The study area covered by hard rock formations, faces acute water scarcity problem both for irrigation as well as drinking purposes. Occurrences of groundwater in this type of area is confined in secondary permeable structures i.e. fractured and weathered horizons and in upper unconsolidated materials. The traditional methods of searching sites for drilling of bore hole, have not only had a poor success rate but even the places where such efforts have succeeded, the borewells are known to have dried up in a short period of time. The concept of integrated remote sensing and GIS has proved to be an efficient tool in groundwater studies (Saraf, A.K. et.al. 1998, Krishnamurthy et.al 1996 and Murthy 2000). Inclusion of subsurface information inferred from geoelectrical survey can give more realistic picture of groundwater potentiality of an area. Keeping this in view, the present study attempts to delineate suitable locations for groundwater exploration using integrated approach of remote sensing, geoelectrical and GIS techniques.
The study area, covered by hard rock formations, is situated in Mirzapur district of Uttar Pradesh, India bounded by longitudes 82°26′ E and 82°36′ E and latitudes 24°56′ N and 25°10′ N, (fig. 1) covered in Survey of India toposheet no. 63K/12, K/8, L/5 & L/9. The total geographical area of subwatershed is 248 sq.km. Delhi-Howrah rail rout and National Highway no. 7 passes through the area which connect the area from other part of the country.
Geologically the area comprises of upper Vindhyan formations consisting of sandstone, quartzite and shale (CGWB, 1985). Vindhyan formation is overlain by quaternary alluvium, which was deposited on the eroded basement. Upper Vindhyan formation represented by Kaimur series are divided into two groups, the Upper & Lower. The Lower Kaimur consists of quartzite and silicified shales at the base followed by Susnai conglomerate, breccia and then quartzite & sandstone. The top of Lower Kaimur is characterised by thick shales belonging to Vijaigarh shales. The Upper Kaimur are represented by brown to red, fine grained sandstone followed by white Dhandraul quartzite.
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.
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.
- 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.
Analysis and Discussion
1 Generation of thematic layers
a) Hydrogeomorphology, Lineament & Drainage
A hydrogeomorphological map was prepared from remotely sensed data. On the basis of specific relief and characteristic nature, the hydrogeomorphological features, present in study area were classified into (i) Valley fill (VF) (ii) Moderate weathered buried Pediplain (BPP-M) (iii) Shallow weathered buried Pediplain (BPP-S) (iv) Ravines (RA) (v) Pediment on plateau P(PT) and (vi) Dissected plateau (DPT) (Fig, 2).
Lineaments derived from satellite data have seven azimuth directions (a) NE-SW (b) NW-SE (c) ENE-WSW (d) NNE-SSW (e) E-W (f) N-S (g) NNW-SSE (Fig. 3)
The study area is drained by Harrai river. The map prepared from SOI toposheet at 1:50,000 scale and satellite data indicate that drainage pattern is mainly dendritic but locally exhibits structural control (Fig. 4).
Topographic information has been collected from SOI toposheet at 1:50,000 scale and a TIN has been generated from elevation contour at 20m intervals and spot elevations. Most of the area shows more or less flat topography excepting a few parts. The maximum and minimum elevations are 218 m and 76 m respectively. A three dimensional perspective model of the study area has been prepared using TIN to understand the role of surface drainage pattern and their topographic locations in controlling groundwater conditions (fig. 5). Slope map in degree have been prepared from TIN and the same was verified by superimposing drainage (fig. 6).
c) Subsurface Lithology
In most of the cases the first layer is predominantly clay / clay with kankar and is characterised by resistivity range of 4 ohm-m to 29.0 ohm-m depending upon the proportion of constituents, its thickness varies between 2 m to 43 m. The second layer is weathered and / or hard sandstone which is non-water bearing, poorly fractured and is characterized by resistivity range of 30 ohm-m to 200 ohm-m, its thickness varies between 6 m to 57 m. The third layer with resistivity ranges from 40 ohm-m to 300 ohm-m indicating the presence of hard and fractured sandstone which is water bearing and forms the aquifer zone in the area. The thickness of aquifer zone varies between 0 m to 47 m . Depth to the hard rock having very high resistivity in general, (compact & massive, occ. fractured sandstone) varies from 11 m to 105 m below ground surface (Table 1). Geo-electrical sounding locations and details of the layer parameters of representative sites are shown in fig. 7 and fig. 8.
