بررسی تاثیر فارو بر میزان حمل رسوب، فرسایش وگرانولومتری رسوبات‌بادی (مطالعه موردی : شهرستان نیمروز استان سیستان و بلوچستان)

تداوم خشکسالی و تسریع روند بیابانزایی باعث تشدید وقوع طوفان‌های گرد و خاک و حرکت ماسه‌های روان در منطقه سیستان شده است که ضمن ایجاد بحران‌های زیست محیطی، خسارات زیادی را نیز به تاسیسات و زیر ساخت‌های شهری و روستایی در این منطقه بهمراه داشته است. هدف از اجرای  پژوهش حاضر بررسی تاثیر فارو بر افزایش زبری خاک به منظور کنترل ماسه‌های روان و کاهش بار رسوبی آن در کانون‌های فرسایشی منطقه کاروانسرای شهرستان نیمروز است. تیمارهای این پژوهش متشکل از نوع زبری (فارو و شاهد)، فاصله (1، 16، 31، 46، 61 و 76 متر)، و زمان (فروردین، اردیبهشت، خرداد، تیر، مرداد، شهریور، مهر) است که به صورت فاکتوریل در بلوک تصادفی و در 3 تکرار اجرا شد. با نصب تله رسوبگیر و پیکه چوبی، میزان رسوب حمل شده در تیمار و عمق فرسایش در بازه زمانی مورد مطالعه اندازه‌گیری شد. همچنین با نمونه برداری از تله‌های رسوبگیر پارامترهای آماری میانگین ترسیمی (mz)، جورشدگی انحراف معیار جامع (σi)، کج شدگی ترسیمی (ski) و کشیدگی (ku) برای هریک از تیمارها با استفاده از نرم افزار gradistat آنالیز  شد. یافته‌ها نشان داد که تفاوت معنی‌داری در میزان رسوب به دام افتاده در تله‌های رسوبگیر در تیمارهای آزمایشی وجود دارد (05/0p >). بطوریکه با احداث فارو و افزایش زبری سطح خاک میزان رسوب از 2/454 گرم در منطقه شاهد به 3/68 گرم در محل احداث فاروها کاهش یافته است. همچنین بررسی پارامترهای رسوب‌شناسی نیز بیانگر کاهش محسوس اندازه ذرات رسوبات‌ بادی در محل احداث فاروها (39/88  میکرون) نسبت به منطقه شاهد (220 میکرون) بودکه باعث تغییر بافت رسوب از کلاس شنی- لومی در منطقه شاهد به کلاس لومی در محدوده اجرای فاروها شده است. بر اساس نتایج  پژوهش حاضر احداث فارو با افزایش زبری سطح خاک باعث کاهش میزان رسوب انتقالی توسط باد می‌شود که بستری مناسب برای کنترل حرکت ماسه‌های روان در کانون‌های فرسایشی منطقه سیستان را فراهم می‌نماید.   

the impact of furrow on aeolian sediment transport, erosion, and granulometry changes (case study: nimroz city of sistan and baluchestan province)

1- introductioncurrently, continued drought and accelerated desertification in the sistan region have led to sandstorms and created environmental and humanitarian crises. this has not only devastated the region’s ecosystem but also faced significant challenges to the lives of its residents. in addition, the consequences of these destructive phenomenon cause a lot of damage to urban and rural facilities and infrastructures. the most important factors affecting wind erosion in arid areas include low humidity, poor vegetation, destruction of soil structure (physical and chemical) and flat land surface. in response to the dehydration crisis and the limitations of biological measures, as well as the prevalence of high erosive winds, increasing soil roughness by creating barriers to control the movement of soil and flowing sand is a practical approach to prevent the destructive consequences of wind erosion in this region. hence, this research aims to investigate the effect of furrow on increasing soil roughness to control sand movement and reduce sediment transport in the wind erosion centers of the nimroz city.2- methodologythe study area located in the west of hamon lake with geographical coordinates between 61°8 ’ 40 to 61°8 ’ 46 east longitude and between 31°9 ’ 24 to 31°9 ’ 29 north and at an altitude of about 473 meters above sea level. the average annual precipitation of the study area is less than 50 mm, which often falls sporadically in the winter. regarding topography, the studied area has a low slope and is free from low and high elevations. moreover, this area due to severe erosion is one of the active dust sources in iran. the experiment had been conducted in a randomized complete block design with 42 treatments in 3 replications. the treatments included: type of soil roughness (furrow and control), distance of sediment traps (1m, 16m, 31m, 46m, 61 and 76m) and times (march, may, june, july, august, september, october). using tractor and furrower blade, the farrows were built in such a way that they were perpendicular to the wind direction. sediment traps were set up in each treatment at a height of 0.18 cm above the soil surface. after each sand storm, samples were collected to analyze the sediment particle size and granulometry parameters such as mid-average, kurtosis, skewness, and sorting. to analysis the mean of parameters among different land uses were used the duncan test.3- results the result showed that under the type of soil roughness there is a significant difference in the amount of aeolian sediment (p<0.05). thus, the amount of sediment in the control area is equal to 454.2 grams, which has decreased to 68.3 grams with the construction of the furrow and the increase in the roughness of the soil surface. beside that, the findings indicate the amount of sediment trapped is different in the experimental treatments too (p<0.05). so that with the increase of wind speed during the months of july and august and (with an average wind speed of 25.1 and 2.23 m/s, respectively) the amount of sediment in the furrow area at intervals of 1, 16, 31, 46, 61 and 76 m was associated with an average decrease of 4.7, 4.8, 6.4, 7.3, 8.6 and 1.14 times compared to the control area. according to the obtained results, the mean and average values of aeolian sediment in the control area are equal to 2.04 phi (equal to 235 microns) and 2.18 phi (equal to 220 microns), respectively. while, by furrow construction the median and mean values of particles size turned to 3.28 phi (105.11 microns) and 3.55 phi (88.39 microns), respectively. according to result the sediment texture in control area is in the sandy-loamy class, which with a decrease of 1.6 times of sand and an increase of 2.6 and 1.1 times of clay and silt has been changed to the loamy class in furrow area.4- discussion & conclusionsin this research, we investigated the effect of furrow construction on soil roughness to control sand movement and reduce erosion in the erosion zone of nimroz city. as results depicted, under the effect of furrows construction, the amount of sediment trapped decreased by 6.4 times compared to the control area (p<0.05). also, the particles size of aeolian sediment in the control area were equal to 235 microns, which in the furrows area has decreased to 88.39 microns. this process implies that the increment of soil roughness along contour lines, directly alters the wind flow and decreases the destructive power of the wind and consequently sediment transport potential. overall, the construction of furrows in the erosion zone of the sistan region, which is mostly devoid of vegetation and has flat topography, by increasing the roughness of the ground surface, caused the sand movement significantly decreased. in addition, this practice is adapted to harsh weather conditions in the sistan region and can implemented with minimal facilities in fragile areas. additionally, due to the scattered rainfall in these areas, the furrow system acts as a rainwater catchment system to collect the runoff and provide a suitable condition for restoring vegetation and consequently stabilizing and controlling erosion zones in these areas.