تحلیل مورفودینامیک ساحلی با هدف تعیین مرز سلول‌های رسوبی (مطالعه موردی: استان هرمزگان)

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشیار گروه جغرافیای طبیعی، دانشگاه تربیت مدرس.

2 دانشجوی دکتری ژئومورفولوژی، دانشگاه تربیت مدرس.

3 دانشیار پژوهشکده علوم زمین، سازمان زمین‌شناسی و اکتشافات ‌معدنی کشور.

4 دانشیار گروه سنجش از دور، دانشگاه تربیت مدرس.

10.22034/gmpj.2020.118222

چکیده

بررسی تعادل رسوبی ساحل و استفاده از مفهوم سلول رسوبی رویکرد جدید و موثر در مطالعه انتقال رسوب و تغییرات خط ساحل در چند دهه اخیر است که بر اساس نگرش سیستمی به تحولات ساحل پایه­گذاری شده است. در این نگرش بخش قابل تفکیک از ساحل که به سلول رسوبی موسوم است به صورت یک سیستم مدل می شود که دارای ورودی نظیر ورودی رسوب و وضعیت فعلی ساحل است. در این سیستم ناشی از یک­سری فرآیندهای انتقال رسوب، خروجی سیستم حاصل می­گردد که همانا رسوب خروجی از سیستم و وضعیت جدید ساحل اعم از فرسایش و رسوبگذاری و تغییر خط ساحل است. سواحل استان هرمزگان از مهمترین و استراتژیک ترین سواحل ایران است که دارای محیط ساحلی بسیار پیچیده و تنوع فرم و فرآیند‌‌ است. از این­رو این سواحل براساس واحد‌‌های ژئومورفولوژیکی، الگوی موج و جریان خط ساحلی به سلول و زیرسلول­های رسوبی تقسیم شد‌‌ند. جهت نیل به این هدف از نقشه­­های توپوگرافی 1:25000 و زمین­شناسی 1:100000، تصاویر ماهوار‌‌ه­ای LandSat8، داده­‌‌های هیدرودینامیک، آمار باد، هیدرولوژی، لایروبی بنادر بزرگ و رسوب­شناسی (تهیه شده توسط سازمان بنادر و دریانوردی) استفاده شده است. داده­‌‌ها در محیطArcGIS10.3  تحلیل شده و محیط ساحل براساس ویژگی­‌‌های مشترک فرم و فرایندی طبقه­بندی و بر مبنای هدف مطالعه، مرز سلول­های رسوبی با استفاده از معیارهای ژئومورفولوژیک و درطی شش مرحله تعیین شد. سپس در هر سلول، با استفاده از داده­های گل­موج، گل­جریان، گل­رسوب، نت رسوبی و نقشه ژئومورفولوژی، مخازن و منابع رسوبی و جهت جابجایی رسوب تعیین شد. نتایج بدست آمده نشان می­دهد که به منظور تعیین راهبردها و سیاست­های مدیریت خط ساحلی، بر اساس تفاوتهای محیطی سلول­ها به به 6 سلول اصلی و 17 زیرسلول قابل تفکیک هستند که این تفاوت­های سلولی می­تواند در تعیین نوع و شیوه کاربری­های آتی قلمرو ساحلی مورد استفاده مدیران و بهره­برداران ساحلی قرار گیرد.

کلیدواژه‌ها


عنوان مقاله [English]

Coastal morphodynamic analysis with the aim of determining the sediment cell boundaries (Case study: Hormozgan province)

نویسندگان [English]

  • Siavosh Shayan 1
  • Zahra Dadashzadeh 2
  • Razyeh Lak 3
  • Mohammad Sharifikia 4
1 tarbiyat modares university
2 tarbiyat modares university
3 geology organization
4 tarbiyat modares university
چکیده [English]

