تحلیل و پهنه بندی مخاطره سیل مطالعه موردی: حوضه آبخیز طالقان

سیل یکی از مخاطرات طبیعی است که هر ساله خسارات مالی و جانی فراوانی را به‌دنبال دارد. نقشه‌های پهنه‌بندی سیلاب،حاوی اطلاعات پایه و مهم در مطالعات طرح‌های عمرانی  دنیا می‌باشند و قبل از هر‌گونه سرمایه‌گذاری و یا اجرای طرح‌های توسعه، بررسی آن در دستور کار سازمان‌های ذی‌ربط قرار دارد. رودخانه طالقان طی سالیان متمادی با بروز سیلاب‌های متعددی مواجه بوده است.  اما تاکنون مطالعات جامعی در این ارتباط صورت نگرفته است. با توجه به اینکه  بدون توجه به مخاطره سیل، سکونتگاه‌های چندی در حاشیه شاخه‌های فرعی و اصلی رودخانه احداث گردیده و حتی شهرک طالقان اصلی‌ترین استقرارگاه جمعیتی در منطقه در حاشیه آن قرار دارد، همچنین ساخت و ساز بناهای مسکونی و تجاری در حاشیه رودخانه رو به گسترش است پژوهش حاضر به‌دنبال این است تا  با هدف تعیین پهنه‌های با خطر سیل‌گیری در محدوده حوضه آبخیز طالقان به تعیین مناطقی که بیشترین آسیب از خطر سیل دارند،  پرداخته و با استفاده از نرم‌افزار arc gis این اراضی را به‌صورت نقشه پهنه‌بندی مشخص نماید. تهیه نقشه پهنه‌بندی خطر سیل با استفاده از روش fuzzyvikor و با تعیین وزن از طریق critic برای 7 معیار موثر در ارزیابی پهنه‌های سیل‌گیر شامل: ارتفاع از سطح دریا، شیب، جهات شیب، کاربری اراضی، زمین‌شناسی، فاصله از آبراهه و میانگین بارش، انجام شد. نتایج این پژوهش که در پنج طبقه تهیه گردیده است، نشان می‌دهد 83 درصد از کل مساحت حوضه شامل پهنه‌های بی‌خطر یا با خطر کم می‌باشد. اما 17 درصد از اراضی آن، دارای خطر سیل‌گیری متوسط و بالا هستند که شامل عرصه‌های اطراف آبراهه اصلی و آبراهه‌های فرعی با کاربری‌های مسکونی و کشاورزی در حوضه می‌باشند. بنابراین لزوم رعایت حریم رودخانه طالقان در اراضی پست با شیب کم و متوسط، در توسعه کاربری‌های شهری روستایی منطقه، به منظور کاهش آسیب‌های ناشی از سیل، باید اجرایی گردد.

Flood risk analysis and zoning Case study: Taleghan Watershed

Extended AbstractIntroductionFloods are one of the natural hazards that cause a lot of financial and human losses every year. Flood zoning plans contain basic and important information in the study of development projects in the world, and before any investment or implementation of development plans, its review is on the agenda of relevant organizations. The Taleghan River has faced numerous floods over the years. However, no comprehensive studies have been conducted in this regard regarding the damage caused by the flood of Taleghan River and its zoning. The town of Taleghan, which is the main population settlement in the region, passes through and the construction of residential and commercial buildings along the river is expanding. Taleghan has identified the areas most affected by flood risk and using ARC GIS software to determine these areas in the form of a zoning map. Preparation of flood risk zoning map using FuzzyVIKOR method and by determining the weight through critic for 7 effective criteria in evaluating flood zones including: altitude, slope, slope directions, land use, geology, distance from waterway and average rainfall, Done. The results of this study, which has been prepared in five categories, show that 83% of the total area of the basin includes safe or lowrisk areas. However, 17% of its lands have moderate and high flood risk, which includes areas around the main waterway and subwaterways with residential and agricultural uses in the basin. Therefore, the need to respect the Taleghan River in low and medium slope lowlands, in the development of rural urban uses in the region, in order to reduce floods, should be implemented. Materials and methodsThe present research is descriptiveanalytical in terms of method and applied research in terms of purpose. Many factors must be considered in flood zoning, each of which has a different degree of importance. In this study, based on previous experiences, the factors that had the greatest impact on flood occurrence in the Taleghan watershed were selected in the VIKOR Fuuzy model. The data used in this study include sea level elevation, slope, slope directions, average rainfall, distance from waterway lines, land use and formation, which were used to determine areas vulnerable to floods.Some part of the required data including Digital Elevation Model (DEM), land use map of the region and map of geological formations be collected in raw form with a shape file format in the scale of 1: 250,000 from the rangeland and watershed management department of the Faculty of Agriculture and Natural Resources, University of Tehran. Elevation, slope and geographical aspect maps were extracted from DEM 10 m. The layer of waterways, including permanent canals and rivers, was provided by the National Forests, Rangelands and Watershed Management Organization.The map contains same rain line is received from the Meteorological Organization. the raster map of the average precipitation of the basin it was prepared based on the information of the precipitation rain lines and the statistics of rainfall data related to 5 stations of Dizan, Ciancranchal, Gotehdeh, Jostan, Glird, Armut and Zidasht, using the Interpolation technique. The criteria were normalized after preparing the maps (GIS READY) and applying the required edits such as defining the unit coordinate system for the maps, eliminating the errors that occurred during digitization and reducing the descriptive data by adding a new column to the related descriptive information table.All the maps were converted from Vector format to Raster, after the normalization step, and then the layers were weighed through the Critic method. Using the VIKOR model and the weights that obtained by the Critic method, which were calculated in Excel software, the value of the Vikor index (Q) was obtained for each of the options (pixels). Finally, the ultimate map of flood risk zoning in Taleghan watershed was obtained by assigning the values of Vikor index (Q) obtained from the previous step to each of the relevant points (options), by ARC GIS software. Results and discussionThe results of flood zoning map show that 83% of the total area of the basin includes safe or low risk areas. However, 17% of this area has a moderate and high flood risk, which mostly includes urban, rural settlements, orchards and agricultural lands, which shows the importance of paying attention to proper management in these areas. According to the obtained results, it can be said the distance from the waterway in Taleghan watershed has had a significant effect on the amount of flooding, so that by moving away from the main waterway and subwaterways of the basin, the risk of floods and flooding is reduced. Becomes. The results of the terming flood risk zoning, show that 27 villages and settlements out of 68 villages in the region are in highrisk areas, including the villages of Eskan, Gotehdeh, Narian, Prachan, Mehran, Joostan, Nisa Olya , Hasanjoon, Jazan, and Mochan are at the highest risk. ConclusionMulticriteria decision analysis methods in GIS have been proven to be a robust approach to generating risk maps with acceptable accuracy. Judgment of the acceptable feature of the model can be made using external information from real ground data. In this study, relatively high compliance with the final zoning map was obtained by examining the history of floods in the study area.