهش سرعت آستانه‌ي فرسايش بادي در منطقه‌ي موردمطالعه مي‌شود. نتايج پژوهش نشان داد كه رطوبت، مهم‌ترين و بارزترين پارامتر مؤثر بر سرعت آستانه‌ي فرسايش بادي در كانون گردوغبار است.

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.