مدل سازي سرعت جريان و تعيين محدوده فرسايش و رسوب گذاري در ورودي رودخانه اروند به خليج فارس با استفاده از GIS

Modeling Flow Velocity and the Area of Erosion and Sedimentation at the Entrance of Arvand River to the Persian Gulf Using GIS

رودخانه ها تحت تأثير پديده فرسايش و رسوب گذاري دست خوش تغييرات گوناگوني مي شوند؛ از آن جمله مي توان اشاره كرد به: تغيير راستا؛ جابه جايي هاي عرضي و طولي؛ تغيير تراز بستر؛ تغيير دانه بندي؛ و دگرگوني ويژگي هاي هندسي مسير. هدف از اين مطالعه تعيين محدوده فرسايش و رسوب گذاري در ارتباط با سرعت جريان و پخش آلودگي در ساحل اروندرود با استفاده از مدل كوهيرنس و GIS است. در اين تحقيق از مدل سه بُعدي و هيدروديناميكي كوهيرنس براي شبيه سازي سرعت جريان استفاده شده است كه معادله پيوستگي، معادلات ناويراستوكس در سه بُعد، و معادله هاي انتقال شوري و دما به روش جداسازي حل مي شوند. شرايط مرزي اعمال شده شامل تغييرات دما، شوري، و دبي براي مرز باز رودخانه و تغييرات دما و شوري و اعمال مؤلفه هاي جزرومدي M2، S2، O1، و K1 براي مرز باز دريا در مدل به كار گرفته مي شود. با توجه به مقاطع عرضي و خروجي سرعت جريان از مدل كوهيرنس، پهنه تحت پوشش بيشترين آلودگي منطبق با سرعت جريان آب كمتر و رسوب گذاري بيشتر است. همچنين، در مقطع دهانه رودخانه ميانگين سرعت در وسط رودخانه بيشتر و در دو طرف ساحل رودخانه كمتر است؛ در نتيجه، در دو ساحل ايران و عراق رسوب گذاري بيشتر و فرسايش كمتري انجام گرفته است.

ntroduction The rivers usually affected by erosion and sedimentation are subject to various changes in transverse and longitudinal movements and variations in river bed elevation, particle size and geometrical properties. Erosion and sedimentation studies provide the opportunity to identify the behavior of river morphology and the effects of different measures to reorganize its behavioral performance on quantitative and qualitative data. Arvand is a vital river in southwestern Iran serving as the Iran-Iraq border. The purpose of this research is to determine the area of erosion and sedimentation in relation with flow velocity and pollution dispersion in the banks of Arvand River using Coherence model and GIS. Materials and methods In this study, three-dimensional hydrodynamic model of coherence is used to simulate the flow velocity in Navier-Stokes equations in three dimensions. Boundary conditions including changes in temperature, salinity and flow rate, temperature and salinity changes are considered and for open border river and tidal components including O1, S2, M2 and K1 are used in open sea in the model. We have used bathymetric maps of the Armed Forces and also hydrographic maps in the scale of 1: 25,000 in GIS through digital interpolation. In this study, we employed a computational grid of 80 x 83 meters with an accuracy of 96.52 * 97.48 km. Aerial photos are one of the most effective tools in the interval erosion and unsustainable use. The aim of this study is to determine the scope of erosion and sedimentation in Arvand River using GIS. The GIS is a computer-based technology that uses geographic information systems as a framework for managing and combining data, solving problems and understand situations in the past, present and future applications. The application can identify the areas of erosion and sedimentation in Arvand River and classification of pollution scattering. Results and discussion To show the flow rate in different parts of the river, three cross-sections have been gathered in different times and different places upstream, mid-stream and river mouth for measuring the average speed. According to the average values of the speed upstream, it is observed that the water flow rate of are greater on bank of Iranian coast. In the middle and downstream sections of the river, the average flow rate values can be observed as Table 1. Table 1. erosion and sedimentation in different parts of the Arvand river coast Long range (%) Long range (km) 62.57 45.54 Sediment on the beach 26.75 19.47 Beach erosion 10.67 7.77 Established beach 100 Total Conclusion Most of the beaches in the study area are related to sedimentation, about 62 percent of the length. Due to different horizontal sectioning of speed on the river and the output flow velocity of the coherence we conclude that in the places where the water flow rate is higher, we can observe more erosion, less flow speed, and more sedimentation. The places covered more with the sediments, there is the highest pollution. The average water flow rate on the Iranian coast is higher than the coast of Iraq. As a result, it is observed that the rate of erosion on the coast of Iran is greater than that in the coast of Iraq and that on the coast of Iraq we can see more sedimentation and less erosion. In the mouth of the river, the average speed is lower than that in the middle of the river and on the other side of the river beach. Therefore, there are more sedimentation and erosion on the two shores of Iran and Iraq.