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Groundwater prospects analysis through hydrogeophysical parameters and hydrogeomorphic zonation – A case study in parts of Kewta Watershed, upper Barakar basin, Bihar

Ashok Kumar, Savita Tomar* and L.B. Prasad
Remote Sensing Application Centre, IGSC-Planetarium, Patna – 800001, India
* Noida, UP, India

Abstract
The study area is parts of ‘Kewta watershed’ of Koderma (lower Hazaribagh) plateau. It is located in between the latitude 240 09′ – 240 13′ and longitude 850 20′ – 850 28′. In the present study, hydrogeomorphic zonation has been carried out through remote sensing technique. Hydrogeophysical characteristics of aquifer have been analysed with the help of vertical electrical sounding. Study deals integrated approach for groundwater exploration. The results of hydrogeomorphic and hydrogeophysical approach have been correlated and outcomes have been highlighted in the paper. Analysis has indicated that each hydrogeomorphic zone can be further divided on the basis of hydrogeophysical parameters. Numerous depressions (sub-surface basin) on basement surface have been identified with the help of Digital Basement Terrain Modeling (DBTM). These depressions play important role in understanding the aquifer storage and retrieval. But these features have not been resolved as separate identity in hydrogeomorphic zonation. The hydrogeomorphic zonation coupled with hydrogeophysical parameters has given better understanding of groundwater storage and retrieval. Integrated approach has also increased the authenticity of ground water prospects determination. Analysis of deep buried pediplain shows that the top layer (10 m) consists of silt and clay (may be depositional) and principal aquifer material i.e. weathered horizon is lying below the depositional material. This has important bearing in planning utilisation and development of groundwater. 

Introduction
The Kewta watershed (Upper Barakar basin) is a part of Koderma plateau of Bihar. It is located between the latitude 240 09′ – 240 13′ and longitude 850 20′ – 850 28′. It is a typical undulating granite gneiss pediplain and regional slope is towards west with maximum pediplain height 450 meters in east and minimum 430 meters in the west from m.s.l.. The areal extent of study area is 29 sq. km. 

Groundwater occurs under water table condition and aquifer is un-confined / semi confined in nature. The yield of dugwell depends on the thickness of weathered and fractured horizon (Karanth, 1987). Study area has limited groundwater reserves due to unconfined nature of aquifer system. At present available reserve is under utlised. Analysis of 3-D aspects of the aquifer is essential to understand the aquifer storage and reterival system unconfined aquifer. 

It has been observed that dugwell depth normally does not go beyond 11 m b.g.l.. The pre-monsoon variation of water table is 7 to 10 m in deeply weathered zone. Seasonal fluctuation in water table is about 1 m. In moderately weathered zone, water table varies between 4.5 – 7.5 m on uplands and 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 fluctuation is between 3 – 4 m. 

In present paper, authors have tried to demarcate different hydrogeomorphic zones with help of remotely sensed data. Systematic vertical electrical sounding (VES) has been also carried out and digital basement topographic model (Kumar, 1997) has been generated. The ground water prospect has been determined through both the approach and results are further correlated to improve the groundwater prospects zonation.

Fig 1: Hydrogeomorphic map of parts of Kewta watershed

Fig 2: Depth of Basement zonation map parts of Kewta watershed

Fig 3: Resistivity Zonation at depth of 11m b.g.l. of parts of Kewta watershed

Methodology
In the present study, hydrogeomorphic zonation (NRSA, 1995; and Kumar et al, 1999) has been carried with the help of 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). With the help of field level geohydrological inputs i.e. lithology, weathering etc., groundwater prospects of each geomorphic class has been assessed (Fig. 1 & Table – 1). Broad geomorphic classes have been further sub-divided on the basis of depth of weathering/ thickness of cover material i.e. shallow/ moderately/ deep buried pediment/ pediplain. Attempt has also been made to further sub-divide each sub-class on the basis of relative location i.e. upland/ midland/ lowland (Kumar et. al., 1998 and 1999). Further to visualise the 3-D aspects of aquifer, Digital Basement Topographic Model (DBTM) has been generated based on the depth of basement information derived from the 52 Vertical Electrical Sounding (Kumar, 1997). Aquifer hydrogeophysical parameter at depth of 11m has also been analysed to know the behaviour of aquifer material at most common depth of groundwater exploitation in the area. The interpretation of VES data has been authenticated by the litho-logs of PHED drilled borewell and with vertical section of newly constructed dugwell. The spatial and non-spatial data of hydrogeomorphic and hydrogeophysical layers have been analysed in GIS environment (GRAM++, DST, 1999). 

Discussion of Results

Hydrogeomorphic Zonation
It has been observed that the broader geomorphic classe have distinct geohydrological characteristics. The results indicate that 59 per cent of study area comes under moderate groundwater prospect zone and 39.20 per cent area under poor to moderate groundwater prospect zone. Hydrogeomorphic classes having depth of weathered/ cover material less than 5 m account 33.52 per cent, 5-15 m zone accounts 25.98 per cent , greater than 15 m zone accounts 39.33 per cent of the study area (Table 2). 

