چکیده:
ﻣﻨﺎﻃﻖ ﻣﺠﺎور رودخانهها ﻛﻪ ﺑﻪ دﻟﻴﻞ ﺷﺮاﻳﻂ ﺧﺎص، ﻓﻀﺎﻫﺎﻳﻲ ﻣﻨﺎﺳﺐ ﺑﺮای اﻧﺠﺎم ﻓﻌﺎﻟیتهای اﻗﺘـﺼﺎدی ﻣﺤﺴﻮب ﻣﻲﺷﻮﻧﺪ، ﻫﻤﻮاره در ﻣﻌﺮض ﺧﻄﺮات ﻧﺎﺷﻲ از وﻗﻮع ﺳﻴﻼبها ﻗﺮار دارﻧﺪ. ازاینرو در اﻳـﻦ ﻣﻨـﺎﻃﻖ ﺗﻌﻴﻴﻦ ﻣﻴﺰان ﭘﻴﺸﺮوی، ارتفاع و خصوصیات سیلاب در دوره ﺑﺎزﮔـﺸﺖﻫـﺎی مختلف ﻛﻪ ﺗﺤﺖ ﻋﻨﻮان ﭘﻬﻨهﺑﻨﺪی ﺳﻴﻼب ﺻﻮرت ﻣﻲﮔﻴﺮد، ﺣﺎﺋﺰ اﻫﻤﻴﺖ ﻓﺮاوان ﺧﻮاﻫﺪ ﺑﻮد. رودخانه نکارود با توجه به شرایط خاص حوضه آبریز و تغییر ناگهانی شیب از مناطق مرتفع به جلگه ساحلی در چند دهه اخیر شاهد سیلهای متعدد و ویرانگری بوده، که اثرات جبرانناپذیر اقتصادی در این منطقه بجا گذاشته است. هدف از این تحقیق تهیه نقشه خطر سیل برای قسمتی از رودخانه نکارود میباشد. برای این منظور با تلفیق سیستم تحلیل رودخانه مرکز مهندسی هیدرولوژیکی(HEC-RAS) با سیستم اطلاعات جغرافیایی پهنه عمق و سرعت سیل این رودخانه برای دورههای بازگشت 200-100-50-25-10-5 ساله مدلسازی شده است. بهمنظور دستیابی به تابع مناسب برای پهنهبندی خطر جریان از ویژگی انرژی جریان برحسب تغییرات عمق و سرعت استفادهشده است. بر اساس آن نقشه خطر سیل بهدستآمده و مناطق با درجات مختلف خطر ازنظر انرژی جریان طبقهبندی و تجزیهوتحلیل شده است. نتایج بیانگر آسیبپذیر بودن منطقه در برابر سیل با دوره بازگشت بالاتر از 25 سال میباشد. با افزایش زمان دوره بازگشتهای سیل، سطح منطقه تحت تأثیر سیل افزایش مییابد. با استفاده از تابع خطر بهدستآمده مناطق تحت تأثیر سیل به پنج گروه خطر نسبی کم، متوسط، زیاد، نسبتاً زیاد و فوقالعاده طبقهبندیشده است. در تمام دوره بازگشتها بیشترین مساحت تحت پوشش ازلحاظ میزان خطر از نوع خطر نسبی بسیار زیاد میباشد. نتایج پژوهش ضرورت برنامهریزی و مدیریت راهکارهای حفاظتی جهت کاهش خسارات ناشی از سیل را نمایان میسازد. این پژوهش بهوضوح نشان میدهد که سیستم اطلاعات جغرافیایی یک محیط مناسب برای تجزیهوتحلیل و تهیه نقشه خطر سیل فراهم میکند.
