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Importance of Dry Season Importance of Dry Season Recharge for Maintaining Recharge for Maintaining

Environmental Environmental UnderflowUnderflow

in Hard Rockin Hard Rock Terrain in Terrain in IndiaIndia

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By By

Dr Shrikant D. LIMAYEDr Shrikant D. LIMAYEDirector, Ground Water InstituteDirector, Ground Water InstitutePune, INDIAPune, INDIAProject Leader, Project Leader, UNESCOUNESCO--IUGSIUGS--IGCP IGCP Project no. 523: "GROWNET "Project no. 523: "GROWNET "<limaye@vsnl.com><limaye@vsnl.com>

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PROBLEMPROBLEMINDIA HAS 2.5% OF TOTAL INDIA HAS 2.5% OF TOTAL GEOGRAPHICAL AREA OF THE GEOGRAPHICAL AREA OF THE WORLD AND ONLY 6% OF WORLD WORLD AND ONLY 6% OF WORLD WATER RESOURCES, WATER RESOURCES, BUT BUT IT IS SUPPORTING 16% HUMAN IT IS SUPPORTING 16% HUMAN POPULATION AND 18% OF THE POPULATION AND 18% OF THE GLOBAL LIVESTOCK POPULATION.GLOBAL LIVESTOCK POPULATION.

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67% of geographical area is 67% of geographical area is occupied by Hard Rocks and 30% of occupied by Hard Rocks and 30% of Hard Rock area is in semiHard Rock area is in semi--arid zone.arid zone.

Proper management of surface water Proper management of surface water and ground water is therefore a and ground water is therefore a prime necessity.prime necessity.

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The hard rock aquifers in The hard rock aquifers in Monsoon climate,Monsoon climate, as in India, as in India, have certain special features:have certain special features:

1) Surface water divide 1) Surface water divide coincides with ground water coincides with ground water divide.divide.

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i.e. Ground water flow does i.e. Ground water flow does not take place under surface not take place under surface water divides.water divides.

A watershed is therefore, A watershed is therefore, taken as taken as ‘‘Unit of planning of Unit of planning of ground water developmentground water development’’..

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2) 2) The depth of ground The depth of ground water occurrence, in useful water occurrence, in useful quantities, is usually quantities, is usually limited to limited to a hundred meters a hundred meters or so.or so.

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3) The saturated portion of 3) The saturated portion of the mantle the mantle of weathered rock, alluvium or laterite,of weathered rock, alluvium or laterite,overlying the hard fractured rock, often overlying the hard fractured rock, often makes a significant contribution to the makes a significant contribution to the yield obtained from a dug well, a bore yield obtained from a dug well, a bore well or a dugwell or a dug--cumcum--bore well, bore well, either either directly or through the fissure network directly or through the fissure network within the hard rock..within the hard rock..

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4) Only a modest quantity of 4) Only a modest quantity of ground water, in the range of ground water, in the range of ““one one cu.m. up to 100 cu.m. or socu.m. up to 100 cu.m. or so”” per per day,day, is available at one spot. is available at one spot. Drawdown in a pumping dug well Drawdown in a pumping dug well or bore well is often almost equal or bore well is often almost equal to the total saturated thickness of to the total saturated thickness of the aquifer.the aquifer.

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5) Ground water recharge 5) Ground water recharge from rainfall is available only from rainfall is available only during 3 to 4 months of during 3 to 4 months of Monsoon rains, (June to Monsoon rains, (June to September). September).

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This storage gets depleted in the This storage gets depleted in the postpost--Monsoon prolonged dry Monsoon prolonged dry period of period of winter (Octoberwinter (October--January) and summer (February January) and summer (February to May),to May), due to pumpage from due to pumpage from dugdug--wells / bore wells and wells / bore wells and due to due to drydry--season underflow of ground season underflow of ground waterwater below the stream bed.below the stream bed.

