Role of Geographical Information System for Water Quality Evaluation

Abstract

Water quality evaluation is an overall process of evaluating physical, chemical and biological nature of water in relation to natural quality, human effects and intended uses particularly uses which may affect human health and the health of the ecosystem itself. Interpretation of enormous water quality data in a convenient manner for visual inspection is an important but often underestimated or omitted step in a water quality evaluation program. Recently, need of modern approaches and tools for interpreting water quality is emphasized for efficient water quality management. Geographic Information System (GIS), with an ability of capturing, storing, analyzing, manipulating, retrieving and displaying spatial data, has emerged as a powerful tool for decision-making in several areas including environmental field. This chapter aims at highlighting the role of GIS in synthesising, compiling, presenting and interpreting chemical data of both surface and ground waters. Firstly, few relevant fundamental terms and process of water quality evaluation are defined and/or described. Thereafter, the chapter contains theoretical procedure for applying GIS to assess spatial change or variability in water quality by characterizing extent and patterns of contamination. In general, a water quality monitoring network consists of a group of point locations with known chemical attributes of water. GIS helps converting the point values into areal information through spatial interpolation. Hence, an overview of spatial interpolation techniques is provided, together with the methodologies for employing geostatistical modelling (kriging) and inverse distance weighting techniques and for computing spatial statistics (mean, median, standard deviation and coefficient of variation). The major application of GIS in past groundwater studies has been for assessing groundwater vulnerability. Therefore, the concept of groundwater vulnerability along with its historical perspective is described and different GIS-based overlay and index methods used for groundwater vulnerability assessment are summarized. Methodologies for applying different GIS methods in evaluating the groundwater vulnerability are illustrated through flowcharts. The major tools for describing groundwater vulnerability in GIS framework include DRASTIC, modified DRASTIC, DRAMIC, GOD, AVI, SINTACS, EPIK, GLA, PI and COP. Furthermore, the development of GIS-based water quality index for evaluating water quality is discussed. Finally, combined use of GIS and multivariate statistical analysis techniques in delineating water quality zones is discussed. It is concluded that GIS is a promising geospatial tool which offers efficient framework for sustainable management of freshwater resources.