Remote Sensing and GIS Approach for Delineating and characterization of Groundwater Potential Zones in Hard Rock TerrainThe Index Overlay Method is one of the best methods of intergrating geological data to generate final hydrogeomorphological map and demarcate the potential zones for groundwater prospecting. Firstly, primary water prospecting map (1:50,000) was generated. This was followed by two weeks of field investigations along selected traverses for verification purposes and water quality analysis. Final hydrogeomorphological map was generated according to ground truth data and identified suitable sites of groundwater extraction for human consumption. TABLE 2 - Theme Ranking for Index Overlay Method
7. THEMATIC LAYERS  8. RESULTS  Figure 9 - Final Hydrogeomorphological Map TABLE 3 - Groundwater potential
 9. CONCLUSION This study shows the importance of Remote Sensing technique, which is an information tool and provides synoptic coverage sufficiently accurate and comprehensive spectral, spatial and temporal information of the earth surface. Further, this study confirmed that the effectiveness of GIS as a system that provides ample opportunity to efficiently store and manipulate Remote Sensing data and other spatial and non spatial data. In generation of hydrogeomorphological map, Index Overlay Method was used. This simple and straightforward method enabled for combining multilayer thematic maps. The accuracy of this method is totally dependant on human judgment. Determination of weightage of each class is the most crucial aspect in integrated analysis, as the output is mostly dependent on the assigning of appropriate weightage. Primary porosities are almost nil in hard rocks and therefore lineaments are very much important for groundwater occurrence and recharging; therefore, high rank and high weightages were given for lineament. In this study, a single weightage of 7 was given for all the lineaments including faults and folds. Permeability and porosity controls the groundwater occurrence and recharging of the area and porosity and permeability directly depend on the lithology of the area; accordingly, geology was ranked 8 and different weightages were given for different formations. Highest weightage was given to unconsolidated rock types of the study area. Slope is also a crucial parameter for occurrence and recharging conditions of groundwater in a particular area; runoff will be more and infiltration is less in steep slope areas; therefore, slopes were ranked 9 and different weightages were given for different slope classes. Drainage density is also an important parameter for groundwater occurrences and recharging; in hard rock terrains, high drainage density and low infiltration were observed; therefore, drainage density was ranked 7 and different weightages were given for different drainage densities. Annual rainfall is another crucial parameter for groundwater occurrence and thus ranked 6; different weightages were given for different rainfall classes. In final hydrogeomorphological map, area covering highly dissected structural hills (3.2%) indicated very poor groundwater potential. Moderate(33.92%) to lower(52.24%)dissected hilly areas indicated moderate to low groundwater potential. Very high groundwater potential was indicated in river terraces, lower piedmont zones, sand bars, point bars, highly fractured areas, braided river and alluvial planes. Low recharging rate, generally high runoff mostly due to hard rock terrain and excessive withdrawal of groundwater for irrigation which has led to continuous depletion of groundwater table over the years would have resulted in depletion of groundwater in many places. Detailed lithological studies have to be conducted to confirm the actual causes. Water quality analysis indicated that most of the water quality parameters were within the permissible limit for human consumption. However, iron content was very high in few places and this may be due to reasons such as rusted iron casing of tube wells, and, or, contamination of groundwater with the presence of iron rich rock and soil. Again, to confirm the real cause(s) for the presence of high iron content, a detailed lithological study has to be conducted. Hardness is comparatively high since this area is rich in limestone. Rainwater harvesting or any other artificial recharging method is more suitable for improve the groundwater potential in low potential areas. Artificial recharging is the process of augmenting the natural movement of surface water into underground formations by artificial methods. This is accomplished by constructing infiltration facilities or by inducing recharge from surface water bodies. In hard rock areas, the underlying lithological units do not have sufficient porosity and permeability. In these areas, groundwater recharge falls short of the water that is being taken out of the aquifers. Thus, additional recharge by artificial methods becomes a sheer necessity to meet the water deficit. Recharging process can be made effective and efficient to meet the demands for water for human consumption through planning and using appropriate scientific methodology and tools. In this context, integrated Remote Sensing and GIS can be used as a powerful and an effective tool for planning for artificial recharging structures. However, this tool is yet to be used widely for planning and designing for artificial water recharging in India. 10. REFERENCES
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