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In hardIn hard--rock regions, especially in rock regions, especially in semisemi--arid zones, the streamarid zones, the stream--flow flow stops within a few weeks from the stops within a few weeks from the Monsoon rains. Monsoon rains. Afterwards, the Afterwards, the streamside ecosystem of streamside ecosystem of phreatophytic trees and irrigated phreatophytic trees and irrigated farms totally depends upon the farms totally depends upon the UNDERFLOW of ground water in UNDERFLOW of ground water in the sand, alluvium, and weathered the sand, alluvium, and weathered rock below the streamrock below the stream--bed & near bed & near the stream bank.the stream bank.

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This vulnerable ecosystem in the This vulnerable ecosystem in the central valley portion by the central valley portion by the streamside, comprising streamside, comprising trees, trees, bushes, nesting birds, grazing bushes, nesting birds, grazing animals, irrigated farms, fruit animals, irrigated farms, fruit trees, and tiny villagestrees, and tiny villages is the only is the only greenery & life in an otherwise greenery & life in an otherwise dry and barren postdry and barren post--Monsoon Monsoon landscape.landscape.

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Protection and Augmentation Protection and Augmentation of the of the underflowunderflow below the below the streamstream--bed bed is therefore, a is therefore, a prime necessity for prime necessity for sustainability of this sustainability of this ecosystem and for survival of ecosystem and for survival of the people and cattle within the people and cattle within the ecosystem..the ecosystem..

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Quantitative aspect for underflowQuantitative aspect for underflow: :

1 liter of water is required to grow food 1 liter of water is required to grow food grains which supply ONE food calorie.grains which supply ONE food calorie.Daily 3,000Daily 3,000--5,000 lit of water/capita. 5,000 lit of water/capita. Dry season underflow should support a Dry season underflow should support a part of this requirement part of this requirement PLUS 70 PLUS 70 lit/capita for domestic use.lit/capita for domestic use.

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AIM:AIM:To increase recharge/rainfall ratio in the To increase recharge/rainfall ratio in the Watershed so as to augment underflow Watershed so as to augment underflow BY:BY:(A) Undertaking activities during the (A) Undertaking activities during the Monsoon (rainy) season andMonsoon (rainy) season and

(B) Storing runoff during rains for the (B) Storing runoff during rains for the postpost--Monsoon recharge in dry season.Monsoon recharge in dry season.

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ACTIONS spread all over the ACTIONS spread all over the watershedwatershed::Soil and water conservation Soil and water conservation techniques like hilltechniques like hill--slope slope trenching, contour bunding of trenching, contour bunding of farms, excavation of farm ponds, farms, excavation of farm ponds, constructing small stream bunds, constructing small stream bunds, etc. to check velocity of runoff etc. to check velocity of runoff and promote recharge during the and promote recharge during the Monsoon rains. Monsoon rains.

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But there is a limit to recharge But there is a limit to recharge augmentation during the augmentation during the Monsoons. Monsoons. Recharge to ground water during Recharge to ground water during postpost--Monsoon winter season Monsoon winter season (October(October--January) is what the January) is what the Ecosystem demands.Ecosystem demands.

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Construction of Percolation Construction of Percolation Tanks is the preferred solution:Tanks is the preferred solution:1. Catchment area : 10 to 50 sq 1. Catchment area : 10 to 50 sq kms for storing Monsoon runoff. kms for storing Monsoon runoff. 2. Size: Usually 50 m to 150 m 2. Size: Usually 50 m to 150 m long and about 6 to 8 m in height.long and about 6 to 8 m in height.3. In a drought year, it can 3. In a drought year, it can provide employment for 1,000 to provide employment for 1,000 to 1,500 villagers for 6 to 8 months.1,500 villagers for 6 to 8 months.

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Reservoir Efficiency (R.E) = Stored Runoff / Available Runoff(About 70 to 80 %)

Percolation Efficiency (P.E) = Water Recharged / Stored Runoff(About 35 to 50% )

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Overall Efficiency = R.E x P.E

A typical Percolation Tank costs between US$ 50,000 to 100,000 and can employ up to 500 people for 4 to 6 months.

