Environmental Erosion Research

fa بررسی اثرات مقاومت برشی درختی بر پایداری رودخانه (بازه‌ای از رودخانه بشار استان کهگیلویه و بویراحمد شهر یاسوج) Effects of Tree Shear Strength on River Stability (Reach of BESHAR River) مدلسازی و تحلیل زمانی و مکانی رخداد انواع مختلف فرسایش محیطی مستخرج از پایان‌نامه / رساله / طرح پژوهشی درک و پیش‌بینی فرسایش کناره‌ای، نیازی حیاتی برای مدیریت رودخانه است. در این پژوهش از مدل پایداری کناری و فرسایش پنجه‌ای (BSTEM)، به‌منظور بررسی پایداری بازه‌ای از رودخانه بشار در استان کهگیلویه و بویراحمد استفاده شد. این مدل، یکی از جامع‌ترین مدل‌های مورد استفاده در عملیات مهندسی و ساماندهی رودخانه در دنیاست که علاوه بر پایداری، امکان محاسبه میزان گسیختگی، ضریب ایمنی، میزان فرسایش، میزان بارگذاری رسوبات و پیشروی رودخانه را فراهم میسازد. به‌منظور افزایش دقت در اجرای مدل، با بررسی نقشه توپوگرافی و تصاویر ماهواره‌ای، نقشه زمین‌شناسی و بررسی‌های صحرایی، بازه‌ای از رودخانه بشار انتخاب شد که از نظر مورفولوژی، زمین‌شناسی و کاربری اراضی شرایط یکسانی داشت (طول بازه انتخابی 600 متر). این بازه به دو بخش شاهد (بدون پوشش) و آزمایشی (دارای پوشش) تقسیم شد. با توجه به ماهیت مدل BSTEM، به انتخاب تعدادی از مقاطع در بازه انتخابی پرداخته شد؛ بدین منظور، از هر بخش سه مقطع به فاصله‌های مساوی 100 متری انتخاب و مشخصات هندسی مقطع، خصوصیات ژئوتکنیکی، خاکشناسی، پوشش گیاهی، هیدرولیکی، هیدرولوژیکی و مقاومت برشی گونه‌های درختی در هر یک از آنها اندازه‌گیری ‌شد. تجزیه و تحلیل مقایسه داده‌ها نیز با نرم‌افزار HEC-RAS و مدل BSTEM انجام شد. نتایج اجرای این مدل نشان داد که از نظر پایداری، بین مقاطع دارای پوشش (Fs<1) و فاقد پوشش (1<fs)< span=""></fs)<> تفاوت زیادی وجود دارد. همچنین نتایج نشان داد که میانگین عرض و حجم گسیختگی کناره رودخانه به ترتیب در بازه فاقد پوشش، 72/2 متر و 6280 مترمکعب و در بازه دارای پوشش، به میزان 42/1 متر و 33/1686 مترمکعب است<fs)<fs< span="">.</fs<></fs)   <ol> <li style="margin-top:8px; text-align:justify">Introduction</li> </ol> So much of the river sediment occurrs due to bank erosion. Understanding and predicting bank erosion is a vital requirement for river management. During<del cite="mailto:MR" datetime="2022-01-03T11:55"> </del><ins cite="mailto:MR" datetime="2022-01-03T11:55"> </ins>a<ins cite="mailto:MR" datetime="2022-01-03T11:55"> </ins><del cite="mailto:MR" datetime="2022-01-03T11:55"> </del>flood, river flow shear stress exceeds river bank materials shear strength and causes a meandering. To prevent a river accresion in a floodplain, it is necessary to understand the river and perform river management and organization operations, especially in erosion reaches. Bank erosion occurs commonly during a relatively long reaches of the river. Due to the high cost, stabilization practices are only possible locally. In order to reduce this phenomenon, it is necessary to create vegetation in river reaches. The Bank Stability and Toe Erosion (BSTEM) model is one of the most widely used models in the world in most river engineering projects developed by the National Sediment Laboratory in Oxford, Mississippi, USA. The BSTEM model was initiallly developed by Pallen Benkhead and Simon to investigate riverbank stability under vegetation and water <ins cite="mailto:MR" datetime="2022-01-03T11:57">conditions.</ins><ins cite="mailto:MR" datetime="2022-01-03T11:57"> Subsequently</ins>, <ins cite="mailto:MR" datetime="2022-01-03T12:07">i</ins><ins cite="mailto:MR" datetime="2022-01-03T11:58">n </ins>BESTEM model<ins cite="mailto:MR" datetime="2022-01-03T12:03">,</ins> various plant and hydraulic parameters such as slope patterns<ins cite="mailto:MR" datetime="2022-01-03T12:05">,</ins><ins cite="mailto:MR" datetime="2022-01-03T12:08"> </ins>roughness, angle, and pore water pressure<ins cite="mailto:MR" datetime="2022-01-03T12:06"> are used</ins>. BSTEM is a bank erosion model that examines hydraulic processes, toe erosion and bank failure in soil homogeneous layers and is a suitable tool for determining riverbank conditions in order to protect river from streamflow erosion. A review of the research studies conducted in this regard showed that although the BSTEM model is a model with a long history and validity (based on numerous projects, articles and dissertations) and had been used in different countries and important rivers of the world to study the stability and bank erosion<ins cite="mailto:MR" datetime="2022-01-03T12:09">.</ins> <ins cite="mailto:MR" datetime="2022-01-03T12:09">In </ins>Iran, few studies have been done on the BSTEM model, which shows the need to conuct further studies for the purpose of validating this model. Therefore, this study was designed using the BSTEM model to investigate the stability of the river bank with respect to existing plant species in a section of the Bashar River in the city of Yasuj. <ol start="2"> <li style="margin-top:8px; text-align:justify">Methodology</li> </ol> In this study, the Bank Stability and Toe Erosion (BSTEM) model has been used to investigate the stability of the reach of Bashar River in Kohgiluyeh and BoyerAhmad Province. This model is one of the most comprehensive models used for river engineering and management operations in the world, which besides stability<ins cite="mailto:MR" datetime="2022-01-04T15:31">,</ins> the failure rate, safety factor, erosion rate, sediment loading rate, and river accrestion rate are calculated<ins cite="mailto:MR" datetime="2022-01-04T15:46">.