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Recharge of deep borewells in hard rock terrain
ShareIndia's dependence on the underground aquifer especially deep bore wells are well known. With over 22 million wells India has perhaps one of the largest such structures in the world. Since most of peninsular India is hard rock with basalt/granite/gneiss underlying they present a particular challenge for understanding. A series of experiments are on in Bangalore to determine what is the possible rate of recharge in some of these deep bore wells (depth greater than 150 feet) in hard rock terrains. This is primarily with a view to recharge these bore wells using filtered rooftop rainwater especially in urban areas. In Bangalore there are an estimated 200,000 bore wells and half of them are believed to have yielded well and are now non-yielding .
The video demonstrates a recharge/slug test for one such bore well which has now stopped yielding water after 3 years - one day suddenly - as is usual with such bore wells in Bangalore. Add your suggestions to take this forward in the comments section!
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2009
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Dear Dr. Regade,
I read with interest the valuable information provided by you, including details of your book on "Self-Reliance in Water – A Practical Guide for Town and City Dwellersâ€. As your experience appears to have been onfined to Chennai where unconsolidated sediments such as sand, clay etc occur for considerable thickness, it cannot be so easily applied in urban areas in hard rock areas such as Bangalore where the thickness of unconsolidated sediments is usually quite low. Your work would have been more useful had you incorporated a chapter on subsurface geological exploration using geological, geophysical, remote sensing and exploratory boring/drilling methods to select well sites and well designs best suited for recharging in various geological environments. You may note that the problem of clogging of wells by silt can be tackled effectively by making use of permeable well bricks and capsules patented by T. Damodar Rao, Retired Superintending Engineer, TWAD Board, 15, Chidambaram Street, Mylapore, Chennai, TN 600004 Phone 044-24997052. His son T Vedadri has a company, M/s. Indra Aqua Tech Engineers Pvt. Ltd which constructed a large number of recharge infiltration wells and recharge bore wells for groundwater recharging at several places in south India including near Tirupati where I live. Please find attached a picture of a recharge infiltration well.
Regards,
Rao
R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com
Friends, Sekar Raghavan had sent Mr. Thakar's message to me. My comments are attached. I am also attaching a mailer about the book that I have authored and released. With good wishes to all.
As one with 16 years of experience in meeting the challenge of providing water security to the occupants of more than 225 four storeyed residential apartment complexes comprising over 3500 apartments in various types of soil all over Chennai city for, I offer my comments on Mr. R. Jagadiswara’s query on recharge of deep bore wells. This experience extends over harvesting of both roof-top rainwater and surface run-off, recycling of grey water using sunlight, plants and soil, and simple conservation techniques.
First, a few lines on the traditional shallow dug well:
The shallow dug well is the most effective receptive receptacle to receive rainwater because of the large area and volume it provides. Roof-top rainwater can be safely put directly into a service dug well without any prior filtration. I have yet to come across a filter that is user friendly and at the same time effective. The surface run-off should be put only in recharge dug well. The shallow dug well can be termed as our insurance for our future water security.
My method of charging a bore well with rainwater is to dig a pit around it and line it with bricks or RCC rings. Then either replace the exposed portion of the casing pipe of the bore well with machine slotted pipe or introduce 2 mm slits on it by using a hacksaw fitted with double blades. The slots (or slits) are then covered with fine nylon mesh cloth which is kept in place with copper wire in a couple of places. Then wind polythene cord over its entire length in a spiral fashion. The top one foot section and the bottom one foot section should not have slots or slits. If the bottom is not rocky, give a 2 or 3 inch layer of blue metal pieces. This will neutralize the momentum of the water falling into the pit and prevent the soil at the bottom of the pit being disturbed and muddying the water.
Many recommend the filling of the pit with blue metal or brick bats. This is actually counterproductive in three ways: i) If the filter material gets clogged with fine mud, the system fails totally and removing the mud is very inconvenient. ii) In places where the rain occurs in short heavy spurts, the rate of inflow of water will be far higher than the rate at which the water can infiltrate thro the limited area available thro the slots. Much of the water will therefore flow away from the pit. If the pit is kept empty, it can hold its own volume of water which can then slowly infiltrate thro the mesh cloth.
When the mesh is clogged with mud, it can be hosed with a jet of water and the muddy water collected at the bottom can then be pumped out. If the terrace is swept clean prior to the onset of rains, the inflow of mud will be marginal and clogging will be necessary only infrequently.
One method of improving the area of infiltration would be to replace the existing exposed casing pipe with one of a bigger diameter. I would not advocate the channeling of the water into the casing pipe directly because if it tends to bring mud along with it, this may block the inflow of water into the casing from the aquifer.
