عنوان مقاله [English]
Given the escalating demanded for high water quality, this paper is to identify the locations of karst aquifers. The karst aquifers are known as one of the cleanest source for drinking water (Munch and Conway, 2007; Krause et al., 2007; Gondwe et al., 2011). So, conservation of drinking water resources in sim-arid parts of Iran is an open issue and needs to be studied. The karst aquifers pollution hinders the development of urban, industrial, and agricultural regions and imposes a lot of costs to these areas and, at the same time, the flaws can spread the pollution. These main issues indicate the high importance of studying and managing the karst pollution problems. surface karst development maps can play an important role in protecting the karst groundwater. These maps can also contribute to the implementation of groundwater resources management strategies to prevent climate change (Mimi et al., 2009). due to karst water resources vulnerability and high sensitivity them, protection of karst water resources is one of the most important steps in the management of them (Afrasiabian, 2007). It is worth mentioning that hydrological characteristics make karst aquifers different from other water resources (White, 1988; European, 1995; Bakalowicz, 1995; Ford and Williams, 2007; Ford and Williams, 2007; Ford and Andreo, 2011).
The purpose of this study is to evaluate the level of the sources of karst aquifers in the Sheshpier and Bergan regions using fuzzy model. In this model have been used the distance from fault, height, slope, precipitation, temperature, lithology, land use, soil, slope and climatic conditions as input data (Moameni, 2010).
Lotfi Zadeh presented fuzzy set theory in 1965. Zadeh, in his theory of fuzzy sets, proposed using a membership function (with a range covering the interval (0,1) operating on the domain of all possible values. For any set X a membership function on X is any function from X to the real unit interval [0,1].
For preparing the fuzzy map for each parameters should definite membership function. A membership function assigns to each object a grade ranging between 0 and 1. The value 0 means that x is not a member of the fuzzy set, while the value 1 means that x is a full member of the fuzzy set. A fuzzy set is an extension of a classical set. If X is the universe of discourse and its elements are denoted by x, then a fuzzy set A in X is defined as a set of ordered pairs:
The function assigns a value to any member of the set A, and gives zero value to any member out of the set A.
For factor maps integration, some fuzzy operators such as OR, AND, product, SUM. Gamma can be used. A script can be written in GIS to employ this method. In this study was used Gamma operator to prepare karst karst aquifer map. Gamma operator can be expressed mathematically as (Carter, 1996):
In this equation, is the resulting layer of the fuzzy gamma and γ, the parameter specified in the 0 and 1 range. When γ = 1, the compound is the fuzzy algebraic sum and when γ is equal to zero, the composition is the fuzzy algebraic multiplication (Carter, 1996).
Results and discussion
The karst development map was prepared using natural fracture method that consist of four classes: without development, less developmnt, medium development and high development. The overlaping of the layers and the final map of the karst surface development showed that 75 % of region was located in the high development and 22 % was in medium development.
According to results, the regions with maximum slope, aspect of the north, and with flaws are known as the most vulnerable region in karst regions. More than 80% of the aquifer is located in the karst range with moderate vulnerability. There are also limited portions of the Shepshir aquifer in the class. Moderate karst vulnerability is about 22 percent in the Firouz anticline and Bergan area. This range corresponds to an altitude of 2500 to 300 meters and receives rainfall of about 1200 mm that about 20 percent of the Bergan aquifer and 80 percent of the Shepshir aquifer are surrounded by highly karst surface vulnerable zones, which correspond to the highest altitude of the area at about 3000 to 3700 meters and receive precipitation of about 1700 mm. It is also showed that the region is located in the limestone formation of Soruk and Bangestan group, which with the thickness of about 800 m, have the importance role in development of the surface karst of Gar and Barmfiruz.