هزینه‌های مستقیم-ملموس در پهنه‌های سیلابی شبیه‌سازی شده با مدل هیدرولیکی دو بعدی hec-ras-رودخانه ارازکوسه استان گلستان

شبیه‌سازی پهنه سیل‌های احتمالی از مسائل مهم در مدیریت مناطق در معرض سیل جهت کاهش خطرات آن است. گسترش پهنه سیل در حاشیه رودخانه‌ها و سواحل می‌تواند خسارت‌های اجتماعی-اقتصادی و محیطی فراوانی را بر منابع طبیعی و انسانی در بر داشته باشد. استفاده از مدل‌های هیدرولیکی در شبیه‌سازی پهنه سیل، تعیین مناطق پرخطر و در نتیجه برآورد خسارت‌های احتمالی قابل توجه است. رودخانه ارازکوسه در پایین‌دست سه آبخیز کوهستانی مینودشت، نرماب و نوده‌خاندوز قرار دارد که در مواقع بارش شدید مستعد سیلابی شدن است. هدف پژوهش حاضر، ارزیابی عملکرد مدل هیدرولیکی دوبعدی hec-ras در شبیه‌سازی پهنه سیل رخداد مورخ 26 اسفند 1397 و برآورد خسارت‌های مالی مستقیم-ملموس در بازه‌ای به طول نه کیلومتر از رودخانه ارازکوسه در دوره‌بازگشت‌های مختلف است. در اجرای مدل دوبعدی hec-ras، از نقشه مدل رقومی ارتفاعی یک متری استفاده شد. عملکرد مدل در شبیه‌سازی پهنه سیل، با استفاده از تصاویر ثبت شده ماهواره سنتینل-2 در دو زمان مختلف (3 و 13 فروردین 1398) از رخداد سیل مورخ 26 اسفند 1397 از طریق واسنجی مقادیر ضریب زبری مانینگ برآوردی بر اساس مشاهدات میدانی بررسی شد. نتایج نشان می‌دهد که مدل دوبعدی hec-ras بر اساس شاخص f (79 و 71 درصد به‌ترتیب برای مورخ 3 و 13 فروردین 1398) عملکرد قابل قبولی در شبیه‌سازی پهنه سیل رودخانه ارازکوسه دارد. سپس هیدروگراف‌های شبیه‌سازی شده توسط مدل هیدرولوژیکی hec-hms در دوره‌بازگشت‌های مختلف به‌عنوان ورودی نرم‌افزار hec-ras به‌منظور تهیه نقشه پهنه سیل در دوره‌بازگشت‌های مختلف در نظر گرفته شد. نتایج پهنه‌بندی سیل در دوره‌بازگشت 100 سال به‌عنوان سیل مبنا نشان می‌دهد که به‌ترتیب کاربری‌های زراعی، باغ غیرمثمر، جاده خاکی، مناطق مسکونی و جاده آسفالت بیش‌تر در معرض غرقابی شدن قرار دارند. بیش‌ترین مقدار خسارت نیز مربوط به اراضی زراعی و مناطق مسکونی در دوره‌بازگشت 100 سال به‌ترتیب برابر با 20889 و 8650 میلیون ریال است. با توجه به مجموع مساحت کاربری‌های در معرض خطر سیل (حدود 23 هکتار) و مجموع خسارت وارده بر آن‌ها (حدود 41042 میلیون ریال)، برنامه‌ریزی و مدیریت در حاشیه رودخانه به‌منظور کاهش ریسک سیل از موارد ضروری است.

direct-tangible costs in flood zones simulated using the hec-ras 2-d hydraulic model – the arazkuseh river, golestan province

introductionflood events are the most complex natural hazards that endanger human and animal lives, social and economic structures, and environmental resources more than any other natural disaster. this phenomenon is caused by water flow exceeding the river's channel capacity. the expansion of flood zones along riverbanks in recent years due to climate change and inappropriate use of natural resources is associated with irreparable socio-economic and environmental damages. the simulation of potential flood zones is crucial for managing flood-prone areas. hydraulic models have proved to be useful in simulating flood zones, identifying hotspot areas, and thus, estimating potential damages. the arazkuseh river is situated downstream of three watersheds, namely minodasht, narmab, and nodeh khandooz. it is prone to flooding during periods of heavy rainfall in the watersheds. this research aims to assess the performance of the hec-ras 2-d hydraulic model in simulating the flood zone for the march 17, 2019, event and to estimate the direct and tangible damages incurred along a 9-km river reach of the arazkuseh river due to floods with different return periods.materials and methodsthe hec-ras software can calculate water levels in rivers while considering hydraulic structures. to estimate velocity vectors, the two-dimensional diffusion wave method was used, which provides more stable numerical solutions and reduces the calculation time. a digital elevation model (dem) map with a resolution of one meter was used to create input terrain data for this model. the flood event hydrograph from march 17, 2019, with a peak discharge of 355 m3/s, was recorded at the arazkuseh hydrometric station located at the joint outlet of the upstream watersheds. manning's roughness coefficient values estimated based on field observations in the channel and flood plain were also calibrated with the f-index during the evaluation of the model's performance. to evaluate the performance of the hec-ras 2-d model, the model’s outputs for the flood event on march 17, 2019, were compared with the flood zones identified by sentinel-2 satellite images on two different days (march 23 and april 2, 2019). the pilgrim's computational method was used to identify the temporal distribution model of the design rainfalls in the arazkuseh watershed for different return periods. additionally, the co-kriging geostatistical method was used to estimate the spatial pattern of the design rainfalls. thus, the hydrographs simulated by the hec-hms hydrological model for the design rainfalls were considered as inputs to the hec-ras software. following the identification of the elements exposed to flooding, direct and tangible damages caused by the simulated floods on different land uses were estimated by collecting information from different sources along with field observations.results and discussionthe f-index values (79% and 71% for march 23, 2019 and april 2, 2019, respectively) indicate that the hec-ras 2-d model has an acceptable performance in simulating flood zones in the arazkuseh river. however, the simulated flood zone was overestimated compared to the flood zone observed in the sentinel-2 images. the overestimation of the flood zone by the hec-ras 2-d model can be related to the accuracy of the dem map and manning's roughness coefficient estimation. analysis of the flood zone for the 100-year return period, as a base flood, reveals that crops, trees, dirt roads, residential areas, and asphalt roads are the most likely to experience inundation, in that order. even in a 10-year return period, croplands are likely to be included in the flood zone due to the gentle slope and their proximity to the river bank. the highest amount of direct-tangible costs for the 100-year flood is associated with croplands, residential areas, trees, dirt roads, and asphalt roads, with values of 20889, 8650, 7503, 2250, and 1750 million iranian rials, respectively.conclusionthe use of dem data with appropriate spatial resolution is crucial in creating terrain data and simulating flood zones in two-dimensional models. damages to agricultural products and costs attributed to the removal of sediments and cleaning in croplands will be significant due to flood water spreading across this land use. the high damage incurred in the residential areas is due to costly repairs required after flooding and the price of houseshold contents. the total area of land use exposed to a 100-year flood is about 23 ha, and the total damage incurred is approximately 41042 million iranian rials. therefore, due to the expansion of residential areas along the river, it is necessary to mitigate flood hazards, enhance adaptive and coping capacities, and reduce the level of exposure.