Ground water potential in a semi-arid region of Andhra Pradesh - a geographical information system approach

Continuous and adequate supplies of potable water from ground reservoirs ar e important for sustained agriculture, industry and domestic use throughout huge semi-arid regions of India. The present paper describes an approach t o investigating groundwater potential over extensive geographical areas and illustrates its potential with reference to watershed planning in the larg e Varaha River Basin (VRB), Andhra Pradesh, India. The method involves the creation of a systematic database of information from satellite data for re connaissance survey before going for field exploration. Colour composite im ages from Landsat Thematic Mapper and Indian Remote Sensing (IRS) satellite were used to interpret various thematic maps of the Varaha river basin. SP OT 1 MLA data of band 3 on a 1:250 000 scale was used for improving the acc uracy of interpretation of topographic units due to its higher resolution a nd stereo coverage. Slope and other coverages were derived from topographic maps. The thematic and topographic information was digitized and ERDAS Ima gine GIS software was used to analyse this information. Groundwater potenti al zones were delineated through subjective weights assigned to interpreted thematic and derived topographic units according to their likely infiltrat ion capacities. Seven categories of groundwater potential ranging from very good to poor were derived automatically. Field measurements were then made within a selection of these categories to check the groundwater potential at selected sites. The validity and effectiveness of using remote sensing a nd CIS techniques for improving the targeting of field observations for gro undwater for a huge river basin is shown by comparing the inferred groundwa ter potential with the held measurements.