بررسی تغییرات دوره‌ای خط ساحلی دریای عمان با استفاده از داده‌های سنجش ‌از دور و تحلیل‌های مکانی

خط ساحلی که به عنوان رابط فیزیکی زمین و آب تعریف می‌شود، از نظر طبیعت پویاست و امنیت اقتصادی و اجتماعی را برای سکونتگاه‌های ساحلی فراهم می‌کند. دینامیک و تحول‌پذیری سواحل هر چند پدیده ی شناخته شده‌ای است، اما فرکانس و شدت این تغییر و تحول در زمان، الگوهای متفاوتی را معرفی می‌کند که فرآیندهای مختلفی را در پی دارد. این تحول‌پذیری، پیامدهای خاصی در ابعاد انسانی اقتصادی و زیست محیطی برای سواحل دریای عمان پدید می آورد که درک و شناخت آن می‌تواند ابزاری کارآمد در مدیریت مساله باشد. هدف این مطالعه، شناسایی تغییرات خط ساحلی در امتداد سواحل دریای عمان در ایران با استفاده از داده‌های سری زمانی سنجش ‌از دور و سیستم اطلاعات جغرافیایی (gis) و سیستم تجزیه و تحلیل دیجیتال ساحل (dsas) است. از تصاویر ماهواره‌ای landsat، سنجنده‌های tm و etm در سه دوره ی زمانی 2000، 2009 و 2019 پس از اجرای پیش پردازش و تصحیحات استفاده شد. همچنین برای استخراج خط ساحلی در دوره‌های زمانی، از شاخص mndwi و برای بررسی و آشکارسازی تغییرات فیزیکی نوار ساحلی، از ماژول dsas در محیط نرم‌افزار arcgis استفاده شد. میزان تغییرات خط ساحلی نیز به صورت الگوهای فرسایش و رسوب توسط چهار پارامتر آماری نرخ نقطه انتهایی (epr)، حرکت خالص ساحل (nsm)، سرعت رگرسیون خطی (lrr) و حداقل میانگین مربعات (lms) اندازه گیری شد. نتایج lrr مشخص می‌کند که ساحل دریای عمان با ویژگی فرسایش متوسط 10 متر و رسوب 8.39 متر در سال، یک ویژگی بسیار پویا را تجربه کرده است. همچنین نتایج حاصل از این مطالعه نشان می‌دهد که طول خط ساحلی در این دوره ی 20 ساله، افزایش قابل توجهی داشته است. بهبود مدیریت زمین، کنترل فرسایش، محافظت از موانع طبیعی موجود و تقویت زیرساخت‌ها بهترین گزینه‌های سازگاری برای محافظت از مناطق ساحلی است.

Investigation of periodic changes of the Oman Sea coastline using remote sensing data and spatial analysis

Extended abstract 1 IntroductionCoastal environments are one of the most sensitive environmental systems under the influence of dominant hydrodynamic processes. Coastal changes and evolution are occurring very fast. Coastal areas are now gradually becoming known as severe natural and manmade disturbances, including sea levels rising, coastal erosion and sedimentation, and overexploitation of resources. A deep understanding of the regionchr('39')s coastline dynamics (erosion and sedimentation) is essential for the proper planning, land use, and conservation strategies to reduce potential losses. Development of the southern coast of Iran has not only destroying the geomorphological landforms but also led to a change in the process of erosion and sedimentation in coastal areas. Understanding the behavior of the coastline would assist the management and planning of coastal facilities construction and determining the margins of the coast. Today, remote sensing methods, while being economical and promoting high accuracy, make it possible to continuously observe and manage beaches. These benefits have led to the increasing use of satellite imagery to determine the accurate position of the coastline in the world. The goal of this research is the investigation of periodic change of the Oman sea coastline from 2000 to 2109 using the Landsat timeseries dataset. 2 MethodologyThe study area in this article is related to the coastal line between Gwatr port and the Strait of Hormuz. The years of 2000, 2009, and 2019 were selected for the periodical coastal changes analysis in the last two decades. According to the time interval, the images of two Landsat 5 and 8 sensors were selected. The numbers of images that were mosaiced in each period are 15 scenes. Then, to discrete the water and land border, the modified normalized difference water index (MNDWI) in ENVI 5.3 software was used. This indicator is a combination of Green and MidInfrared bands. After applying the water and land boundary discrimination index, shoreline digitization in ArcGIS software has been done manually and with high accuracy. Thus shoreline from satellite images extracts by the Digital Shoreline Analysis System (DSAS). This method calculates the shoreline mobility and its changes based on satellite imagery. DSAS v4.3 is an extension developed by the US Geological Survey, which is adding to the ESRI ArcGIS 10.3 software. It is calculated the number of shoreline shifts from the past to the present. In this study, shoreline shifts are calculated using four data analysis methods (e.g., EPR, LRR, LMS, and NSM). 3 Results Identification of erosion and sedimentation transects indicates that the shoreline has been progressing ahead in most areas of coastline. During the last twenty years, 172.47 km of coastline length increased which is indicated by coastline sedimentation. These changes are apparent in most transects; 49% of transects were sediment, and 36% were erosive transects. The highest progress of coastlines observed in the Yekboni estuary (river mouth) area, western Jask Kohneh area which the sedimentation rate has reached 295.25 m/y. The sedimentation rate in the area of Chakha estuary, Gurdim, Gwadar port, and Bahu estuary has been above 100 meters per year. Also, the area between Brys to Pasabander and the upper area of Gashmi and Kartan estuaries has been high. The reasons for this can be attributed to the dock construction and the large volume of sediment in the estuaries by rivers. The highest amount of erosion rate in the nose of Jask port was 178.15 meters per year. The construction of stone walls in this area is the main cause of severe erosion. The length of the coastline in the year 2000, 2009, and 2019 were 1228.54, 1397.56 and 1394.08 km, respectively. The change of beach length is observed from 2000 to 2009; 169 km, from 2009 to 2019; 3.47 km, and from 2000 to 2019; 172.47 km. 4 Discussion Conclusions The nature of coastlines is dynamic; therefore, the management of such sensitive ecological environments requires accurate timeseries data. In this research, Landsat satellite imagery of TM and ETM sensors in the three periods of 2000, 2009, and 2019 have been used to detect shoreline changes. Coastal changes and spatial analysis are extracted by using the DSAS Extension in ArcGIS software. The length of the coastline in the year 2000, 2009, and 2019 were 1228.54, 1397.56, and 1394.08 km, respectively. Maximum sediment/erosion rates have been observed 290.25 and 178.15 m per year in the Yekboni estuary area and the cape of Jask port respectively along the coast of the Oman Sea. During twenty years, the eroded areas have experienced a recession, an average of 11.28 meters per year. The reasons are the rocky shores of the Oman Sea, desert landforms of some beaches and their exposure to severe wind erosion, dunes movement, and human activities. The areas of the coast where sedimentation was higher had an average of 9.74 meters per year. Human activities such as port construction and large volumes of sediment at the mouth of rivers have caused part of the coast to move toward the sea. In general, 36% of the study area has been eroded, and 49% has been more sedimented. Remote sensing and geological techniques with DSAS will be useful methods for monitoring longterm coastal changes and provide a comprehensive view of coastal erosion and sedimentation patterns. Continuing the coastline monitoring is necessary to observe future changes and is economically significant.