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An integreted approach of Remote Sensing, geophysics and GIS to evaluation of Groundwater Potentiality of Ojhala Subwatershed, Mirzapur district, U.P., India
Physiographically, the area is mainly flat and gently undulating terrain except in few part. The occurrence and movement of groundwater is mainly restricted within the weathered & fractured sandstone/shale. Groundwater usually occurs in unconfined to confined condition at depth. The area is fed by south-west monsoon rainfall which starts in last week of June and extends until the end of September. The average annual rainfall is about 1043 mm.
Data Used
The followings data were used for the study :
- Remotely sensed data, viz. IRS 1C LISS III, geocoded of scale 1:50,000.
- The survey of India toposheet 63K/12, K/8, L/5 & L/9 of scale 1:50,000.
- Field data, viz. geo-electrical sounding data and drilling data.
Methodology
- In order to demarcate the groundwater potential zones of study area different thematic maps on 1:50,000 scale were prepared from remote sensing data, topographic maps and resistivity data.
- The thematic maps on hydrogeomorphology and lineaments were prepared using IRS 1C LISS-III data by visual interpretation on 1:50,000 scale.
- Drainage map was prepared from SOI toposheet & satellite data.
- Contour map and spot elevation map were prepared from SOI toposheets.
- All primary input maps (hydrogeomorphology, lineament, contour & spot elevation, drainage and geo-electrical sounding location) were digitized in Arc/Info, GIS software package and slope map was prepared from digital elevation data.
- Interpretation of geo-electrical soundings data of 68 sites.
- Correlation of geoelectrical parameters of drilled sites with lithology.
- Based on above co-relation lithology was inferred at other sounding locations for identifying horizontal and vertical variation in subsurface lithology and estimating depth to the hard rock.
- Using inferred lithology and thickness from geoelectrical parameters at respective locations, aquifer layer thickness and overburden thickness maps were prepared through GIS.
- The different polygons in the thematic layers were labelled separately and then they were registered. In the final thematic layer initially each one of the polygons were qualitatively visualized into one of the categories like (i) very good (ii) good to very good (iii) good (iv) moderate and (v) poor in terms of their importance with respect to groundwater occurrence and suitable weights have been assigned.
- Finally thematic layers were converted in to grid with related item weight and then integrated and analysed, using weighted aggregation method. The grids in the integrated layer were grouped into different ground water potential zones by a suitable logical reasoning and conditioning. The final ground water potential zone map thus generated was verified with the yield data to ascertain the validity of the model developed.
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