GROUNDWATER PROSPECT EVALUATION USING INTEGRATED REMOTE SENSING AND GIS TECHNIQUE IN HARD ROCK TERRAIN

Abstract

The groundwater is precious dynamic source of water in hard rock terrain. In India, nearly 60 % of the geographic area is covered with hard rock terrain. The availability of groundwater in these areas is very less. Mainly it is confined to fractures and joints i.e. secondary porosity. So the proper management of the groundwater is required. Water availability is very less and whatever water comes in the form of rainfall washed away without augmenting groundwater because of the impermeable nature of the hard rock. So it is necessary to develop an integrated technique to find out some recharge sites where runoff water can be stopped by and augment the groundwater. The present study is all about to develop an integrated remote sensing and GIS technique to find out such recharge zone. In such kind of integrated study, vast amount of data from various sources like satellite image, depth to water level data in analogue format, published maps etc. has to be used. Some of which is in digital format and some in analogue format. So first these published maps have to be converted into digital format by scanning. Geographic Information System provides a platform to analyse all these types of data together as it provide best interface. LANDSAT TM data along with other published maps and Digital Elevation Model are used to create various thematic layers like geology, geomorphology, Landuse/Landcover etc. Digital image processing is very important to extract these information. Lineament has been delineated from satellite image with linearly stretched and equilized seventh band. Other factors like vegetation growth, lithology disruption and drainage pattern also helpful for lineament delineation. Landuse/Landcover has been created from FCC 7,4,2 bands of Landsat TM image. Google Earth also plays very important role in these analyses as it provide true colour picture with very high resolution. Likewise geomorphology, soil, lithology has been delineated. Digital Elevation Model play very important role in hydrological studies. Slope map has been created from DEM. 3D perspective map can also be prepared from DEM as it provide pseudo-relief image of the topography of the study area. This helps to interpret various geomorphologic features. DEM can also be used to develop an aspect map. From this DEM, watershed and drainage networked has been delineated which is the study area. The study area is bounded by longitude of 77°30'E to 79°30'E and by latitude of 24°N to 26°N and covers 17527 sq. Km. area. Drainage network also delineated from Survey of India Toposheets. Then overlay analysis of both simulated and surveyed drainage network shows misfit at some areas. Considering the evapo-tranispiration constant for whole area, these misfits suggest recharge sites. After creating various thematic layers, weighted index overlay analysis has been performed as this method is simple and straightforward for combined analysis of multi-class maps. Each parameter has given % influence in which some of all parameters should be 100. Each class within a parameter has been reclassified by using 1 to 10 scales, 1 is least suitable and 10 is most suitable. By weighted index overlay analysis, groundwater water prospect map and artificial recharge map has been prepared. The groundwater prospect map has been prepared by assigning appropriate weightage according to their influences toward the objective. It has been found out that good groundwater prospect region lies within weathered basalt and alluvial plain. Weathered granite also shows good groundwater prospect. It has been found out that lineament density has direct control over groundwater prospect. It is also found out that the areas downstream of the reservoirs have moderate to good prospect. Artificial recharge zonation map has also been prepared. Here slope has given greater importance as gradient has greater control over artificial recharge. From artificial recharge zonation map, we can conclude that for better artificial recharge the slope of the area should be between 0 to 5°. It should be within alluvial plain and alluvial fill and Pedipiain region can also be preferred.