B. C. Sarkar
Department of Applied Geology,
Indian School of Mines,
Department of Applied Geology,
Indian School of Mines,
Department of Applied Geology,
Indian School of Mines,
B Basu Roy
Department of Applied Geology,
Indian School of Mines,
Central Mine Planning and Design Institute,
In the present study, delineation of potential groundwater zones in and around Jharia coalfield has been attempted following a multi-criteria evaluation GIS approach using Geomatica and SPANS software tools. Various data layers such as, litho-stratigraphy, drainage, lineament (fault), slope and water table elevation have been emphasized for delineation of groundwater potential zones owing to their relative importance in holding groundwater. A probability weighted approach has been applied for overlay analysis that allows for a linear combination of weights of each thematic map. The resultant map indicates buried river channels in the southwestern part of the coalfield flood plains and river channels near Damodar river are suitable groundwater potential zones. The southeastern part of the coalfield although considered suitable for groundwater zones but exhibits poor groundwater potentiality due to active mining activities in that part of the coalfield.
Jharia coalfield is characterized by gently undulating to a rolling topography with an overall slope towards east-southeast. The average topographic slope varies in the range of 0.01% to 2.18 % and above. The ground elevation of the area generally varies from 240 m in the western part to 140 m in the southeastern part near the Damodar river (NRIMS, 1995). The entire area is subjected to denudational process. The different physiographic units of the area consist of hillocks and escarpments, pediplains, monad rocks, valley side slopes and valley flats. Vegetation cover is mainly sparse and degraded in nature. The important rock types exposed in the area include sandstone and shale of Gondwana Supergroup that lie unconformably over the Precambrian metamorphics.
In Jharia coalfield, the groundwater level is dependent mainly upon the presently existing topography, geomorphic features such as, abandoned channels, losing streams, etc. and human-induced recharge condition. Due to scarcity of drinking water and unhygienic condition around Jharia coal belt, the active population of the Jharia coalfield faces acute shortage of drinking water, which becomes even worse in the summer months. Some part of the coalfield faces water crisis so much so that the habitants use mine water discharge as potable water. Hence, there is a need for the groundwater potentiality mapping to delineate the potential groundwater zones. In this context, in the present study, an attempt has been made to evaluate different morphometric parameters of the Damodar river basin in around Jharia coalfield and delineation of suitable groundwater potential zones within the study area.
Methodology and Database
Thematic maps, viz. litho-stratigraphy, slope, drainage and lineament have been generated using Survey of India (SOI) topography maps, viz. 73 I/1, 73 I/2, 73 I/5, 73 I/6 in1:50,000 scale and Geological Survey of India (GSI) map of Jharia coalfield (Fox, 1930; revised by Mehta and Murthy,1957) in 1:63,360 scale. Ground truth has been collected on the litho-stratigraphic units through field various traverses. Dug well data are collected at different locations in and around the Jharia coalfield. Digital Elevation Model (DEM) of the study area has been generated from the topographic contours and bench marks. The elevation contour map has been generated from the DEM. These layers are generated in steps viz. digitization, editing, building topological structure and finally polygonization in SPANS Topographer software for GIS overlay analysis.
The database used for generation of various thematic layers include:
- Contour and spot height data collected from SOI Topographic maps viz. 73 I/1, 73 I/2, 73 I/5, and 73 I/6 in 1:50,000 scale;
- Litho-stratigraphic data collected from GSI map of Jharia coalfield (Fox, 1930; revised by Mehta and Murthy, 1957) in 1:63,360 scale;
- Lineament data collected from GSI map of Jharia coalfield (Fox, 1930; revised by Mehta and Murthy, 1957) in 1:63,360 scale and Central Mine Planning and Design Institute (CMPDI) map of Jharia coalfield in 1: 25,000 scale (Verma et al.1989) and;
- Dug well data collected by the authors from different networking stations in and around Jharia coalfield.
GIS Data Layer Generation
Digital elevation model (DEM)
Various thematic layers generated from the SOI Topographic maps, GSI map of Jharia coalfield, CMPDI map and from field data lead to creation of a DEM (Fig. 1) exhibiting spatial distribution of elevation continuously over a region in digital format. It has been generated by interpolation of bench marks, contours data collected from SOI Topographic maps. The contours at 20m intervals have been traced from the topographic maps and are digitized, edited and rasterised in the Geomatica software. The thematic layers are then generated through input of the data as point data with their respective Z-value field and then analysed through nonlinear interpolation. Ground elevation is taken as the Z-value field and the elevation contour map is obtained by contouring. The contour layer is generated through a Triangular Irregular Network (TIN) to the points. When a TIN is applied, the points are joined in a network of triangles with each point representing a vertex of a triangle. Each vertex of a triangle represents three values, viz. X, Y and Z. The X and Y values are the two dimensional locational values of the points. The Z-value is an attribute for point data, e.g. elevation, dug well data, etc. This procedure generates output in a quadtree data format.