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Villagers engaged in watershed workVillagers engaged in watershed work

BEFORE

AFTER Plantation Continuous Contour Trench

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CONCLUSIONS:CONCLUSIONS:

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* In hard rock regions in India, * In hard rock regions in India, especially in semiespecially in semi--arid zones,arid zones, the the environmental flow is environmental flow is NOT the NOT the surface water flowing in a surface water flowing in a stream, stream, because the flow of because the flow of surface water in the stream exists surface water in the stream exists only for a few days in a year.only for a few days in a year.

The streamside ecosystem, The streamside ecosystem, therefore depends on the therefore depends on the

UNDERFLOW.UNDERFLOW.

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* Sustainability of the * Sustainability of the Streamside Streamside EcosystemEcosystem comprising trees, bushes, comprising trees, bushes, nesting birds, grazing animals, nesting birds, grazing animals, irrigated farms, fruit trees, and tiny irrigated farms, fruit trees, and tiny villagesvillages is related to augmentation of is related to augmentation of underflow, which in turn depends underflow, which in turn depends upon the augmentation of recharge, upon the augmentation of recharge, especially the dry season recharge, to especially the dry season recharge, to ground water body within the ground water body within the watershed.watershed.

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*Small water storages or *Small water storages or percolation tanks created in the percolation tanks created in the minimini--watersheds by constructing watersheds by constructing bunds across streams and gullies, bunds across streams and gullies, store runoff water during the store runoff water during the Monsoon season and cause Monsoon season and cause recharge to ground water during recharge to ground water during the next few months of dry the next few months of dry season.season.

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* However, by February or * However, by February or March the tank should be dry, so March the tank should be dry, so that the water body is not that the water body is not exposed to high rates of exposed to high rates of evaporation in summer months.evaporation in summer months.

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* Whatever quantity percolates * Whatever quantity percolates from the Tank between October from the Tank between October and March is available as and March is available as underflowunderflow onon downstream side of downstream side of the tank even in summer months.the tank even in summer months.

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* Treatment of catchment area is * Treatment of catchment area is necessary for reducing the siltnecessary for reducing the silt--load coming into a Percolation load coming into a Percolation Tank. Tank.

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* However, accumulation of silt takes * However, accumulation of silt takes place slowly and deplace slowly and de--silting of the bed silting of the bed of percolation tank is necessary from of percolation tank is necessary from time to time, for maintaining its time to time, for maintaining its reservoir efficiency and percolation reservoir efficiency and percolation efficiency. efficiency. A well maintained A well maintained percolation tank increases underflow percolation tank increases underflow and even in summer season,and even in summer season, scarcity of scarcity of drinking water is not felt in the valleydrinking water is not felt in the valley..

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"GROWNET"GROWNET:: GroGroundund WWateraterNetNetwork for best practices in work for best practices in ground water management in ground water management in lowlow--income countries" is a income countries" is a project sponsored by UNESCO project sponsored by UNESCO & IUGS & IUGS as IGCP Project no. 523.as IGCP Project no. 523.I am the Project Leader of this I am the Project Leader of this Project.Project.

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Please visit our website:Please visit our website:www.igcpwww.igcp--grownet.orggrownet.orgGROWNET recognizesGROWNET recognizesconstruction of Percolation Tanks construction of Percolation Tanks as one of the 'best practices' in as one of the 'best practices' in augmentation of recharge to augmentation of recharge to ground water.ground water.

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T H A N K Y O U T H A N K Y O U Visit our Website: www.igcpVisit our Website: www.igcp--grownet.orggrownet.org

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A Request:A Request:Due to my impaired hearing,Due to my impaired hearing,I request that any Question on this I request that any Question on this presentation be kindly written on presentation be kindly written on Paper and given to the SessionPaper and given to the Session’’s s Chair. Chair. THANKS.THANKS.