بررسي تغييرات خط ساحلي با استفاده از روش پلي گون تغييرات محدوده موردمطالعه : قاعده دلتاي سفيدرود

Measuring Historical Coastal Change using the change Polygon method

مديريت پايدار سواحل مستلزم آگاهي از روند تغييرات خط ساحلي است و آشكارسازي تغييرات خط ساحلي مي‌تواند در شناسايي و تجزيه‌وتحليل ميزان جابجايي خطوط ساحلي كمك نمايد. هدف از اين تحقيق بررسي تغييرات خط ساحلي قاعده دلتاي سفيدرود با استفاده از روش پلي گون تغييرات طي شش دهه گذشته مي‌باشد. براي دستيابي به اين هدف، اطلاعات دبي و رسوب سفيدرود، باد و نوسانات تراز آب به همراه عكس هوايي1955 به مقياس 55000/1، تصاوير ماهواره‌اي TM سال 1989ماهواره لندست و تصوير 2014 ماهواره اسپات از نرم‌افزار گوگل ارث به‌عنوان ابزار و داده هاي اصلي پژوهش بهره گرفته‌شده است. روش كار استفاده از پلي گون تغييرات در سنجش ميزان تغييرات خطوط ساحلي در سه مقطع زماني مي‌باشد. در اين تحقيق ابتدا عكس هوايي سال 1955 با روش تصوير به تصوير و با مشخص نمودن نقاط نظير تصوير گوگل ارث سال 2014، در نرم‌افزار ENVI زمين مرجع شد. سپس با تفسير بصري، خط ساحلي در عكس هوايي و تصوير سال 2014 ترسيم شدند. اما با توجه به ماهيت رقومي تصوير سال 1989، جهت بارز سازي تصوير مذكور با اجراي شاخص NDVI و محاسبه پيكسل‌هاي كوچك‌تر از صفر، منابع آبي محدوده موردمطالعه مشخص شد و در محيط ArcGIS خط ساحلي فوق‌الذكر استخراج گرديد تا در ادامه تصاوير به‌صورت زوجي تجزيه‌وتحليل شوند. نتايج نشان مي‌دهد كه نوسان تراز آب درياي خزر، شدت و ضعف آورد رسوب از رودخانه سفيدرود در مقاطع زماني مختلف و انجام عمليات شاس طي سال‌هاي 1998-1981 از عوامل اصلي ايجاد تغيير در قاعده دلتاي سفيدرود مي‌باشد. همچنين نرخ مثبت تغييرات طول خط ساحلي در روش پلي گون تغييرات، از ادامه روند دلتاسازي سفيدرود طي 60 سال اخير حكايت دارد.

The coastal zone has been considered one of the most physically and socioeconomically vulnerable environments due to the complexity of shore processes, the fragility of its ecosystems, high population density and its importance in tourism(Albuquerque et al ,2013). The study area for this research is located in the coastline of the Caspian Sea in an approximate length about 15 km in Sefidrud delta. Delta Sefidrud in the Kiashahr is located in 55 Km away from Northeast Rasht in lat. from 37° 26 to 37° 28 N and long. from 49° 50ʹ to 50 E. Also itʹs located at under zero above sea level. The purpose of this study is to evaluate coastline change used of Change Poligon Method over the last sixty years. Methodology To achieve the purpose of this research, some data including sediment discharge from rivers, wind and sea level changes statistics, aerial photo and satellite images in several times have been used as the material of the research. To do this, after atmospheric and geometric corrections Landsat images and aerial photo in ENVI software, the images were processed for better visualization and interpretations. The images, then, have been imported into ArcGIS 9.3 software. The shoreline positions have been separately extracted from each of the images as distinct layer files. Methodology of the work is based on poligons measurment in two separate coastline. Instead of using an arbitrary baseline as a basis for comparative analysis, the change polygon approach utilizes two separate coastlines to construct a polygon topology that represents the total areal difference between two coastlines. In this method, in addition area of poligons, is calculated length of coastline. Results and discussion In measurement of historical coastline used change polign is analysis changes of shoreline area and length. During the years 1955-2014, many changes occurred in the area between poligons. The results show that The maximum increase area with a rate of positive during the period of 1989- 1955 equivalent 13/94 KM and increase in net rate of land equivalent 12/22 KM. the average length of coastline since 1955 to 2014 is show equivalent 19/1km. 2/ 2km range changes between two timeframe 1989- 1955and 2014- 1989 implies on the existence of a great changes along the coastline. the central line and length of the sub - line , shows a similar situation. The two parameters is concerned maximum changes in a period of 1989- 1955and minimum changes for the period 2014- 1989. as well as the rate of positive changes in the method changes polygon, indicates an increase in the size of Delta Sefidrud Over the past 60 years. Conclusion Coast line changes is created in connection with the land and sea processes. study of pictures show that most of the coastline change occurred in the period 1955 to 1989. Most of the changes must be before the construction of the dam Sefidrud. the main reason that can be found in the river sediment and discharge before and after the Sefidrud dam construction. also after 9 year from Shas operation to year 1989, has occurred the second wave maximum changes in the area and length of coastline. But during the years of 2014- 1989, especially after years 1995 has so far with a drop in water levels and also stop Shas operations due to the climatic conditions , Delta basal under the influence of the sea processes, is located in the picked up phase. So can be concluded that main factors the creation of a change in the Sefidrud Delta basal are sea level change, rising and falling of the river sediment and Shass operation Over the years 1981- 1998.