</ins> The appropriate reaches of the Bashar River for modeling<ins cite="mailto:MR" datetime="2022-01-04T15:55">,</ins> should have the same characteristics in terms of morphology, geology, land use and have a suitable length (300 meters). The study was condcuted by analyzing two parts: control (without cover<ins cite="mailto:MR" datetime="2022-01-04T15:57">, length = 300 </ins><ins cite="mailto:MR" datetime="2022-01-04T15:58">meter</ins>) and experimental (with cover<ins cite="mailto:MR" datetime="2022-01-04T15:58">, length = 300 meter</ins>). Because of using the BSTEM model, it has been necessary to select several sections in the selected range. For this purpose, topographic maps and aerial photographs of the area were prepared. Then, with the help of these maps and Google Earth satellite images, a reach of the Bashar River was selected <ins cite="mailto:MR" datetime="2022-01-04T16:04">near the Darshahi region </ins><ins cite="mailto:MR" datetime="2022-01-04T15:56">for modeling</ins>. Then, the selected reach was divided into two parts: control (without cover) and experimental (with cover) with the same length of 300 meters, and each part was divided into 3 sections of 100 meters. <ins cite="mailto:MR" datetime="2022-01-04T16:03">Shear strength of tree species was measured in cross-sections. </ins>The reserachers performed data comparison analysis with HEC-RAS software and BSTEM model. <ol start="3"> <li style="margin-top:8px; text-align:justify">Results</li> </ol> The results of flood simulation in the HEC-RAS model in section 1 with cover reach and section 4 without cover reach showed that, in a 2-year flood, the average flow velocity in the middle of the cross section is 2.18 and 1.41 m/s, respectively (the estimated speed of the HEC-RAS model), and the flow height were 1.39 and 2.72 meters, respectively. The results of this study also showed that in terms of stability, there is a difference between sections with land cover (Fs <1) and no cover land (Fs <1). The results also pointed to the fact that the average width and volume of failure of the river bank in the no land cover section was 2.72 meters and 6280 cubic meters, respectively, and in the land cover section was 1.42 meters and 1686.33 cubic meters. <ol start="4"> <li style="margin-top:8px; text-align:justify">Discussion & Conclusion</li> </ol> The results showed that in terms of stability, there is a significant difference between covered and no covered sections because of the safety factor, which confirmed the instability of the <ins cite="mailto:MR" datetime="2022-01-04T16:10">studied </ins>reach. Based on the results of uncovered sections, due to fact that their geometric condition are unstable, the need for river management operations intesifies. The results showed that for sections with vegetation, the safety factor is higher than one, which indicated the bank stability in the studied reach, while in sections of no cover, the river is unstable. Increasing tensile crack depth, and bank angle resulted in bank instability, and increasing river flow level, groundwater level and suction matrix can lead to bank stability. In order to prevent bank river erosion, cultivation and growth of plants that are compatible with the climate and the erosive conditions are necessary. Therefore, it is suggested that native plants and other various plant forms be used to prevent bank river erosion. In addition, comparative studies need to be performed on other species in order to determie the role of plant cover on river bank stability in other rivers.   واژگان کلیدی:پوشش گیاهی, فرسایش کناری, گسیختگی, رودخانه, مدل پایداری. Bank Erosion, Failure, Land Cover, River, Stability Model 160 182 http://magazine.hormozgan.ac.ir/browse.php?a_code=A-10-736-1&slc_lang=fa&sid=1 fatemeh roushannasab فاطمه روشن نسب fatemerooshan72@gmail.com 10031947532846006838 10031947532846006838 No Forest-Rangeland and Watershed Management Department, Faculty of Agriculture & Natural Resources, Yasouj University, Yasouj, Iran گروه جنگل مرتع و آبخیزداری، دانشکده کشاورزی و منایع طبیعی، دانشگاه یاسوج، یاسوج MohammadReza Mirzaei محمد رضا میرزایی قره لر mmirzaei@yu.ac.ir 10031947532846006839 10031947532846006839 Yes Forest-Rangeland and Watershed Management Department, Faculty of Agriculture & Natural Resources, Yasouj University, Yasouj, Iran گروه جنگل، مرتع و آبخیزداری، دانشکده کشاورزی و منابع طبیعی، دانشگاه یاسوج، یاسوج Majid Khazaei مجید خزایی khazayi64@gmail.com 10031947532846006840 10031947532846006840 No Forests, Rangelands and Watershed Management Engineering, Department, Kohgiluyeh & Boyerahmad Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension, Yasouj, Iran بخش تحقیقات جنگل‌ها، مراتع و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان ‌کهگیلویه و بویراحمد، سازمان تحقیقات، آموزش و ترویج کشاورزی، یاسوج