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

P. K. Sikdar ¹

Affiliations
1 Center for Study of Man and Environment, CK- 11 Sector 11, Salt Lake City, Calcutta - 700 091, IN

Abstract

The twin city of Calcutta-Howrah is underlain by a succession of Quaternary sediments consisting of clay, silt, fine to coarse sand and occasional gravel. Below these sediments at depths beyond 296 m, there is a thick sequence of Pliocene clay. The top clay bed of Quaternary sequence contains peaty intercalations indicating bog or marshy condition at depths of 2-5 m and 12-12.6 m. The peat layers were deposited during the period c.3990 years B.P. to c. 7030 years B.P. Grain size analysis of the sandy horizons indicates that the sands were deposited in a fluvial environment. Lithofacies analysis of the Quaternary sediments indicates that the gravelly sand horizons occurring in E-W and NNE-SSW trends in the depth range of 80-120 m are potential aquifer zones. These two trends of deposition of very coarse sediments probably indicate the route of sediment movement where high energy condition prevailed. The sandy sediments at a depth span of 24 to 81 m are yellowish to brownish coloured suggesting oxidising conditions of deposition. The sediments occumng above and below this horizon are grey to light grey in colour indicating reducing conditions of deposition. The over-extraction of groundwater from the aquifer has resulted in the change of the groundwater flow pattern from an "open" system in 1956 to a "closed" one in 1993 with the formation of a groundwater trough in the south-central part of Calcutta. Rased on depth of the aquifers, status of the piezometric surface, lithofacies and grain size ratio, an aquifer development plan has been proposed for a sustainable groundwater development in the twin city.

Keywords

Groundwater, Lithofacies, Aquifer Management, Calcutta and Howrah.

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Dipankar Saha ¹, Y. R. Dhar ¹, P. K. Sikdar ²

Affiliations
1 Dept. of Applied Geology, Indian School of Mines, Dhanbad, IN
2 Dept. of Environment Management, Indian Institute of Social Welfare and Business Management, Kolkata, IN

Abstract

The study area is spread over 1950 sq. km and covers apart of Pleistocene deposists in the Ganga Plain. A two tier aquifer system made up of sands of various grades occurs in the area and caters to the entire water demand to the tune of 0.12 MCM/sq. km/year. The top 30 m of the alluvial deposits are dominated by clay, sandy clay, silt with thin lenses of sands. The latter constitutes the Shallow Aquifer, occurring under unconfined condition. The Deep Aquifer is made up of interconnected sand layers below 30 m depth, forming a potential zone, where groundwater occurs under semiconfined condition. Sluggish hydraulic conductivity in Shallow Aquifer results in higher mineralization of groundwater than In Deep Aquifer. Principal Component Analysis with 10 chemical constituents, and plots in Expanded Durov Diagram indicate distinctly different geochemical processes in Shallow and Deep Aquifers. In Shallow Aquifer the processes shaping up the chemical character of groundwater are non-exchange, sediments dissolution return seepage from irrigation water and rain-water lnfiltration. But the major processes in Deep Aquifer are leakage from Shallow Aquifer, followed by ion-exchange and weathering of silicate minerals. In the process of ion-exchange, Na⁺ from the aquifer matrix dominated by clays and sandy clays replaces Ca⁺² in groundwater, resulting in formation of patches of calcium carbonate nodules.

Keywords

Hydrochemistry, PCA, Ion-Exchange, Leakage, South Ganga Plain, Bihar.

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P. K. Sikdar ¹, S. K. Adhikari ², B. B. Bhattacharya ³

Affiliations
1 Department of Environment Management, Indian Institute of Social Welfare and Business Management, Kolkata - 700 073, IN
2 Central Groundwater Board, Kolkata - 700 091, IN
3 S. N. Bose National Center for Basic Sciences, Kolkata - 700 098, IN

Abstract

Nawapara and Kalahandi districts located in the south western part of Orissa are drought prone areas. Geologically the area comprises Eastern Ghats Group and Purana (Chhattisgarh) Group. Laterite occurs as capping over the older formation and alluvium of Recent origin occurs as thin discontinuous pockets in and around the rivers. Based on visual interpretation of Landsat imagery four sets of prominent lineaments could be identified. The trends of lineament are broadly NE-SW, NW-SE, E-W and N-S. The lineament trending NE-SW is the most prominent one.

Groundwater in the districts occurs under water table condition mainly in the weathered mantle and narrow zones of unconsolidated sediments along major river valleys. The water yielding fracture zones are generally restricted within a depth of 100 m and groundwater occurs under semi confined to confined condition. The average transmissivity of the shallow and deeper aquifers is 36.8 m²/day and 53.4 m²/day respectively. The groundwater flow directions are mainly from SW to NE, NW to SE and SE to NW. Long-term water table fluctuation indicates that in the northern and central parts of the study area the water table during April 1997 has gone down compared to April 1988. On the other hand in the southeastern part the water table in April 1997 has risen. The long-term rise in the water table has taken place in khondalite to the tune of 0.37 m, in granite gneiss there is a long-term fall in the water table by 0.63 m and in charnockite there is practically no fluctuation of the water table. On an average there is a fall in the water table during this period by an average of 0.39 m, which indicates increase use of groundwater during the pre-monsoon periods. Productivity frequency plots indicate that there is no significant difference in the productivity values of the wells tapping at various depth ranges. But it seems that the productivity of wells is relatively on the higher side in the 50-100m depth followed by 100-150 m depth span.

Lineament density modelling indicates that the major lineament density axes show NE-SW and NW-SE trends. These two trends indicate that the regional ground water flow system is controlled mostly by the Tel river. Lineament density in most of the area is low i.e. below 0.2 km/sq. km. To demarcate potential aquifer zones for future development, 'technique of thematic overlay has been utilized using lineament density and long-term water table fluctuation. The overlay procedure indicates that in general the potentiality of the aquifer for future development is medium. In the Nawapara district the potentiality of the aquifer for future groundwater development is more than in Kalahandi district. Therefore in Kalahandi district artificial recharge of groundwater including roof top rainwater harvesting should be carried out to overcome the shortage of water for drinking purpose.

Keywords

Groundwater, Water Table, Lineament, Lineament Density Axis, Potential Aquifer Zones, Nawapara And Kalhandi Districts, Orissa.

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P. K. Sikdar , S. Das ¹

Affiliations
1 18 Madhusudan Nagar, Unit 4, Bhubaneswar - 751 001, IN

Abstract

No Abstract.

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