پتانسیل خروجی آب از چین خوردگیهای زاگرس به حوضه آبریز خلیج فارس (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
بر اثر شکل گیری تنگ ها در رشته کوه زاگرس آب فراوانی به حوضه خلیج فارس هدایت می شود که در صورت نبودن تنگ ها، آب ها موازی با چین خوردگی های زاگرس، به سمت جنوب شرق هدایت می شدند. هدف از پژوهش حاضر برآورد آب انتقال یافته با تنگ های زاگرس است. به این منظور از نقشه های 1:50000 توپوگرافی، 1:100000 زمین شناسی، مدل رقومی ارتفاع ایران و منابع کتابخانه ای استفاده شد؛ بنابراین در این پژوهش لایه ایستگاه های هیدرومتری انتخاب و به عنوان نقطه خروجی، زیرحوضه های مسلط به آنها استخراج شد. در پژوهش حاضر روابط بین بارش با ارتفاع هر حوضه برآورد و بر اساس آنها لایه های هم بارش و متوسط بارش هر زیرحوضه محاسبه شد. با در نظر گرفتن وسعت زیر حوضه ها حجم بارش دوره های مدنظر برآورد و با دبی های ایجاد شده مقایسه و تجزیه و تحلیل شد. نتایج حاکی از آن است که با جریان های ناودیسی رشته کوه زاگرس، 110،695 میلیارد متر مکعب آب به خلیج فارس هدایت می شود. در میان پنج حوضه گیلوان، سیمره، سرتنگ دولاب، قره آغاج و دز زیرحوضه هایی که دبی کم دارند در دامنه های شرقی و زیرحوضه های با دبی زیاد در دامنه غربی تراست اصلی زاگرس واقع شده است. علت تفاوت در دبی دو دامنه را می توان در چند ویژگی زاگرس ردیابی کرد: 1- شیب دامنه های کوهستانی؛ 2- موقعیت دامنه ها نسبت به جریان های ورودی؛ 3- کارست و گسل خوردگی. هرچند حجم دبی حوضه های شرقی نسبت به دبی حوضه های غربی کمتر است، زمان آبدهی آنها طولانی تر است.The Potential of Water Outflow from the Folds of Zagros Mountains to the Persian Gulf Watershed
The Zagros Mountain range channels a significant volume of water towards the Persian Gulf basin due to the presence of gorges, diverting it from a potential southeast trajectory parallel to the Zagros folds. This study aimed to assess the water flow through the Zagros straits, utilizing 1:50,000 topographic and 1:100,000 geological maps, Iran's Digital Elevation Model (DEM), and various library sources. Hydrometric stations were used as the starting point and their associated sub-basins were delineated. The relationship between precipitation and elevation in each basin was analyzed to extract the precipitation layer of each sub-basin and calculate its average precipitation. Considering the sub-basin areas, the precipitation amount over a specific period was estimated and compared with the recorded discharges. The findings revealed that approximately 110,695 billion cubic meters of water were channeled to the Persian Gulf via the tidal currents of the Zagros Mountains. Notably, the sub-basins with lower discharge relative to the received precipitation, including Gilvan, Simre, Sartang Dolab, Qara Aghaj, and Dez, were situated to the east of the Zagros main thrust, while those with higher discharge were located to the west. This disparity in discharge on either side of the Zagros main thrust could be attributed to various mountain features, such as land surface slope, position in relation to incoming streams, karst, and faulting.Keywords: Debit, Gap, Karst, Watershed, Zagros. IntroductionIran, spanning an area of 1,648,195 km2, is characterized as one of the arid countries globally. Recent climate classifications indicate that approximately 90% of Iran's territory experiences dry and semi-arid conditions with over 40% facing a critical water scarcity crisis (Masoudian, 2011, p. 60). Notably, the intricate nature of the Zagros system has led to the water network often intersecting the folds perpendicularly and forming narrow gaps en route to the Persian Gulf's base level, facilitating substantial water transfer to the external watershed area. This study aimed to investigate the water transfer through the Zagros Gorges. While previous research has focused on the role of karst and fault systems in the sub-surface and underground water potential within the sub-basins of the Zagros Mountain range, their specific impacts on water transfer have received comparatively less attention. This article addressed this gap by evaluating their influence on a basin-specific basis while examining the effects of these gaps on water transfer from the Zagros Rivers. Materials & MethodsTo assess the impact of karst on surface water resources and the volume of water conveyed through the Zagros Gorges on a basin-specific basis, we employed 1:50,000-scale topographic and 1:100,000-scale geological maps, Iran's Digital Elevation Model (DEM), and various library sources. The initial step involved identifying the hydrometric stations and extracting their associated sub-basins. In the Zagros Mountains, local topographical features and the positioning of basin areas in relation to incoming rainfall significantly influence precipitation levels in addition to the well-established correlation between rainfall and altitude. To comprehensively evaluate the climatic