Environmental Erosion Research

fa طبقه بندی و تحلیل وضعیت مورفولوژیکی و دینامیکی تپه های ماسه ای (مطالعه موردی: ریگ خوزستان) Classification and analysis of the morphological and dynamic status of sand dunes (Case study: Khuzestan Reg) مدلسازی و تحلیل زمانی و مکانی رخداد انواع مختلف فرسایش محیطی مستخرج از پایان‌نامه / رساله / طرح پژوهشی موقعیت جغرافیایی و وضعیت طبیعی ایران سبب شده است تا ریگزارهای آن دارای گستردگی زیادی باشد. از جمله ریگزارهای ایران، ریگ خوزستان است که از تعداد زیادی ریگهای کوچک و بزرگ تشکیل شده است. با توجه به اینکه نواحی سکونتگاهی و فعالیتهای انسانی دشت خوزستان در معرض تغییرات این ریگزارها قرار دارند، مطالعه و بررسی آنها حائز اهمیت است که در این تحقیق به آن پرداخته شده است. در این تحقیق از تصاویر ماهواره لندست، تصاویر گوگل ارث و اطلاعات آماری مربوط به سرعت و جهت بادهای منطقه بهعنوان مهمترین دادههای تحقیق استفاده شده است. مهمترین ابزارهای تحقیق، ArcGIS و WRplot بوده است. همچنین در این تحقیق از شاخصهای سرعت و جهت باد استفاده شده است. در این تحقیق ابتدا محدوده دقیق ریگزارهای خوزستان ترسیم شده و سپس از نظر مورفولوژی طبقهبندی شده است. در ادامه، وضعیت دینامیکی تپههای ماسهای ریگ خوزستان ارزیابی شده است و سپس به تحلیل ارتباط بین سرعت و جهات بادهای منطقه با مورفولوژی و دینامیک تپههای ماسهای پرداخته شده است. نتایج این تحقیق نشان داده است که ریگ خوزستان با 2629 کیلومترمربع وسعت، از اشکال مختلفی از تپههای ماسهای تشکیل شده است. نتایج آنالیز وضعیت فعالیت ریگ خوزستان نشان داده است که حدود 43 درصد از وسعت آن را مناطق فعال دربرگرفته است و در مجموع، تپههای ماسهای ریگ خوزستان تحت تاثیر عوامل مختلف طبیعی و انسانی در طی سالهای 2005 تا 2020 بین 1 تا 55 متر جابجایی داشتهاند. همچنین نتایج آنالیز بادهای منطقه نشان داده است که سرعت زیاد باد در بعضی از فصول از جمله بهار نقش مهمی در جابجایی تپههای ماسهای دارد و جهات مختلف باد نیز باعث تنوع مورفولوژیکی تپههای ماسهای منطقه شده است. همچنین فعالیتهای انسانی از جمله تثبیت تپههای ماسهای توسط پوششگیاهی سبب شده است تا در بسیاری از مناطق، با وجود فراهم بودن شرایط، تپههای ماسهای بدون جابجایی باشند.   1-Introduction One of the important phenomena of arid and semi-arid regions is sand dunes, which are composed of a series of sand dunes. Sand dunes cover about 5 million square kilometers of the earth's surface. One of the most important features of sand dunes in sand dunes is their active dynamics. In fact, sand dunes do not remain in place after formation and are moved by the winds of the region. According to a report by the United States Geological Survey, the changes and displacement of sand dunes are increasing, as is climate change. In fact, climate change and land use changes have caused the displacement and expansion of sand dunes in recent years. The hazards caused by sand dunes are considered one of the important environmental issues of arid and semi-arid regions. In fact, the most important feature of sand dunes is their dynamism and movement, which makes them a source of crisis and a problem for urban and rural centers, economic centers, etc. The geographical location of Iran has led to the presence of numerous sand dunes in many eastern and southern regions of the country. Among the sand dunes in Iran, the Khuzestan Sand Dune is very important because it is located in the path of westerly winds and has been a challenge for planners in recent years. The Khuzestan Sand Dune consists of a large number of small and large sand dunes, each of which has its own dynamics and morphology. Given the importance of the subject, the aim of this research is to evaluate the morphological status and movement of the Khuzestan Sand Dune and analyze their relationship with the characteristics of the winds in the region. 2-Materials and Methods In this study, Landsat satellite images, Google Earth images, and statistical information related to the speed and direction of the winds in the region were used as the most important research data. The most important research tools were ArcGIS (to prepare the desired maps) and WRplot (to analyze the speed and direction of the winds in the region). Considering the subject and objectives, this research was conducted in several stages. In the first stage, using Google Earth images, the exact area of the Khuzestan sand dune was drawn, and then its morphometric status was examined. In the second stage, according to the shape of the sand dunes, the Khuzestan sand dune was divided into different classes. In the third stage, in order to evaluate the displacement status of the sand dunes, sample points (112 sample points) were used. In fact, using Google Earth images, individual sand dunes were selected and then, based on Google Earth and Landsat images, their movement rate was evaluated during the years 2005 to 2020. In the fourth stage, in order to analyze the winds in the region, information from 8 meteorological stations was used and based on them, the speed and direction of the winds in the region were evaluated. In this stage, first, the seasonal and annual average wind speed (m/s) of the stations was calculated and then, using the IDW interpolation method, a map of the wind speed of the region within the sand dunes was prepared. 