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GROUNDWATER RECHARGE IN THE BASALTIC TERRAIN FOR RAINWATER HARVESTING : EVERYWHERE BUT NOT ANYWHERE

TERREYuCon

ISBN : 978-93-85311-04-8

TERRE magazine for youth

Vol 1 Issue 1 | March 2015 Groundwater recharge in the Basaltic Terrain for Rainwater Harvesting : Everywhere but not Anywhere

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TERREYuCon

ISBN : 978-93-85311-04-8

AbstractFor The last Decade or so one has seen the revival of traditional practices

of Rainwater harvesting to meet the ever increasing shortfall of clean drink-ing water. Rainwater harvesting is being projected as the means of achieving sustainability for meeting the demands of clean water. This is true for all cen-ters of urbanization viz. metros, and big cities. Where, due to constraints of space one cannot think of common large surface reservoirs, which definitely have proven to be unreliable during drought years.Though Rooftop Rainwa-ter Harvesting, is definitely a social responsibility of every citizen, as it en-sures that the natural groundwater system is maintained and the groundwater abstraction for daily use is replenished to its maximum during the rainy sea-sons, which is what normally takes place within the natural Hydrogeological cycle.The Deccan basalts also referred to as “The Deccan Traps”, occupy nearly 90% of area within the state of Maharashtra. From Hydrogeological point of view which takes into account the conditions for the Occurrence and movement of Groundwater, the Traps have been wrongly interpreted as be-ing similar to granites and other hard-rocks.The multilayered aquifer system, which is seen to be commonly occurring within the Trap Terrain are very het-erogeneous in nature, both vertically as well as horizontally. This makes the task of exploration for groundwater a very difficult task, which also is the case when it comes to designing systems for achieving the desired Groundwater recharge. The present paper tries to highlight the issues related to the Dec-can Basaltic aquifer system which renders the implementation of Rainwater harvesting systems using a pre-defined design and pattern to achieve ground-water recharge non-functional and a shear waste of resources especially in Neo- development areas where, hard rocks are usually exposed on surface.

Keywords: Rainwater harvesting, Groundwater Recharge, Deccan Basaltic Aquifer.

KANIKA LALWANI | ANIL LALWANI | BHARAT MANE1 Dept of Geology & Petroleum Technology, Nowrosjee Wadia College, Pune 411001, India. [email protected] & Water Works,1088/ B1-2 Amritiwell Society Model Colony, Pune 411016, , India. [email protected]



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TERREYuCon

ISBN : 978-93-85311-04-8

Introduction

For the last Decade or so one has seen the revival of traditional practices of Rainwater harvesting, to meet the ever increasing shortfall of clean drinking water. Rainwater harvesting is being projected as the means of achieving sustainability for meeting the demands of clean water. This is true for all centers of urbanization viz. metros, and big cities. Where, due to constraints of space one cannot think of common large surface reservoirs, which definitely have proven to be unreliable during drought years.

Though Rooftop Rainwater Harvesting, is definitely a social responsibility of every citizen, as it ensures that the natural groundwater system is maintained and the groundwater abstraction for daily use is replenished to its maximum during the rainy seasons, which is what normally takes place within the natural Hydrogeological cycle.

The Deccan basalts also referred to as “The Deccan Traps”, occupy nearly 90% of area with-in the state of Maharashtra. (Figure 1 A) From Hydrogeological point of view which takes into account the conditions for the Occurrence and movement of Groundwater, the Traps have been wrongly interpreted as being similar to granites and other hard-rocks.

Unlike other hard rocks the Basalts are unique in their Hydrogeological characteristics, and unlike the granites the basalts form multilayered

aquifer systems. Groundwater within the basalts are not restricted to fracture zones and joint which cut across the individual flows, but are seen to be flowing along the sheet joints which are developed along flow unit contacts.

The multilayered aquifer system, which is seen to be commonly occurring within the Trap Terrain are very heterogeneous in nature, both vertically as well as horizontally. This makes the task of explo-ration for groundwater a very difficult task, which also is the case when it comes to designing systems for achieving the desired Groundwater recharge.

The enigmatic nature of the Deccan Basaltic aquifer system renders the implementation of Rainwa-ter harvesting systems using a pre-defined design and pattern to achieve groundwater recharge non-functional and a shear waste of resources especially in Neo- development areas where, hard rocks are usually exposed on surface.

The Deccan basalt aquifer system

According to Deolankar, 1980 The Deccan basalts are hydrogeologically anisotropic and heterogeneous in nature. According to Singhal 1997, Deccan traps behave as a multi-aquifer system, somewhat similar to a sedimentary rock sequence. One can find a potential water bear-ing horizon (vesicular, amygdaloidal, jointed or weathered basalt), sandwiched between com-



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TERREYuCon

ISBN : 978-93-85311-04-8

paratively massive basaltic flows, the former behaves as confined aquifer and the latter as Aquifuge or Aquitard. He goes further to highlight the importance of Geophysical in-vestigation, lithological mapping of different flow units, fracture trace, and lineament map-ping for higher success of water well drilling in Deccan traps.

It is obvious from the drill time observa-tions, that all the depths at which the water is encountered represent the upper and lower contact zones between the Amygdaloidal ba-saltic flow unit and the Compact basaltic flow unit. These zones are termed as INTER UNIT ZONE - IUZ (Kulkarni, 1987; Kulkarni and Deolankar, 1995, Lalwani 1993) (Figure 1B).

