Amaresh Kr. Singh, S. Raviprakash, D. Mishra and Samarendra Singh
Remote Sensing Applications Centre, Uttar Pradesh
Water plays a vital role in the development of any activity in the area. Thus, the availability of surface and ground water governs the process of planning & development. The surface water resources are inadequate to fulfill the water demand. Productivity through groundwater is quite high as compared to surface water, but groundwater resources have not yet been properly developed through exploration. Keeping this in view, the present study attempts to select suitable locations for groundwater exploration in hard rock areas using an integrated approach of remote sensing, geoelectrical & GIS.
The study area is situated in a part of Sonebhadra, Mirzapur and Chandauli districts of UP, India, bounded by longitudes 83000’39” E & 830 09’28” E and latitudes 24043’15”N & 24051’56” N falling in SOI toposheet no. 63 P/1 & P/2. Geologically the area comprises of upper Vindhyan formations consisting of sandstone, quartzite and shale (CGWB 1985).
Hydrogeomorphological and lineament maps have been prepared using IRS 1B LISS-II data by visual interpretation. Topographic information has been collected from SOI toposheet at 1:50000 scale & TIN has been generated from elevation contour at 20m interval and spot elevation. A slope map has been prepared from TIN. Surface drainage map has also been prepared from SOI toposheet and satellite data on 1:50,000 scale. Hydrogeomorphologically, the entire area comes under BPP-S, BPP-M and DPT category. The drainage pattern is mainly dendritic but locally exhibits structural control.
Vertical electrical soundings (VES) were conducted at 57 sites in the study area for identifying horizontal & vertical variation in subsurface lithology and depth to the hard rock. The geoelectrical data of layer parameters have been correlated with the lithological data obtained from 16 drilled sites in the study area. The study reveals that the aquifer thickness varies between 2 m to 39 m, clay thickness 1 m to 46 m and depth to the hard rock 4 m to 66 m below ground surface. Discharge of drilled sites varies between 135 lpm to 640 lpm. The resistivity of clay, clay kankar varies between 4 ohm-m to 23 ohm-m. Aquifer resistivity ranges from 30 ohm-m to 110 ohm-m. Using the geoelectrical data, clay thickness & aquifer thickness maps have been prepared through GIS technique.
The groundwater potentiality of the area has been assessed through integration of the relevant layers which include hydrogeomorphology, lineament, slope, aquifer thickness and clay thickness, in Arc/Info grid environment. Criteria for GIS analysis have been defined on the basis of groundwater conditions and appropriate weightage has been assigned to each information layer according to relative contribution towards the desired output. The groundwater potential zones map generated through this model was verified with the yield data to ascertain the validity of the model developed. The verification showed that the ground water potential zones demarcated through the model are in agreement with the bore well yield data. Since the present approach was built with logical conditions and reasoning, this approach can be successfully used elsewhere with appropriate modifications. Thus, the above study has clearly demonstrated the capabilities of remote sensing, geoelectrical and GIS technique in demarcation of the different groundwater potential zones.
The study area covered by hard rock formations, facing 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 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 part of Sonebhadra, Mirzapur and Chandauli district of Uttar Pradesh, India bounded by longitudes 83000′ 39″E and 83009′ 28″ E and latitudes 24043’15” N and 24051′ 56″ N,(fig. 1) covered in Survey of India toposheet no 63P/1 & 63P/2. The total geographical area of watershed is105 sq.km.
Table – 1
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 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 1065 mm.
The followings data were used for the study :
- Remotely sensed data, viz. IRS 1B LISS II, geocoded of scale 1:50,000.
- The survey of India toposheet 63P/1 & 63P/2 of scale 1:50,000.
- Field data, viz. vertical electrical sounding data and drilling data.
Table – 2
|Integrated Groundwater categorised with lower and upper weight value|
|Sl. No.||Groundwater Category||Lower & upper weight value|
|1.||Very Good||13 – 16|
|2.||Good||11 – 12|
|3.||Moderate to Good||9 – 10|
|4.||Moderate||7 – 8|
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 1B LISS-II data by visual interpretation on 1:50,000 scale.
Contour map and spot elevation map were prepared from SOI toposheets.
Drainage map was prepared from SOI toposheet & satellite data.
All the prepared primary input maps (hydrogeomorphology, lineament, contour & spot elevation, drainage and VES location) were digitized in Arc/Info, GIS software package and slope map was prepared from digital elevation data.
Vertical electrical soundings (VES) data of 57 sites were interpreted and geoelectrical parameters of drilled sites were co-related with lithology and based on this 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 thickness and clay 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) (iii) moderate and (iv) 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 of cell size 30 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.
Table – 3:
|Validation of model with actual bore well yield data|
arrived through this model
|Moderate to good||9||Hinauta||135|
Analysis and Discussion
Generation of thematic layers
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) moderate weathered buried pediplain (BPP-M) (ii) Shallow weathered buried pediplain (BPP-S) and (iii) Dissected plateau (DPT) (fig. 2).