The litho-stratigraphic map of the area is generated from the GSI map of Jharia Coalfield. The different lithologies have been traced from the geological map and digitized as an area layer and then edited and this generated a thematic map in SPANS Topographer software. In Jharia coalfield Gondwana sediments (Talchir, Barakar, Barren Measure, and Raniganj formations) lie unconformably over the Precambrian metamorphics. The dominant lithologies include sandstone, shale and granite gneiss (basement rock). The litho-stratigraphic map of the study area is shown in Fig. 2.
Slope is the change of elevation of a surface and it is expressed as a percentage of rise over run. A value of 0% represents a slope of 0? while a value of 100% represents a slope of 45?. The relationship between percentage and degrees as represented on this case is non-linear. In the present study, slope map is generated from the DEM. Slope plays a very significant role in determining infiltration vs. runoff. Infiltration is inversely related to slope i.e. more gentle the slope is, infiltration would be more and runoff would be less and vice-versa. The slope map of the study area is presented in the Fig. 3, which shows an overall gentle slope towards east-southeast.
Drainage pattern of an area is very important in terms of its groundwater potentiality. It is the source of surface water and is affected by structural, lithological and geomorphological control of an area (Schumm, 1956). The drainage pattern in the present study area is dendritic in nature. This may be due to more or less homogeneous lithology and structural controls. Damodar river is the main control of drainage system along the Jharia coalfield. It is a fourth order stream to which a number of third to first order streams, viz. Jamunia, Khudia, Katri, Ekra, Tisra, Chatkari etc. join. Damodar river flows along the southern periphery of the coalfield and is guided by the Great Boundary Fault. The main flow direction is from west to east. The drainage map of the study area is shown in the Fig. 4.
In Jharia coalfield, faults are the dominant linear feature. The Gondwana sediments of Jharia basin are largely disturbed by a large number of various types of fault system. In the southern part of the basin, Southern Boundary Fault is present with a trend approximately along WNW- ESE direction. Besides Southern Boundary Fault to the south, a number of interbasinal faults also exist (E-W trending faults, NW-SE and NNW-SSE trending faults, NE-SW trending faults, low angle faults). The lineament data have been prepared by various lineaments from the geological map of Jharia coalfield that have been digitized as a line layer. The fault frequency indicates the infiltration of water into the sub-surface. A high frequency of faults provides an indication of higher infiltration and vice versa. The lineament map along with the litho-stratigraphic map is shown in the Fig. 2.
The study area mainly depends on the rainfall during the monsoon in order to meet the requirements of domestic as well as agricultural purposes, the scarcity of which could lead to acute water crisis resulting in severe drought conditions. The study area is a part of the Permo-carboniferous Gondwana basin. It comprises of lower Gondwana sedimentary formations overlying the Precambrian metamorphics. In the study area, groundwater condition in various litho-stratigraphic units can be described under three broad divisions, viz. weathered formation, fractured formation and abandoned water logged area.
To determine the status of the groundwater table, water level data have been collected from different dug wells of Jharia Coalfield. Water level data from dug wells are taken during pre-monsoon period (May, 2004) and post-monsoon period (November, 2004). Figure 5 shows the location of the dugwells from where water level data at 46 networking stations have been collected. The pre-monsoon and post-monsoon water table elevation maps generated from the dataset are shown in Figs. 6a and 6b.
In the present study, the choice among a set of zones for evaluation of groundwater potentiality has been based upon multiple criteria such as drainage pattern, control of lithological units, steepness of slope, lineament frequency and water table elevation. The process is known as Multi-Criteria Evaluation (Sarkar et al., 2001). For a multi-criteria geospatial modelling, firstly a template has been created by identifying the quadtrees used in the analysis. If a basemap has been assigned to the study area, this function would confine the analysis to the data falling within Class 1 as defined by the basemap and the number of input quadtrees that can be selected is reduced to one less than the total number. A default weight is calculated by dividing 100 by the number of quadtrees used in the overlay and is assigned to each quadtree in the analysis. A default of 0 for each class score is assigned to each quadtree class. Each class is labelled with the short legend title taken from the input quadtree. Different categories of derived thematic maps have been assigned scores in a numeric scale of 0 to 5 depending upon their suitability to hold groundwater. An aggregation of these product values leads to the final weight map.
Mathematically, this can be defined as:
GW = f (Dr, Lin, Lith, Sl, WTE)
where, GW is groundwater, Dr is drainage, Lin is lineament, Lith is lithology, Sl is slope and WTE is water table elevation.
The groundwater potential map value, thus derived is given in the equation:
GWP = Σ Wi CVi with Σ Wi = 1.
where, GWP is the groundwater potential map value, Wi is the probability value of each thematic map, and CVi is the individual capability value.
GWP can be expressed as the summation of:
(0.294* CVLin) + (0.118* CVLith) + (0.235* CVDr) + (0.235* CVWTE) + (0.118* CVSl).
