6. Selection of artificial recharge sites
A remote sensing and GIS based method is found to be very useful in suitability analysis for artificial recharge sites in the hard rock terrain (Saraf and Choudhury, 1998). For such analysis the first task was to identify the factors facilitating recharge to take place. The existing artificial recharge system in the area has been studied with respect to its hydrogeology, topography and response in the water level of the wells. Based on these observations, a set of rules has been designed to demarcate the most suitable zones and also to find out the exact sites for artificial recharge. The thematic information layers used in this suitability analysis and weighted indexed overlay model are: (a) Geology, (b) Geomorphology, (c) Soils, (d) Slope, (e) Distance to lineament,(f) Recharge map.

In weighted index overlay, the individual thematic layers and also their classes are assigned weightage (Table 2) on the basis of their relative contribution towards the output. In the present study, weighted indexing method has been used to demarcate the suitability zones for artificial recharge sites (Figure 4). The classes with higher values indicate the most favourable sites for artificial recharge structures.


Figure 4 Potential zones for future artificial recharge sites to provide better groundwater recharge conditions. This map is prepared using the slope map derived from DEM together with the geology, geomorphology, groundwater recharge and lineament maps
7. Results and Discussion
In order to make an accurate prediction of hydrologic response due to landuse changes, it is required (i) to be able to track changes as they actually occur and (ii) to quantitatively understand the effect caused by such changes. Landuse change studies with respect to groundwater hydrological changes have become extremely necessary for planning of any development activity on the earth’s surface. However, in order to understand the landuse changes various influencing factors and interdependent intricacies, a GIS based modeling approach is required.

The land surface is subjected to continuous change due to natural and man–made causes. As the landuse in a watershed is altered in space and time, the factors that influence the hydrologic response of the watershed also changes. Evaluation of the relationship between landuse changes and such factors is one of the goals of the study of landuse-groundwater. The following observations are made after the landuse change analysis:

1. A mixture of forest cover, agricultural activities and wasteland characterized the landuse of the study area. The major part of the study area was predominantly wasteland especially in the western part of the watershed, which decreased significantly within last 8 years. The next predominant category of landuse was fallow land. The total forest cover inclusive of the plantation increased significantly. Irregular patches of arable land occur in a random fashion in the study area.
2. The landuse maps of 1988 and 1996 generated from satellite images show that the wasteland is the most dominant class followed by fallow land in the year 1988. However, on comparing with the landuse map of 1996 reveals a decline in the wasteland from 48.17 percent to 8.65 percent, an increase in fallow land from 33.63 percent to 58.8 percent, dense forest increased from 2.9 percent to 7.1 percent. Water bodies had decreased marginally from 0.8 percent to 0.61 percent. While arable land increased from 13.88 percent to 24.1 percent, settlement increased from 0.21 percent to 0.25 percent and river sediment increased from 0.41 percent to 0.49 percent (Figure 2).
3. Nature of landuse change: The maps pinpointed the spatial locations where landuse changes have taken place. These landuse maps show the areal extent of landuse change (1988 to 1996) of a single particular category into other categories (Figure 2).

In order to establish the impact of future landuse change on the groundwater resources of a watershed, it is necessary to understand the existing groundwater conditions of the watershed and to quantify the extents to which the water resources will be modified. The hydrological factors influencing the landuse change are rainfall and groundwater conditions. The rainfall is considered to be one of the major factors in causing landuse change. Despite sufficiently high rainfall, droughts are a major problem owing to the uneven distribution of rainfall. As it is clear from the rainfall map, both the eastern and western parts of the watershed receive relatively a good amount of rainfall. However, comparing with the recharge map, groundwater recharge is relatively high on the eastern part due to the presence of dissected pediment, flood plain, alluvial fill and alluvial plain, which facilitate better recharge conditions. In the hard rock terrain in the western part, the suitability is poor. This can be attributed to the changes in the landuse along the eastern part where there is a sufficient conversion of wasteland into other categories of landuse. Whereas, in the western part, mostly dominated by wasteland due to the lithology being impermeable, there is little chance of recharge and most of the water flows as runoff.

The rainfall volume calculated for the years 1994-1996 shows a minor variation in rainfall volume, which in comparison with recharge volume, it was found that runoff has been more in the year 1994 than subsequent years, when the recharge increased sufficiently causing changes in landuse. This is supported by the fact that the fluctuation of water level along the eastern part of the watershed is due to the extraction of water for irrigation purposes.

The watershed shows a low and high fluctuation (0.5-1.9 and 6.3 m) along the central part and it gradually increases towards the southwest and southeast. The maximum fluctuation in the southeast is 4.9 m b.g.l (CSME, 1993). This fluctuation could be attributed to the presence of agricultural tracts in these areas where sizable extraction of water takes place. Further, it can also be justified by the landuse change image, where the eastern part of the watershed is mainly covered by fallow and arable land. Further, it has been observed that high groundwater recharge areas are associated with maximum landuse change areas (eastern part of the watershed), however, the western part of the study area though showing rapid landuse change but less recharge to groundwater regime. The reason for this could be the presence of highly impermeable zone mainly consisting of pink granite.

Page 4 of 5
| Previous | Next |