TABLE – 1
|Geoelectrical Parameters and their Hydrogeological Significance|
|Resistivity Stratification||Inferred Lithology||Hydrogeological Significance|
|Resistivity (Wm)||Thickness (m)|
|4 – 29||2 – 43||Predominantly Clay/Clay with Kankar||Generally lies in unsaturated zone very poor aquifer at depth.|
|30 – 200||6 – 57||Sandstone, weathered and / or hard||Non-water bearing, poorly fractured, very poor aquifer.|
|40 – 300||0 – 47||Sandstone, hard and fractured||Main aquifer saturated with Potable water.|
|> 300||Indeterminate (Bottom layer)||Sandstone, hard & compact, occ. Fractured||Bedrock, poorly fractured very poor aquifer.|
From the above inferred lithology & their thickness, overburden thickness and aquifer layer thickness were prepared (fig. 9 and 10).
2 Integration of thematic layers and modelling through GIS
As discussed in earlier sections, each one of the classes in thematic layers was qualitatively placed into one of the following categories, viz. (i) very good, (ii) good to very good (iii) good, (iv) moderate and (v) poor depending on their ground water potential level. After understanding their behavior with respect to groundwater control, the different classes were given with suitable weights, according to their importance with respect to other classes in the same thematic layer. The weights assigned to different classes of all the thematic layers are given in table 2. To cite an example, the maximum weight assigned for the aquifer thickness was 5 for thickness greater than 35m, whereas the lower weight of value 1 was assigned to thickness less than 5 m. On the other hand, in a hydrogeomorphology layer, a maximum weight of 5 was assigned for valley fill and a minimum weight of 1 for DPT.
TABLE – 2
|Weightage of Different Parameter for Groundwater Prospects|
|DPT, P(PT) & RA||1|
|2.||Slope (degree)||0 – 0.5||5|
|0.6 – 2.0||4|
|2.1 – 5.0||3|
|5.1 – 10.0||2|
|3.||Lineament (around 200 m )||Present||2|
|4.||Drainage||Vth order ( around 500 m)||3|
|IVth order (around 400 m) & IIIrd order (around 300 m )||2|
|IInd order (around 200 m) &Ist order (around 100m )||1|
|5.||Overburden thickness||> 25 m||3|
|6.0 – 25.0 m||2|
|< 6.0 m||1|
|6.||Aquifer thickness||> 35 m||5|
|26.0 – 35.0 m||4|
|16.0 – 25.0 m||3|
|6.0 – 15.0 m||2|
|< 6.0 m||1|
The thematic layers which include hydrogeomorphology, lineament, slope, drainage, overburden thickness and aquifer thickness were converted into grid with related item weight and integrated with one another through GIS (Arc / Info grid environment). As per this analysis, the total weights of the final integrated grids were derived as sum of the weights assigned to the different layers based on suitability (ESRI 1997). In the present study, groundwater prospects map has been generated by integration of hydrogeomorphology, lineament, slope, drainage and overburden thickness (Fig. 11). The delineation of groundwater prospects zones was made by grouping the grids of the integrated layers into different prospect zones, very good, good to very good, good, moderate to good, moderate, poor to moderate and poor. Table 3 gives the way in which upper and lower limits of the weights derived for ground water prospect of the areas. This provides a broad idea about the groundwater potentiality of the study area. Groundwater potential map generated by integration of aquifer thickness, with hydrogeomorphology, lineament, drainage, overburden thickness and slope gives the more realistic picture. The delineation of groundwater potential zones was made by grouping the grids of final integrated layer into different potential zones, very good, good to very good, good, moderate to good, moderate, poor to moderate and poor. Table 4 gives the way in which the upper and lower limits of the weights derived for demarcation of the ground water potential areas. Theoretically, the upper weight 23 and lower weight 6 could be possible, and derived by combining all the upper and lower categories in all layers. However, in the study area, 22 was the highest and 5 was lowest value obtained. By utilising the above discussed model a map showing different groundwater potential zone was prepared (fig. 12).