3-Discussion and Results The morphology of sand dunes is directly influenced by the conditions prevailing on the sandbanks (obstacles, vegetation, etc.) and also by the wind characteristics of the region. The study of the morphology of sand dunes in the Khuzestan Sand Dunes and their movement rate indicates that in addition to natural factors, human factors, including the stabilization of sand dunes through the creation of vegetation, have also played an important role. Based on the results of calculating the wind speed in the Khuzestan Sand Dunes area, the southern regions of the main Khuzestan Sand Dunes had the highest average wind speed. Considering that some of these areas are considered active areas and also, based on the results of monitoring the movement of sand dunes, they had the highest displacement, therefore, the wind speed of the region has been the determinant of the activity and movement of sand dunes in the region, although in some areas, due to the stabilizations, the displacement rate did not match the wind speed. In terms of sand dune morphology, the main sand dune of Khuzestan has a variety of shapes of sand dune types, which reflects the influence of winds from different directions, the morphological state of the region, and the intervention of human factors. Also, in terms of morphology, the isolated sand dune formations of Khuzestan, because they are mostly stabilized, have very little diversity and are mainly in the form of thin and medium-thick sand covers, so in these areas, the intervention of human factors has prevented the movement of sand dunes and created a specific morphology in them. 4-Conclusion                                     The Khuzestan Sand Dune is one of the largest sand dunes in the country, covering an area of 2629 square kilometers and consisting of many small and large sand dunes. The influence of various factors on this sand dune has resulted in the formation of various types of sand dunes in the Khuzestan Sand Dune, including complex sand dunes, parabolic, barkhan and barkhanoid, simple transverse, compound transverse, and sand cover. The results of evaluating the extent of various forms of sand dunes have shown that a large part of the region is covered by medium-thick sand covers, covering 697.5 square kilometers of the region, equivalent to 26.5 percent of the area of the Khuzestan Sand Dune. The results of analyzing the activity status of the Khuzestan Sand Dune have also shown that many parts of this sand dune are semi-active, covering 1,379.5 square kilometers, equivalent to 52.5 percent of its area. Also, active and inactive areas cover 1120.8 and 129 square kilometers, respectively, equivalent to 42.6 and 4.9 percent of the sandbank area. Based on the results, the sand dunes of Khuzestan's Rig have moved between 1 and 55 meters during the years 2005 to 2020, with the highest amount of movement being in the middle areas of Khuzestan's main Rig. Also, the results of the analysis of the winds in the region have shown that high wind speeds in some seasons, including spring, play an important role in the movement of sand dunes, and different wind directions have also caused morphological diversity in the sand dunes of the region. Also, human activities, including the stabilization of sand dunes by vegetation, have caused sand dunes to remain stationary in many areas, despite the availability of conditions.   ریگ خوزستان, سرعت و جهت باد, شکل تپه‌های ماسه‌ای Khuzestan Reg, Wind speed and direction, Shape of sand dunes 1 19 http://magazine.hormozgan.ac.ir/browse.php?a_code=A-10-901-3&slc_lang=fa&sid=1 Mehran Maghsoudi مهران مقصودی maghsoud@ut.ac.ir 10031947532846009596 10031947532846009596 Yes University of Tehran, Tehran, Iran دانشگاه تهران، تهران، ایران Hamid Ganjaeian حمید گنجائیان h.ganjaeian@ut.ac.ir 10031947532846009597 10031947532846009597 No University of Tehran, Tehran, Iran دانشگاه تهران، تهران، ایران