S. K. Nag

Morphometric analysis using remote sensing techniques in the chaka sub-basin, purulia district, West Bengal

Remote sensing techniques using satellite imagery have proved to be an indispensible tool in morphometric analysis and groundwater studies. In the present area, morphometric analysis using temote sensing techniques have been carried out in Chaka river sub-basin of Manbazar Block, Purulia district, West-Bengal, which is one of the most drought affected area in West-Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu). Form factor (Rf), Circulatory ratio (Rc), and Drainage density. The morphometric analysis suggests that the area is covered by fractured, resistant, permeable rocks, the drainage network not so affected by tectonic disturbances.Using satellite imageries of LANDSAT and IRS, different hydrogeomorphological units have been delineated. The study shows that moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration.

Influence of rock types and structures in the development of drainage network in hard rock area

Remote sensing techniques has proved to be an extremely useful tool in morphometric analysis and groundwater studies. Remote sensing techniques with an emphasis on lineament identifications can play a great role in groundwater prospecting in semi-arid hard rock areas of Purulia district. In the present study, morphometric analysis using remote sensing technique has been carried out in parts of Baghmundi block, Purulia district, West Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu), Form factor (Rc), Circulatory ratio (Rc), and Drainage density (D). The morphometric analysis suggests that fractured, resistant, permeable rocks cover the area, the drainage network not so affected by tectonic disturbances. Using satellite imageries of two dates of IRS, different hydrogeomorphological units have been delineated. Among different hydrogeomorphic units (i) very shallow weathered pediment and (ii) Structural hills/ residual hills/inselbergs have very poor ground water prospects, while moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration.

Application of lineament density and hydrogeomorphology to delineate groundwater potential zones of Baghmundi block in Purulia District, West Bengal

Groundwater being a valuable resource in today’s world needs proper evaluation and management for overall development within the region for its judicious use. The Baghmundi Block of Purulia district, West Bengal is within the hard rock terrain of Ayodhya hills and Matha Protected forest. The groundwater in this region is confined within the fracture zones and weathered residuum. Hydrogeomorphologically, the entire area is classified into following categories such as - i) Very shallow weathered pediment, ii) Moderately weathered pediment, iii) Valley fills, iv) Erosional gullies, v) Lateritic Upland and vi) Accumulation gullies.The hydrogeomorphic map of the area prepared by Department of Science and Technology, Govt. of West Bengal has been digitized for the present study. The lineament map has been prepared from the satellite imagery. The lineament map has also been digitized for the present study. From this the lineament density contour map has been prepared. An integrated remote sensing and Geographic Information System (GIS) based methodology has been used for the delineating Groundwater potential zones in the study area. Here the Geomorphology and Lineament density maps are overlaid following the Weighted Index Overlay Method, which delineates groundwater potential zones.

Behaviour of fractures in hard rocks — A study by surface geology and radial VES method

Abstract In hard rock terrain the exploration of groundwater is essentially the detection of thick weathered residuum or of zones of intense jointing and fracturing and hence is extremely complex. The present study incorporates the radial vertical electrical sounding (VES) method in understanding the behaviour of rock fracturing at shallow depths in an area of Purulia district, West Bengal, India. The results show that the trends of joints and fractures derived from the radial VES are in striking agreement with those obtained from detailed measurement on the rock exposures. This study further reveals that a saturated fractured system exists at shallow depth and occurs at places in more than one horizon. In this area, granites have developed predominant joints and fractures trending along NESW and E-W directions, while in amphibolites and metabasics the trends are consistently along N-S and WNW-ESE directions. An attempt has also been made to infer the subsurface rock types from this integrated study.

Variation in groundwater levels and water quality in Chhatna Block, Bankura district, West Bengal — a GIS approach

Ground water levels and quality in Chhatna Block of West Bengal were studied based on different indices for irrigation and drinking purposes. A detailed hydrogeological investigation was carried out to have an overall idea of the aquifer system of the area. The ground water occurs under shallow to moderately deep water table condition. The groundwater is stored mostly in the weathered residuum and fractured — hard rock. Sodium absorption ratio (SAR), soluble sodium percentage (SSP), residual sodium bi-carbonate (RSBC), electrical conductance (EC), magnesium adsorption ratio (MAR) Kelly’s ratio (KR), total hardness (TH), permeability index (PI) were calculated as derived parameters, to investigate the ionic toxicity. From the results of chemical analysis, it was revealed that the values of Sodium Adsorption Ratio indicate that, ground water of the area falls under the category of low sodium hazard. So, there was neither salinity nor toxicity problem of irrigation water, and hence the ground water can safely be used for long-term irrigation. Plotting of analytical results of the groundwater collected from different areas in Piper’s trilinear diagram (1944) indicate that, the waters of the study area fall under fresh and sulphate rich region of the rhombus.

Hydraulic significance of fracture correlated lineaments in precambrian rocks in Purulia district, West Bengal

Filter analysis of lineaments in Precambrian metamorphic rocks was used to delineate fracture-correlated lineaments and hydraulically significant fractures. The unfiltered analysis technique fails to show correlation between major lineaments and fractures. Domain-based and discrete filtering techniques successfully identify fracture-correlated lineaments within the brittle-ductile shear zone in conjunction with fractures characterized by high fracture frequencies (>10/m). The locales of hydraulically significant fractures can thus be assessed if the geological controls governing the spatial distribution of fracture frequencies are computed using structural domain approach. The concurrence of fracture-correlated lineaments and hydraulically significant fractures within the brittle-ductile shear zone is evident.

The origin of andesite from Rajmahal traps, eastern India: A quantitative evaluation of a fractional crystallization model

Abstract Major-element mass balance calculation supplemented by trace-element modelling indicates that the andesite and tholeiitic andesites in the northwestern portion of Rajmahal traps, Bihar, eastern India might have originated by about 50% fractional crystallization of a quartz-tholeiitic magma (represented by the Rajmahal traps), leaving a cumulate phase of plagioclase (An 67–74), clinopyroxene (augite), orthopyroxene (hypersthene), and magnetite in the proportion 23.19:20.38:2.67:3.76. Scanty occurrences of coarse-grained gabbroic rocks within the tholeiitic traps of adjacent areas have been noted; modal, major- and trace-element compositions of these rocks show marked similarities with those of the computed cumulate phase and furnish support to the fractionation model. The temperatures and oxygen fugacities estimated from coexisting iron-titanium oxide equilibration range from 920 to 955°C, and from 10−10.85 to 10−10.35 bar, respectively, for the andesites. The temperature estimated from the two-pyroxene geothermometer for the trap-tholeiites is c. 1120°C, while the pressure estimated from the olivine-orthopyroxene-quartz assemblage is of the order of 9 kbar. However, the oxygen fugacities estimated from the two-oxide geothermometer range from 10−11.1 to 10−10.45 bar and the temperatures from 978 to 1015°C, which is possibly the quenching temperature of the tholeiitic lava.