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

P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai 600 025, IN

Abstract

Rasipuram and surrounding areas in Namakkal district of Tamil Nadu are known to be a zone of historically low groundwater levels, caused by large scale abstraction of groundwater. Study of hydrogeological conditions in the area has helped in identifying parameters that characterise an over-exploited zone. Majority of the dug wells in the area has been rendered unproductive due to lowered groundwater levels. The density of borewells is very high in certain pockets and the depths have been steadily increasing over the years. In the year 1998 the average depth of agricultural borewells was 192m, while that of drinking water borewells was 135m. It is estimated that if the present trend continues, the average depth of agricultural borewells in the year 2020 may reach 270m. The average yield (at the time of drilling) of agricultural borewells, is seen to be approximately the same despite the increasing depths. Over-exploitation of groundwater in the area has caused deterioration in the quality of groundwater with high levels of total hardness noticed in zones having deep groundwater levels. The role of baseflow in maintaining the quality of groundwater is discussed.

Keywords

Groundwater, Pollution, Over-Exploitation, Rasipuram Area, Tamil Nadu.

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P. N. Ballukraya ¹, R. Ravi ¹

Affiliations
1 Department of Applied Geology, University of Madras, Madras - 600 025, IN

Abstract

Subsurface lithological mapping has shown the presence of a crystalline rock ridge along the east coast of Madras City, and the aquifer above this ridge shows some characteristic features distinct from those on the western side. The presence of a fresh water ridge along the coast has checked the intrusion of sea water even though water levels are as low as 3m below mean sea level at certian places. Several pockets of brackish ground water have been identified which have been established as due to the presence of tanks and depressions therein. Identification of marine sands below the alluvium in some places gives an idea of the marine transgression that had occurred during Tertiary periods. Studies indicate that most of the alluvium is of estuarine origin, and that the crystalline ridge along with part of the east coast may be updergoing slow uplift.

Keywords

Hydrogeology, Madras, Tamil Nadu.

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P. N. Ballukraya ¹

Affiliations
1 Dept. of Applied Geology, University of Madras, Madras - 600 025, IN

Abstract

Over a period of 15 years, as many as 84 bore wells were put into operation within an area of 160 hectares. The consequent groundwater over-exploitation led to serious decline in water levels as well as depth to producing zones resulting in the failure of a large number of borewells. The initial trend of increasing area under groundwater irrigation got reversed due to reduced availability of water. The cropping pattern also changed along with groundwater extraction pattern: from predominantly cereals to cash crops. The depth of borewells drilled has been on the increase each year as shallower aquifers dried up. The yield fluctuation in the pre-and post-monsoon periods has indicated that recharge is largely restricted to about 60m depth and therefore, the optimum depth of borewells in the study area should not exceed this limit. The present practice of tapping deeper fracture aquifers is a case of groundwater mining, without any aonual replenishment occurring and will lead to severe problems in the near future.

Keywords

Groundwater, Over-Exploitation, Karnataka.

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P. N. Ballukraya ¹, R. Ravi ¹

Affiliations
1 Department of Applied Geology, University of Madras, Guindy Campus, Chennai, 600 025, IN

Abstract

Hydrogeochemical characterisation is a very important aspect of groundwater management. The unconfined aquifer of Chennai city is heavily exploited for meeting the water requirements of the city. Hydrogeochemical investigations carried out showed the existence of diverse hydrogeochemical facies of groundwater. Analysis of the data indicates that the quality of groundwater is related to hydrogeological environment, both in the present and the geological past. Relationship between water level fluctuations and groundwater quality in the area has been established and this is controlled by the lithology of the host rock and overlying material. The enrichment of various ionic constituents in groundwater is controlled by recharge-discharge processes as well as the local environment. Increase of TDS in groundwater after the recharge is observed in predominantly clayey areas while in sandy aquifers, it is seen to decline with recharge. The hydrogeochemistry of the groundwater shows that most of Chennai area can be classified as recharge area pointing to the dominance of vertical recharge processes.

Keywords

Groundwater Management, Hydrogeochemistry, Unconfined Aquifer, Chennai.

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P. N. Ballukraya ¹, R. Ravi ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai 600 025, IN

Abstract

Hydrogeological studies of the groundwater in Chennai area have shown that the alluvial aquifers have several geochemical facies with distinct characteristics. Factor analysis of the data has been helpful in characterising these facies, since it is noticed that the factor 1 measures salinity, hardness and alkalinity, while factor 2 measures pollution. It is observed that lithology, land use and hydraulic characteristics exercise significant control on the geochemistry of groundwater. The behaviour of groundwater quality in coastal areas, river banks and surface reservoirs is also well explained by factor scores and many of these form distinct hydrogeochemical facies. The study further shows that the geochemistry of the groundwater in these categories gets much more distinct in the pre-recharge periods indicating the effectiveness of the rock-water interaction in the aquifers.

