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Analysis of hydrogeophysical properties of aquifer and reserve estimation for sustainable development of Groundwater in Kewta Watershed, Hazaribagh

Methodology

1. Lineament Identification
   Remotely sensed data of IRS-1B ( L2, B-2,3 & 4 FCC, path-row : 21-51 of 21.2.95 ) and IRS-1C ( L3, B-2,3 & 4 FCC, path-row : 105-055 of 29.1.99 ) have been used to demarcate the linear planner features i.e. probable fractures ( lineaments ). Reproducibility test ( ........... ) has been also carried out by two independent observers to ascertain the reliability of the inferred lineaments have been analysed
   
   
2. Digital Basement Topographic Model ( DBTM )
   Hydro-geophysical parameters derived with the help VES data has been used as inputs to the Terrain Modeling Program and Digital Basement Terrain Model ( Kumar et al., 1997 ) has been generated.
   
   
3. Analysis of hydro-geophysical parameters at 11 m Depth
   Lateral variation of hydrogeophysical property particularly aquifer resistivity has been analyzed at the depth of 11m in regional perspective ( Kumar et. al. 1999 ). This has been carried out to categorize the entire area into different groundwater development feasibility classes.
   
   
4. Estimation of replenished groundwater reserves
   Groundwater reserves are generally estimated on the basis of National Ground Water Estimate Committee norms ( Battacharya, 1990). In present study parameters selected for the calculation are as follows : Normal rainfall = 1200 mm , Natural recharge = 12 per cent of total precipitation ( Rangrajan et. al., 1999 ), Irrigation requirement = 0.40m (CGWB norms), Drinking water requirement = 40 liters per head ( PHED norms). Total average porosity of weathered aquifer material has been taken as 0.4 (effective porosity = 5.94 per cent and retention porosity = 34.06 per cent )
   
   
5. Estimation of total available groundwater reserves within the aquifer
   Aquifer material lying below the lower extreme ( i.e. post monsoon ) of water table ( taken as 10 m b.g.l) up to the basement surface is also storing utilisable groundwater. Due to lack of information about the basement topography, realistic estimation is generally not being carried out. The utilisable groundwater reserves can be estimated if volume of aquifer material is known. In present study volume of aquifer has been calculated with the help of DBTM ( Kumar et al, 2000 ). Total volume of groundwater stored in aquifer material has been estimated by multiplying average aquifer porosity to the volume of the aquifer material.

Result and Discussion
Remotely sensed lineaments


Fig.1: Lineament map of study area based on remotely sensed data

In present case, lineaments have been identified in two independent trials using two different sensor of IRS of two different years. It has been observed that 38 lineaments ( total length 55 k.m.) are drainage controlled out which 13 are reproducible ( total length 26 k.m. ). There is 18 ( total length 22 k.m. ) other types of lineaments out of which 4 are reproducible ( total length 6 k.m. ). Reproducibility test shows that 30 per cent lineaments are reproducible in their length and azimuth ( Fig. 1 ). These reproducible planner features (lineaments) have been further analysed through DBTM to work out its 3-D aspects. Few lineaments particularly trending in NE-SW direction have shown correlation with the basement depression ( Fig. 2 ). It has been noticed that lineament density is higher in the area where basement depth is shallow and less and subtler in deep buried pediplain area.

Hydrogeophysical properties

1. Digital basement topographic model (DBTM)
   
   
   Fig.2 a : Digital Basement Terrain Model ( DBTM ) of study area
   
   
   Total nine sub-surface basins have been identified ( Fig. 2 ). The feasibility for development of groundwater structures has been determined on the basis of depth of basement. The 33.94 per cent area falls within 5- 10 m b.g.l. depth of basement range. This zone is marginally suitable for dugwell development. The 66.05 percent area falls in depth of basement contours greater than 10 m b.g.l. and this zone is suitable for dugwell development. The 36.40 per cent area falls in depth of basement contours greater than 20 m b.g.l. and in this zone dug-cum-borewell is best alternative to tap the possible aquifer thickness. The 4.00 per cent area falls in depth of basement contours greater than 25 m b.g.l. and this zone is suitable for borewell development.
   
   It has been observed that there is deviation in the existing main drainage line of Kewta river and deepest basement surface line. This indicates that earlier river was following the trend of deepest basement line. After successive deposition, riverbed had been elevated and river shifted towards the north. Now it is stablised after touching the hard rock boundary in north.
   
   Good correlation exists between depth of water table and depth of basement/ weathering. One can predict the depth of basement from water table itself. If water table is greater than 6 - 7 m in month of January then at that place basement depth is greater than 15 m.
   
   
2. Hydrogeophysical property of aquifer at depth of 11 m b.g.l.
   
   
   Fig. 3 : Variation of aquifer resistivity at depth of 11 m b.g.l. in study area
   
   
   Keeping average depth of dugwell in the area, hydrogeophysical property of the aquifer at the depth of 11 m b.g.l. has been analysed to know the lateral variation of aquifer property i.e. aquifer water saturation (Fig. 3 The resistivity zone representing ranges 20 to 50 ohm-m ( 6.61 per cent of study area ) has been given first priority, then 50 - 100 ohm-m ( 10.23 per cent of study area ) as second priority, 100 - 150 ohm-m ( 8.86 per cent of study area ) as third priority, 150 - 200 ohm-m ( 11.00 per cent of study area) as last priority and resistivity zone representing value greater 200 ohm-m ( 63.71 per cent of study area) is not to be utilised.