The efficiency of this arrangement would be determined by a) the pattern of rainfall in the locality involved; b) the collection area; c) the capacity of the pit in relation to the collection area; d) length of the slotted pipe exposed which depends on the depth of the pit and the diameter of the casing pipe; and d) the condition of the nylon mesh cloth. My experience has been only with casing pipes of PVC. I have no first hand experience with casing pipes made of metal.
One extension of this which I have tried with good results in areas with weathered rock at shallow depths was to drill a bore well inside an existing shallow dug well and provide the slots on the exposed length of the casing pipe. This has two advantages: i) the well and the bore well both get charged with rain water. ii) The slots can be provided over a greater length of the casing pipe and so the area of infiltration into the casing pipe is much more. This concept can be implemented in non-rocky areas also. Bore well diggers are however reluctant to dig a bore well in a dug well because they have to dewater the well first and fixing the plumb in the well bottom is not as straight forward as at ground level. Therefore, wherever possible, one should dig a borewell first and then dig the shallow well around it.
Incidentally, the bore well is best positioned at the .centre of the well or the pit but if this is not possible it can be off centre also. If off centre, the absorption part is not affected, but the hosing down of the nylon mesh mud may not be as easy as ii will be if centred.
If others have any better solutions or any modification to suggest, I will be happy to ger them. (Note: My experience has been solely with PVC casing pipes. I have no experience with cast iron or steel casing pipes. The principle should be applicable here also, but making holes may not be that easy.)
TROUBLED BY WATER (SHORTAGES? LOOKING FOK A SOLUTION?
READ "Self-Reliance in Water" (A Practical Guide for Town and City Dwellers)
By Dr. Indukanth S. Ragade
Here is a book that gives practical methods for reducing, if not eliminating, your dependence on external sources for water. In simple language, free of jargon, it tells you all you need to know about water:
* How to economically harvest all the rainwater falling on your home and garden and get water for cooking, drinking and other needs.
* How to purify and reuse throughout the year, more than 50% of the water you have used by a simple, self-sustaining, eco-friendly soil process within your premises. No chemicals or electricity needed.
* How to store and advantageously use different qualities of water available in your premises, including brackish water.
* Simple methods to use water more efficiently and make available water last that much longer.
* What is potable water? Do mineral water and bottled water mean the same?
* How to decide that the water available to you while travelling is safe to drink.
* How to improve the quality of your ground water.
* Why does sweet water turn saline in coastal areas?
* What can you do about it.
* What to do when ground water turns yellow and stains clothes.
* If there is no sewerage in your town, how to dispose of your sewage hygienically without contaminating your ground water.
* How to select the right spot to dig a well or drill a borewell.
* How relevant is RO (Reverse Osmosis) in apartment complexes.
* How to reduce / eliminate inundation on ths road in front of your home during the monsoon.
* And a host of information on many other matters related to water.
The first of its kind, this book, based on a decade and a half of hands-on experience, is a one-stop source of information and guidance for every town and city dweller grappling with water shortages. A book that Architects and Builders can use to design and install, efficient and economic water management systems in their constructions. A book that larger water users like hostels, hotels, hospitals and industries can use profitably to get more water for their needs. A book that will be a valuable addition to the library of every school, college, universiry and water-related in stitution. A book that environmentalists would love to have. The Author Indukanth S. Ragade holds a Ph.D. in organic chemistry from the Presidency College, University of Madras (1963) and was a Post-doctoral Research Associate in the University of lllinois and South Carolina from 1964-1967. He was with M/s. Atic Industries Ltd., manufacturers of synthetic dyestuffs in Gujarat, from 1968 to 1984. Since 1984, he has been with M/s. Alacrity Foundations Pvt. Ltd., Chennai, an organisation reputed for the manufacture of quality apartment complexes and good corporate practices. A keen urban environmentalist and a passionate believer in sustainable development, he has, over the past decade and a half, pioneered the practice of eco-friendly methods for water management, practicable in the urban environment. In recent years, he has also been involved in the development of simple methods of managing domestic solid waste and has also developed a re-engineered proto-type of a solar water heater that can be made available at a low cost.
Copies of the book available from
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B-9, Atandra, 25, Thirumalai Road,
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e-mail : iragade@yahoo.co.in
Pages : 220
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Dear All,
I thank Vishwanath and Avinash for their valuable comments.
As part of the FAO's humanitarian programme in three Iraqi Northern Governorates, a comprehensive remote sensing/GIS methodology was developed to identify potential sites for groundwater exploitation and construction of water harvesting strucutures (http://www.fao.org/docrep/005/Y4639E/y4639e00.HTM). I have given outputs of this work as links here. The first one shows the potential sites for construction of wells and recharge structures, while the second one shows the location with reference to a water-bearing fracture. In the absence of this work, wells and recharge structures have to be located evenly spreading over the entire governorates with many failing to discharge or recharge adequate water. This is exactly what is happening with Bangalore.
