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GIS application in hydrogeological studies
D. Das
Department of Environmental Science, University of Kalyani
W.B. - 741235, India
ddas@klyuniv.ernet.in
Abstract
GIS is a tool for storing, manipulating, retrieving and presenting both spatial and non-spatial data in a quick, efficient and organised way. Since most land information elelments have a geographic connotation, geographically referenced data with GIS techniques come to the fore in such and application. The term 'geographic' in GIS refers to the locational attributes which define the spatial positioning of the piece of information on the face of the earth. Preparation and maintenance of data in the form of maps and referenced tabular files itself can be considered as a primitive form of GIS. However, with the advent of digital computers, with high data processing speed and the development of analytical tools thereon to handle geographically referenced data with ease and flexibility, computer aided GIS has become a reality of late. Such systems generally deal with data classified/segregated into the spatial type (locationally referenced), attribute type (without locational connotation) and the time variant or repetitive types of data. The three components-location, attributes and time-represent the content of most GIS. Using of GIS in hydrogeology is only at its beginning, but there have been successful applications that started to develop. As an example there is the Sali river basin, Bankura district, West Bengal, where sites for groundwater exploration and artificial recharge have been demarkated applying GIS technique using ARC/INFO and ILWIS 2.1 Software.
Key Words: GIS, Hydrogeology, ARC/INFO.
Introduction :
Groundwater resources are dynamic in nature as they grow with the expansion of irrigation activities, industrialization, urbanization etc. As it is the largest available source of fresh water lying beneath the ground it has become crucial not only for targeting of groundwater potential zones, but also monitoring and conserving this importanat resource. The expenditure and labour incurred in developing surface water is much more compared to groundwater, hence more emphasis is placed on the utilization of groundwater which can be developed within a short time. Besides targeting groundwater potential zones it is also important to identify suitable sites for artificial recharge usage cycle. When the recharge rate cannot meer the demand for water, the balance is disturbed and hence calls for artificial recharge on a country wise basis (Sameena et. al. 2000).
Remote sensing with its advantages of spatial, spectral and temporal availability of data covering large and inaccessible areas within short time has become a very handy tool in assessing, monitoring and conserving groundwater resources. Satellite data provides quick and useful baseline information on the parameters controllig the occurrence and movement of groundwater like geology, lithology/structural, geomorphology, soils, landuse/cover, lineaments etc. However all the controlling parameters have rarely been studied together because of non-availability of data, integrating tools and modeling techniques. Hence a systematic study of these factors leads to better delineation of prospective zones in an area which is then followed up on the ground through detailed hydrogeological and geophysical investigations. Visual interpretation has been the main tool for evaluation of grounwater prospective zones for over two decades. It has also been found that remote sensing besides helping in targeting potential zones for groundwater exploration provides inputs towards estimation of the total groundwater resources in an area, the selection of appropriate sites for artificial recharge and the depth of the weathering area. By combining the remote sensing information with adequate field data, particularly well inventory and yield data, it is possible to arrive at prognostic models to predict the ranges of depth, the yield, the success rate and the types of wells suited to various terrain under different hydrogeological domains. Based on the status of groundwater development and groundwater irrigated areas (though remote sensing), artificial recharge structures such as percolation tanks, check dams and subsurface dykes can be recommended upstream of groundwater irrigated areas to recharge the wells in the downstream areas so as to augment groundwater resources.
Apart from visual interpretation, digital techniques are used by many researchers for deriving geological, structural and geomorphological details. The various thematic layers generated using remote sensing data like lithology/structural, geomorphology, landuse/cover, lineaments etc, can be integrated with slope, drainage density and other collateral data in a Geographic Information system (GIS) framework and analysed using a model developed with logical conditions to derive at groundwater zones as well as artificial recharge sites. Digital enhancement techniques are found to be suitable since they improve the feature sharpness and contrast for simple interpretation.
This paper addresses the strategies for an integrated approach of remote sensing and GIS for groundwater targeting, management and conservation of groundwater resources that ensures optimum and judicious use of groundwater and in identification of artificial recharge sites.
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