خلاصة:
مشخصات مخروط افکنه از جمله حجم آنها در ارتباط با عوامل و پارامترهای مختلف و متعددی است که میتوان آنها را در شش گروه عمده شامل عوامل اقلیمی و تغییرات آن، ویژگیهای هندسی حوضه های بالادست مخروط افکنه، لیتولوژی حوضه ها، تغییرات تکتونیکی بویژه تغییرات سطح اساس حوضه ها، تغییرات کاربری زمین و جهت جغرافیایی دامنه ها دسته بندی نمود. هدف این پژوهش بررسی نقش جهات جغرافیایی بر حجم مخروط افکنه ها در کوه بزرگ شیرکوه از کوههای پراکنده ایران مرکزی است. برای انجام این کار از تصاویر ماهواره ای، نقشه رقومی ارتفاعی با قدرت تفکیک 5 متر و همچنین نقشه های توپوگرافی برای مشخص نمودن محدوده مخروط افکنه ها و همچنین حوضه های آبریز بالادست استفاده گردید. بدین ترتیب، 24 مخروط افکنه بزرگ و قابل ملاحظه با محدوده حوضه های آبریز بالادست مشخص گردیدند. با استفاده از مدل کمی در سیستم اطلاعات جغرافیایی حجم مخروط افکنه ها محاسبه و میزان همبستگی آنها در SPSS با 8 پارامتر هندسی اندازه گیری شده حوضه های آبریز بالادست تعیین گردید. سپس، در مدل رگرسیون ضریب تعیین و سطح معناداری آنها نیز مشخص گردید. نتایج حاکی از آن است که در دامنه های جنوبی ضلع شرقی شیرکوه همبستگی بالایی بین حجم مخروط افکنه ها با عوامل هندسی بویژه مساحت(0.99)، محیط(0.98)، طول حوضه(0.95) و شیب متوسط حوضه(0.55) با سطح معنی داری صفر و نزدیک به صفر وجود دارد. این امر برای دامنه های غربی شیرکوه نیز صدق نموده و عوامل هندسی به ترتیب شامل مساحت، محیط و ضریب شکل(با همبستگی 0.99) طول حوضه(0.94)، شیب و ارتفاع متوسط(0.85) مهمترین عوامل تعیین کننده حجم مخروط های افکنه بوده اند. اما برای دامنه های شرقی با ضلع شمالی تنها شیب(0.64) و ضریب شکل(0.59) و برای دامنه های شمالی شیرکوه، ضریب گراویلیوس(0.43) و طول حوضه(0.37) همبستگی متوسطی را نشان میدهند که آن هم از سطح معنی داری قابل قبولی برخوردار نمی باشند. بنابراین در این دامنه ها عوامل هندسی حوضه ها کمترین نقش را در حجم مخروط افکنه ها ایفا کرده اند.
Introduction Alluvial fans are considered as one of the geomorphical features of dry and semi-dry areas which is the result of intense runoffs in the past and present. Thus, it can be considered as a Quaternary climate heritages. However, it is now visible in all climate conditions across the globe such as arid regions, Alpine environments, humid climates, and even tropical environments. Several studies have been done on their structure, morphology and hydrology. These studies have shown that cone-shaped characterization is associated with various and different parameters and factors which can be classified into six major groups including climatic factors and changes, geometric Properties of upper catchments, Lithological conditions, Tectonic variations, in particular in base level, land-use changes and geographic directions of slopes. The main goal of this study is to investigate the morphometric role of catchments in the volume of alluvial fans in the different slopes of Shirkouh Mountain in the south of Yazd with emphasis on geographical orientation. Since Shirkooh is a granite mass relatively cone-shaped that has created a number of alluvial fans in all its aspects, and in terms of lithology, its various directions are similar, the orientation of slopes against the air masses can play a major role in the volume of alluvial fans. Methodology To do this project, we used satellite images, a digital elevation model with a resolution of 5 meters and topographic maps of 1: 50000 . Initially, using these data, the boundary of alluvial fans and their upstream watersheds were determined.So, 24 significant alluvial fans and their watersheds were identified that there were 9 of them in the eastern slopes with the southern direction, 6 of them in the same range with the northern direction, 5 in the western slopes and 4 in the northern slopes of the mountain. Using the quantitative model in the geographical information system, the volume of alluvial fans was calculated. Then, the boundary of the upstream watershed of each alluvial fan determined in ArcGIS 10.3 software and ArcHydro add-ons and their geometric characteristics include area, environment, average height, average slope, the length of the basin, and the Gravilius coefficient were measured individually. In fact, by converting the information layers into the Raster's format, quantitative geomorphic characteristics and morphometric parameters of the catchment were calculated in four directions. Then, the correlation between the volume of alluvial fans and watershed morphometric parameters were