These zones are characterized by a large percentage of amygdales and also by the presence of sub-horizontal interconnected sheet joints. Such a sheet jointed Inter Unit Zone in Amygdaloidal ba-saltic flow units acts as inflow zones within wells. Photographs of such sheet joints exposed in a dug

well and also encountered in borewell have been shown (Photos 1 and 2).

According to, Kulkarni et. al. 1997, Lalwani 2000, borewells in close proximity do not neces-sary tap the same aquifer nor do they have the same yield, this fact confirms that Deccan basal-tic flow units forming aquifers are extremely Het-erogeneous in nature and extreme caution has to be adhered while dealing with them. A completely dry borewell near high yielding borewells could be a case of very poorly developed or improper connections with the aquifer. Lalwani (1994).

Rainwater Harvesting In Basalts

The multilayered aquifer system commonly seen to be occurring within the Trap Terrain are very heterogeneous in nature, both vertically as well as horizontally. This makes the task of exploration for groundwater a very difficult task, which also is the case when it comes to designing systems for achieving the desired Groundwater recharge.

As recommended by CGWB, 2000, CPWD 2002; Gupta, 2006, to achieve artificial recharge in hard rock areas one needs to tap the aquifers by means of drilling of borewell.

Kulkarni (1987) has shown the lithological controls on the development of trasnmissive sheet joints within the Amygdaloidal basaltic flow units. According to Lalwani 1994, it is very difficult to predict such lithological controls with the help of resistivity data and the limited Hydrogeological data col-lected at different sites.



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TERREYuCon

ISBN : 978-93-85311-04-8

The recharge of the ground water system within the trap terrain needs to be done keep-ing in mind the heterogonous nature of the Deccan basaltic Aquifer and also the possi-bility of the borewells drilled not being con-nected to the aquifers. Hence making it es-sential to properly identify locations where in the recharging borewells need to be in hy-draulic continuity with the Aquifer system and the connections of the trasnmissive Inter unit zones need to be well developed to achieve the desired recharge.( Photo 3)

Conclusion

Designing a rainwater harvesting system within the Basaltic where in groundwater needs to be recharged is a difficult task, Groundwater Recharge in the Basaltic Terrain for Rainwater Harvesting is possible Everywhere But Not Anywhere. Any attempt to recharge groundwater should be restricted to locations where the recharging structure is well connected to the Aquifer system via the trasnmis-sive inter unit zones providing an avenue for the recharging water to enter into the Aquifer system. To achieve Ground water recharge in the hard rock areas within the basaltic the borewells drilled need to have successfully encountered prolific aquifer system. Where the recharge borewells are drilled only based on alignment and positions of building and the locations of the down take pipes from terrace, there is a high probability that the desired ground water recharge will not take place.

Trying to achieve Groundwater recharging in to the deeper basaltic aquifers, large number of re-charge structures, systematically placed all around the building or within a cluster of building prob-ably would not achieve the desired results as compared to a few properly identified & strategically located recharge structures that are in hydraulic continuity with the Aquifer system.

Dry borewells, which have not encountered any water while drilling indicates that the borewell is not connected to the aquifer via the trasnmissive Inter Unit Zones and any attempt to utilize such borewells for recharging purpose would be a shear waste of resources. As the surface waters need to be directly connected to the Groundwater systems precautionary measures needs to be taken to ensure that the recharging water is free of contaminants before it gets diverted for recharge in to the subsurface.

References

1. A.K. Gupta, Rainwater Harvesting- pub. Indian Railways Institute of Civil Engineering, Pune, August, 2006.

2. CGWB - UNESCO, Rainwater Harvesting and Artificial Recharge to Groundwater: A Guide to Follow. Central Groundwater Board – International Hydrological Program (IHP), New Delhi. 2000

3. CGWB Manual on Artificial Recharge of Ground water, Government of India, Ministry of Wa-ter Resources, September 2007.



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4. CPWD, Rainwater Harvesting and Conservation Manual, New Delhi. 2002

5. Deolankar, S.B. The Deccan Basalts of, Maharashtra, India- Their Potential as aquifers, vol 18,No 5, GROUNDWATER, September-October 1980

6. Kulkarni, H.C., A study of Deccan Basaltic unconfined groundwater system from Pabal area of Shirur talua, Pune district Maharashtra state, Ph.D. Thesis, University of Pune, India 1987, 285 pp.,

7. Kulkarni, H.C & Deolankar, SB, Hydrogeological mapping in the Deccan Basalts – an ap-praisal. Jour. Geol. Soc. India. 1995, 46(1) 345-352.

8. Kulkarni, HC, Deolankar, S.B, Lalwani , A, Joeshep, B, Pawar, S.,Hydrogeological Frame-work of Deccan basalts groundwater systems, west-central India, Hydrogeology Journal, 2000, 8:368-378

9. Lalwani , A Practical aspects of exploration of the Deccan basaltic aquifer for bore well de-velopment from parts of Haveli taluka, Pune district, Maharashtra, Ph.d. Thesis University of Pune, India 1993, 09pp

10. Lalwani, A, Study of deeper Basaltic aquifer(s) in Pune city & environs, Maharashtra., CSIR –RA Report, No 9/137(249)M-EMR-I, council of scientific & industrial research, New Delhi, 2000

11. Singhal, B.B.S. , Hydrogeological characteristics of Deccan trap formations of India, Hard Rock Hydrosystems (Proceedings of Rabat Symposium S2, May 1997).IAHS Publ. no. 241, 1997

12. UNEP, Sourcebook of Alternative Technologies for Freshwater Augmentation in Some Coun-tries in Asia. TechPub-8e, IETC, United Nations Environment Program, August 1998.

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groundwater recharge in terre yucon the ......water recharge non-functional and a shear waste of...

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