Ashok Kumar, Savita Tomar, L. B. Prasad and B. B. Prasad
Remote Sensing Application Centre, IGSC-Planetarium, Patna- 800001, India
In unconfined aquifer system of hard rock terrain ground water occurrence mainly depends upon thickness of weathered material, its physical and chemical composition and its saturation. Relative geomorphic location of aquifer and basement topography also plays important role. Basement topography helps in understanding the aquifer storage and retrieval system. Due to unconfined nature of principal aquifer, seepage loss through channel also needs attention. Precipitation and agro-climatic situation also governs the aquifer system behavior. Therefore multi-layer information is required for sustainable utilisation and development of groundwater.
In present study hydrogeophysical parameters generated from vertical sounding, geohydrological, inferred fractures and geomorphic zones derived from remotely sensed data has been analysed in Kewta watershed of upper Barakar Basin, Hazaribagh. The study area is part of lower Hazaribagh plateau and is part of pediplain developed over Chotanagpur granite gneiss and meta- sedimentary. Study area falls between latitude 240 09′ – 240 13′ and longitude 850 20′ – 850 28′. Topography varies from 600 – 450 m.s.l. In study area electrical resistivity survey ( VES ), remote sensing and routine geohydrological studies have been carried out. DBTM has also been prepared to understand the aquifer storage and retrieval system. Attempt has been also made to estimate the groundwater reserves of entire aquifer system Various spatial and non-spatial data base related to groundwater has been analysed in GRAM++ window based Geographic Information System ( GIS ) for planning and management of groundwater.
Result indicates that there are numerous sub-surface basins/ underground reservoirs, which can be used for groundwater storage and retrieval. Reserve estimation indicates that entire aquifer has storage capacity to irrigate 50 per cent geographical area of watershed. But present replenished groundwater reserve has potential to irrigate only 30 per cent of the geographical area of the study area and it has not been fully utilised. With the help of DBTM, old river channel has been also traced out.
In the study area, principal aquifer system is unconfined in nature and groundwater occurs under the water table condition. The unconfined aquifer system permits time varying continuous decrease in water table after the end of monsoon even without withdrawal from the aquifer. For optimal development and utilisation of the available groundwater reserves, detailed information for basement topography, aquifer geometry and fracture systems are essential. These parameters will help in understating groundwater storage & retrieval system. Estimation of groundwater reserve of entire aquifer system is essential for planning utilisation and development of groundwater. Existing conventional planning process only looks into utilisation and development of replenished groundwater and its utilisation beyond the limit will create imbalance in intake and outtake to the aquifer. Utilisable groundwater reserve is also available in addition to replenished reserve between dugwell base and basement surface. For its utilisation, proper recharge mechanism has to be developed so that the balance between intake and outtake to the aquifer can be maintained.
At present only 10-12 per cent of annual rainfall is contributed to the groundwater through natural recharge process. But at the same time nearly 40-60 per cent of the replenished reserves gets lost as seepage in nala / drainage channel due to unconfined nature of aquifer. There is need to utilised the yearly-replenished groundwater reserves before it get lost. In case we exceed the replenished limit, then recharge to the aquifer is to be increased to that limit. For this purpose suitable sub-surface basins/ fractures system are to be located so that additional recharge other than natural recharge may be stored and optimally utilised.
Study Area & Physiography
The study area is part of ‘Kewta watershed’ of Upper Barakar basin of Chotanagpur plateau of Bihar and is administratively a part of Hazaribagh district. Geomorphologically, it is a part of Koderma plateau (Lower Hazaribagh) of Bihar. It is located in between the latitude 240 09′ – 240 13′ and longitude 850 20′ – 850 28′. The southern fringe of the watershed is a scarp zone of upper and lower Hazaribagh plateau and is limited between topographic contours of 600 – 450 meters m.s.l. Area other than scarp zone is typical undulating pediplain developed over granite gneiss. The regional slope of pediplain is towards west with maximum height 450 meters in east and minimum 430 meters in the west. In the present study only pediplain area of Kewta watershed has been taken into consideration and its areal extent is 2961 hectares.
Weathered granite gneiss serves as principal aquifer in the study area. Groundwater occurs under water table condition and aquifer is un-confined / semi confined in nature. The geohydrological condition predominantly permits utilisation of groundwater through dugwell. Dug-cum-borewell and deep borewell is possible in limited area having thick weathered horizon or fractured basement. Water table varies between 4 – 11 m b.g.l. The yield of dugwell depends on the thickness of weathered and fractured horizon and nature of aquifer material. In study area, dugwell depth normally does not go beyond 11 m b.g.l.. It has been observed that variation of water table in deeply weathered zone is between 7 to 10 m. Seasonal fluctuation in water table is about 1 m. In moderately weathered zone, water table varies between 4.5 – 7.5 m on uplands. In this zone, there is less seasonal fluctuation in water table. In shallow weathered zone, water table in the month of January is below 6.5 m on uplands and less regional variation. But seasonal variation is between 3 – 4 m.