Suppose work similar to that made in northern-most Iraq is available for Bangalore and such a work proved localisation of most groundwater to some well-defined zones. This should allow the Corporation or NGOs to take up construction of high-yielding wells and recharge structures of proper design to maximise both discharge and recharge to make that water available to a number of households without the need for them to take up individual discharge/recharge structures.
Thanks
Rao
R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com
Dear All,
Picking up points from different responses of this conversation, certain key points in the urban ground water context that has emerged are:
a)The urban context has its own specific ground water catchment and quality contamination issues.
b)Urban groundwater over extraction is more a result of limited atomized extraction which is nonetheless large-scale and unsustainable when aggregated
c)There is a need for engaging with urban communities to make them more water literate.
d) Citizens and communities HAVE to be a part of the solution to manage ground water. Acknowledging and leveraging Community participation and effort may mean action is not hydro-geologically optimal.
e) Urban Communities – largely formed around property boundaries - will have to see value for themselves while engaging in such action. Or Urban community action is driven through a mixture of self-interest and the interest of the larger good.
However, to me the above also raises the following questions:
1. What is the process by which a direct dialogue driven engagement with these communities be achieved to catalyse action ?
2. In this process, how can knowledge be integrated and brought to bear at the community action level in the urban context – the knowledge may be such as the maps Prof Rao is speaking about, the hydro-fracturing that started the conversations, the borewell / well diggers / plumbers knowledge of years or that of rainwater-harvesting. ?
3. Can this process however be more & more informed by the sciences of geology, hydrology and hydrogeology.? Will this enhance the value perception of communities in such an engagement and therefore aid increased community participation?
4. How does this process relate to / fit in, in the larger picture of an urban ground water management systems, building bye-laws, legislation etc ?
Everybody thanks for the engaging conversation,
Regards
Avinash
Dear All,
Thank you for a stimulating set of responses. A set of points I would like
to bring which may help take this issue forward
- the absence of any management systems ( I hate to use the word regulatory institutions) for urban groundwater as is well known to all in this field
- that there are clear differences in urban groundwater as compared to say rural/regional groundwater systems with its high density of bore wells , limited withdrawal but huge nonetheless because of the huge numbers, the propensity for pollution primarily from domestic sewage but also from non-point sources such as garbage/urban solid waste, the covering up of the recharge area through building/road activity, urban activity based pollution
etc etc
- the inability of the state to respond with any coherent ,sustained response for urban groundwater. Consider the study pointed out by Prof Jagadiswara Rao, here lie the learnings? How are people in the city of Bangalore helped by a :1:50,000 scale map? Private bore well diggers also report a over 90% success rate without these maps , how come? In Bangalore
there is not a single hydro-geologist with the BWSSB yet anywhere between 200 mld to 400 mld of water to Bangalore comes from groundwater.
- the need for rainwater harvesting, not simply to meet the demand of water or to top up the aquifer, but also to make people water literate and aware of the scarcity value of water. In any case in Bangalore it is simply impossible to collect all rainwater economically but householders can recharge the aquifer with the surplus. Therefore when rainwater harvesting is made mandatory it becomes possible for the over 10 lakh homes of Bangalore to become part of the solution through rainwater harvesting..
- correct me if i am wrong , in a situation where there is construction on a site/plot the average amount of recharge actually topping up ground water is in the range of 5 -10%. If a house is built , the hard surface enables collection and recharge of up-to 90 % of incident rainwater. Rainwater harvesting where, recharge rates permitting, would actually do better for
groundwater recharge or ASR than unbuilt areas.
- that many people want to contribute to harvesting rain and enhancing groundwater levels irrespective of the state encouraging it or not. In such a case like Sekhar Raghavan has been doing in Chennai for long, it helps to arm people with the knowledge of how they can actually recharge groundwater and at what rates such recharge occurs. The storativity and transmissivity numbers if available to people also helps them understand groundwater
better.
- that building bye-laws when they make rainwater harvesting and recharge mandatory, can be helped if they specify how this recharge is to be done and what volume should be provided as a minimum. For example in Bangalore given the rainfall and intensity it seems to help if a minimum of 20mm of rain is collected or recharged. This would mean a minimum storage/recharge volume of 2000 litres for a 100 square metre roof/built up area. Putting such numbers helps optimize design of rainwater for the individual and for the city.
