Dewashish Kumar

Efficacy of electrical resistivity tomography technique in mapping shallow subsurface anomaly

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.

Linking the morphology of fluvial fan systems to aquifer stratigraphy in the Sutlej‐Yamuna plain of northwest India

The Indo-Gangetic foreland basin has some of the highest rates of groundwater extraction in the world, focused in the states of Punjab and Haryana in northwest India. Any assessment of the effects of extraction on groundwater variation requires understanding of the geometry and sedimentary architecture of the alluvial aquifers, which in turn are set by their geomorphic and depositional setting. To assess the overall architecture of the aquifer system, we used satellite imagery and digital elevation models to map the geomorphology of the Sutlej and Yamuna fan systems, while aquifer geometry was assessed using 243 wells that extend to ∼200 m depth. Aquifers formed by sandy channel bodies in the subsurface of the Sutlej and Yamuna fans have a median thickness of 7 and 6 m, respectively, and follow heavy-tailed thickness distributions. These distributions, along with evidence of persistence in aquifer fractions as determined from compensation analysis, indicate persistent reoccupation of channel positions and suggest that the major aquifers consist of stacked, multistoried channel bodies. The percentage of aquifer material in individual boreholes decreases down fan, although the exponent on the aquifer body thickness distribution remains similar, indicating that the total number of aquifer bodies decreases down fan but that individual bodies do not thin appreciably, particularly on the Yamuna fan. The interfan area and the fan marginal zone have thinner aquifers and a lower proportion of aquifer material, even in proximal locations. We conclude that geomorphic setting provides a first-order control on the thickness, geometry, and stacking pattern of aquifer bodies across this critical region.

Hydrogeological and geophysical study for deeper groundwater resource in quartzitic hard rock ridge region from 2D resistivity data

Electrical resistivity method is a versatile and economical technique for groundwater prospecting in different geological settings due to wide spectrum of resistivity compared to other geophysical parameters. Exploration and exploitation of groundwater, a vital and precious resource, is a challenging task in hard rock, which exhibits inherent heterogeneity. In the present study, two-dimensional Electrical Resistivity Tomography (2D-ERT) technique using two different arrays, viz., pole–dipole and pole–pole, were deployed to look into high signal strength data in a tectonically disturbed hard rock ridge region for groundwater. Four selected sites were investigated. 2D subsurface resistivity tomography data were collected using Syscal Pro Switch-10 channel system and covered a 2 km long profile in a tough terrain. The hydrogeological interpretation based on resistivity models reveal the water horizons trap within the clayey sand and weathered/fractured quartzite formations. Aquifer resistivity lies between ∼3–35 and 100–200 Ωm. The results of the resistivity models decipher potential aquifer lying between 40 and 88 m depth, nevertheless, it corroborates with the static water level measurements in the area of study. The advantage of using pole–pole in conjunction with the pole–dipole array is well appreciated and proved worth which gives clear insight of the aquifer extent, variability and their dimension from shallow to deeper strata from the hydrogeological perspective in the present geological context.

Geophysical Characterization of Hard Rock Aquifers

Geophysics plays a major role for characterizing the hard rocks for groundwater studies. The qualitative and quantitative application has increased since past few years due to rapid development and advancement in microprocessors and associated numerical modelling solutions. Although geophysics has ability to probe deep earth interior (say >1000 m), but its application for groundwater studies is usually restricted to depths less than and around 250 m below the surface. These include mapping the depth and thickness of aquifers, mapping aquitards or confining layers, locating fractures and fault zones and mapping contamination to the groundwater such as that from saltwater intrusion. The theoretical and practical background to geophysics has been extensively reviewed and can be studied in standard texts on the subject, for example Kearey & Brooks (1991); Telford et al. (1976); Parasnis (1979); Dobrin (1976); Grant and West (1965); Reynolds (1997); Miller et al. (1996); Murali et al. (1998); etc.

Reconstruction of Water Level Time Series in an Aquifer Using Geostatistical Technique

Water level is the only parameter that is measured from the aquifer directly and also depicts the dynamics of the aquifer. It is measured normally in static condition but in spite of all precautions taken while measuring the water level there are data gaps. In aquifer modelling, particularly in the calibration of the model in transient condition, a sufficiently long time series of water level is required on all the wells that are used as control points. So to deal with two different situations that are to have a sufficiently long time series of water level at any well, geostatistics was applied to fill the data gap, at the time when the water level could not be measured. With this we obtained a mixed time series of water level at any well containing measured water levels without any error term and the estimated water level with estimation errors at uniform frequency.