conditions of the Zagros region, we utilized data from the statistical stations (rainfall, temperature, and discharge), the Esfazari Database spanning 49 years, and discharge data from the Water Organization. Employing Excel software, we determined the relationships between precipitation, temperature, and station elevation, focusing on those with an explanatory coefficient exceeding 70%. This facilitated the extraction of the precipitation layer for each sub-basin and the calculation of their average precipitation. Considering the sub-basin areas, we estimated the precipitation volume over a specific period and compared it with the recorded discharge data. Subsequently, we estimated the annual average rainfall and temperature for 156 basins in the Zagros region. Leveraging the DEM layer, we calculated the maximum and minimum basin elevations and determined their respective areas using GIS software. While 36 out of the 156 sub-basins were equipped with hydrological stations, we utilized Justin's method to estimate the discharge for the remaining basins, leveraging the similar functions of watersheds within the Zagros unit. Research FindingsThe comprehensive survey of the expansive basins of Simre, Karun, Qara-Aghaj, Dez, and Gilvan within the Zagros Mountain range revealed that the alluvial rivers channeled an impressive 110,695 billion m3 of water from the internal basins to the Persian Gulf basin through the creation of gorges and hydrological connections between the alluvial areas via depressions. It was evident that the volume of water output was not solely contingent on the basin areas. Notably, the sub-basins of Sartang Dolab and Tang Dez exhibited the highest outflow of water. The deep incisions of the folds coupled with faulting and limestone dissolution facilitated the transfer of water from the interior regions, particularly in basins characterized by varying elevations. The substantial proliferation of carbonate formations and the water potential of upstream karst aquifers manifested through the emergence of karst waters from springs significantly augmented surface water volume and played a pivotal role in sustaining underground streams within the karst aquifers. Limestone and karst formations were notably more prevalent on the eastern slope of the primary Zagros thrust than on the western slope. Furthermore, the density of faults was higher on the eastern slope, contributing to the creation of seams and cracks in limestone formations and the expansion of karst features. The springs originating from karst formations were more prevalent on the eastern slopes. It is noteworthy that the sub-basins with lower discharges relative to the received precipitation among the five basins of Gilvan, Simre, Sartang Dolab, Qara Aghaj, and Dez were situated to the east of the Zagros main fault. Conversely, those with higher discharges relative to the received precipitation were located to the west of the Zagros main fault. This disparity in discharge on either side of the Zagros main thrust could be attributed to various mountain features, including the slopes of the mountain land surfaces, their positioning in relation to the incoming streams, as well as the presence of karst and faulting. Discussion of Results & ConclusionThe towering Zagros range is characterized by an extensive network of faults and folds, spanning approximately 1600 km from Lake Van in eastern Turkey to Bandar Abbas at the mouth of the Persian Gulf, encompassing significant portions of Iran and Iraq (Oberlander, 2000, p. 13). Within the Zagros region, the mountains correspond to anticlines, while the valleys correspond to synclines. Anticlines and synclines are formed as a result of upward and downward movements of rock layers during folding and their physical appearance is linked to the undulating nature of folding waves (Zomordian, 2013, p. 209). Many of the rivers originating from the heights of the Zagros are perennial with some exhibiting substantial flow and turbulence. This hydrological characteristic has led to the natural evolution of basin limitations and expansions, as well as river capture during the Quaternary period (Ramesht, 2014). The majority of the basins within the Zagros Mountain range are situated within the folded Zagros or accordion levels characterized by expansive synclinal currents. The interconnection of these synclinal currents through saddles has resulted in the formation of numerous gaps, facilitating the outflow of significant water volumes to exoreic basins in Iran. Furthermore, geological factors, faults, and topography of the area may have influenced the modulation of output flow, either reducing or increasing it.
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