بررسی تغییرات مورفولوژی و الگوی پیچان‌رودی رودخانه‌ی‌زهره با استفاده از تصاویر google earth

فرسایش و رسوب گذاری دو پدیده ای است که به تغییرات مورفولوژیکی در رودخانه‌های آبرفتی منجر می ‌شود. تغییرات مورفولوژیکی در رودخانه‌ها می ‌تواند مشکلات عدیده ای را در پی داشته باشد؛ از این رو، مطالعه و بررسی شکل رودخانه ‌های آبرفتی در علم مورفولوژی اهمیت به سزایی دارد. در این تحقیق، تغییرات مورفولوژی رودخانه ی زهره واقع در جلگه ‌ی هندیجان، برای طول حدود 23 کیلومتر در بین طول های جغرافیایی acute;30 °49 و acute;38 °49 و عرض های جغرافیایی acute;2 °30 و acute;6 °30 شمالی مطالعه و بررسی شد. بدین منظور، تصاویر google earth مسیر رودخانه برای سه دوره ‌ی زمانی شامل مسیر قدیمی، سال 2000 و 2014 میلادی بررسی شد. ذکر این امر لازم است که مسیر قدیمی بر مبنای آثار به ‌جای مانده از رودخانه، در تصویر google earth سال 2000 میلادی در محیط gis بازسازی شد. سپس این تصاویر در محیط gis، تجزیه ‌و تحلیل و پارامترهای مهم در تغییرات مورفولوژی رودخانه از قبیل ضریب خمیدگی، زاویه ی مرکزی، طول قوس و شعاع انحنا نیز محاسبه شد. نتایج نشان داد که درگذشته‌ در این رودخانه، چهار قطع‌ شدگی یا میانبر رخ داده است و در آینده نیز ایجاد یک میانبر، قابل پیش بینی است. تعداد پیچش ‌ها در طول این سه بازه زمانی، از 35 به 21 کاهش یافت و میانگین ضریب خمیدگی از 1.64 به 1.58، شعاع انحنا از 450.1 به 632.3 متر، زاویه ‌ی مرکزی از 196.6 به 193.3 درجه و طول قوس از 1197 به 1154.6 متر تغییر داشت. بر اساس معیار ولفرت، بر حسب ضریب خمیدگی رودخانه‌ ها (به نقل از راهنمای مطالعات ریخت ‌شناسی رودخانه ‌ها، نشریه ‌ی شماره ‌ی 592 وزارت نیرو: 96) و زاویه‌ ی مرکزی کورنایس، رودخانه ‌ی زهره واقع در جلگه ی هندیجان در رده‌ ی رودخانه ‌های پیچان رودی و پیچان رود بیش از حد توسعه ‌یافته قرار می ‌گیرد.

Study of the morphological changes and meander pattern of the Zohre River using satellite images

Extended abstract1 IntroductionThe Hedijan coastal plain around the Zohreh River is a hub for essential agriculture, fisheries, trade, and the military. Any change in the regime and territory of the Zohreh River will have significant economic, social, and security effects in the region. Due to the privation of the region and preserve the available resources and capital, it is necessary to carefully study the hydraulic parameters affecting the morphological changes and the complex pattern of the meandering of the Zohre River. In this study, considering the special conditions of this coastal plain, it has been tried to study geometric features such as curvature coefficient, curvature radius, central angle, and river arc length in three time periods by studying and examining satellite images in a GIS environment. 2 MethodologyIn this study, to study the morphological changes and meandering pattern of the Zohre River in the coastal plain of Hindijan, Google Earth satellite images from 2000 and 2014 were used. Based on these two images, the old route of the Zohreh River can be identified in the study area. In the next step, to investigate the meandering and morphological changes of the river, the route drawn from Google Earth entered the GIS environment. Using the ArcMap 10.2 software, to examine essential parameters in river morphological changes, circles with a suitable radius tangent to the existing curves in the river path were drawn. In the old route, 35 meanders were detected, and in the 2000 and 2014 routes, 21 meanders were identified and examined. 3 Results In order to study the morphology and meandering pattern of the Zohre River in the study area, various parameters such as bending coefficient, central angle, arc length, halfwavelength, and radius of curvature were calculated. According to Wolfert (2001), four types of rivers, including direct, sinusoidal, meander, and more meander, have been introduced in terms of the degree of curvature of rivers. According to this criterion, the Zohre River can be placed in a meandering river in the study area. Also, the number of meander from previous years, 2000 and 2014, was 35, 21, and 21. The maximum radius of the meander of this river was 450.1, 661.8, and 632.3 m. The lengths of the arch were 1197, 1118.2, and 1154.6 m, respectively. There have been alternating positive and negative changes in the values of the central angles in all three study periods. The average central angle from the old route to 2000 has been declining, and from 2000 to 2014, it has been increasing. In the old route, based on the size of the central angles, 57.14% of the torsions are in the overdeveloped area, 14.30% of the torsions are in the developed inverted 11.42% are in the undeveloped area. 17.14% was the size of a cowchr('39')s horn, and no percentage was found for quasitwisting curves. In 2000, based on the size of central angles, 42.86% of turns were overdeveloped, 14.30% of the turns were overdeveloped, and 23.80% of the turns were twisted. The average amount of radius in the old path increased from 450.1 to 66.81, and from 2000 to 2014, it decreased to 632.3. In total, this parameter has increased over three time periods. Finally, the obtained values for this parameter indicate that the river is meandering and the morphological changes in these three periods. 4 Discussion ConclusionsThe results showed that significant changes have taken place and are taking place over the years under study. During the three times of periods, four significant shortcuts and other significant morphological changes occurred. It is predicted that in the place of the 18th meander at the location of the existing bottleneck, there will be a shortcut in the future, which will eliminate the existing meander and create new ones.Also, according to the Wolfert classification criterion based on the bending coefficient (1.52) and the Corneiss classification based on the central angle (158296), the Zohreh River is located in the Hindijan Plain is in the category of meandering and the meander is overdeveloped.