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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
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
- 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.
- 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.
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