Keywords

Groundwater, Geochemistry, Factor Analysis, Chennai.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology University of Madras, A. C. College Campus Guindy, Chennai - 600 025, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹, V. S. Singh ²

Affiliations
1 Department of Applied Geology, University of Madras, Chennai, IN
2 NGRI, Hyderabad, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology University of Madras, Chennai - 600 025, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai - 600 025, IN

Abstract

Crop water requirement and rainfall recharge factor were used to estimate the recharge and discharge in the over-exploited terrain near Rasipuram. The water balance study shows that the level of groundwater utilization is well over 100%, reaching levels as high as 225%. The spatial pattern of groundwater utilization shows good correspondence with dynamic groundwater level pattern in the area. A comparison of the two indicates the possibility of the presently existing groundwater trough enlarging and moving eastwards in the future, if the present day pattern of groundwater abstraction continues.

Keywords

Groundwater Balance, Over-Exploitation, Fracture Aquifer, Rasipuram, Tamil Nadu.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai - 600 025, IN

Abstract

Presence of a hydrogeological barrrel boundary was identified from the interpretatron of time-drawdown data obtained by conducting pumping test in an area underlain by hard rocks Interpretation of electrical resistivity data also confirmed that a geological boundary exists in the zone identified as barrier boundary, indicating a role for resistivity surveys in the characterization of hard rock aquifers.

Keywords

Bounded Aquifer, Pumping Test, Resistivity Investigations, Alathur Area, Tamil Nadu.

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N. Lakshmi Narayana ¹, P. N. Ballukraya ², K. S. Subramanian ³

Affiliations
1 Geohouse, H.No.2-4-38/C/2, Road No.2, Adarsh Nagar, Nagole, Hyderabad - 500 068, IN
2 Department of Applied Geology, University of Madras, Guindy Campus, Chennai - 600025, IN
3 Plot 283, 17th East Street, Kamraj Nagar, Chennai - 600 04, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹

Affiliations
1 Department of Applied Geology, University of Madras, Guindy Campus, Chennai - 600 025, IN

Abstract

Results of high-Density vertical electrical soundings in an over-Exploited area show that the borewell yields are not generally correlatable with any of the geoelectrical parameters. Many of the lineaments mapped from satellite imageries could be identified from geoelectrical profiles/Sections, but the same could not be done from spatial distribution maps of either hydrogeological or geoelectrical parameters. Two lineaments could be identified from the depth to bedrock map, though wells along these lineaments do not necessarily have higher yields. It appears that most of the so-Called lineaments mapped from satellite images/Aerial photographs are in reality, not structures controlling groundwater occurrence and movement, at least in an over-Exploited area, where the water-Bearing zones are at considerable depths. However, the usefulness of both the techniques in identifying deep fractured rock zones is established from the results of the study. In view of the pronounced inhomogeneity present in hard rock areas, it is clear that the soundings must be as close as possible to each other in order to get a clear picture of the sub-Surface.

Keywords

Groundwater, Lineaments, Resistivity Investigations.

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P. N. Ballukraya ¹

Affiliations
1 Dept. of Applied Geology, University of Madras, Guindy Campus, Chennai - 600 025, IN

Abstract

No Abstract.

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P. N. Ballukraya ¹, R. Ravi ¹

Affiliations
1 Department of Applied Geology, University of Madras, Chennai - 600 025, IN

Abstract

Hydrogeological investigations along the Chennai (Madras) coast showed that groundwater levels are lower than mean sea level, often as much as -3 to -6m. However, the quality of groundwater in the near-surface unconfined aquifer, tapped by shallow wells, is reasonably fresh, though deeper wells show distinct signs of sea-water intrusion. Presence of fresh water below mean sea level in the absence of positive fresh water head is not possible in a coast line having hydraulic continuity with the marine environment. Detailed studies show that a narrow fresh water ridge, created by the beach dune complex, exists along the coast. Along most of the beach ridge groundwater abstraction is relatively less and also there is regular recharge into the aquifers from monsoon rains, and thus the static water level remains slightly above mean sea level along a narrow zone for most of the coastline. This fresh water ridge prevents contamination of the shallow aquifer to the west of the ridge, even though the water levels fall below mean sea level in the aquifer. Where the beach area has been urbanized or where there is large-scale abstraction from beach zone, groundwater has been contaminated with saline water as there is no fresh water barrier in such locations. Thus, the beach area has, to a large extent, safeguarded the shallow aquifers from serious saline water intrusion in Chennai city. This is a fortuitous situation which also selVes as a warning not to urbanise beach zones in coastal cities.

Keywords

Hydrogeology, Freshwater Ridge, Electrical Conductivity, Coastal Aquifer, Chennai, Tamil Nadu.

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