پهنه‌بندی خطر زمین‌لغزش از طریق ارزیابی متغیرهای محیطی با استفاده از مدل تحلیل شبکه (مطالعه موردی: شهرستان بیجار)

شهرستان بیجار در شمال شرق استان کردستان یکی از مناطق مرتفع و کوهستانی است که از پتانسیل بالایی برای حرکات دامنه‌ای برخوردار است. اگر این فرایند به‌صورت علمی مطالعه نگردد یکی از مخاطرات جدی برای توسعه محسوب می‌گردد و برنامه‌ریزی را با مشکل مواجه می‌کند. این پژوهش با هدف شناسایی سهم متغیرهای مختلف بر روی زمین‌لغزش به‌عنوان یکی از حرکات دامنه‌ای و پهنه‌بندی آن در محدوده شهرستان بیجار صورت گرفت. بدین منظور ابتدا مطالعات کتابخانه‌ای برای شناسایی معیارهای تاثیرگذار در این فرایند انجام شد. با توجه به پیشینه تحقیق و داده‌های موجود معیارهای شیب دامنه، جهت شیب، کاربری اراضی، لیتولوژی، تراکم زهکش، فاصله از جاده و ارتفاع برای بررسی این فرایند انتخاب شدند. سپس معیارها باهم مقایسه و وزن آن‌ها در زمین‌لغزش تعیین گردید. برای تعیین وزن نهایی معیارها و زیر معیارها، ابرماتریس با استفاده از نرم‌افزار super decision تشکیل داده شد. وزن‌های نهایی جهت تلفیق، همپوشانی لایه‌ها، اجرای مدل ساختار شبکه و نقشه پهنه‌بندی بکار رفت. سپس محدوده مطالعاتی بر اساس مدل موجود(anp) به لحاظ خطر زمین‌لغزش به پنج منطقه خطر تقسیم گردید. نتایج پژوهش نشان داد که  41 درصد از محدوده شهرستان بیجار جزو مناطق دارای قابلیت خطر محسوب می‌شود. نتایج دقیق تر نشان‌ داد که از بین متغیرهای محیطی موثر، فاصله از گسل و ارتفاع، بیشترین و کاربری اراضی کمترین تاثیر را در زمین‌لغزش در محدوده شهرستان بیجار دارند. نتایج حاصل از صحت سنجی نیز نشان داد که همپوشانی مناسب بین پهنه بندی و نقاط زمین لغزش موجود بوده و بنابراین مدل به کار گرفته‌شده کارا بوده و نتایج آن در نظام برنامه ریزی و پایداری محیطی منطقه می تواند به کار گرفته شود.

Landslide hazard zonation by evaluating environmental variables using network analysis (case study: Bijar city)

Introduction:Predicting landslides in a region, in addition to the reduction of risks and losses caused, can be useful in analyzing and forecasting the development of a region. Many factors are involved in the occurrence of these natural phenomenon. In addition to natural factors such as lithology, tectonics and climate, human role is also significant.Identifying these factors and landslide hazard zonation can help in better evaluating of area potential talents. And it divides the area in terms of risk to the several subdistricts to make planning easier. Iran is largely due to the mountainous topography, the tectonic and seismic activity has high natural potential for extensive landslides.Kurdistan province is the third largest province in terms of landslide after Mazandaran and Golestan. If the ranking criterion is the area, the province is ranked the highest.Bijar city in the Kurdistan province, with a combination of factors mostly mountainous topography, climatic and lithological conditions and locating between two fault of Tabriz in East and Zarineh River in the West which a large number of subdirectories are between these two faults, has great potential for the occurrence of extensive range of landslides.In recent years, extensive researches have been carried out by scientists including geomorphologs, with the aim of identifying risk factors for landslide hazard zonation and also to choose the best model for optimal management of the area.The study, amid at the investigating the slide system in the Bijar area and the importance of effective factors, has applied ANP method as a new model in the landslide. MethodologyGeneral method of this research is a combination of theoretical studies, fieldwork along with the application of model and software statistical analysis.To achieve the goal, first, the effective layers of slope, aspect, elevation, distance from fault, distance from roads, distance from the river, floodway density, lithology and land use in GIS were prepared. And then weighting to the subcriteria within the group and the criteria between groups were performed.In the next step, available weights were put into Super Decision. Matrix and final weighting, according to input data, were done by the software to reduce the high rate of error.Finally, by pooling layers, landslide hazard zonation map was prepared on the basis of the range model with high risk, relatively high risk, medium risk, relatively low risk and low risk. In the last step, the assessment and verification of ANP model was done with real data to determine how well the model for the area is.DiscussionTo achieve the goal, binary comparison of each of the main criteria and subcriteria was performed based on a quantitative scale 9 hours.In comprising the criteria, one of the criterion was controlled to gain its importance and its special vector. After comparing the criteria and doing the matrix, their adjustment coefficient was controlled which was not over 0/1, considered by the Thomas hour.After the comparison, their special vector was put into Super Decision in the form of raw data and were used as the imbalanced matrix.Then, imbalanced super matrix became balanced by multiplying into cluster matrix. In the next step, to show and provide significant weight of parameters, the balanced matrix was limited.In the final step, the vector of ultimate importance was normalized and contribution of each of the variables was presented in landslides. These numbers were obtained as a decimal and between one and zero which, in fact, are as the same criteria in effect.The results showed that the distance from the fault has the greatest impact and land use has less impact on the occurrence of landslide and landslide zonation. Finally, in Arc GIS using model data of ANP, the final map was drawn which is the same zonation map.Reviewing the criteria affecting landslide of the area, using ANP, showed that the impact of the fault and height above sea level is more than the other criteria on the process.In the final stage of the study, to evaluate the effectiveness of the model as well as the accuracy using GIS, the landslide hazard zonation map was prepared through integrating and comparing the amount of overlap. The results showed that 94 landslides are at the relatively high and relatively high risk range which shows the accuracy of the study.ConclusionZoning and mapping out of landslide within the Bijar city shows that Bijar city and its dependencies are relatively disposed and susceptible to landslides.Systematic results, based on zoning and validation, showed that 41 percent of the study area is at relatively high and high risk that, in the planning process, should be taken into consideration through the assessment of variables.Validation results showed that the ANP, according to network analysis model is successful and can be used in other regions of Iran.