Table – 1 Hydrogeomorphic Zonation and Groundwater Prospects
Hydrogeomorphic units Area of each unit (ha) Groundwater prospect zone (ha) Area of prospect zone (ha) Per cent to the study area Development feasibility for irrigation purposes
Structural Hill (SH) 3.9 Very poor 24.2 0.8 Not suitable for dugwell development
Residual Hill (RH) 20.3
Shallow Buried Pediments (SBP-U) 88.5 Poor to Moderate 1155.0 39.2 Less suitable for dugwell development. Risk of failure is high, limited utilisation possible
Moderately Buried Pediments (MBP) 190.3
Dissected Pediplain (DPP) 26.5
Shallow Buried Pediplain (SBPP), 0-5m 240.0
Shallow Buried Pediplain (Midland) (SBPP-M), 0-5m 609.7
Moderately Buried Pediplain (MBPP), 5-15m 222.0 Moderate 1739.5 59.0 Suitable for dugwell development
Moderately Buried Pediplain (Upland) (MBPP), 5-15m 219.3
Channel Depression 138.4
Deep Buried Pediplain (DBPP), > 15-m 1159.8 Dugwell-cum-borewell is feasible in DBPP, No risk of failure. Depth of dugwell should be more than 10-m. Depth of 15-m is most appropriate
Rock outcrop (RC) 29.5   29.5 1.0  
TOTAL 2948.2   2948.2 100  

Table – 2: Hydrogeomorphic Zonation Based Depth of Basement
Hydrogeomorphic Zones Depth Zone Area (ha)
Structural Hill ( SH ), Residual Hill ( RH ), Shallow Buried Pediments (SBP-U), Disected Pediplain (DPP), Shallow Buried Pediplain (SBPP), Shallow Buried Pediplain-Upland ( SBPP-U) < 5 m 988.4
Moderately Buried Pediment (MBP), Moderately Buried Pediplain-Upland ( MBPP-U), Moderately Buried Pediplain ( MBPP ), Valley fill/ Depression ( LL ) 5 – 15 m 770.0
Deep Buried Pediplain ( DBPP ) >15 m 1159.8

Table – 3: Relation Between Hydrogeomorphic Class and Hydrogeophysical Parameters
Hydrogeomorphic Class Area (ha) between different depth of basement range (m) Area ( ha ) between different resistivity ranges (ohm-m) at 11 meter depth
  5- 10 10- 15 15- 20 20- 25 25- 30 >30 0- 50 50- 100 100- 150 150- 200 >200
Structural Hills ( SH) 3.8* 0 0 0 0 0 0 0 0 0 3.9
Residual hills (RH) 19.6* 0.6* 0 0 0 0 0 0 0 0 20.2
Shallow buried pediment- Upland (SBP-U) 58.2* 30.3* 0 0 0 0 0 0 0 0.6 87.9
Moderately buried Pediment Midland (MBP-M) 49.4 83.2 57.6 0 0 0 0 15.6 43.7 48.3 82.7
Shallow buried pediplain (SBPP) 156.1* 42.2* 38.2* 3.5* 0 0 0 0 1.5 4.5 234.1
Shallow buried pediplain- Midland (SBPP-M) 281.2* 211.1* 99.2* 16.5* 1.8* 0 0 11.2 15.6 28.5 554.3
Dissected buried pediplain (DPP) 6.7 13.7 6.2 0 0 0 2.7 4.8 3.0 5.0 11.1
Moderately buried pediplain (MBPP) 85.1 56.6 47.4 31.7 1.2 0 43.0 30.9 23.0 20.6 104.6
Moderately buried pediplain- Upland (MBPP-U) 101.8 99.3 4.8 13.4 0 0 0 0 0 20.3 211.8
Deep buried pediplain (MBPP) 188.6* 215.7* 379.5 260.6 108.3 6.9 139.6 224.4 165.4 179.0 451.4
Channel Depression/ Valley fill (LL) 45.5 62.7 20.5 9.7 0 0 9.7 14.9 2.4 6.6 104.8
River Channel (RC) 4.7 3.7 18.4 2.7 0 0 0 0 6.6 11.2 11.8
TOTAL 1000.7 819.1 671.8 338.1 111.3 6.9 195.0 301.8 261.2 324.6 1878.6
NOTE * : star marked shows deviation between hydrogeomorphic and depth of basement

Hydrogeophysical Properties

  1. Digital Basement Topographic model (DBTM)
    Depth of basement derived from the interpretation of VES data has been used as basic input to this model. Correlation of electrical log and dugwell section has indicated that there is reasonably good accuracy exists between actual field condition and interpreted VES sounding data. The DBTM model depicts the basement topography. Results can be further improved if more and more control points will be included in the model. Total nine depressions on basement surface (also termed as sub-surface basins) have been identified (Fig.4). These depressions can also be used for development of high yield borewell and recharge sites identification. 