The resultant final weight map indicates the potentiality of groundwater occurrence in the Jharia Coalfield (Fig. 7). To derive this final weighted map, a probability weighted approach (Sarkar et al., 2001) has been adopted that allows a linear combination of probability weight of each thematic map (W) with the individual capability value (CV). Using Baysian statistics, the capability values are calculated from their assigned scores in a numeric scale. These capability values are then multiplied with respective weight of each thematic map (Table 1). This map has then been classified into four categories of potentiality, namely, Excellent, Very Good, Good, Poor and Very Poor.
Results and Discussion
In the Archean metamorphics of the Jharia coalfield, groundwater occurs in semi-confined to confined aquifer condition. Groundwater occurs under unconfined condition in the top weathered mantle of the variegated Barren Measures and the Barakar and Raniganj sandstones except for Talchir shales. This is because the original rocks being nonporous and nonpermeable, even weathering of top layer does not become conducive to groundwater movement, example being Shastrinagar inhabited area where boring of tube well has been unsuccessful. It is under semi-confined condition in the deeper fractures zones that have imparted secondary porosity and permeability in these rocks. The Gondwana sandstone, in general, is known to constitute good aquifers at many places. However, the yield potential of the areas adjoining active mines in the coal belt is poor. With continued dewatering of the mine pits, the neighbouring wells register gradually lowers water levels long before the advent of summer and many of them ultimately get dried up. Thus, the active mines often act as groundwater ‘sinks’. Apart from this, the boring of deep tube wells at many places decreases the water level considerably and causes lowering of water level in the neighbouring wells.
The groundwater potentiality map derived by the multi-criteria evaluation technique reveals distribution of various potential zones of groundwater in and around the Jharia coalfield. The northwestern and southwestern part of the basin shows poor to very poor groundwater potentiality while along the flood plain, river terraces, it shows good to excellent groundwater potentiality. In the southeastern part of the coalfield, groundwater potentiality is good though in reality many areas in the southeastern part show poor groundwater reserve. This may be due to the active mining activities in that part which have disturbed the groundwater reserve in that area. Areas in the northeastern part of the coalfield show good to poor groundwater potentiality. In the eastern side, some areas near the river shows excellent groundwater potentiality.
More than century old coal mining activity in Jharia coalfield has substantially modified the groundwater level, movement and flow direction. Following are the observations of resultant effect of the present day set-up of ground water regime:
- General lowering of ground water level of about 30 m because of 10th level of underground mining activity on an average up to an average depth of 150 to 200 m.
- Re-circulation of pumped out groundwater from mines and discharging to surface drainage system, followed by percolation through fracture system and further recharging to neighbouring mines as well as in the periphery of the same mine.
- Main flow of groundwater in Jharia coalfield is through a networking of existing fault system with 275 faults of varying throws.
- Flood plains, abandoned river channels, valley flats provide potential groundwater zones.
- Generally, 60 to 70 years old goaf filled with water has become part of the present day groundwater regime resulting in high potential source of groundwater that can be exploited for domestic use.
The authors acknowledge the Department of Applied Geology, and Centre of Mining Environment, Indian School of Mines, Dhanbad for the necessary laboratory facilities and to Bharat Coking Coal Limited Dhanbad and Central Ground Water Board Patna for necessary data support.
- Fox, C.S., 1930. The Jharia Coalfield. Memoir Geological Survey of India, vol. 56, 255 pp.
- Mehta, D.R.S. and Murthy, B.R.N., 1957. A revision of the geology and coal resources of the Jharia coalfield, Memoir Geological Survey of India, vol. 84, Part. 2, 142 pp.
- NRIMS, 1995. Report on the soils of Jharia coalfield, Natural Resources Information Management Services, Hyderabad, Part a, pp. 1-5, 12-14, 25-26, 32, 61-68, 79-83.
- Sarkar, B.C., Deota, B.S., Raju, P.L.N. and Jugran, D.K., 2001. A geographic information system approach to evaluation of groundwater potentiality of Shamri micro-watershed in the Shimla taluk, Himachal Pradesh., Journal of the Indian Society of Remote Sensing, vol. 29, no. 3, pp. 151-163.
- Schumm, S.A., 1956. Evolution of drainage system and slopes in badlands at Perth Amboy, New Jersey, Bulletin Geological Society of America, 67, pp. 597-646.
- Verma, R. P., Jaipuriar, A. M., Paul, P. R., 1989. Compendium on updated and revised geology of Jharia coalfield. Central Mine Planning and Designing Institute Ltd., Ranchi, 282 pp.
Fig. 1 Digital Elevation Model (DEM) of Jharia coalfield.
Fig. 2 Litho-stratigraphic and Lineament map of Jharia coalfield.
Fig.3 Slope map of Jharia coalfield.
Fig. 4 Drainage network of Jharia coalfield.
Fig. 5 Location of dugwells in Jharia coalfield.
Fig. 6a. Water table elevation map of pre-monsoon period.
Fig. 6b. Water table elevation map of post-monsoon period.
Fig. 7. Groundwater potentiality map of Jharia coalfield.