- 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
- 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.
- 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.
- 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 )
- 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.
- 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.
- 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.
Sustainable Development of Groundwater
Based on water-table, depth of weathered material & its saturation, generalised yield prospects and analysis of hydro-geophysical properties of aquifer at depth of 11m helped in identifying the area most suitable ( 195 ha. i.e. 6.60 per cent of study area), suitable ( 310 ha., 10.16 per cent ) and marginally suitable ( 261.4 ha., 8.82 per cent of study area ) for groundwater development through dugwell ( Fig. 4 and Table – 1 ) . Suitable zone is an area where large-scale dugwell development is possible without disturbing the regional groundwater resources. In the less suitable area besides groundwater development stress should also be given on development of surface water harvesting structures. Similarly in marginally suitable area more stress should be given on development & utilisation of surface water resource and groundwater development should be given lowest priority.
Fig. 4 Dugwell development feasibility map of study area
Similarly area suitable for dugwell cum borewell has been identified which has been further cateogrised into different prospect zone ( Fig. 5 and Table – 1 ) i.e. most suitable ( 118 ha., 3.98 per cent ), suitable ( 338 ha., 11.42 per cent ) and marginally suitable zone ( 672 ha., 22.70 per cent ). The development as per feasibility map will reduce the chance of over exploitation of groundwater in area where aquifer is not suitable for dugwell cum borewell development.
- Deep borewell
Fig. 5 : Dugwell cum borewell development feasibility map of study area
Based on DBTM and hydro-geophysical parameters, total 15. deep borewell sites have been identified which is supposed to provide sustainable yield without affecting the regional groundwater environment. Most of the sites are located in the broader fracture zones or in the sub-surface basins where high recharge to the aquifer is expected.
Groundwater Development and Management Possibility
In the entire Kewta watershed ( 2961 ha ), 362.42 ha.m replenished utilisable groundwater reserves are available. The utilisable groundwater reserve has potential to provide irrigation to 906.00 ha (30.60 per cent ). Besides that huge amount ( 830 ha. m ) of utilisable groundwater reserves lies below the existing dugwell depth ( i.e. 10 m b.g.l. ) and basement surface. This untapped groundwater reserve has potential to irrigated 2075 ha. (70 per cent ) land ( Table – 2. ). But this untapped groundwater reserves can only be utilised when suitable recharge mechanism will be developed for balancing the intake and outtake from the aquifer.
Table – 1: Feasibility for Dugwell and Dug-Cum-Borewell Development
Dugwell Development Dug-Cum-Borewell Development
Areal extent Per cent Areal extent Per cent
(ha.) ( ha. )
Most suitable zone 195.00 06.60 118.00 03.98
Suitable zone 301.00 10.16 338.00 11.42
Marginally suitable 261.00 08.80 067.00 22.70
Not suitable zone 2204.00 75.42 1833.00 61.90
Table – 2: Groundwater Reserve Estimation
Area of watershed ( ha ), (under consideration) 2961
Aquifer effective porosity / specific yield (per cent) 5.94
Average generalised seasonal fluctuation of water table ( m b.g.l.) 5 – 10
Replenished groundwater reserve ( ha. m ) 426.38
Utilisable groundwater reserves ( ha. m ) 362.42
Irrigation potential of utilisable groundwater reserves (ha) 906.05
Volume of aquifer material between two extreme of water table ( ha.m ) 8489.14
( i.e. 5 – 10 m b.g.l. )
Volume of aquifer material below 10 m b.g.l up to basement surface ( ha. m ) 16434.90
Utilisable groundwater reserve lying between 10 m b.g.l. up to basement
surface ( ha. m ) 830
Irrigation potential of available groundwater reserves below the 10 m b.g.l ( ha ) 2075
The analysis of hydroheophysical properties of aqufier in hard rock area has helped in understaing the aquifer properties with limited geohydrological inputs. On the basis of hydrogeophysical properties, study area has been cateogarised in different zones for groundwater development and management. Further DBTM has helped in estimating the groundwater reserve beyond the replenished reserve by estimating the entire volume of aquifer above the basement surface. Results indoicate that the groundwater reserve lying below the lower extrem of watertable ( pre monsoon ) which not replenished at present has potential to irrigate 2075 ha of land. Therefore there is enough scope for providing irrigation through groundwater. This can be utilised only when recharge to the aquifer will increased simultaneouly. The sub-surface basin may be used for retrieval and storage of groundwater. DBTM has helped in understanding the lineaments derived from remotely sensed data in better manner.
Authors are thankful to Prof. D. P. Singh, Project Director, Bihar Council on Science and Technology, Patna for giving constant encouragement for research work. Authors are thankful to Deptt of Science and Technology, Govt. of India for providing financial assistance to the project.
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