    Geographical area between different depth zone has been also calculated (Fig. 2 and Table – 3). The zonation of watershed on the basis of basement depth facilitates in deciding/ accessing feasibility of the dugwell/ dug-cum-borewell/ borewell development. The 33.94 per cent area falls within 5- 10 m b.g.l. basement depth range. This zone is marginally suitable for dugwell development. The 66.05 percent area having basement depth greater than 10-m. and this zone is suitable for dugwell development. The 36.40 per cent area having depth of basement greater than 20-m and in this zone dug-cum-borewell is best alternative to tap the maximum possible aquifer thickness. The 4.00 per cent area having depth of basement greater than 25-m and this zone is suitable for borewell development. 

  2. Aquifer Hydrogeophysical properties at depth of 11 m b.g.l.
    Keeping local field practice in mind, hydrogeophysical property of the aquifer at the depth of 11-m b.g.l. has been analysed to know the variation of aquifer property i.e. aquifer water saturation so that the groundwater development can be prioritized (Fig. 3 and 5). The areal extent of different resistivity zones are given Table – 3. The zone of 20 to 50 ohm-m (6.61 per cent) should be given first priority. The zone of 50 – 100 ohm-m (10.23 per cent) as second priority, 100 – 150 ohm-m (8.86 per cent) as third priority, 150 – 200 ohm-m (11.00 per cent) as last priority. Resistivity zone having value greater 200 ohm-m (63.71 per cent) should not be utilised.

Relation between Hydrogeomorphic and Hydrogeophysical Properties

  1. Hydrogeomorphic and Depth of basement zones
    Shallow buried pediments/ pediplain are supposed to have depth of basement/ cover material thickness less than 5 m. But depth of basement contours map shows that depth of basement is more than 5 m in some area (Table – 3) such type of variation is expected in hydrogeomorphic zonation. Out of total 1159.73 ha of deep buried pediplain (cover material thickness more than 15 m), 188.61 ha comes under the 5-10 m depth zone and 215.75 ha comes under the 10-15 m depth zone in basement contour map. Hydrogeomorphic zonation permits 1739.50 ha land whereas DBTM permits 1947.52 ha land suitable for dugwell development. The areal extent obtained through both the approaches has provided nearly similar results but class/ zone wise variation in areal extent exits in shallow buried pediment/ pediplain and deep buried pediplain. It has been observed that there is no distinct surface characteristic of sub-surface basins on the basement surface in remotely sensed data.

    The moist river channels/ depressions identified in hydrogeomorphic map have relevance in groundwater development. These zones are getting enhanced recharge. Water table is shallow and seasonal fluctuation is less. Groundwater seepage also takes place in this zone. These zones have importance in shallow buried pediments / pediplain where groundwater prospects is poor. But these narrow and linear zones have not been resolved in DBTM due to lack of closely spaced field data set. In some parts of denudational hill, 5-10 m depth zone is passing. This is due to lack of sufficient ground control point taken into account in DBTM generation. 

  2. Hydrogeomorphic zones and Hydrogeophysical parameters at depth of 11 m b.g.l.
    The priority for groundwater development within the same hydrogeomorphic zone can be determined on the basis of variation of aquifer saturation at the depth of 11 m b.g.l. More than three priority classes exits within the individual hydrogeomorphic zone (Table – 3). In moderately buried pediment (midland) – 43.46 per cent, shallow buried pediplain – 97.53 per cent, shallow buried pediplain (midland) – 90.91 per cent, moderately buried pediplain – 47.09 per cent, moderately buried pediplain (upland) – 91.25 per cent, deep buried pediplain – 38.91 per cent of lands are not to be utilised for groundwater development. Lateral variation of aquifer saturation at 11 m depth does not permit entire land of same hydrogeomorphic zone suitable for sustainable utilisation of groundwater through dugwell. Based on integration of hydrogeomorphic and lateral aquifer saturation, 1879.59 ha land is not to be used for groundwater development. Hydrogeophysical parameter of deep buried pediplain indicates that top 10 m cover material consists of silt -clay and potential aquifer material (weathered) lies below this layer. Therefore effective utilisation of groundwater is possible only when depth of dugwell will go beyond the depth of silts-clay layer i.e. more than 10 m b.g.l.

Conclusion
It has been observed that hydrogeomorphic approach for groundwater prospects analysis is not a complete process. Hydrogeomorphic zonation coupled with DBTM and hydrogeophysical property of aquifer has helped in further delimiting the groundwater prospects zone. Similarly DBTM has not resolved narrow moist depression channel but it has been clearly mapped through remotely sensed data. The integrated outcome seems are more realistic as it has looked into the 3-D aspects of aquifer. Even the present study should not be treated as complete and it can be further improved if more and more well distributed field inputs i.e. porosity, yield, transmissivity etc. will be incorporated in analysis. 

Acknowledgments
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.

References

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