شبيه‌سازي سيلاب‌هاي رودخانه دره ائورت با استفاده از مدل هيدروليكي HEC-RAS در محيط GIS (محدوده موردمطالعه: از روستاي شورستان تا تلاقي رودخانه ارس)

Simulation of Dare Ourt River floods using Hydrodynamic Model HEC-RAS in GIS environmental (Case study: from Shorestan Village to Confluence of Aras River)

سيلاب‌ها ازجمله فراوان‌ترين مخاطرات طبيعي مي‌باشند كه همه‌ساله خسارات جاني و مالي بسياري را براي مردم به همراه دارند. مناطق مجاور رودخانه‌ها به دليل بهره‌برداري از شرايط خاص اجتماعي و اقتصادي، همواره مورد دست‌اندازي به بستر و حريم رودخانه قرارگرفته‌اند كه اين عمل باعث شده خطرات ناشي از وقوع سيلاب‌ها در طي سال‌هاي اخير افزايش يابد. رودخانه دره ائورت يكي از رودخانه‌اي دائمي استان اردبيل مي‌باشد كه در طي سال‌هاي اخير همواره با رخداد سيلاب‌هاي بزرگي مواجه بوده است. در اين پژوهش سعي شده است خطر وقوع سيلاب در اين رودخانه با استفاده از مدل هيدروليكي HEC-RAS در محيط GIS شبيه‌سازي‌شده و موردبررسي قرار گيرد. داده‌هاي اصلي موردنياز براي اين پژوهش شامل: نقشه‌هاي توپوگرافي 1:2000رودخانه دره ائورت، داده‌هاي هيدرومتري و شرايط مرزي رودخانه مي‌باشد كه از سازمان آب منطقه‌اي استان اردبيل تهيه گرديد. بر اساس تجزيه‌وتحليل‌هاي صورت گرفته و بررسي ميداني مشخص گرديد كه به دليل دست‌اندازي‌هاي كشاورزان منطقه، تغييرات زيادي در عرض بستر فعال رودخانه اتفاق افتاده است. اين عمل سبب تنگ‌شدگي مجراي رودخانه گرديده و باعث مي‌شود جريان آب رودخانه از مجراي اصلي خارج‌شده و وارد محدوده‌ي دشت سيلابي گردد. خروجي نقشه پراكنش فضايي سيلاب‌هاي شبيه‌سازي‌شده در منطقه نشان داد پل‌هايي كه سازه بتني ندارند در سيلاب‌هاي با دوره بازگشت‌هاي 2-5-10 ساله با احتمال تخريب روبه‌رو خواهند شد. همچنين در سيلاب‌هاي با دوره بازگشت‌هاي 50-100-200 بسياري از زمين‌هاي زراعي و روستاها در معرض خسارت قرار خواهند گرفت.

Introduction A flood is an unusually high stage in a river. It is an overflow of water outside its normal course. A flood results when a stream runs out of its confines and submerges surrounding areas. Among natural catastrophes, flooding has claimed more lives than any other single natural hazard. In the decade from 1986 to 1995, flooding accounted for 31% of the global economic losses from natural catastrophes and 55% of the casualties. The damaging effects of flooding are likely to become more frequent, more prevalent and more serious in the future. The burgeoning population of our planet is leading to the increasing exposure of people and property to the hazards of flooding. Today, river behavioral studies and engineering activities are one of the most important concerns of engineers involved in this field. The flood is an unusual stage in the river bed, which is an overflowing stream of river hydrologic power. Because of the placement of many urban and agricultural communities near the river this one great threat around the world. One of the important discussions of river geomorphology is the analysis of the effects of flood on the duct and sediment transport. Flood hazard maps for different return periods is one of the most popular maps that are used to show the potential hazards in floodplains. Management of the floodplain of the river is felt more than ever. Improved data collection and real-time modelling of flood events allows emergency services and relevant authorities to make more-informed decisions about where they direct their attention. In some instances, the areas where explicit reports of flooding are received are not those requiring the most urgent attention .The purpose of flood management was to maximize the benefits and reduce damage and casualties. The study area is River Dare Ourt one of the permanent rivers in Ardebil province, which during recent years has always faced major flood events. Materials & Methods This research is based on filed studies and 1:2000 scale topographic maps that provided by Ardabil regional water authority. The 1:100000 scale geological maps, satellite imagery such as IRS and Google Earth and also hydrometric data, considered as essential data. The HEC-RAS model could calculate the water surface profile in stable flow gradual variable in rivers and artificial channels in the subcritical, supercritical and complex regimes. The calculation of water surface profile carried out from one cross section to other cross, step by step, solving energy equation in standard way. Results & Discussion The present research has identified the risk of flooding in a range of 70 km. HEC-RAS is a one-dimensional steady flow hydraulic model designed to aid hydraulic engineers in channel flow analysis and floodplain determination. The results of the model can be applied in floodplain management and flood insurance studies. HEC-RAS is based on the U.S. Army Corps of Engineers’ HEC-RAS water surface profile model used for modeling both steady and unsteady, one-dimensional, gradually varied flow in both natural and man-made river channels. HEC-RAS also allows sediment transport/mobile bed computations and water temperature modelling in this research, after simulating the flow of the river in the HEC-RAS software environment, the output of this software is included in the Arc GIS software, and detailed maps of flood zones for different return periods are depicted in this software. In this research, the risk of flood occurrence in this river has been simulated and analyzed using the HEC-RAS hydraulic model in the GIS environment. The main data required for this research are topographic maps 1: 2000 of the Dare ourt River and hydrometric data and river boundary conditions. Conclusion Field analysis showed that due to the encroachment of farmers in the area, a lot of changes occurred across the river's active bed. This action causes narrowing of the duct and causes the flow of water from the main duct to enter the flood plain. The outflow of spatial distribution of flood simulated in the region showed that in the event of a flood with a return period of 25 years, about 1743 hectares of flood plain lands will fall under water and cause many damage to farmers. The results also showed that the maximum width of the catchment for flood with a return period of 25 years in some parts of the river will be about 896 meters. Accordingly, the need to pay attention to the liberation of the land of the land and the privacy of the river in the Dare ourt for the proper management of the flood plain of the river is felt more than ever.