چکیده:
در این پژوهش بخشی از مجرای رودخانه قرهسو با استفاده از مدل ژئومورفولوژیکی رزگن مورد تحلیل و طبقهبندی قرار گرفت. این پژوهش متکی بر نقشههای توپوگرافی 1: 2000 و مطالعات میدانی بوده است. در این تحقیق، برای محاسبه پارامترهای نسبت گود شدگی و نسبت عرض به عمق لبپری از مدل هیدرودینامیکی HEC-RAS به همراه الحاقی HEC-GeoRAS استفاده گردید. بررسی نتایج مدل رزگن نشان داد که اکثر مقاطع رودخانه قرهسو در طبقهی C و E مدل سلسله مراتبی رزگن قرارگرفتهاند. رودخانه قرهسو در طبقه C دارای مجرای پهنتر و کمعمقتری میباشد و همچنین پهنه سیلابی رودخانه در این طبقه توسعهیافته و درههای آن عریض است. این رودخانه در طبقه E نیز دارای مجرای عمیق و باریک (نسبت عرض به عمق کم) بوده ولی پهنه سیلابی آن عریض و توسعهیافته است. با در نظر گرفتن متغیر شیب و مواد بستر میتوان گفت رودخانه قرهسو، در بازه اول در طبقهی C3b وE3b، در بازه دوم، سوم، چهارم و پنجم در طبقهی C4b، E4b، C5، در بازه ششم در طبقهی E5 و C5 و درنهایت در بازه هفتم در طبقهی C5c و E5 قرارگرفته است. همچنین با توجه به نتایج بهدستآمده میتوان بیان کرد که رودخانه قرهسو در بخشهایی که مقاطع در طبقهی C قرارگرفته است، دارای حساسیت به آشفتگی بسیار بالا، پتانسیل بازیابی خوب، تامین رسوب بالا، کنترل پوشش گیاهی بسیار بالا و در بخشهایی که مقاطع در طبقه E واقعشده است، رودخانه دارای حساسیت به آشفتگی بسیار بالا، پتانسیل بازیابی خوب، تامین رسوب متوسط، و کنترل پوشش گیاهی بسیار بالا میباشد.
IntroductionStreams typically have similar suites of channel morphologies, with repeatable patterns of occurrence that have resulted in numerous classification efforts (Roper et al., 2008: 417-427). Recent approaches for river classification focus on watershed analysis related to land management and stream restoration, using a hierarchical approach that nests successive scales of physical and biological conditions and allows a more holistic understanding of basin processes (Shroder, 2013: 739). One of the most widely used hierarchical channel classification systems was developed by Rosgen (Shroder, 2013: 742). In the current study, Gara Sou river channel planform are studied by using Rosgen geomorphological model in combination with HEC-RAS model.Materials and methodsThis study is based on fieldworks and topographic maps of scale 1: 2000 (Ardabil Regional Water Authority). To determine the friction coefficient distribution of channel and floodplain, land cover maps was generated using Google Earth satellite imagery. Rosgen (1985, 1994, and 1996) hierarchical system was used to analysis of river channel morphology. The Rosgen system uses six morphological measurements for classifying a stream reach-entrenchment, width/depth ratio, sinuosity, number of channels, slope, and bed material particle size. In this research, some of these parameters were calculated using HEC-RAS hydrodynamic model. For steady, gradually varied flow, the primary procedure for computing water surface profiles between cross-sections is called the direct step method. The basic computational procedure is based on the iterative solution of the energy equation. Given the flow and water surface elevation at one cross-section, the goal of the standard step method is to compute the water surface elevation at the adjacent cross-section. The flow data for HEC-RAS consists of flow regime, discharge information, initial conditions and boundary conditions (HEC, 2010).Results and discussionAccording to calculations made in seven reach has been in class C and E, hierarchical model Rosgen. Gara Sou River in class C has a wider and shallower channel and floodplain width significantly developed. Gara Sou River in class E also has a deep and narrow channel (width to depth ratio) but floodplain width developed. In reach (1) floodplain width due to low geological control variable. In