عنوان مقاله [English]
Evaluation of the vulnerability of Davarzan Aquifer
by DRASTIC method using GIS
Assistant Professor of Geomorphology, Department of Geography, Hakim Sabzevari University
Bachelor of Environmental Science & Cooperator of Geographical & Social Research Centre
Master’s Degree of Physical Geography, Islamic Azad University of Mashhaf
Groundwater is one of the most important natural resources of the world. In current conditions, a noticeable part of drinking water consumption of Iran will be supplied by ground water. About 95 percent of the water needed for drinking, agriculture and industry in Davarzan is supplied from groundwater resources. The concept of vulnerability for the first time in France in late 1960 for partial knowledge about ground water pollution is presented. Relative vulnerability of a character, and non-measured and aquifer characteristics, environmental geology and hydrogeology depend on it. Various methods for vulnerability assessment are presented which can be divided as groups of processing methods, methods of statistical overlapping. One common method for the inherent vulnerability of aquifers, the application method, has been DRASTIC. The world in areas such as South Korea, UAE, India, Algeria, Portugal, Japan and Jordan have been used. DRASTIC method vulnerability in Iran for the zoning case has been applied. Statistics and information required for this method is not restricted to the higher plains of Iran. The study area for groundwater vulnerability DRASTIC model for mapping the GIS environment is used. The aim of this study, vulnerability mapping and identification of areas with groundwater contamination in the study area is high. Given the importance of groundwater resources for drinking purposes, shall be used for agricultural and industrial, aquifer vulnerability study and protect these areas for optimal development and management of water resources seems necessary.
A) Material: vulnerability zonation has been done in GIS environment. For this purpose, statistics and information were entered into GIS databases. In this study a variety of information sources, including topographic maps with a 1:50000 scale geological map1:100000, soil maps, statistics, meteorology, hydrology, groundwater levels, pumping tests, drill log, observation wells , exploration and exploitation, and geophysical maps of water sources and uses of Khorasan Razavi Regional Water Company were prepared.
B) Methodology: The simplest and most common method for groundwater vulnerability to pollution, use of models is weight. The characteristics of these methods are based on the impact of groundwater contamination are scoring. The most common method for evaluating the intrinsic vulnerability of aquifers, the groundwater DRASTIC the National Association in cooperation with the U.S. Environmental Protection Agency has been created. In this method, seven factors or measurable criteria for hydrogeologic system are estimated. These include: deep water, feeding systems, aquifer media, soil type, topography, and hydraulic conductivity of unsaturated zone are. These factors are calculated numerically, so that each of them with regard to potential contamination, the rate of 1 to 10 is assigned. DRASTIC method of characteristics affecting the vulnerability is used and therefore the uncertainty due to possible decrease in the specifications. Coefficients in this way according to the characteristics of the study area can be changed.
3- Discussion and Conclusion
Raster GIS layers in the composition of the overlap function is used. The data used were all converted to raster format, so the overlap was used for this purpose. The mathematical function of both the composition and weight data will do. According to the desired layer in the model were DRASTIC a certain weight, the weight through a combination of data from overlapping function menu Raster calculator in ArcGis software was used for maps. To do this all the layers together with the coefficients for the model was defined as the percentage of the combined layers were then performed. Aquifer vulnerability to contamination final map, divided into five areas with low vulnerability, low vulnerability, medium vulnerability, high vulnerability, high vulnerability is shown. The zoning map obtained approximately 23/2 percent of the study area in the range of low vulnerability, 21/4 percent of low vulnerability, 17/38 percent moderate vulnerability, 25/43 percent and high vulnerability12 /59 the vulnerability is very high percent range. Verifying the final map of vulnerability to nitrate ion (as a natural contaminant in the region) were used.Compliance with the nitrate ions on the final map DRASTIC was clear that all parts that have high nitrate are located within a high pollution load that can be used to verify the accuracy of the model. Based on the results of modeling DRASTIC, Aquifer vulnerability Davarzan almost in the eastern half of the low vulnerability and high vulnerability lies in the western half. The results show that high levels of contamination and potential contamination of aquifers and the importance of groundwater resources in the study area are used for different purposes, protection and management of these areas to prevent contamination of water resources optimization is necessary.