Extended Abstract
Introduction
Coastal management needs to be organized at scales which are fully representative of the dynamics of the coastal system. A littoral cell is a coastal compartment that contains a complete cycle of sedimentation including sources, transport paths, and sinks. The cell boundaries delineate the geographical area within which the budget of sediment is balanced, providing the framework for the quantitative analysis of coastal erosion and accretion. The sediment sources are commonly streams, sea cliff erosion, onshore migration of sandbanks, and material of biological origins such as shells, coral fragments, and skeletons of small marine organisms. The coast of the Hormozgan province is marginal sea type and geomorphologically, it has coastal complexities of this type. It is difficult to determine a steady approach to sedimentation processes due to the diversity of coastal structures and the complexity of the coastal processes. Therefore, using the concept of sediment cell as well as the source and sink determining, reduce the complexity of Hormozgan coasts study. Hence, the uncertainty in the results can be greatly reduced by determining the boundaries of sediment cells and their geomorphologic explanation.
Methodology
The present research framework is based on the geomorphological inductive analysis research method. The stages of the study were conducted in this way: The first step is library and documentary studies, reviewing existing data and collecting data using field measurement, the second step is computer processing and the third step is the conclusion. The tools used for data collection include field observations, geological map 1: 100,000, topography map 1: 25000 and Landsat5 satellite imagery. Other analyzes are based on data such as wind statistical data, river sedimentation, hydrodynamics (wave rose, tides, high waves, and tsunami), large ports dredging data and sea level.
Results and discussion
The coasts of the Hormozgan province are classified according to the combination of two models of Valentin's classification (1952) and geomorphologic classification of Inman and Nordstrom (1971). These beaches include Mountainous beaches, Delta beaches (Inman and Nordstrom) and Submergent beaches (Valentine). Therefore, sediment cells 1 and 2 are located on the Mountainous beaches, sediment cells 3 and 4 are located Submergent beaches, and sediment cells 5 and 6 are located on the Delta beaches. Generally, the sedimentation volume in sediment cells 1 and 2 respectively is 261000 and 174000 m3/yr.And the sediment volume stored in the sinks of these cells respectively is estimated at 102000 and 223000 m3/yr.
Sediment cells 3 and 4 are Submergent beaches. Sedimentation volume in sediment cells 3 and 4 respectively is about 10920000 and 1813000 m3/yr., and the sediment volume stored in the sinks of cell 3 respectively is about 57,000 m3/yr. In sediment cell 4, due to the complexity and instability of the bay and estuaries behavior, the stored sediment volume has not been calculated. The sediment pathway direction in sediment cell 3 is from east to west and in sediment cell 4 under the influence of the Hormuz Island is bidirectional.
Sediment cells 5 and 6 are located in the eastern plain of Hormuz Strait and are classified as delta beaches. Sedimentation volume in these cells respectively is about 1553000 and 8818000 m3/yr.And the sediment volume stored in the sinks of cells 5 and 6 respectively is about 379000 and 780000 m3/yr. The sediment pathway direction in sediment cell 5 under the influence of alongshore is from south to north and in the sediment cell 6 is from east to west.
Sediment budget of subcell 5-1: The values obtained from the estimation subcell 5-1 sources and sinks are included in the sediment budget equation. The summary of the obtained results is shown in Table 1.
Table 1: Values of factors in the subcell 5-1 sediment budget (Ports and Maritime Organization, 1396)



Residual (thousand  m3/yr.)
Entrance littoral drift (thousand  m3/yr.)
Changes (thousand  m3/yr.)
Sinks (thousand  m3/yr.)
Sources (thousand  m3/yr.)


41
21
-26
270
264



 
As we can see, this sub-cell contains about 41,000 m3/yr. of sediment surplus that is likely to precipitate in spits and deltas existing along the shoreline.
Conclusion
In order to determine the coastal management strategies and policies, the coast should be divided into specific and limited intervals according to dominant dynamic processes and landform characteristics. Thus, after determining the coastal area in a study and collecting required information on the behavior of natural phenomena in this area, the length of the coastline is divided into a series of cells and subcells. The tectonic and sea level rise is one of the key issues that are the basis of long-term changes in the coast. The uplift coasts are one of the most important geomorphologic landforms of the study area. These forms are influenced by the plate tectonics and the oceanic plate of the Oman Sea subduction under the continental crust of the Makren. Over the next 50 years by comparing the coastal uplift (about 100 mm) and sea level rising (24 cm/yr.), the beaches will be exposed to the sea progress. This will have a significant effect on the cell boundaries changes. So that all the parameters that were studied and measured to determine the littoral cell boundaries are affected, and consequently the littoral cell boundaries will also be displaced. The results show that on the Hormozgan province coasts, like the boundaries introduced in international studies, the boundary of sediment cells consists of headlands and estuaries. The sediment produced by the rivers is the main source of sediment in all littoral cells. Just in sediment cell 1, the main source of sediment is the coastal erosion. Sinks identified on the coasts of the Hormozgan province include estuaries, spits, lagoons, and beaches on the one side of small gulfs. This research is based on the international scientific and practical methods used to determine the sediment cell boundaries, sources, and sinks. The difference is that the point of view of geomorphology (considering scale, form, and processes with the holistic approach) used as methods for explaining the problem.
 

کلیدواژه‌ها [English]

  • Coastal geomorphology
  • Sediment Cell
  • Coastal management
  • Hormozgan province coasts
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