TABLE – 3
|Integrated Groundwater Categories for Groundwater Prospects with lower and upper weight value|
|Sl. No.||Groundwater Category||Lower & Upper weight Value||Area (Sq.km)|
|1.||Very Good||18 – 20||0.20|
|2.||Good to very good||15 – 17||10.8|
|3.||Good||13 – 14||24.1|
|4.||Moderate to good||11 – 12||67.9|
|7.||Poor to moderate||7 – 8||50.5|
3 Model Evaluation and Results
The validity of the model developed was checked against the bore well yield data which reflects the actual groundwater potential. Table 5 shows that groundwater potential zones prepared through this model are in good agreement with yield data. Yield of drilled sites covered in this model have ranges from 793 to 1160 lpm in good to very good zone, 300 to 1160 lpm in good zone, 100 to 300 lpm in moderate to good zone, 50 to 100 lpm in moderate zone, 25 to 50 lpm in poor to moderate zone and less than 25 lpm in poor zone.
TABLE – 4
|Integrated Groundwater Categories for Groundwater potential with lower and upper weight value|
|Sl. No.||Groundwater Category||Lower & Upper weight Value||Area (Sq.km)|
|1.||Very Good||20 – 22||3.2|
|2.||Good to very good||17 – 19||32.3|
|3.||Good||15 – 16||38.0|
|4.||Moderate to good||13 – 14||26.1|
|5.||Moderate||11 – 12||34.1|
|6.||Poor to moderate||9 – 10||43.1|
|Validation of model with actual Borewell yield data|
|Sl. No.||Category of Groundwater prospect||Category of Groundwater potential||Site location No.||Village||Actual yield (in lpm)|
|1.||Moderate to Good||Good to V. Good||5||Amoi||793|
|2.||Good||Good to V. Good||17||Sirsigaharwar||1160|
|3.||Moderate to Good||Good to V. Good||21||Vindhyachal||1160|
|4.||Moderate to Good||Good to V. Good||22||Ghamahapur||1160|
|5.||Moderate to Good||Good to V. Good||23||Ghamahapur||1160|
|6.||Good||Good to V. Good||25||Amoi||1160|
|8.||Poor to Moderate||Good||11||Vindhyachal||1160|
|9.||Poor to Moderate||Good||20||Tulsitalia||793|
|10.||Poor to Moderate||Good||24||Tulsitalia||793|
|13.||Moderate to Good||Good||58||Sirsigaharwar||505|
|14.||Moderate to Good||Moderate to Good||38||Hinauti||100|
|15.||Moderate to Good||Moderate to Good||40||Hinauti Sarupur||130|
|16.||Poor to Moderate||Moderate||34||Sirsigaharwar||80|
|17.||Moderate||Poor to Moderate||28||Sirsigaharwar||25|
In order to delineate the groundwater potential zones, in general, different thematic layers viz: hydrogeomorphology, lineaments, slope, drainage and overburden thickness are used to be integrated without considering aquifer thickness. This provides a broad idea about the groundwater prospect of the area. Presently groundwater potential zones have been demarcated by integration of aquifer thickness derived from surface electrical resistivity survey and drilling data with above thematic layers, using a model developed through GIS technique. The groundwater potential zones map generated through this model was verified with the yield data to ascertain the validity of the model developed and found that it is in agreement with the bore wells yield data. This illustrates that the approach outlined has merits and can be successfully used elsewhere with appropriate modifications. The above study has demonstrated the capabilities of using remote sensing, geoelectrical data and Geographical Information System for demarcation of different ground water potential zones, especially in diverse geological setup. This gives more realistic groundwater potential map of an area which may be used for any groundwater development and management programme.
The authors are gratefully to Director, RSAC-UP, Lucknow for his kind permission to undertake this study.
- Central Ground Water Board, (CGWB), 1985, Report on hydrogeology and groundwater potential of Mirzapur district U.P.
- Environmental System Research Institute (ESRI), 1997 user guide Arc / Info: The geographic Information System Software, (Redland, CA :ESRI, Inc).
- Krishnamurthy, J. Venkataesa Kumar, N, Jayraman, V. and Manivel, M. 1996 : An approach to demarcate groundwater potential zones through Remote Sensing and GIS. International Journal of Remote Sensing, 17, No. 10, 1867-1884.
- Murthy K.S.R., 2000, Groundwater potential in a semi-arid region of Andhra Pradesh: A geographical Information System approach, International journal of Remote Sensing, Vol. 21 No. 9, 1867-1884.
- Saraf, A.K. and Chaudhary, P.R., 1998: Integrated remote sensing and GIS for groundwater exploration and identification of artificial recharges sites, International Journal of Remote Sensing, Vol. 19, No. 10, 1825-1841.