پایش روند تغییرات تپه های ماسه‌ای با رویکرد سنجش از دور (مطالعه موردی: دشت سیستان)

دشت سیستان از جمله مناطق خشک ایران می‌باشد که دارای بارندگی بسیار کم و پوشش گیاهی ضعیفی می‌باشد. وزش بادهای شدید بر سطح این اراضی لخت باعث تشدید فرسایش خاک شده و خسارت جبران ناپذیری به راه‌های مواصلاتی، اراضی کشاورزی و روستاهای مجاور وارد کرده است. در این پژوهش با استفاده از تصاویر ماهواره‌ای لندست با قدرت تفکیک 30 متر از سال 1995 تا 2018 به بررسی روند تغییرات تپه‌های ماسه‌ای در منطقه دشت سیستان پرداخته شده است. بر اساس نتایج حاصله از این  مطالعه، وسعت تپه‌های ماسه‌ای در ماه آگوست از 23/8  درصد در سال 1995 به 11 درصد در سال 2018، و در ماه جولای از 55/7 درصد به 10 درصد از سطح کل حوضه مورد مطالعه افزایش یافته است که تقریباٌ روند افزایشی چشمگیری را نشان می‌دهد. همچنین تغییرات مساحت دریاچه هامون از سال 1995 تا 2018 نشان می‌دهد که وسعت آب دریاچه به شدت کاهش یافته است و گویای این موضوع است که گسترش تپه‌های ماسه‌ای در سال‌های مختلف ارتباط مستقیمی با تغییرات سطح دریاچه در زمانهای مختلف دارد. همچنین مطالعات میدانی حاکی از آن است که در طی خشکسالی‌های مکرر منطقه سیستان، حرکت تپه‌های ماسه‌ای به حدی زیاد بوده که باعث مدفون شدن تعداد زیادی از خانه‌های روستایی و از بین رفتن اراضی کشاورزی شده است که این امر خود مهاجرت ساکنان بومی منطقه در سالهای اخیر را به دنبال داشته است. این مسئله همچنین باعث بیکاری بخش زیادی از کشاورزان منطقه گردیده و خسارات شدیدی به تاسیسات و کانال های آبرسانی رسانده است، به طوری که جبران آن، مستلزم هزینه و زمان زیادی می‌باشد.

Investigating changes in sand dunes with remote sensing approach (Case study: Sistan plain)

Introduction:Animated sand dunes are a major threat to wind erosion, causing severe damage to transportation networks, agricultural products, water resources and residential areas ) Ahmadi, 2006). Sand hills are also one of the most important facets of wind erosion. Sometimes the speed and direction of the winds in the area can help a lot to understand the morphometric properties of sand dunes (Pourmand et al., 2015). The use of remote sensing over the past few decades as a tool to study the characteristics of sand dunes and study its changes over time has made it possible to extract former climatic diets and monitor marginal areas that are prone to desertification (Otterman, 1981; Tucker et al., 1994). Image processing is one of the techniques used in data analysis and interpretation of satellite data to study natural hazards such as sand dunes. In general, monitoring the changes and spatialtemporal progress of sand dunes as one of the most important environmental hazards in arid regions of the world is essential. Therefore, Sistan plain in eastern Iran in recent decades due to environmental and human factors, influx The flow of sand and the advance of the sand dunes in it have stopped human activities in most parts of it and have caused irreparable damage. Studying this environmental risk in this area will not be without merit to reduce its destructive effects and sustainable management in the area.Materials and methods:This study uses the time series of Landsat satellite data to monitor the trend of changes in the sand dunes of Sistan plain and its effects on people’s social life. To do this, Landsat 5 and 7 satellite images (July and August images between 1995 and 2018) were used. After obtaining the required data from USGS site and forming a database, the steps of correction and analysis were applied to them with the help of GIS and ENVI software, and then four Landsat image tiles were mosaiced together to completely cover the study area. . In this study, a field visit was made to identify the location of hills and other sand forms and during the maximum likelihood classification in Envi.5.3 software environment, the affected areas of hills and other sand forms were identified and The changes in this phenomenon were compared between 1995 and 2018.Results and discussion:Several factors affect the movement of quicksand in the Sistan plain. One of the most important is the 120day winds in the dry seasons, which burn at 110 to 170 kilometers per hour. The results of the Golbad drawing for July are shown in Figure 3. July, like June, which is affected by the 120day winds of Sistan, offers a similar pattern both in terms of direction and speed of wind. This month’s wind direction is northwest to southeast. Satellite images were taken over six periods to study how sand dunes developed and spread in the region in July and August. Between 1995 and 2000, with the drying up of Hamoon Wetland, the spread of sand dunes on the shores of the lake is clearly visible. Although Lake Hamoon has been flooded in 2015, the spread of sand dunes affected by the lake’s dryness in the past is still visible, due to strong winds and the loss of vegetation during the prebasin period. It’s time. In 2010 images, the lake’s flooding during this period had a positive effect on stabilizing and reducing the surface of the sand dunes. However, in the following years, with the decrease of the lake’s water level, the amount of sand dunes in Sistan plain has increased again, which can be clearly traced from the prepared images.Conclusion:Analysis of meteorological data on wind direction and speed in this area showed that the prevailing winds determine the movement of sand dunes, 120day winds, and there is a direct relationship between wind speed and the rate of movement and progress of sand dunes. Landscape sandstone expansion plans from the Landsat Measures Processing for July and August, the most turbulent months in terms of winds, were developed in 1995 and 2018 to monitor changes in the region’s sand dunes. Which clearly depicts the dynamics of sand dunes in different years. According to the results of a study of Landsat satellite remote sensing data, the area of sand dunes in August increased from 8.23 percent in 1995 to 11 percent, and in July 2018 from 7.55 percent to 10 percent of the range Cover the study. Which indicates an almost dramatic increase in sand dunes. Also, the drastic changes in the area of Lake Hamoon from 1995 to 2018 can be clearly seen in the prepared maps, and it is said that the expansion of sand dunes in different years is directly related to changes in lake level at different times.Field studies show that during the frequent droughts in the Sistan region, the movement of sand dunes has been so high that it has buried a large number of rural houses and destroyed agricultural lands. This has led to the unemployment of a large number of farmers in the region and has caused severe damage to water supply facilities and canals, so that its compensation requires a lot of time and money. Many people in the area have migrated to escape the situation, and many have resorted to false jobs to earn a living, including fuel smuggling, smuggling and tourism.Comparing the results of this study with the study of writing (2007) that examined the damages caused by the relocation of sand dunes in eastern Zabul, shows almost the same results, with the difference that this study generally considers the Sistan plain. Data and a complete study of the trend of changes in sand dunes in Sistan plain show, but the study study in 2007 was only focused on sand dunes in the east of Zabol.