ارزيابي پتانسيل توسعه كارست در تاقديس كبيركوه استان ايلام با استفاده از تلفيق فازي و روش تحليل سلسله مراتبي(AHP) و سنجش از دور و GIS

Karst development evaluation in the KabirKuh anticline, (Ilam Province) Using combined fuzzy and Analytical Hierarchy Process (AHP) methods and RS- GIS techniques

كشف منابع آب زير زميني به عنوان يكي از راه هاي تامين آب شرب در جهان با توجه به نياز روزافزون جهانيان به آب، امري ضروري و اجتناب ناپذير است. در اين تحقيق به بررسي درجه اهميت عوامل موثر در توسعه كارست در بخشي از پهنه كارستي زاگرس در محدوده تاقديس كبيركوه در استان ايلام پرداخته شده است. بدين منظور لايه هاي اطلاعاتي ليتولوژي، چگالي خطواره ها، شيب سطح زمين، بارش، ارتفاع، پوشش گياهي و تراكم آبراهه‌ها با استفاده از اطلاعات رقومي سنجش از دور، نقشه هاي زمين شناسي، نقشه هاي توپوگرافي و آمار بارش فراهم شد و براي تهيه مدل پتانسيل توسعه كارست به نرم افزار ArcGIS معرفي شد. لايه‌هاي اطلاعاتي مختلف با اعمال قضاوت كارشناسي و بازديد هاي صحرايي به صورت نقشه-هاي معيار طبقه‌بندي شده و با توجه به درجه اهميت هركدام از پارامترها رتبه اي از 1 تا 9 داده شده و همچنين به هر لايه براساس اولويت در پتانسيل توسعه كارست و با استفاده از فرآيند تحليل سلسله مراتبي (AHP) وزن مناسب اختصاص داده شد. سپس لايه‌ها به نرم افزار Idrisi انتقال يافته و با استفاده از روش فازي استاندارد سازي روي آنها اعمال شده است. سپس براي تهيه نقشه پتانسيل توسعه كارست لايه هاي موجود با روش هم پوشاني در محيط نرم افزار Idrisi با استفاده از ماژول Image Calculator با هم تلفيق شدند. در اين روش وزن هر لايه با توجه به تاثيري كه آن لايه در توسعه كارست دارد به صورت درصد و نقشه يا مدلي بدست آمد كه توسعه كارست را در سازندهاي مختلف داراي پتانسيل نشان مي-دهد. آناليز حساسيت مدل مذكور نشان داد كه مهمترين پارامتر تاثيرگذار بر روي توسعه كارست در تاقديس كبيركوه، پارامتر ليتولوژي مي‌باشد. اين مدل با استفاده از آمار چشمه هاي منطقه و حوضه آبگير آنها بويژه چشمه هاي پر آب منطقه ارزيابي و صحت سنجي گرديد. بطوريكه همخواني مطلوبي بين حوضه آبگير چشمه هاي پر آب منطقه و مناطق با توسعه كارست مشاهده گرديد.

Introduction Karst carbonate formations cover about 11% of Iran’s land area and 55.2% of the Zagros Ranges (Raeisi 2002). Due to the special rainfall shortage, and non-uniform spatial and temporal distribution of precipitation and decreasing of quality and quantity of alluvial in one hand and, and wide spread of karst formations in the country, studies on karstic water resource is an important issue of interest. Remote sensing and GIS are useful tools to proccess data for large areas and during a short time for accessing, monitoring , and the maintenance of ground water resources.(Yeh et al, 2008). Methodology This study evaluates the main factors whichimpact karstification, in Kabir Kuh Anticlines karstic area in the Zagros Mountain Ranges. Therefore, data layers including lithology, lineament density, the slope of the land, precipitation, elevation, vegetation and drainage density were prepared using digital remote sensing, geological and topographic maps, and precipitation data which were introduced to Geographic Information System (GIS) to provide a potential model of karst development. The weight of different layers was assigned from 1 to 9 in the base of judgment and field survey And the priority of each layer was rated based on their potential of karstificatio using the analytic hierarchy process (AHP). The layers were transferred to Idrisi media and standardized. In order to prepare the karstification potential map the layers overlaid and combined together using image calculator modules. The resulting potential map was verified by karstic spring locations. Results and Discussion Considering the importance of lithology in the development of karst, the highest rating assigned to lithology and the lowest to slope. On the lithology layer, the highest rating was given to the limestone formations and the lowest to the alluvial deposits. About the vegetation, the highest and lowest ratings were allocated to forest and urban areas, respectively. Precipitation, fracture density and elevation have a direct relation with karstification and so the further ranking was given to their higher values. Because of the inverse relationship between the value of slope and drainage density less rating number was allocated to the higher values. Weight of the parameters was calculated using the analytic hierarchy process method which ranged 0.032 to 38.39 for the lithology and slope area, repectiveley. At the next step the layers were overlaid using weighted linear combination (WLC) method. On the method WLC, each standardized factor is multiplied on the associated weight. Then the factors summed to produce the desired map. In this method, the weight of each layer was determined based on its role in karstification and the krstification map was obtained. Sensitivity analysis of the parameters using the map omission technique showed that the most important parameter influences the karstification in the Kabir Kuh anticlines is lithology. The model was verified using the springs location and catchment area, so that the catchment area of the big springs was coincided on the areas which regarded with high potential of karstification. Conclusion The purpose of this study was identification and zonation of karst development potential in the Kabir Kuh anticline in the south west of Iran in Ilam province using the AHP method. Based on the principles of karst hydrogeology and field observations seven parameters which have the main role in karstification of limestone formations regarded as seven rasterised layers to evaluate the potential of the anticline to karstify and produce karstic aquifers. The results showed that lithology is the most important factor controlling the karstification potential. The model was verified using location of springs and their catchment area, which coincided to the areas assigned as areas with high potential karstification. The model results and springs location showed that the limestone formations Asemary and Elam-Sarvak, has been experienced more developed karstification. Also sensitivity analysis of the parameters by map omission technique showed that lithology is the most important parameter influences the karst development in the Kabir Kuh anticlines. Kay word: AHP, Karst development, Kabirkuh Anticline, GIS,