ارزیابی و پهنه‌بندی خطر سیلاب‌های ناگهانی براساس مدل Mffpi (مطالعۀ موردی: حوضۀ اسلام‌آباد غرب)

سیلاب‌های ناگهانی پاسخ هیدرولوژیکی عوامل فیزیوگرافی حوضه به رخداد بارش‌های سنگین است و وقوع آنها سبب خسارات مالی و جانی می‌شود. به‌دلیل ماهیت پیچیدۀ سیلاب ناگهانی، پیش‌بینی آنها با دشواری زیادی روبه‌روست و ویژگی‌های فیزیوگرافی حوضه‌ها نقش مهمی در شکل‌گیری آنها دارد. مدل mffpi با استفاده از شاخص‌های فیزیوگرافی حوضه‌ها به ارزیابی خطر سیلاب ناگهانی می‌پردازد. حوضۀ‌ اسلام‌آباد غرب به‌علت شرایط فیزیوگرافی و رخداد بارش‌های سنگین مستعد وقوع سیلاب ناگهانی است و در طی چند دهۀ گذشته رخداد سیلاب سبب خسارات گسترده در شهر اسلام‌آباد غرب و در سطح این حوضه شده است. هدف پژوهش حاضر، ارزیابی و پهنه‌بندی خطر سیلاب ناگهانی حوضۀ اسلام‌آباد غرب با استفاده از مدل mffpi است. نتایج پژوهش نشان داد که نقشۀ نهایی پتانسیل خطر سیلاب ناگهانی در مرحلۀ اول نشان می‌دهد که 45 درصد مساحت حوضۀ اسلام‌آباد غرب در پهنه با پتانسیل خطر زیاد قرار دارد. توزیع فضایی پهنه‌های خطر پنج‌گانه از شرایط توپوگرافی و تجمع جریان حوضه تبعیت می‌کند. در ادامه با بهره‌گیری از رگرسیون خطی پارامترهای موثرتر در تجمع و انباشت آب مشخص شده و چهار متغیر شیب توپوگرافی، تجمع جریان، انحنای دامنه و کاربری اراضی 96.6 درصد از شاخص پتانسیل سیلاب را توضیح می‌دهند. حذف پارامترهای کمتر موثر بافت ‌خاک و نفوذپذیری سنگ در مرحلۀ دوم اجرای مدل، سبب کاهش مساحت نواحی با پتانسیل خطر زیاد سیل و افزایش مساحت نواحی با پتانسیل خطر کم و متوسط سیل شده و مناطق با پتانسیل خطر خیلی زیاد در ارتفاعات و حواشی آن که با واقعیت همخوانی نداشته حذف شد. نتایج مدل mffpi در هر دو مرحله بیانگر پتانسیل زیاد خطر سیلاب ناگهانی در سطح دشت اسلام‌آباد غرب است و این شهر و همۀ روستاها و زیرساخت‌های سطح آن در معرض خطر سیلاب ناگهانی قرار دارند.

Assessment and Zoning of Flash Flood Risks based on MFFPI Model (Case Study: Islamabad Basin)

IntroductionAn immediate flood is a rapid flood that is caused by heavy rainfall or sudden release of water over a short period of time while water flowing over the earth (Huang et al., 2013, p. 325). Great floods have the same consequences, hydrogeomorphological effects (Martin et al., 2012, 49), biological effects (Richter et al., 2000, 1469), and socioeconomic effects (Mirz, 2007, 233). This means creating high financial costs and reducing socioeconomic development (Moses et al., 2010, 112). Flash floods are causing severe material damage, human casualties and extreme erosion (Farhan and Ayid, 2017, 718). Although flooding is only heavy rainfall, the hydrological response varies depending on the slope physiognomic features, soil texture, ground cover, rock permeability, and range curvature (Tinco et al., 2018,593). In order to reduce the risk of flash flood, it is necessary to identify and classify areas with high flood hazard potential (Minya, 2013, p. 345). The Islamabad basin is located in the Zagros zone, and the lithologic and geological conditions have caused the geomorphologic features of the Jurassic mountains and the lagging mountains around the syncline plain of Islamabad. This basin is sometimes faced with the risk of flood and river floods due to the severe and shortlived rainfall (W., 1391, 79). Considering the flood history of the Islamabad basin, it is necessary to assess the potential risk of the flash flood. The purpose of this study is to evaluate and map the potential for a flash flood hazard using physiographic parameters.Materials and methodsThe Predicted Flood Potential Model (MFFPI) uses six parameters of physiognomy with specific coefficients to capture the potential flood hazard potential (Table 1). Each of the six parameters, classified according to the impact of the flash flood event, is classified into five classes, and each of these classes has a weight of 1 to 5 according to the role played by the amount of water accumulation. The weight of each parameter in each of the five subparameters is multiplied and the final score of each layer is calculated (Tinco et al., 2018,596). In this research, the MFFPI model is implemented in two stages. In the first step, each of the six parameters is used in the preparation of a potential risk map for the basin’s sudden risk. In the second stage, based on Spearman correlation and linear regression, the effective parameters are selected and based on which the MFFPI model is implemented.FindingsIn the first step, the MFFPI’s final potential mapping map shows that areas with very low potential and very low flood peculiarities are consistent with the basin’s heights. These areas were not susceptible to water accumulation because of topographic conditions and the possibility of flooding was very low in these areas. Areas with a high potential hazard flash flood is within the reach of the Islamabad plain of the west and the bedrock of the main rivers of the Ravand River, and the topographic conditions of the area are the main cause of the high potential of the sudden flood in these areas. Using Spearman method, the correlation coefficient between six variables was used. The results of this method show that all parameters are correlated and the Sig value is zero. The results of linear regression show that four topographic slope variables, flow accumulation, domain curvature and land use are statistically significant and account for 96.6% of the potential flood index. The twosoil texture and rock permeability variables are not significant. In the second step, the final potential map of the MFFPI model is prepared using four parameters. The survey shows that areas with a low flood hazard potential correspond to the heights of the basin and are not prone to accumulation due to the slope. Areas with a high potential hazard has potential of a sudden flood within the reach of the Islamabad plain and on the main bed of the Ravand River.ConclusionThe final map of the potential risk of flashflood event from the MFFPI model in the first phase indicates that 45% of the area of the Islamabad subbasin has a highrisk potential. Also, 13% of the area in the basin has a medium risk potential and 42% of the area is located in a dangerous and very low area. The spatial distribution of hazard potential zones is subject to the topographic conditions of the basin and areas with a potentially hazardous location in mountainous areas that do not contribute to the accumulation and accumulation of water. Areas with a highrisk potential the flash flood in the plain areas of Islamabad and around the Ravand River bed is due to the fact that these areas are prone to accumulation and accumulation due to topographic conditions and the existence of a river. Four variables of topographic slope, flow accumulation, domain curvature, and land use explains 96.6% of the flood potential index and the potential flood event map in the second phase was based on them using the MFFPI model. A final flood potential map survey in the second stage showed that areas with a potential high risk of 34% of the basin area, areas with an average potential of 17%, and areas with a potential risk of 49% of the area of the Islamic Basin have been allocated. In the map of the potential for flash flood, in the second stage, the spatial distribution of hazard zones follows the topographic conditions and flow accumulation. The removal of soil texture parameters and rock permeability in the second stage reduced the area of highrisk areas and increased the area of low and middle areas. Finally, it can be acknowledged that the results of the MFFPI model at both levels indicate a high risk of flash flood in the area of the west Islamabad, and that the city and all its villages and its surface infrastructure are at risk of flash flood.