Lineament analysis for ground water exploration in Vindhyan formations has considerable importance as joints and fractures serve as conduits for movement of groundwater. It is not practical to map lineaments solely on the basis of satellite data without a thorough knowledge of the structural conditions in an area. For extraction of lineaments, the procedure of Moore and Waltz (1986) has been followed. In this study, lineaments derived from satellite data have been carefully matched with previously mapped structural features and a good degree of correlation between the two has been found. There are six azimuth directions (a) NE-SW (b) NW-SE (c) ENE-WSW (d) NNE-SSW (e) ESE-WNW (f) N-S (fig. 3).
A surface drainage map has been prepared from SOI toposheet at 1:50,000 scale and satellite data. The study area is drained by chandraprabha river. The 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. Elevation contour at 10m interval and slope in degree have been prepared from TIN and the same was verified by super imposing drainage. Nearly 40 percent of the of the total area shows 0-1 degree slope. Maximum slope of 9.2 degree is found in the area around Bharwagobar (fig. 5). Subsurface Lithology
In most of the cases the top layer resistivity ranges from 5.0 ohm-m to 45.0 ohm-m with thickness varying from 1.0 m to 2.0 m which indicates the variable nature of surface soil (loose and moist, dry and hard). The second layer is predominantly clay / clay with kankar and is characterised by resistivity range of 4 .0 ohm-m to 23.0 ohm-m depending upon the proportion of constituents, its thickness varies between 1.0 m to 46.0 m . The third layer with resistivity ranges from 30 ohm-m to 110 ohm-m indicates the weathered / fractured sandstone which is water bearing and forms the aquifer zone in the area. The thickness of aquifer zone varies between 2m to 39m . Depth to the hard rock having very high resistivity in general, (compact & massive, occ. fractured sandstone) varies from 9m to 66m below ground surface. VES locations and details of the drilling results and layer parameter of representative sites are shown in fig. 1 and fig. 6.
From the above inferred lithology & their thickness clay (top impermeable layer) thickness and aquifer thickness maps were prepared (fig. 7, 8).
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, (iii) moderate and (iv) 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 1. To cite an example, the maximum weight assigned for the aquifer thickness was 4 for thickness greater than 25m, whereas the lowest value of 1 was assigned to thickness less than 5m. On the other hand, in a hydrogeomorphology layer, a maximum weight of 3 was assigned for BPP-M and a minimum weight of 1 for DPT.
The thematic layers which include hydrogeomorphology, lineament, slope, aquifer thickness and clay 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, the delineation of groundwater potential zones was made by grouping the grids of the final integrated layer into different potential zones ; very good, good, moderate to good, moderate and poor. Instead of just dividing the maximum and minimum values into different categories, which does not have any logical reasoning, a model has been developed using relevant logical conditions. Table 2 gives the way in which the upper and lower limits of the weights derived for demarcation of the groundwater prospecting areas. Theoretically, the upper weight of 17 can be possible, and derived by combining all the upper categories in all layers. However, in the study area, 16 was the highest value obtained.
The areas which are very good for groundwater prospects were delineated by grouping the grids which have weight between 13 to 16 in the final integrated layer. The upper limit of the weight was derived by good category of hydrogeomorphology and very good category in all other layers. The lower value was derived by good category of hydrogeomorphology, aquifer thickness, slope, and clay thickness, without the presence of lineament.
The grid which comes under good category were obtained by grouping grids having weights between 11 to 12. The lower weight 11 was derived from the combination of good category of hydrogeomorphology and clay thickness and moderate category of aquifer thickness and slope without presence of lineament.
The moderate to good category potential groundwater zones involve grids which have weights from 9 to 10. The lower value of this category was derived by adding the good category of hydrogeomorphology and moderate categories of aquifer thickness, and clay thickness and poor category of slope with the absence of lineament.
Moderate groundwater potential zones were delineated by grouping the grids which have weights from 7 to 8. The lower value of this category was derived by the combination of a moderate categories of hydrogeomorphology, aquifer thickness and poor categories of clay thickness and slope without the presence of lineament.
All other grids which have less than 7 weight, were grouped as a poor category. The lowest weight 5 was obtained in the study area. By utilising the above discussed model a map showing different groundwater potential zones was prepared (fig. 9).
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 3 shows that groundwater potential zones prepared through this model have in good agreement with yield data. Yield of drilled sites occurred in this model have ranges from 162 to 639 lpm in very good zone, 135 to 225 lpm in good zone, 135 to 145 lpm in moderate to good zone and less than 100 lpm in moderate zone.
In order to delineate the groundwater potential zones, in general ,different thematic layers viz: hydrogeomorphology, lineaments, and slope, are used to be integrated without considering subsurface lithology .This provides a broad idea about the groundwater potentiality of any area. Presently, groundwater potential zones have been demarcated by integration of aquifer thickness and clay 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 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 Dr. A.N. Singh, Director, RSAC-UP, Lucknow for his kind permission to undertake this study. The authors wish to acknowledge the help and suggestion of Dr. A.K. Tangri, Scientist-SF & Technical Secretary to Director, RSAC-UP.
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