بدیهی است که فرسایش دارای پیامدهای متعددی چون ازبین رفتن خاک، آلوده شدن آبها ،کاهش ظرفیت مخازن آب و پرشدن سدها،تهدید سلامت و تندرستی عمومی و... میباشد. لذا توجه به فرسایش و پیامدهای آن گام مهمی در جهت نیل به توسعهی پایدار است. منطقهی مورد مطالعه شامل حوضههای آبریز جنوب مشهد (طرق، مایان، دهبار و جاغرق) بوده و طبیعتاً نتایج حاصل از فرسایش این حوضهها متوجه کلانشهر مشهد نیز میگردد. این حوضهها حدود 429 کیلومترمربع وسعت دارند و از لحاظ ژئومورفولوژی بخشی از دامنهی شمالی ارتفاعات بینالود میباشند. از نظر لیتولوژی نیز شیستهای متامورفیک و فیلیت مشهد حدود 90 درصد این حوضهها را پوشش دادهاند. چند گسل نیز منطقهی مورد مطالعه را تقطیع نمودهاند که معروفترین آن گسل سنگ بست- شاندیز است. این تحقیق بر پایهی روش تجربی. تحلیلهای کمّی و کیفی و بررسیهای میدانی انجام گرفته و با توجه به ویژگیهای طبیعی منطقه (9عامل زمینشناسی، خاک،آب و هوا، رواناب، توپوگرافی، پوشش گیاهی،کاربری اراضی، فرسایش سطحی خاک، فرسایش رودخانهای)، با استفاده از مدل ام پسیاک مورد بررسی قرار گرفت و نتایج حاصل با دادههای ایستگاههای رسوبسنجی مقایسه گردید. نتایج این بررسی حاکی از آن است که اولاً حوضهی آبریز جاغرق نسبت به سایر حوضههای مورد مطالعه بیشترین فرسایش و رسوب را دارد. ثانیاً مدل ام پسیاک در این منطقه به خوبی پاسخ میدهد. زیرا به عنوان نمونه مقدار رسوب برآورد شده در حوضهی جاغرق با مدل ام پسیاک 531 تن در کیلومترمربع در سال بوده، در حالیکه در ایستگاه رسوبسنجی حوضه مربوطه 547 تن در هکتار در سال میباشد. ثالثاً مقدار فرسایش و رسوب در منطقهی مورد مطالعه رو به افزایش بوده و این امر حاصل تغییرات کاربری اراضی و دخل و تصرفهای انسانی میباشد. همچنین این افزایش فرسایش و رسوب نیز پیامدهای زیست محیطی را در منطقه به دنبال داشته است.
Quantitative and Qualitative Analysis of Erosion on Southern River Basins
Adjacent to Mashhad and its Environmental Impact
Dr. Mohammad Jafar Zomorodian
Associate Professor of Geography
University of Ferdowsi Mashhad Ramin Rahimi
M.Sc in Geomorphology
Erosion and especially soil erosion can be considered as one of the most threatening factor for the environment in general and for soil and water resources in particular. Because soil is made from the composition of fine material, mineral and homos and its a natural-dynamic environment in which plants are grown. Nowadays, soil erosion is one of the problems and challenges which cause huge damages, particularly in Iran. This happens because erosion has many other consequences including soil loss and degradation, water pollution, reduction of water reserves and dams water filling operation, threatening general health and etc. Therefore, the assessment and control of erosion and its consequences can be considered as a major step for moving towards sustainable development. As a result, many researches and administrative activities are done and many models are employed in this field. Fundamental research related to soil erosion was started in 1915 for the first time and Wotiy was the first person who did comprehensive research in this field. Many researches also carried out in this field in Iran in general and in khorasan Province in particular and present study is in parallel with these research, because city of Mashhad is located in northern slope part of Binalood Mountain range, and it is surrounded by four river basins including Torogh, Mayaan, Dehbar, and Jaghargh. Unsurprisingly, the negative consequences of soil erosion in these areas have an impact on city of Mashhad and its citizens. This study was carried out to identify the details of this erosion in this area and appropriate ways to control it.
This research is designed based on experimental method, quantitative and qualitative analysis, field study and also laboratory research. This study employed MPSIAC Model with consideration of data and natural features of the selected area (9 factors including: geology, climate, run-off and discharge , topography, soil, plant coverage, land use, river erosion, and superficial soil erosion). Results of this study are compared and analyzed with data from sediment analysis stations in the region. In order to obtain better results, this research employed variety of maps including Topographic maps, Geological maps, etc. Moreover, this research also used Remote Sensing images in order to achieve its objectives.
Quantitative and Qualitative Analysis of Erosion on Southern ...
Discussion and Results
Area covered in this study is located in the North-East of Iran (Khorasan-Razavi Province) between 36,4 -36,21 North latitude and 59,10-59,37 East altitude. The flow of these mentioned four river basins are derived from the north slope of Binalood Mountain range and they are flowing into Mashhad - Chenaran plain and ultimately joining Kashafrud River. These river basins covered area is about 429 km2 and with respect to geomorphology are agree with Binalood. From litho logic point of view, metamorphic schist and Mashhad filith (slate, schist, schale, ophiolith, and etc) have covered 90% of these basins. Also several faults exist in this area in which Sangbast Shandiz is the most famous one. Climate of this area can be categorized as semi-dried and cold and the annual average of rainfall is about 256.3 mm. Length of the major branches of these river basins is about 25 km in average and they seems to be in the form of permanent rivers. The average of annual water flow is 4.455 M3/S. The land coverage in these areas is mainly cliffs, Scree, roads and civil structures and in terms of plant coverage can be considered as a relatively poor area. This area also includes agricultural land area that in the recent years were converted to restaurants and constructions in which Jaghargh can be considered as the first place regarding this ranking. These environmental and natural characteristics and features as independent or as a common or a combination of factors were effective in creating the erosion and sedimentation processes of the area and has had particular environmental consequences.
Results of quantitative and qualitative analysis indicate that, firstly, Jaghargh River basins has the most erosion and sediments compared to other river basins studied in the region. Secondly, the MPSIAC Model is applicable in this region, because as an example, according to MPSIAC Model, the amount of sediments measured in Jaghargh river basin was 531 Ton/Km2 per year, whereas, in sediment measuring station in this area, amount of sediment measured was 547 Ton/Km2 per year. Thirdly, the amount of erosion and sediment in the region studied in this research were constantly increasing which is affected by changes in land use patterns and also human disruptions. Increasing erosion and sediment in the region also had a negative impact on the environment (changes in linear river section, reducing the life-cycle of dams in the region, dusty weather conditions in Mashhad, and etc).
In terms of qualitative analysis, it is needed to mention that, in addition to the above quantitative analysis and its results, the existence of series of factors in the region led to increase erosion and also intensified it. These factors mainly include: the characteristics and features of elements and environmental and natural factors (e.g. Schistozite, the range of temperature variation in a day and during the season which intensify Thermoclasty and Cryoclasty in one hand and on the other hand, topography, high levels of rainfall with relatively high snow coefficient, and high water flow in rivers which strengthening the process of erosion and sediment), changes in land use patterns in recent decades (particularly in Jaghargh river basin), and (due to population increase) in recent years.
Keywords: Quantitative and qualitative analysis, River basin, Erosion and sediment, Environment, Sediment measuring, MPSIAC.
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کلیدواژه ها [English]
Quantitative and qualitative analysis, River basin, Erosion and sediment, Environment, Sediment measuring, MPSIAC