ارزیابی و پهنه‌بندی سیل‌خیزی حوضه گیوی‌چای

حوضه گیوی چای در جنوب استان اردبیل با مساحت 1554 کیلومتر مربع، از زیر حوضه‌های درجه سه سفیدرود است که این خطر هر از چندی در آن رخ می دهد؛ به همین منظور، پهنه‌ بندی سیل خیزی حوضه گیوی چای همواره قابل توجه است. پس از تهیه نقشه پهنه‌بندی، حوضه مورد مطالعه بر اساس شدت سیل‌خیزی به پنج کلاس بسیار کم، کم، متوسط، زیاد و بسیار زیاد تقسیم‌بندی شد. همچنین نقشه نهایی سیل‌خیزی حوضه با روستاهایی که در سال‌های اخیر به‌ سبب سیل آسیب‌ دیده‌اند، اعتبارسنجی شد. بیشترین مساحت مناطقی که در پهنه‌های با خطر بسیار بودند، شیب و بارش‌های زیاد داشتند و از لحاظ لیتولوژی و هیدرولوژی خاک نیز دارای نفوذپذیری بسیار پایینی بودند و در مناطقی که پوشش گیاهی کمتر و ضعیف است، همپوشانی داشت و بیشتر در معرض سیلاب‌ها بود. برای پهنه‌بندی سیل‌خیزی از داده‌های ارتفاع، شیب، لیتولوژی، بارش، پوشش گیاهی، هیدرولوژی خاک، فاصله از رودخانه، تراکم زهکشی و کاربری اراضی استفاده ‌شد. لایه‌های خاک، لیتولوژی و کاربری اراضی با استفاده از نرم‌افزار idrisi و بقیه لایه‌های مورداستفاده با استفاده از ابزار fuzzy membership فازی سازی و تمام لایه‌ها در نرم‌افزار expert choice وزن دهی شد. تحلیل و مدل‌سازی نهایی نیز با استفاده از مدل fahp فازی گاما انجام شد. نتایج نشان داد که تراکم زهکشی، بیشترین تاثیر و پوشش گیاهی، کمترین تاثیر را در سیل‌خیزی داشت. با توجه به همبستگی بالای گاما 0/9 با معیارهای سیل‌خیزی، نقشه نهایی انتخاب شد. بر این اساس، قسمت‌های مرکزی حوضه دارای ارتفاع بالاتری بود و نسبت به مناطق پست‌تر قسمت‌های غربی، توان بالایی برای سیل‌خیزی داشت.  

assessment and zoning of flood risk in givi chai basin

1- introductionthe natural hazards are impossible to avoid, and infrastructure elements and communities cannot be made totally invulnerable. the only viable solution is the complex risk analysis and subsequent development of combination of mitigation and adaptation strategies floods are the most common natural disaster type worldwide. between 1995 and 2015, 2.3 billion people were affected by floods, con siderably more than any other type of natural disaster event. in general, the givi chai basin includes two cities, khalkhal and kausar. in recent years, floods have caused damage to gardens and facilities due to spring and summer rains to the extent that the villages that are located under the sangur chai basin because of being located at the source of the rivers and mainly in the course of the rivers are affected by floods; also in the whole basin due to droughts and the destruction of vegetation and the increase of man-made areas, the amount of impermeability has increased. considering that khalkhal is a mountainous area and is one of the areas sensitive to landslides in azariaijan region, heavy rainfall and floods can wash away the slopes of this area.2- methodologythe givi chai basin in the south of ardabil province with an area of 1554 square kilometers is one of the 3rd degree basins of sefidroud, which is located in the geographical coordinates of 48°4’ e longitude to 48°38’ e longitude 37°27’ n latitude 37°55’ n latitude. in order to achieve the goals of this research, firstly, the theoretical foundations and the works done in connection with flood zoning of basins in iran and outside iran were examined. many variables are effective in the flood of basins. in this research, from the 1.100000 geological map, the slope maps were obtained using the digital height model map; the land use map was obtained through the classification of the  maximum likelihood  in envi software. in addition, using the digital model of the height of resolution  to extract, a drainage density map was prepared using the line density tool. in this research, using the fahp fuzzy hierarchical analysis model, expert choise software was used for weighting the layers, and finally, a map was prepared in the arc gis environment using gamma 0.5, 0.7 and 0.9the basin was flooded.3- results after preparing the effective factors for zoning the flood potential of the basin, the gamma fuzzy operators of 0.5, 0.7 and 0.9 were used. 37 floods have occurred in the studied basin from 1365 to 1399 in different parts and villages, which caused the destruction of rural houses, gardens, agricultural lands and livestock. in order to determine the final flood map, points were randomly selected on the zoning map, then the correlation level was obtained based on the specified points with each of the criteria in the arc gis software. based on the results obtained from the correlation, the highest correlation level is related to gamma 0.9. vegetation has the highest correlation of 0.5 and lithology has the lowest correlation with gamma of 0.9 and 0.062. also, the last flood occurred in the studied basin in the villages of mustafa lo, bolokan, morestan and khoda qeshlagi, which are located in the high-risk zone according to the final flood zoning map.4- discussion & conclusionsin this research, using the fahp model, flood potential zoning has been evaluated in givi chai basin. the data of height, slope, lithology, precipitation, vegetation, soil hydrology, distance from the river, drainage density and land use have been used for flood zoning. after preparing the zoning map, the studied basin was divided into five classes based on the severity of flooding: very low, low, medium, high, very high. the results obtained from the flood zoning of givi chai basin have shown that the largest area of the studied basin, which is 0.9 gamma scale, has the highest correlation. the strata with very low, low and medium potential, gamma 0.5  0.7, were showed. cover the area of givi chai basin. also, the final flood map of the basin was validated with the villages that have been damaged by floods in recent years. the areas which are more exposed to floods are in the regions that have very low permeability in terms of lithology and hydrology of the soil and in the areas where the vegetation cover as less as.