Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Sanjeev Kumar ¹, Dewashish Kumar ¹, Shakeel Ahmed ¹

Affiliations
1 lndo French Centre for Groundwater Research, National Geophysical Research Institute. Hyderabad - 500 007, IN

Abstract

Groundwater resources are extremely important in Rajasthan as almost the entlre region lies in arid/semi-arid tropics especially in the hard rock areas. The recharge being less due to scanty rainfall. The study has revealed the advantages of remotely sensed data in identifying the prospects of groundwater in geologically and structurally complex terrain. Remote Sensing (RS) and Geographic Information System (GIS) is a dynamic tool for facilitating the generation and use of thematic information; has been applied to know the groundwater potentiality of the Upper Kali Sindh Chauli watershed in the Jhalawar district of Rajasthan, India. The role of different parameters namely geology, geomorphology, structures, lineaments, slope, land use and land cover, digital elevation model, etc. have been emphasized for delineation of the groundwater potential Zones. The groundwater potentia1 zone map was prepared based on the visual interpretation of satellite Geocoded data of IRS-ID, LISS III, FCC and the topographic maps on 1:50,00 scale. In thc study area major lineaments are identified from the satellite data interpretation, which are surface manifestation of some structural features in the bedrocks as fractures and joints. The study area is divided into mint-watershed and micro-watershed on the basis of area and stream channels. Groundwater prospects are controlled by the lineaments/joints, as the lithology is not much suitable for groundwater development. Ultimate groundwater prospecting map indicatea variable groundwater potentiality in the area i.e. good, moderate, limited, and poor and based on these categorization the depth of wells are recommended for drilling.

Keywords

Topographic map, Satellite data, Mini-Watershed, Micro-Watershed, RS and GIS, Jhalawar, Rajasthan.

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Dewashish Kumar ¹, N. S. Krishnamurthy ¹, Shekeel Ahmed ¹, S. C. Jain ¹, R. L. Dhar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Mise-a-la-masse technique has been applied to map water filled fracture1 struck in bore wells in a small watershed near Hyderabad. The area consists of hard crystalline rock mainly granite where groundwater is mostly tapped from iractured rock. In the watershed, 25 wells have been drilled fairly distributed over the area on the basis of results of Vertical Electrical Soundings (VES) to study the groundwater conditions in the weatheredffractured aquifer system. Mise-a-la-masse and Spontaneous Polarization (SP) investigations were carried out at five out of these 25 sites, to delineate the lateral extension of fractures. The anomalies are clearly indicative at four locations and some indication is seen at the fifth location. Two bore wells drilled on the basis of these results have encountered fractures at the same depth as at the experimental site. It is concluded that mise-a-la-masse technique supplemented with S.P. investigations could be helpful in delineating the extension of fractures.

Keywords

Mise-a-la-Masse, SP, Electrical Mapping, Fractures in Hard Rock, Maheshwaram Watershed, Andhra Pradesh.

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N. S. Krishnamurthy ¹, V. Ananda Rao ¹, Dewashish Kumar ¹, K. K. K. Singh ², Shakeel Ahmed ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 606 (Council of Scientific and Industrial Research), IN
2 Central Institute of Mining and Fuel Research, Dhanbad - 826 001, IN

Abstract

Exploration and exploitation of coal seams is one of the major resources for the energy sector in any country but at the same time water filled voids/water logged areas in the old workings of these seams are very critical problems for the coal mining industry. In such situations, disasters like inundation, landslides, collapsing of the old seams may occur. In this regard, it is necessary to find out the water saturated/water filled voids and zones in the mining areas. Since no established technique is available to find such zones, an experimental study using Electrical Resistivity Imaging (ERI) has been carried out in one of the coal mining areas near Dhanbad, to find out the feasibility of finding the barrier thickness and the water logged area in underground coal mines. The area under study forms part of Jharia coalfield in Dhanbad district, Jharkhand state. The coal bearing rocks of Barakar Formation of Lower Permian age (Gondwana period) occur in the area under a thin cover (10 m to15 m) of soil and or alluvium. Coal bearing Barakar Formations consist mainly of sandstone of varying grain size, intercalation of shale and sandstone, grey and carbonaceous-shale and coal seams.

Since the water saturation reduces the resistivity of a formation to a large extent, water filled voids and old coal workings are expected to have significant resistivity contrast with the surrounding host rock. Hence, ERI technique was applied in such an environment as this technique uses high-density data acquisition both laterally and vertically by using multiple number of electrodes. Along with ERI, mise-a-la-masse (also called charged body) technique was also employed at one of the promising sites to find out the connectivity of water logged areas and also detection of these old workings from the surface measurements was analyzed. The interpreted 2D resistivity sections have clearly indicated the water bearing zone(s) along the profile which was well confirmed with the existing water level in the nearby borewells. On the other hand, this technique did not identify the size of the coal pillar and gallery (air filled voids), which might be due to the small size of the voids (i.e. about 2 m × 2 m) below a depth of 15m and more but have indicated altogether as a high resistive zone ranging from 600-1000 Ohm-m.

Keywords

Coal Seams, Water Filled Voids, Electrical Resistivity Imaging, Jharia Coalfield, Dhanbad, Jharkhand.

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Dewashish Kumar ¹, S. Thiagarajan ¹, S. N. Rai ¹

Affiliations
1 Council of Scientific and Industrial Research (CSIR) - National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN

Abstract

Exploration of Geothermal resources is important from energy point of view. Western margin of volcanic Deccan traps, also known as Western Ghats, is characterized with the presence of numerous hot springs. The resistivity contrast for the geothermal reservoir rock and the surrounding host rock is significantly high in volcanic terrain which is the case of present study. In such cases the resistivity associated with geothermal reservoirs usually varies from <5 to 15 Ohm-m regardless of how high resistivity is outside the reservoir zone. Direct current (DC) resitivity method is proved to be more suitable method for delineation of groundwater reservoirs. The present work describes the results of electrical resistivity tomography survey carried out at four hot spring sites located at Unhavare (Khed), Tural, Rajwadi and Aravali villages of Chiplun taluk in Ratnagiri district of Maharashtra for delineation of the geothermal reservoirs and associated geological features like faults and fractures responsible for vertical movement of geothermal water with the sole purpose of harnessing geothermal energy. In addition to this, the present study is also aimed to delineate the groundwater reservoirs with normal temperature for exploration purpose to meet the local water supply demand. The interpreted results of the field data suggest the presence of two potential geothermal reservoirs at Unhavare (Khed) and one each at Tural and Aravali. Potential groundwater zones with normal temperature are also delineated for groundwater exploration at Rajwadi and Aravali sites.

Keywords

Geothermal Energy Resource, Electrical Resistivity Tomography, Deccan Traps, Hot Springs, Faults, Maharashtra.

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Dewashish Kumar ¹

Affiliations
1 CSIR-National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Electrical Resistivity Tomography is a versatile, fast and cost effective technique for mapping the shallow subsurface anomaly. It covers a wide spectrum of resistivity ranging from <1 Ohm.m to several thousands of Ohm.m. In this paper applications and utility of two-dimensional Electrical Resistivity Tomography (ERT) technique are discussed to look into huge data density coverage, different signal strengths of data from subsurface and their implications in resolving the aquifer zones, related geological structures etc. of the substratum ranging from alluvium to tectonically disturbed hard rock ridge region of the country. The major advantages and flexibility of ERT over conventional resistivity methods are also discussed.

Keywords

Electrical Resistivity Tomography, Subsurface Mapping, Groundwater Hydrology.

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