Integrated geophysical and geological studies for mineral prospecting in Betul-Chhindwara belt (BCB), Central India

Integrated study combining high resolution electrical resistivity tomography and time domain induced polarization was carried out in Betul-Chhindwara belt Madhya Pradesh, Central India in order to evaluate and delineate the polymetallic sulphide mineralization, its nature, type of deposit and depth. On interpretation of the models results clear cut anomalies revealed showing chargeability ∼2 to 54 mV/V up to a maximum depth of 131m. This range of chargeability signify signature of metallic conductor. Nevertheless the basement rock is clearly mapped, showing substantial resistivity contrast. In addition detailed analysis of the integrated results from geology, geochemistry and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy resulted from in situ rock samples shows good correlation with resistivity and IP results. This integrated study confirms the presence of conducting sulphide mineral ore body and the results and findings need test drilling at the geophysical anomalous site(s) to confirm the depth persistence and evaluate the metallic conductor.

Application of Geostatistics in Optimal Groundwater Monitoring Network Design

Appropriate and adequate data are essential for the success of any scientific study such as groundwater hydrology. Scarcity of data and their collection on isolated location mainly in the field of hydrogeology makes it necessary to adopt special procedures such as geostatistical estimation technique for bridging the gap between field measurements and data requirements. However, these estimations are based on a crucial criterion of the structural analysis known as variography and obtaining a true and representative variogram is extremely ambiguous from limited field data. Cross-validation test to determine a representative and optimal variogram as well as to validate the other assumptions has been found very useful in case of hydrogeological parameters.

Efficient Conjunctive Use of Surface and Groundwater Can Prevent Seasonal Death of Non-Glacial Linked Rivers in Groundwater Stressed Areas

The surface and groundwater system is an interdependent system. In the case of alluvial plains, they are best manifested by the relationship between a river and groundwater system. This relationship is vibrant and dynamic in rain-fed rivers or the non-glacial linked rivers. It has been typically observed that many a case such rivers originate from lesser elevation and in downstream stretches; during summers, their flow is maintained by groundwater contribution. In groundwater stressed regions, often these rivers get disconnected from aquifer. Thus there could be different levels of stream-aquifer interaction during monsoon and non monsoon seasons. In this context, the article examines effect of long-term groundwater abstraction on such river flows in a conceptual framework. It also proposes efficient conjunctive use of surface and groundwater to prevent death of such rivers.

Delineation of groundwater resources using electrical resistivity tomography

Chandrabhaga basin of the Nagpur district is a part of the drought prone Vidarbha region of Maharashtra, India. This region is facing acute shortage of water for drinking and irrigation purposes. The basin is located at the eastern fringe of the Deccan traps consisting of volcanic rocks. Presently, dug wells penetrating composite layers of the weathered mantle and highly fractured rocks overlying stratified basaltic lava flows are the main source of water supply. However, water available in the dug wells is inadequate to meet the ever increasing demand for water causing considerable economic losses to the farming community. In this work, we present the results of an electrical resistivity tomography (ERT) survey carried out in the basin for the delineation of groundwater potential zones. Validity of the hydrogeological setup obtained from the ERT results has been confirmed by bore well drillings at two investigated sites. The study demonstrates the efficacy of the ERT technique in delineation of groundwater potential zones in the hydrogeologically complex basaltic terrain of the Deccan traps.

Gold - sulphide mineralization in ultramafic-mafic-granite complex of Jashpur, Bastar craton, central India: Evidences from geophysical studies

Time Domain Induced Polarization (TDIP) investigation in conjunction with high resolution electrical resistivity tomography surveys carried out at seven sites along a 5.2 km line in Jashpur and Raigarh districts of Chhattisgarh State yielded promising results leading to the demarcation of mineralized zones. These sites are confined to ultramafic-mafic-felsic intrusive complexes representing gabbro-pyroxenite-granite sequences characterized by gold - sulphide mineralization. Two dimensional (2D) geophysical datasets yielded interesting results and a good correlation is found between 2D inverted resistivity tomography and time domain induced polarization (IP) models. Both high resistivity-high chargeability as well as low resistivity-high chargeability conditions have been inferred from these datasets. This observation is consistent with conductive metallic mineralization. Interpretation of the Pharsabahar-Pandripani site, reveals a chargeability magnitude of 9-14 mV/V, which represents a strong metallic conductor associated with gold-sulphide ore body. The results at Samarkachar site are equally significant, showing a good correlation with the presence of a low resistivity and high chargeability zone. Hence, the present study suggests a new scope for application of resistivity and IP tomography surveys for mineral prospecting in favourable geological settings.