Finally , we need to demystify groundwater quickly and easily for people to understand and respond to manage sustainably. This may be sub-optimal from a hydro-geological point of view, not respecting recharge zones and discharge zones, but participation is a community effort and not a hydro-geological effort alone hence the best is the enemy of the good here.
zenrainman
Dear Sekar Raghavan,
I fully agree with your contention that the geology of several parts of Chennai are best suited to recharge shallow groundwater through rooftop water harvesting (RTH), while the geology of most parts of Bengaluru are such that it is difficult to recharge even deep groundwater through RTH.
You can read my views on rainwater harvesting in Chenna and Bengaluru the Virtual Water Forum on Human values for water and sanitation - Reviving Traditional and Cultural Practices to restore Water Quality organised by Dr. K.E. Seetharam of the Asian Development Bank (ADB) during 2002-03 at
http://www.waterforum.jp/worldwaterforum3/for/en/stopic.794_1808.html
http://www.waterforum.jp/worldwaterforum3/for/en/spost.794_4441%7B0s=0%7...
http://www.waterforum.jp/worldwaterforum3/for/en/spost.794_4801%7B0s=0%7...
Regards,
Rao
R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com
It is more successful in our Barmer district.
chandanmal jain
Dear Himanshu,
Thank you for endorsing my suggestion that there is need to map groundwater aquifers of Bangalore. Such ground water prospects maps on a scale of 1:50,000 were already prepared for most parts of Karnataka by the National Remote Sensing Agency (NRSA) with the funds provided by the Rajiv Gandhi National Drinking Water Mission (RGNDWM) to select favourable sites for drinking water wells and plan ground water recharge structures.
These maps were prepared during 1999-2002 for 56,682 habitations lying in 316 Survey of India topographic maps in collaboration with a number of agencies including Department of Mines and Geology, Karnataka State Remote Sensing Application Centre, Public Health Engineering Department, Central Ground Water Board (CGWB), Department of Science Headquarters, Bangalore and Regional Remote Sensing Service Centres (RRSSC) in Bangalore. These maps were released by the NRSA in a public function held at Hyderabad on 11th June 2002, while 40 field officers/scientists from Karnataka were trained in the use of maps between 19th and 22nd September 2001. By using these maps, 34,888 wells were drilled with a success rate of 92.7% and 2674 recharge structures were planned and constructed.
It is possible that as part of this work ground water prospects maps for the Bangalore Urban Development Area must have been also prepared.
I shall be grateful if you can use your good offices for making these maps available to all those striving for security of drinking water through construction of successful wells made sustainable through managed aquifer recharge (MAR).
Regards.
Rao
R. Jagadiswara Rao, Professor of Geology Retired, Sri Venkateswara University, Tirupati, AP 517502, India rjagadiswara@gmail.com
Dear Vishwanath,
I agree and disagree with whatever has Prof. Rao has said.
1. While it is true that intensive use of groundwater for domestic and drinking purposes has led to steep decline of groundwater levels in Bengaluru, it is also true that no sincere attempt was made in the past (or being made at present) either at the micro or at the macro levels to recharge the aquifer.
2. I do not agree with Prof. Rao’s observation that “decline in gw levels is so large that it is difficult to raise gw levels to make the shallow wells to become functionalâ€. Chennai is a classic example of how RWH is capable of bringing back the shallow wells alive.
In my own apartment complex, the shallow wells which had gone dry and remained so for more than three years were filled up to two thirds of its volume in January 2006. Thanks to the law which made RWH mandatory and also to the good NE monsoon rains the city received during Oct-Dec 2005. This has been possible with just fifty percent of the residents implementing RWH in a reasonably good manner. The remaining fifty percent had not only cheated themselves but also the government.
Another evidence for the shallow aquifers getting recharged through RWH came from the temple tanks within Chennai. One tank had remained dry for almost thirteen years in spite of the fact that Chennai received record rains in 1996 – 1997. Whereas, they came back alive in Jan. 2006.
3. About surface runoff: In Chennai, almost eighty percent of the residents had not implemented the driveway runoff harvesting within their premises, though it was extremely relevant. In most of the apartment complexes, the driveway area was much more than the rooftop area and all they had to do was to intercept the runoff near the gate(s) and inject it into recharge wells located near the gates.
Regards,
Sekhar Raghavan
I thinks Jagadiswara ji's response gives an excellent map of steps to be taken. I guess mapping groundwater aquifers of Bangalore this way may be a good idea, at the same it can also be checked if there are existing aquifer maps of Bangalore.
On recharging the groundwater with treated surface water, we need to learn more about where it is going on, how long, what is the experience, what was the quality of treated surface water, how that quality was ensured, etc.
Best wihses,
Himanshu
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