Evaluation of ground water quality in GORGAN Township using GIS and Geostatistics

Quality water characteristics for drinking purpose are affected by numerous environmental and human conditions. Distribute of this characteristic in various parts, in according to exploitation and management of the environment and in order to geological and geomorphic structures are different. Factors including waste water infiltration, urban runoff, large livestock, industrial waste water, solid waste place, far and near to the sea are factors that directly and indirectly affect water quality. Theses affect especially if these due to increasing of some sensitive parameters such as nitrate, it is necessary to evaluate systematically. The main purpose of this paper is evaluating the quality of groundwater resource using GIS and geo statistics in Gorgan city. Water quality maps in GIS are created using interpolation methods. In fact, interpolation is estimation of the unknown continuous variable based on the discrete known samples. There are several methods for interpolation of spatial data .all these models are based on the logic of the effects of spatial autocorrelation functions. According to calculation of variables correlation ratio, structural analysis is possible. In general, interpolation methods are divided into two deterministic and non-deterministic methods and local and global. Common interpolation methods are inverse distance weighting (IDW), polynomial, and geo statistic Kriging. Krigging is an estimation of the unknown samples based on weighted moving average. This model notice to land structure, with variogram. The best of unbiased line that include minimum of error variance is used for evaluation of model spatial precision. In this paper the values of some factors such as Mean Bias Error (MBE), Mean Absolute Error (MAE) and Root Mean Square Standardized were evaluated.