this reach was due to power of river, the bed river is cobble and gravel that leads to the river bed is in the Armoring range. With regard to slope variables and bed material, it is placed in the class C. in this class have a mean energy and high sediment load. Energy waste by meandering, bed forms (Pool- Riffle) and vegetation occurs. In the reaches of 2, 3, 4 and 5 width floodplain will be a significant development. In the reaches type of bed river is changed to gravel and sand and more of gravel and sand are. River slope in this reaches are between 0.02 and 0.039. In this reaches (2, 3, 4, and 5) river in the most part located class of C4b Rosgen model and only in some sections of the river have been E4b class. Average width to depth ratio is calculated 16.14 for the total reaches. In this reaches riparian vegetation are mostly dense shrubs that this high density of riparian vegetation plays an important role in the stability of the banks river in this reaches. In the end of reach (5) and reach (6) river slope between 0.001 and 0.02 is located and bed River is sand that often makes the river in this section in class C5 in hierarchical Rosgen model. Average width to depth ratio is calculated 15.46 for the total reaches. In reach (7) river slope to less than 0.001, but the bed river is still sand. According to the results, the major part of this reach is located class C5c and only in small portions cross sections of the E5 is placed class. ConclusionIn this study, Gara Sou River channel was classified using geomorphological Rosgen model on the first and second levels. Despite the widespread use Rosgen model, has been criticized by some researchers. Problems with the use of the classification are encountered with identifying bank full dimensions, particularly in incising channels and with the mixing of bed and bank sediment into a single population. Gara Sou River in parts of Type E has a low sediment supply, average potential bank erosion control and vegetation are very high. The rivers carry sediment are very efficient and river is low energy, loss of energy through the meandering, bed forms and vegetation occurs. Also this river in parts of the Type C has a high sediment supply, very high potential bank erosion control and vegetation is very high. In fact, vegetation combined with the bank erosion, determines the amount of lateral adjustment and sustainability of this river.
خلاصه ماشینی:
در اين تحقيق با توجه به هدف و داده هاي موجود، بخشي از پلان فرم مجراي رودخانه قره سو(پايين دست سد سبلان تا تلاقي رودخانه اهر چاي) به طول ٧٥ کيلومتر با استفاده از مدل سلسله مراتبي رزگن ، در سطح اول و سطح دوم مورد تجزيه وتحليل قرار ميگيرد.
استفاده از يک رويکرد سلسله مراتبي، درک کل نگر تري از فرايندهاي ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ 1 - The Federal Interagency Stream Restoration Working Group 3 - Leopold and Wolman 4 - Lane 5 - Schumm 6 - Van den Berg حوضه اي را امکان پذير ميسازد (شرودر، ٢٠١٣: ٧٣٩).
طبقه بندي رزگن بر اساس چهار سطح صورت ميگيرد: سطح اول : ويژگيهاي ژئومورفيکي شامل توپوگرافي، لندفرم ها ، مورفولوژي دره ، الگو و پروفيل هاي رودخانه سطح دوم : توصيف مورفولوژيکي بر اساس مطالعات ميداني تعيين کننده منابع اطلاعاتي بازه ها سطح سوم : حالت و وضع رودخانه در شرايط پايداري ، واکنش و پتانسيل پاسخ سطح چهار: اعتبارسنجي اندازه گيريها و بررسي روابط بين فرايندها(وارد، ٢٠٠٨: ٣).
نتايج پهنه بندي سيلاب رودخانه قره سو با استفاده از مدل HEC-RAS نشان داد بيشترين عرض پهنه هاي سيلابي براي دوره هاي مختلف در بازه هاي دوم ، سوم و چهارم (از روستاي قديرلو تا روستاي لعل گنج ) قابل مشاهده است .
رودخانه قره سو در طبقه C داراي مجراي پهن تر و کم عمق تري ميباشد و همچنين پهنه سيلابي رودخانه در اين طبقه توسعه يافته و دره هاي آن عريض است .