ارزیابی آسیب‌پذیری سیلاب (مطالعه موردی: رودخانه چشمه ‌کیله تنکابن)

امروزه رشد سریع جمعیت و توسعه پیوسته محیط‌های شهری، تاثیرات نامطلوبی بر هیدرولوژی حوضه های آبریز گذاشته و در بستر زمان سبب تشدید سیلاب، افزایش آلودگی در قسمت‌های پایاب، کاهش جریان‌های پایه و کاهش تغذیه آب‌های زیرزمینی می شود. شاخه اصلی رودخانه چشمه‌کیله از مرکز شهر تنکابن عبور می‌کند که این امر تهدیدات مخاطره‌آمیز را دو چندان می‌کند. در سال‌های اخیر وقوع سیل، خسارات مالی و جانی در این منطقه بر جای گذاشته است. این مسئله نشان می‌دهد که عدم توجه به آسیب‌پذیری شهر تنکابن نسبت به سیلاب‌های گذشته، سبب تکرار هزینه‌ها و خسارات در بازه‌های زمانی کوتاه‌مدت شده است. بنابراین، کنترل، هدایت و مدیریت سیلاب‌ها برای کاهش خسارت امری اجتناب ناپذیر است. هدف این مطالعه، ارزیابی آسیب‌پذیری سیلاب در شهر تنکابن بوده است. برای ارزیابی آسیب‌پذیری سیلاب، بر اساس مطالعه پیشینه تحقیقاتی، اطلاعات مربوط به شاخص‌های نسبت جوانی، نسبت سالخوردگی، نسبت جنسی، کاربری اراضی، تراکم جمعیت و کیفیت سازه و مصالح تهیه شد. در گام بعدی هر یک از شاخص‌ها با استفاده از مدل ویکور وزن‌دهی شد و نقشه نهایی آسیب‌پذیری سیلاب از طریق نرم افزار arcgis تهیه شد. بر اساس یافته ها، بیشترین مساحت پهنه‌های آسیب پذیری ناشی از سیلاب در سطح بسیار زیاد و کمترین مساحت پهنه‌های آسیب‌پذیری در سطح بسیار کم واقع شده است. به طور کلی، نتایج نشان می دهد که در کناره های چپ در حواشی غربی و شمال غربی محدوده مورد مطالعه به دلیل تراکم بالای جمعیت و تراکم بافت مسکونی، سطوح نفوذپذیری خاک کم شده و حجم روانآب افزایش یافته است. بنابراین در این محدوده‌ها پتانسیل آسیب‌پذیری در برابر خطر سیلاب نسبت به سایر نواحی بیشتر است. 

flood vulnerability assessment, case study: cheshmekile tankabon river

introduction flood is one of the most common and widespread natural disasters that occur frequently around the world (patra et al, 2016). in recent years, the damages and casualties caused by floods have been affected by various factors. however, increased population, land use change, and the development of residential areas are considered to be the boosters for the increase in damages. the decrease in the active width of rivers by different factors especially human interventions has increased the vulnerability facing floods. the damages are classified into tangible or intangible types. tangible damages, including the destruction of buildings, agricultural lands, roads and transportation systems, infrastructures, environmental ecosystems, and human casualties impose a major negative emotional burden on the target society (tiryaki and karaca, 2018). among the natural disasters, floods cause the most damage to the agriculture, fisheries, housing, and infrastructure sectors and severely affect economic and social activities. despite the natural cause of the floods in iran, the main cause of the damages may be due to the human settlement in the high-risk areas (mustafa et al, 2018, nga et al, 2018). in recent years, about 70% of the annual budget dedicated to decreasing natural disasters have been allocated to recovering the damages by flood and this trend is increasing, so the 250% growth of flood damages in the last five decades confirms this claim (demir and kisi, 2016).results this applied quantitative research was carried out in the cheshme kile river, located in tonekabon city in 2021-2022. in the first stage, indicators affecting flood vulnerability were prepared using the study of the research background. in this regard, the data of 6 indicators of aging ratio, sex ratio, youth ratio, land use, population density, structure quality, and material quality were prepared as effective indicators of flood vulnerability. data were collected using the statistical yearbooks by referring to the national statistics center of iran, which was recorded in the last census in 2016. in the next step, the relationships defined according to table 1 were used to prepare each index. zoning the floodplain area is applicable to detect the vulnerable area. the map of floodplain zoning is the result of modeling based on the hec-ras model (saffari et al, 2023). the data of each of the indicators was overplayed with the layer of urban blocks of tonekabon using arcgis 10.3 software. then, the vikor method was used to prepare flood vulnerability zoning maps. the data normalization was carried out due to the different data spectrums. then, the weight of each index and sub-index was prepared using the ahp method. after determining the weight of each index, positive and negative ideals were determined. positive ideals are the highest values of each index and negative ideals are the lowest values of each index. the result of subtracting the positive ideal from other sub-indices is the index of usefulness, and the result of subtracting the negative ideal from each of the sub-indices is the regret index (table 2). the regret and usefulness indicators were classified (very high, high, medium, low, and very low) for each of the layers using the reclassify tool through arcgis software. (figures 2 and 3). the classification spectrum for each of the layers is presented in table 2. after calculating the indices of usefulness and regret, a flood vulnerability map was prepared for the study area using equation 5 (figure 3). in this map, values close to zero show the highest vulnerable area, and values close to one show the lowest vulnerable area conditions. to better understand the distribution of risk zones, the target map was classified into 5 spectrums of very high risk, high risk, medium risk, low risk, and very low.