calculated in SPSS software for 4 geographic directions and is also shown in the graph.Finally, to illustrate the effectiveness watershed morphometric parameters on the volume of the alluvial fans, We calculated multivariate regression between alluvial fans volume and morphometric basins in SPSS in four geographical orientations. Results and Discussion Eastern slopes with southern and northern directions extend to the vast plain of Ebrahimabad in the eastern slopes of Shirkouh and west of Mehriz city. Alluvial fans in this range are more numerous than in other slopes of Shirkouh and they have created bajada. However, in the slopes with northern direction, the watersheds are much wider compared to the opposite slopes. Therefore, the size and volume of the alluvial fans in the section are bigger and wider. While the correlation between the volume of alluvial fans and geometric characteristics of the upstream watershed is very high in the eastern slopes with the southern direction. So that the area, the environment and the length of the river show correlation above 95%. But the correlation for the slopes with the northern direction is very low in the range and the significant level between them is unacceptable.In the western slopes of Shirkouh, the geometric factors of the upstream watersheds are the main controllers of the volume of alluvial fans. The correlation between the volume of alluvial fans and geometric parameters of watersheds showed that among the eight parameters studied, only two of them includes Gravilius coefficient and drainage density played a small role in the formation and volume of alluvial fans, and other factors including form factor, area, environment, basin length, average elevation and slope Respectively played a major role in the volume of alluvial fans. But this case is different for the northern slopes of Shirkouh, So that there are the lowest correlations between geometric factors of catchment and volume of alluvial fans Relative to other geographic directions. Conclusion The results indicate that there is a high correlation between alluvial fans volumes and geometric factors especially area (0.99), environment (0.98), and the length of watersheds (0.95), in the eastern slopes with southern direction with a significant level of zero and close to zero. This applies to the western slopes and geometric factors includes area, environment and coefficient of form (with correlation 0.99), length of the catchments(0.94), average slope and elevation(0.85) have been the most important factors effect on the volume of the alluvial fans in the slopes. But the correlation between the volume of alluvial fans for the eastern slopes with northern direction includes only slope (0.64) and form factor (0.59) and for the northern slopes of includes Gravilius coefficient (0.43) and watersheds length (0.37) that have low significant levels. Therefore, in these slopes, geometric factors of watersheds played the least role in the volume of alluvial fans.
ملخص الجهاز:
نتايج حاکي از آن است که در دامنه هاي جنوبي ضلع شرقي شيرکوه همبستگي بالايي بين حجم مخروطافکنه ها با عوامل هندسي بويژه مساحت (۰،۹۹)، محيط (۰،۹۸)، طول حوضه (۰،۹٥) و شيب متوسط حوضه (۰،٥٥) با سطح معني داري صفر و نزديک به صفر وجود دارد.
اين امر براي دامنه هاي غربي شيرکوه نيز صدق نموده و عوامل هندسي به ترتيب شامل مساحت ، محيط و ضريب شکل (با همبستگي ۰،۹۹) طول حوضه (۰،۹٤)، شيب و ارتفاع متوسط (۰،۸٥) مهمترين عوامل تعيين کننده حجم مخروطهاي افکنه بوده اند.
اما از اين زمان به بعد مطالعات در زمينه اين عارضه گسترش و جنبه کمي و مدلسازي به خود ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ 1 -Blair and McPherson 2 -Mial 3 -Proximal 4 -Medial 55 -Distal 6 - Bootroyd & Nummendal 7 - Kostaschuk 8 -Kochel 9 -Kesel & Speicer 10 -Harvey 11 -Wasson 12 -Chamyal 13 -Ballantyne 14 -Teisseyre 15 -Klimek 16 -Coulthard 17 -Zygmunt 18 Bull گرفت (ليس ،۱۹۹۰:۴).
پاکزاد و ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ 1 -Silva 2 -Calvache 3 -Viseras ۴ Kostaschuk et al ۵ -Nanninga & Wasson ۶ Cotton ۷ Bowen ۸ Baylis ۹ KailKoura ۱۰ Giles ۱۱ Bow ۱۲ Absaroka ۱۳ - Beaumont اميني (۱۳۸۸) رخساره ها و فرايندهاي رسوبگذاري نهشته هاي مخروط افکنه اي بخش پاييني حوضه زاينده رود را مورد مطالعه قرار دادند.
بدين شکل در اين مطالعه رابطه بين ۸ عامل هندسي حوضه ها با حجم مخروط افکنه ها در چهار جهت جغرافيايي شيرکوه مورد بررسي قرار گرفت .