بررسي تغييرات زماني خط ساحلي شرق تنگه هرمز از طريق تحليل آماري نيمرخ‎هاي متساوي‎البعد (ترانسكت)

Time Variation Analysis of the Eastern Hormoz Strait Shoreline by Using Unidimensional Transects

سواحل تحت تاثير ديناميك خشكي و حركات آب دريا، همواره در معرض تغيير و تحول قرار دارند و دركل پايدار نيستند. اين عوامل همراه پديده‎هاي ديگري چون ويژگي هاي زمين‎شناسي، اقليمي و زيستي، لندفرم هاي متنوعي را در امتداد خطوط ساحلي ايجاد مي‎كنند. در اين پژوهش تغييرات خط ساحلي و مورفولوژي پيكان‎هاي ماسه اي در ساحل شرقي تنگه هرمز در چهار دوره؛ يعني سال‎هاي 1977، 1989، 2000 و 2005 اندازه‎گيري شده است. تصاوير ماهواره‎اي ETM، نقشه‎ها، نرم‎افزارها و مدل مفهومي ابزارهاي اصلي پژوهش را تشكيل داده‎اند. هدف اصلي، مقايسه تغييرات خط ساحلي مورد بررسي در يك دوره بيست‎وهشت‎ ساله از طريق تصاوير ماهواره‎اي، عكس‎هاي هوايي، مدل رياضي و سپس كنترل ميداني و درنهايت پيش‎بيني تغييرات درازمدت بوده است. موقعيت‎ها روي تصاوير ماهواره‎اي در نرم‎افزار ArcGIS تطبيق داده و ترسيم شده‎اند. پهنه ساحلي مورد مطالعه به سه بازه كلي دسته‎بندي و اين سه بازه به 65 ترانسكت در فواصل يكنواخت تقسيم شده‎اند. ميزان تغييرات در امتداد خط ساحلي با استفاده از روش آماري Unvariate يك‎متغيره، ريشه ميانگين مربع خطا RMSE (99/0) براي سال 2030 تخمين‎زده شد. نتايج نشان مي‎دهد كه بيشترين تغييرات در مورفولوژي پيكان هاي ماسه‎اي و در محدوده خورها و مصب رودخانه‎ها بوده است. همچنين مقايسه زماني تغييرات نشان مي‎دهد كه سدهاي ساحلي در بخش دلتاهاي بيريزك، زنگلي، حيوي و گز، حجيم‎تر بوده و تغييرات وسعت و ابعاد آنها در درجه اول، تابع تغيير مسير دوره‎اي رود خانه ها در سطح دلتا و سپس راستاي امواج غالب است.

Introduction Our case study is located along with a range of over 142 kilometers of coastline in the East strait of Hormoz. During the Quaternary era, factors of erosion eroded a large part of mountains and deposits accumulated along the coastline. The shorelines influenced by the land dynamics and the movements of sea water are always exposed to alteration and are unstable. Such factors along with other phenomena such as geological, climatalogical and geological characteristics create diverse landforms along shorelines .The study of hydrodynamic processes in determining of shoreline changes in a time interval of 28 years is overall goal of this research. Also, the most important factor in determining the change of coastal zone is some factors affecting in the future early coming. Methodology In the current research, alterations of shorelines and morphology of the sand spits in the northern shore of the Hormoz strait in years of 1977, 1989, 2000 and 2005 were measured. The ETM satellite images, maps, softwares and conceptual model are in fact the main research tools. The principal objective of our research has been comparison of the shoreline alterations in a time period of 28 years by satellite images aerial photographs, mathematical model and then field control Ultimately, the alterations in long term have been predicted. The locations on the satellite images have been determined in ArcGIS software and drawn. The studied shoreline has been classified in 3 general range that each one were subsequently divided to 65 transect in uniform distances. Results and Discussion The extent of alterations along the shoreline in 2030 was estimated by using the single variable Unvariate statistical method, Root –mean-square-error (RMSE) (0/99). The results show the most extensive alterations have occurred in morphology of the sand Bikans around Khor and Masab. Also time comparison of the alterations demonstrate that the shore dams in the areas of birizk, … deltas have been larger and their size depended primarily on periodical change of the path of rivers in deltas and then direction of the dominant waves. The maximum error of coastline position calculated based on factors in 1977, 1989, 2000 and 2005 each transect was assessed by comparing changes in the coastline. Conclusion RMSE calculation based on 1977 images showed that the transect T1 to T9 and T22, RMSE was higher than the rate of coastline have been less affected by the changed parameters of coastline. Transect drawn on the images of 1989 showed that the RMSE rate is less than 10. The results show that the coastline has been more effective of some variables. This finding showed that low RMSE referred the less difference between the coastline predicted and the actual coastline. In images of 2005 the transects T1 to T8 also transect T57 to T63 and T40, T41 and the T46, RMSE is more than 10 that indicated of low influence of theses parameters and large variation between actual and predicted coastline.