تحلیل ارتباط بین ویژگی سطوح مختلف مخروط افکنه های مروست با مورفومتری حوضه های آبریز بوانات- مدوار (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
در استان یزد نسل های متعددی از مخروط افکنه ها در قسمت های غربی و شرقی مروست متعلق به حوضه های آبریز بوانات و مدوار تشکیل شده است. هدف از مطالعه حاضر بررسی نقش مورفومتری حوضه آبریز در تحول سطوح مخروط افکنه های فعال و غیرفعال می باشد. با استفاده از شاخص های ژئومورفولوژیک سطوح مختلف تفکیک شد. ویژگی های مورفومتری مخروط افکنه ها و حوضه های آبریز محاسبه شدند. همبستگی منفی بین مساحت حوضه آبریز و شیب مخروط افکنه های فعال بیانگر شکل گیری سطوح جدیدتر با شیب زیاد در حوضه های کوچک تر می باشد. همبستگی مثبت مساحت حوضه با شیب مخروط افکنه های غیر فعال بیانگر این است که با افزیش مساحت حوضه، شیب مخروط های قدیمی تر بیشتر می شود. همبستگی منفی شیب حوضه با مساحت و حجم مخروط-افکنه های غیر فعال نشان می دهد سطوح قدیمی تر، با گذشت زمان پایداری بیشتری یافته و شرایط تثبیت رسوب گذاری و افزایش رسوبات ریزدانه تر ناشی از هوادیدگی موجب کاهش رواناب و تراکم زهکشی شده است. همبستگی مثبت شیب حوضه با مساحت و حجم مخروط افکنه های فعال بیانگر افزایش انتقال رسوب در طی فرایندهای سیلابی، همراه با نرخ پائین نفوذپذیری در رسوبات واریزه ای و غیرهوادیده در سطوح جدیدتر زمینه رشد و گسترش سطوح فعال را فراهم می آورد. مطالعه ی تفکیک سطوح مخروط افکنه ها و ارتباط ویژگی های آنها با مورفومتری حوضه آبریز می تواند اولین اقدام موثر در مدیریت چشم اندازها و منابع طبیعی و شناسایی مناطق مستعد سیلاب باشد. همچنین در زمینه برنامه ریزی کاربری اراضی، مخروط افکنه ها به دلیل مواد رسوبی غنی و دسترسی به منابع آبهای زیرزمینی و بنابراین توسعه کاربری های کشاورزی، بشدت مستعد وقوع انواع مخاطرات مانند فرسایش، زمین لغزش، جریانات واریزه ای و سیلاب می باشند. بطوریکه شناسایی این لندفرم ها و عوامل موثر بر ناپایداری سطوح قدیمی و جدید می تواند زمینه ساز تصمیمات بهینه در زمینه بهره برداری از این چشم انداز ها بوده، ضمن اینکه مخروط افکنه های قدیمی آرشیوهای ارزشمندی برای بازسازی های محیطی گذشته مرتبط با تغییرات اقلیمی و زمین شناختی دوران کواترنری می باشند.Analysis of the relationship between the characteristics of different surfaces of the Marvast alluvial fans and the morphometry of the Bavanat-Madvar catchments
Introduction Alluvial fans are considered to be among the most prominent geomorphic landforms of arid and semi-arid regions. Due to the dominance of arid and semi-arid climatic conditions, numerous alluvial fans are observed in the western and eastern parts of the Sefidkooh and Siahkouh slopes in Yazd province. This study aims to identify active and inactive alluvial fans in the study area and analyze the morphometric relationship between different surfaces of alluvial fans and catchment characteristics. Initially, by using geomorphological indicators including sediment color, drainage pattern, and surface morphology, the active and inactive surfaces of alluvial fans were distinguished. Then, the catchment area and related alluvial fans were determined using satellite images. In the study of the morphology of the catchment, the factors of area, perimeter, average elevation, elevation difference, basin slope, basin length, total length of watercourses, main watercourse length, basin shape factor, main watercourse slope, and drainage density were extracted. For the analysis of the morphometric characteristics of the alluvial fan surfaces, area, volume, cone apex height, cone length, cone slope, and base length were extracted. Finally, by using linear regression, the relationship between the morphometric characteristics of alluvial fans with active and inactive surfaces and the characteristics of the catchments was analyzed. Methodology The study area is located in the center of Iran, 180 km from Yazd province. The area of the region covers 34,000 hectares. Marvast County is located in south of Yazd province, between Mehriz and Khatam. The average elevation of the region is 1,520 masl. the average annual precipitation is 75 mm, and the average annual temperature is 17.5 degrees Celsius. Field observations and Google Earth images were used to identify alluvial fan surfaces in terms of relative age. In total, active and inactive surfaces were distinguished using indicators such as drainage patterns, weathering indices, morphology or surface topography, and sediment brightness. The morphometric factors of the basin, including the area and perimeter of the basin, elevation difference, average elevation, basin slope, maximum basin length, main waterway length, and total waterway length, were calculated. Morphometric factors of alluvial fans including area, cone apex height, cone length, cone slope, and base length were further calculated. Results and discussion In general, the drainage pattern in active alluvial fans has a branched distribution, while in inactive surfaces, channels are formed in a convergent or dendritic network. Active surfaces of alluvial fans are lighter in color than inactive or older surfaces due to less weathering. On the older surfaces, channels and gullies lead to the development of surface topography and valleys and ridges. In young and active surfaces, the morphology is smoother and channels and ridges are less visible. Statistical analysis of the morphometric characteristics of the study area indicates a relatively high correlation between the area of the basin and the area of the alluvial fans so that with the increase in the area of each basin, the area of the alluvial fan associated with it increases. Conclusion Alluvial fans are considered to be among the most prominent geomorphic landforms of arid and semi-arid regions. Due to the dominance of arid and semi-arid climatic conditions, numerous alluvial fans are observed in the western and eastern parts of the Sefidkooh and Siahkouh slopes in Yazd province. To analyze and investigate the effect of the morphometric characteristics of watersheds on the morphometric characteristics of active and inactive alluvial fans, an attempt was made to present the morphometric factors affecting the development and evolution of alluvial fans surfaces. For this purpose, the variables of area, perimeter, elevation difference, average elevation, basin slope, basin length, the total length of the watercourse, length of the main watercourse, basin shape coefficient, and main watercourse slope were calculated and measured separately, and the relationship between the morphometric characteristics of active and inactive alluvial fans with the morphometric characteristics of the basins was investigated. The largest volume of alluvial fans is formed by the Bavanat watershed in the western part of the region. The volume of active alluvial fans increases from the south of the region to the north. The results of the relationship between each factor and the dimensions of active alluvial fans show that the factors of area, environment, and drainage density of watersheds have a higher correlation and have the greater impact on the development of the morphometric characteristics of active alluvial fans. Further, in the case of inactive or older alluvial fans, the results were similar to active surfaces, so it can be said that the shape of the alluvial fans in the region has been strongly influenced by the morphometric characteristics of the watershed.
تبلیغات
