Environmental Erosion Research

fa بررسی اثرات احداث سد سهند بر شرایط هیدرولوژیکی رودخانه و تحلیل تغییرات شکل هندسی مجرای قرانقو‌چای (از بازه پایین‌دست سد سهند تا روستای خراسانک) Investigation of the effects of construction of Sahand dam on the hydrological conditions of the river and analysis of changes in the geometric shape of Qaranqoochay canal (from the lower reaches of Sahand dam to Khorasanak village) مدلسازی و تحلیل زمانی و مکانی رخداد انواع مختلف فرسایش محیطی مستخرج از پایان‌نامه / رساله / طرح پژوهشی رودخانه و فرایندهای رودخانه‌ای در سطح زمین، مهمترین سیستمهای ژئومورفیک فعال است که در اثر کنترل‌کننده‌های محیطی و دستکاری‌های انسانی در سیستم‌های طبیعی، طی مقاطع زمانی و مکانی مختلف، تغییرات متفاوتی را از خود نشان می‌دهند. این تغییرات و جابه‌جایی‌ها مشکلاتی را برای کاربری‌های انسانی و اکولوژیکی ایجاد می‌کند و از مباحث مهم در ژئومورفولوژی رودخانه‌ای محسوب می‌شود. هدف پژوهش حاضر، بررسی اثرات احداث سد سهند بر شرایط هیدرولوژیکی رودخانه قرانقوچای از بازه پاییندست سد سهند تا روستای خراسانک و تحلیل تغییر شکل هندسی مجرا، در بازه زمانی 1374 تا 1397 است. این پژوهش متکی بر کارهای میدانی، استفاده از تصاویر ماهواره‌ای، داده‌های هیدرومتری، نقشه‌های توپوگرافی و زمین‌شناسی است. شرایط هیدرولوژیکی رودخانه با استفاده از 2<a name="_Hlk67740047">6</a> شاخص هیدرولوژیکی، در دو دوره قبل از احداث سد و بعد از احداث آن محاسبه شد. سپس برای بررسی رابطه معناداری شاخص‌ها، از آزمون آماری T جفتی استفاده شد. به منظور بررسی تغییرات شکل مجرا نیز از پارامترهای بررسی شکل هندسی رودخانه شامل ضریب خمیدگی و زاویه مرکزی استفاده و میزان مهاجرت مجرا با استفاده از روش ترانسکت محاسبه شد. با توجه به نتایج مطالعه، از لحاظ شاخص‌های هیدرولوژیکی Q5، Q10، Q15، دبی حداقل، دبی حداکثر و دبی مد، بین دو دوره قبل و بعد از احداث سد تفاوت معناداری دیده می‌شود. میانگین ضریب خمیدگی در سال 1374، 15/1 بود و در سال 1397 به مقدار 18/1 افزایش یافت و الگوی رودخانه از پیچان‌رودی بسیار توسعه‌یافته به توسعهیافته تبدیل شد. میانگین آهنگ مهاجرت مجرای رودخانه در طی بازه زمانی 24 ساله مورد مطالعه، در حدود 143/0 متر در سال بود. بیشترین مقدار جابه‌جایی عرضی مجرا، در ترانسکت یک به میزان 41/0 متر در سال و کمترین جایه‌جایی در ترانسکت یازده، به مقدار 022/0 متر در سال است. در نتیجه، مشخص شد که رودخانه قرانقوچای در بازه مطالعاتی، تغییرات مورفولوژیکی و جابهجایی مجرا داشتهاست و عوامل مؤثر این تغییرات به طور عمده شامل تغییرات دبی به ویژه در زمینه احداث سد، فرسایشپذیر بودن سازندهای بستر و کنار رودخانه و عوامل مختلف انسانی است. Extended abstract 1- Introduction River and river processes are considered the most significant geomorphic systems active on the earth’s surface. Over time, many changes in the morphology and dynamics of the river system can occur. The effects of river adjustment caused by the natural factors require a much longer period to reveal. However, there are few exceptions that natural factors such as river floods, landslides, or earthquakes can induce channel adjustments in a concise time. In contrast, human activities can significantly impact natural processes and trends, resulting in a compressed time scale for river adjustments. Consequently, the flow regime of many rivers has been dramatically altered from their natural flow regime. Redirection, deformation of the canal, destruction of the banks and lands along the river are observed in Qaranqoochay river. Therefore, the purpose of this study is to investigate the effects of Sahand Dam construction on the hydrological conditions of the Qaranqoochay River, determine the geometric components of the river, and investigate the displacement and shape changes of the Qaranqoochay River Canal. 2- Methodology In this research, the topography map with a scale of 1:50000, geology map with a scale of 1:100000, google earth and Landsat images, hydrological data from and field data are used. ENVI 5.3, Arc GIS 10.5, Excel, and SPSS software were also used for image processing and data analysis.  