IntroductionAmong the natural disasters, flood causes heavy losses on the agriculture, fishery, housing and infrastructures. It also strongly affects the economic and social activities. Using of modern science, especially remote sensing and GIS techniques helps the planners to assess the risk map of natural hazards such as floods for a region in the shortest time possible. Area of land adjacent to a river is an rivers are appropriate locations for economic activities due to specific situations. Nonetheless, This area is situted in the danger zone are in jeopardy because of flood risk. Consequently, determining the amount of flood progress, height and features in diverse returning periods which occur as flood zoning, are so essential. The Nekaroud River, according to its basin specific situations and the Sharp transation of the slope from The mountain to the coastal plain, makes catastrophic floods in last decades which give rise to irreparable economic damages in the area. The aim of this study is preparing the flood risk map for part of the Nekaroud River.Materials and methodsInitial data which is used in this study as well as topographic and land use map daily maximum debit statics of last 30 years of the Abloo hydrometric station ere used. Manning roughness coefficients related to the main channel of the river and floodplains were measured according to the land use map as well as field visits and also by the help of the Chow proposed table. In order to prepare the depth zoning map and the flood velocity, three steps are applied on the initial data. In the preprocessing step, so as to determine geometric and morphological characteristics of the river and floodplains such as the flow central line in the river channel, flow path lines, shorelines and cross sections, Arc GIS environment was utilized by using HEC-GeoRAS in order to determine the digital elevation model (DEM), in suitable seasons. In the hydraulic step, hydraulic and hydrological characteristics of the river flow such as cross-path structures, energy loss coefficients, boundary conditions of the studied area, the type of the flow regime, the river debit with different return periods and Manning coefficients, are defined for the hydraulic model of HEC-RAS. In this model, height, level, depth and velocity of the water in each section of the studied area for the flood with various return periods are calculated. The obtained output of the hydraulic model is defined as the GIS input. Then, by using digital depth model and the water level velocity in each of the cross sections as well as macro postprocessors of HEC-GeoRAS in the Arc GIS environment, an exchange file of the digital elevation model which can indicate the level of the flooded, is prepared. Then, by using the spatial analysis capability of the Arc GIS in combining the level of the flooded with the land elevation model, the depth zoning map as well as the flood velocity for various return periods are produced. For this purpose, the combination of hydrologic engineering center-river analysis system (HEC-RAS) and geographical information system were utilized to model the deep zone and the flood speed of this river for returning periods of 5,10, 25, 50, 100 and 200 years. In order to achieve a suitable function for flow risk zoning, the flow energy feature as a function of depth and speed changes was used. Then, the flood risk map was obtained and areas with different degrees of risk were classified and analyzed in terms of the flow energy.Results and discussionObtained results indicate that the flood velocity is different in various return periods and by increasing the return period time, the flood velocity increases. The flood velocity is different in various parts of the riverbed and the floodplains. Depending on the river deviation degree as well as the riverbed and floodplains topographic conditions, the type of the surface vegetation and the Manning roughness coefficient are variable. Flood height maps for various return periods imply that the maximum flood height for return periods of 5 and 200 years are 7 and 10.5m, respectively. The river channel is unable to transfer the heavy water flow during the flood and by increasing the flood return period time, the importance of this issue increases. Results imply the vulnerability of the area against the flood by returning area of above 25 years. By increasing the returning time periods, the area of the affected location by the flood increase. By using the obtained risk function, flood affected areas were classified into 5 risk categories concluding low, medium, high, very high, excessive. In all returning periods, the maximum covered area in terms of the risk, belong to excessive risk category.ConclusionResults actually emphasize the importance of planning and protective strategies management in order to diminish flood damages. This research evidently indicates that the geographical information system can properly create a situation for preparing and analyzing the flood risk map.
خلاصه ماشینی:
هيل ٧ (٢٠٠١)، قابليت هاي ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ 1 Getahun and Gebre 2 Yang 3 Demir and Kisi 4 Geographic Information System 5 Gichamo 6 Khattak 7 Hill سيستم تحليل جغرافيايي رودخانه مرکز مهندسي هيدرولوژيکي (HEC-GeoRAS١) را در پهنه بندي عمق سيل و مزاياي اتصال نرم افزارهاي Arc GIS و مدل هيدروليکي سيستم تحليل رودخانه مرکز مهندسي هيدرولوژيکي (HEC-RAS٢) را بيان نمود.
با توجه به اهميت منطقه موردمطالعه از لحاظ سيل خيزي، هدف از پژوهش حاضر تهيه نقشه خطر سيل رودخانه نکارود براي سيل با دوره هاي بازگشت مختلف بر اساس انرژي جريان با استفاده از مدل هيدروليکي و GIS جهت مديريت و برنامه ريزي راهکارهاي حفاظتي براي کاهش خطرات و خسارات ناشي از سيل ميباشد.
(به تصویر صفحه مراجعه شود) شکل ١: موقعيت جغرافيايي محدوده موردمطالعه ٣- مواد و روش ٣-١- داده ها جهت مدل سازي منطقه ، شبيه سازي سطوح آب گرفتگي و تهيه نقشه خطر سيل از امکانات سيستم اطلاعات جغرافيايي Arc GIS،HEC-GeoRAS و مدل هيدروليکي HEC-RAS استفاده ميگردد.
با توجه به اين که براي بررسي خطرات سيل و ارائه پهنه بندي خطر متناسب با آن ، داشتن اطلاعات مرتبط با تغييرات تراز سطح و سرعت آب در مقاطع مختلف ضروري است بدين منظور از مدل هيدروليکي HEC-RAS سامانه انجمن مهندسين ارتش آمريکا استفاده ميشود.