كليدواژه :
Aras River , Border river , Intensive migration , Lateral movement , جابجايي جانبي , رودخانه ي ارس , شدت جابجايي , رودخانه ي مرزي , قوس خميدگي , Radial curvature
چكيده فارسي :
جابجايي جانبي كانال و تغييرات مسير جريان رودخانه ها به طرفين، يكي از علل اصلي گسترش دشت هاي سيلابي، فرسايش كناري و تخليه خاك هاي دشت هاي سيلابي به رودخانه ها در اثر برش كناري است. رودخانه ي ارس با پيچ و خم هاي زياد داراي جابجايي سالانه قابل ملاحظه است. با عنايت به خط مرزي بودن مسير جريان اين رودخانه بين ايران و كشورهاي همسايه شمالي، تثبيت جابجايي و تعيين جهت جابجايي از ضرورت ها محسوب مي شود. در اين مقاله براي بررسي ميزان جابجايي عرضي رودخانه ي ارس در بازه ي زماني (1985 تا 2015) از تصاوير ماهواره اي لندست 5 و 2 ( Mss) لندست 5 (TM ( لندست 7 (ETM+)، و لندست 8 ((OLIا1) با قدرت تفكيك 30 و 15 استفاده شد. براي برآورد ميزان جابجايي يا پويايي، از شاخص جابجايي يا اندكس حركت (MI) و Rm و براي محاسبه ي سينوزيته از شاخص سينوزيته استفاده شده است. بررسي متوسط شعاع خميدگي قوس ها در طرف ايران نشان مي دهد كه متوسط شعاع قوس خميدگي هاي ايجاد شده در مسيرجريان 62/509 متر است. اين در حالي كه متوسط شعاع خميدگي قوس ها در طرف مقابل 71/515 متر است. اگر به نوسانات پهناي دشت سيلابي دقت شود، مشخص مي شود كه گستره ي جابجايي ها در طول مسير بسيار متفاوت بوده و در جايي كه پهنا بيشتر شده، جابجايي ها نيز بيشتر شده است. بررسي تغييرات اخير نيز حاكي از بروز تغييرات در مسير اين رودخانه است اما ميزان جابجايي ها نسبت گذشته كاهش يافته و تفاوت جابجايي ها در طرف مقابل و ايران به حداقل ممكن رسيده است. متوسط ميزان جابجايي كانال جريان آب به طرف ايران در سال 2010 به 21/27 و اين ميزان در طرف مقابل به 32/28 بوده است
چكيده لاتين :
Introdution
Alluvial floodplains, and in particular those associated with the worldʹs largest rivers, have a complex relief that is produced by recurring erosional, and depositional events.The magnitude, heterogeneity, spatial distribution, and connectivity of this relief controls river floodwater routing and storage, sediment dispersal, and biogeochemical cyclingChannel Lateral movement and course changes are main causes for floodplain extend ,bank erosion and soil loss due to cut bank .Aras river that located in NW of Iran(from 45°E to 48°E), have many curvatures on course and due to this reason Aras is made high rate movement yearly .Aras is a boarder river and for this reason is very important that direction is determined .
Methodology
In this article for determining the rate of lateral movement is used landsats 5,2 (Mss) landsat5™landsat 7(ETM+) and landsats(OLI) with 30 and 15 resoulation in 1985 to 2015 epoch. In this study is used Rm, R and MI for rate and degree movement and rate of river course curvature .
In order to determining of power flow against instability of mater in this article is used MI idex:
MI=S?Q/D50
And for determining of rate of displacement of channel, is used of Rm index:
Rm=(A/L)/Y
Discusses
Investigation on the curvature radial Aras channel show that average rate of radial is 509.62 m. In other site this rate is 515.71 m. The study also show that changes in Aras river course is vary .When wide is high ,channel migration is excess .In recent time this changes is high ,but rate of migration in Iran site and other site is decrease to compare of past time .The average of channel migration to Iran site is 27,21m in 2010 and other site rate is 28,32 m.
Results
Sum all area that located at other site due to displacement are 1410255 m3 (1985-2015).Area in site of Iran is 2230869 m3 (1985-2015).That is to say ,difference is 820614 m3.This has meaning that our land and soil is placed other site due to channel movement .Yearly average displacement of channel Aras river is 475 m at Iran site and 353 m at other site .So ,displacement at two site is vary .Over the past three decades, the fluvial dynamics of meander bends, including processes related to outer bank erosion, have been the focus of numerous scientific investigations. Despite this effort,a comprehensive understanding of the hydraulic processes of outer bank erosion—especially the role of flow turbulence—remains elusive.Because natural river flows are fully turbulent, the erosive stresses acting on the banks of meandering rivers should be related to turbulent stresses. Current models of outer bank erosion, however, rely on simple parameterization of the flow via excess velocity, excess shear stress at the bank toe, or excess flow depth .
Aras River is very dynamic .This river make curvature in its curse and cut bank .When river make meander in flow curse ,cut power of flow is increase .This high power is energy for bank cut and movement .Soil lost is other result for cut bank .This story is happened in northern border of Iran .