To study the hydrological conditions of the study area, the data of the Chapini station were studied using 26 hydrological indices. Then, a paired T-test was used for statistical analysis of indices to study the significance of indices changes and, consequently, the effect of dam construction. The geomorphological parameters of the river and their variations, including bending coefficient and central angle, were measured. The curvature coefficient is one of the few criteria used in river shape segmentation using s = 1/ (y.2), i.e., dividing the valley length by wavelength for each arc (Pitt's coefficient). It is calculated. The central angle of the arcs on each of the intervals was calculated using the relation A = 180L / Rπ, where A is the central angle, R, of the fitted circle radius (Kornias coefficient). The lateral changes of the canal were investigated using the transect method and calculation of river migration rate. According to the Transect method, lines with distinct distances from both sides of the duct are depicted as baselines. These lines are constant for the periods studied and can be calculated quantitatively for duct movements relative to these lines. 3- Results  According to the results of calculating hydrological indices and T-test analysis, in terms of hydrology Q5, Q10, Q15, minimum flow, maximum flow, and Mode flow, between the two periods before and after the construction of the dam, a significant difference was seen. It can be stated that the construction of Sahand Dam and the changes in the flow by the dam can affect the amount, timing and it affects the duration of upstream and downstream currents. Also, it can provide suitable bedding for intensifying hydrological changes and, subsequently, river morphological changes. Downstream changes include sedimentation and erosion in parts of the river, displacement of meanders, flooring, and wall demolition.  The average curvature coefficient had increased from 1.15 in 1995 to 1.18 in 2018, and in 1995, 21.43 of the river patterns were straight (curvature coefficient 1-1/05), but in 2018, there is no direct pattern in the path. The plan of the duct in both periods is sinusoidal (curvature coefficient 1/5-1.05). According to the values of the central angle, in 1995, the studied route from Qaranqoo river was Highly developed as a meandering river (central angle 296-158), and in 2018 it was extended to the meandering river (central angle 158-85), it arrives. With the decrease of the average central angle in 2018, the average radius of the circles has also decreased. The average wavelength and valley length in 2018 compared to 1995, and the decrease in wavelength indicates a decrease in the distance of successive turns. The average rate of river canal migration during the 24 years studied was about 0.143 m per year. The duct's maximum amount of transverse displacement in transect one is 0.41 m per year, and the lowest amount of displacement in transect eleven is 0.022 m per year.  4- Discussion & Conclusions  In general, the changes in the plan of the Qaranqoo river in the studied time and place period have been in the form of expansion of existing meanders, shifting of the river course, and formation of small meanders. Formation and morphological changes of the Qaranqoo river in the studied time and place period are mostly influenced by hydrological processes caused by dam construction (significant reduction of runoff in the river and accumulation of sediment load in the bed path) and lithological conditions of the bed and side. Of the river. Also, human beings have changed the pattern of the Qaranqoo canal in the studied area by harvesting river materials, encroaching on the river area in the form of land-use change, farming in river lands, and pumping water for agricultural lands along the rivers, construction of bridges. پارامتر‌های هیدرولوژیکی, سد سهند, شکل مجرا, قرانقو‌چای. Hydrological parameters, Sahand dam, duct shape, Qaranqoochay. 99 122 http://magazine.hormozgan.ac.ir/browse.php?a_code=A-10-93-6&slc_lang=fa&sid=1 Sayyad Asghari Saraskanrood صیاد اصغری سراسکانرود s.asghari@uma.ac.ir Yes Department of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل Elnaz Piroozi الناز پیروزی piroozielnaz@yahoo.com No Department of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل