پایش تغییرات خطوط ساحلی در واحد ژئومورفولوژیکی مکران (چابهار تا گواتر)

سواحل مکران اهمیت استراتژیکی زیادی دارد و طرح کلان توسعه آن به منظور بهره‌ برداری از پتانسیل‌های این منطقه ساحلی در حال اجرا است؛ از این رو، ارزیابی پایداری سواحل این منطقه اهمیت زیادی دارد و می‌تواند به برنامه ‌ریزان در جهت بهره ‌برداری بهتر از این سواحل کمک کند. هدف این تحقیق، ارزیابی تغییرات خطوط ساحلی مکران از چابهار تا گواتر در بازه زمانی 34 ساله (1989 تا 2020) است. مرز پهنه آبی در سواحل، با استفاده از داده‌ های ماهواره‌ ای لندست و بهره ‌گیری از شاخص ndwi استخراج شد. تغییرات کمی خطوط ساحلی نیز با استفاده از افزونه سامانه تحلیل خطوط ساحلی (dsas)، در سه واحد ژئومورفولوژیکی پادگانه های دریایی، سواحل ماسه ای و سدهای ساحلی برآورد شد. نتایج نشان می ‌دهد که متوسط میزان جابه ‌جایی (lrr) در همه سواحل، حاکی از پسروی خط ساحلی به میزان 0.96 متر در سال است، ولی این میزان جابه جایی در هر یک از واحدهای ژئومورفولوژیکی متفاوت است؛ به گونه ‌ای که تغییرات خطوط ساحلی در سد های ساحلی 2.75، در سواحل ماسه ای 0.11 و در پادگانه‌ های دریایی 0.03 متر در سال است. همچنین نتایج نشان می‌دهد که پایداری خط ساحلی در طول دوره مورد مطالعه، در پادگانه ‌های دریایی بیش از سایر واحدها است و می ‌توان گفت علت آن، مقاومت بیشتر واحدهای مارنی و ماسه ‌سنگی در برابر فرسایش نسبت به سایر واحدهای ژئومورفولوژی است. در کنار آن، بیشترین میزان تغییرات در سدهای ساحلی و دهانه ورودی رودخانه ‌ها به دریا مشاهده می ‌شود و این تغییرات شدید، تابعی از طغیان‌های فصلی رودخانه ‌های باهو کلات، زیردان و شور، و ورود حجم زیادی از آب این دو رودخانه به خط ساحلی و تخریب این خط و بازسازی مجدد آن توسط امواج و جریان‌های موازی ساحل است. علاوه بر تاثیر عوامل طبیعی، تغییرات خطوط ساحلی در هر یک از واحدهای ژئومورفولوژیکی تابعی از فعالیت‌های گستره انسانی در این منطقه است. برآوردهای تغییرات خطوط ساحلی در ده و بیست سال آتی در مجاورت برخی از سازه‌ های ساحلی، نشان دهنده فرسایش و رسوب گذاری بیش از روند طبیعی است و این امر در آینده می‌تواند در بهره ‌برداری از این سازه‌ها تاثیر منفی بر جای بگذارد.

Monitoring and assessment of shorelines change in of Makran geomorphological unit (Chabahar to Quatre)

Extended abstract1 IntroductionCoastlines are defined as the contact line between land and water body and have strategic natural, social and economic importance. One of the most important features of coastal areas is their dynamics. These dynamics lead to advances and regressions along the coastline and lead to erosion and sedimentation in the coastal regions. Coastline changes are one of the significant threats to coastlines. The study area of this research is on the southeastern coast of Makran and between Chabahar and Quatre Bay. This region is of special strategic importance today. The study area is divided into three geomorphological units of marine terraces, sandy beaches, and coastal barriers. The rate and trend of shoreline changes in each of these units were investigated to determine the stability of each geomorphological unit and evaluate and suggest suitable areas for future development. In addition, the future trend of changes in this regionchr('39')s sensitive and strategic areas in some important parts of this region in the next 10 and 20 years will be evaluated.2 MethodologyThe purpose of this study is to investigate the changes in coastlines of the study area. Hence, shoreline changes through shoreline monitored between 1989 and 2020 using Landsat (TM) satellite data (1989, 1995 and 2010, ETM for 2001 and OLI 2015). The extracted shorelines were entered into DSAS software, and shoreline changes were evaluated in this system in ArcGIS software. In this study, endpoint rate (ERP), linear regression rate (LRR), shoreline displacement rate (NSM), and shoreline average change (SCE) indices were evaluated. In addition, the prediction of shoreline changes was examined in the next 10 and 20 years in areas of great importance for development.3 Results One of the purposes of studying coastline changes is to study the sustainability of the coastline to plan for coastal development. Identifying stable and unstable areas along the coastline allows planners to identify areas that have the potential for development in terms of establishing coastal structures and minimizing the risk of future natural damage to coastal structures. Therefore, the study of coastline changes is one of the important parameters in these programs. This study was examined separately to analyze better the shoreline changes in each of the geomorphological units. The average changes were prepared according to LRR, EPR, NSM, and SCE values ​​in each unit. The results show that the highest amount of shoreline changes is observed in the coastal barriers of the study area. The average rate of change in coastal barriers in the LRR index in coastal barriers is 2.75 meters per year, which shows the ratio of sandy beaches (0.03 meters per year) and high beaches (0.11 meters per year) is very high. In addition, according to the NSM index, maximum advance (399.55 m) and the highest regression (725 m) can be seen in the geomorphological unit of coastal barriers, while the average values ​​of NSM on the sandy beach for shoreline are 103.7. the maximum regression rate is about 49.5 meters between 1989 and 2020. In addition, the NSM index values ​​for the terraces beaches are 36 meters forward and 41 meters backward, respectively.4 Discussion ConclusionsChanges and instability of coastlines are some of the major challenges that planners face in developing coastal structures, and not paying attention to these changes in the past and its future trend can impose irreparable damage to development projects. The present study was conducted in a very important area of ​​Chabahar to Goater to evaluate the stability of coastlines using periodic satellite data and DSAS tools. The results showed that the NDWI index separates the water area from the land better than other indicators. This study showed that the analysis of shoreline changes in the coastal region could be more accurate when geomorphological units in the coastal zone are separated and shoreline changes in these areas are evaluated. The results show that the two coastal areas and sandy beaches are relatively stable. Thet changes have occurred in sand dams, which can be attributed to the simultaneous effect of morphodynamic factors of land and sea in this area. Therefore, in the development of beaches and the establishment of coastal structures, coasts have risen, and also sandy beaches can be among the priorities of coastal planners in these areas. In addition, the structures constructed in the coastal zone have greatly impacted changing and intensifying the processes of erosion and sedimentation. Its example can be seen well in the port of Chabahar and Beris, which can cause problems in the future in the field of exploitation. It created ports.