An overview of Transboundary Aquifers of the Indian Sub-continent

INTRODUCTION

Transboundary aquifers are the internationally shared ground water resources across the countries in all parts of the world. India being the largest country of the Indian sub continent has large number of transboundary aquifers. India shares its ground water resources across its international border and at least eight aquifers have been identified as transboundary aquifers in the neighboring countries. The Indian sub-continent is one of the most populated Region and these transboundary aquifers are significant as the water and food securities issues are related to them. Management of transboundary aquifers, particularly extensive and continuous one is required urgently in reference to the retrieving Himalayan glaciers due to climate change.

TRANSBOUNDARY AQUIFERS OF INDIAN SUB-CONTINENT

Transboundary aquifers of the Indian sub-continent are generally shared between India with Nepal, Pakistan, Bangladesh, Bhutan, China & Myanmar (Sharma, 2009), which are as follows.

1. Aeolian, Alluvial & Tertiary Sandstone Aquifers(India, Pakistan),
2. Upper Tertiary & Quaternary Alluvial aquifers Bhabhar Terai Aquifer (India, Nepal)
3. Alluvial/Deltaic aquifers(India, Bangladesh),
4. Tertairy Sandstone/Siltstone & Proterozoic (Granite, phyllite, quartzite) aquifers(India, China, Pakistan),
5. Tertiary (Tipam Sandstone)aquifers(India, Bangladesh),
6. Older Alluvium aquifer(India, Bhutan),
7. Sandstone & Siltstone aquifers(India, Myanmar),
8. Proterozoic (Granite-gneiss) aquifers(India, Bangladesh)

ISSUES OF TRANSBOUNDARY AQUIFERS IN THE INDIAN SUBCONTINENT

There is a need of management plan for Transboundary aquifers in the Indian sub-continent to address various ground water and related issues of concern to the countries involved. Formulation of effective management plan for transboundary aquifer requires detailed information about these aquifers across the borders. The aquifers identified for Indian sub continent have varied geology, geomorphology, climate and groundwater utilization conditions. The common factor controlling these aquifers is the orogeny of the Himalayan Belt.

In the Ganga –Bramhaputra- Meghna and Indus river basin multi aquifer system has been laid down by the Himalayan orogeny. The sediments laid down in the fore deep of the Himalaya is as thick as 5000 meters in Ganga basin. Understanding these complex multi aquifer systems is a Herculian task. In India, so far aquifers have only been explored upto a depth of 750m by Central Ground Water Board ( CGWB, 2001). However, aquifer geometry in 3D is yet to be established for aquifers at greater depth. Similarly the aquifer parameters viz transmissivity, hydraulic conductivity, storativity, groundwater flow ,abstraction, quality, vulnerability, pollution and recharge areas are yet to be established. Detailed aquifer mapping would therefore be needed to reveal vital scientific information. Some of the specific issues prevailing in various transboundary aquifers are discussed below:-

Transbounary aquifer of Indo-Pak Border

India shares its international border with Pakistan along the State boundary i.e Gujarat, Rajasthan, Punjab and J&K. Arid climate prevails in Gujarat-Rajasthan international border area which largely controls the hydrological conditions in this area. The alluvial and aeolian sediments constitute phreatic aquifer which is saline in general in this part. The annual Replenishable resource is small due to scanty recharge. The state wise details are as follows:

Gujarat:- Gujarat State, located in western part of India has international boundary of around 500 km with Pakistan. The district along the Pakistan borders in Gujarat is Kutch. The eastern most 80 km part of the Cori Creek falls in estuarine zone of River Indus. The middle portion of nearly 300 km is part of the Thar Desert, covered by sandy plain in Pakistan and by marshy saline low land of typical salt encrusted Rann in Indian part. Last 120 km stretch, towards Pakistan is underlain by rocky upland with moderately rugged topography, underlain by Quaternary alluvium and Precambrian magmatic rocks; while on the Indian side it is extended parts of Rann in east, consisting of salty marshy land underlain by unconsolidated formations.

In Rann areas the soil is encrusted with salt at the top and there is no scope for fresh quality aquifer at shallow depth. In the adjoining Tharparkar region, (Pakistan) in north, the top soil are loose and porous aeolian sand, which absorbs rain water and percolates down to the ground water to form good quality aquifer at shallow depth. Granite basement are encountered at various depth and have poor to moderate yield prospect. Overall, quality is not good at higher depth. The southern side of the border areas in India has been explored by deep exploration down to 300 m bgl. However, their continuation across the border is remote, as the southern side in India is downthrown portion of Kachchh Tectonic Basin, filled up with argillaceous sediments, as confirmed from exploratory drilling( G.R.M.Rao etal, 1993). The continuation of aquifer system of Precambrian Granites / syenite of Nagarparkar region of Pakistan, across the border in east, below deep & multilayer Quaternary Alluvium is remote, as no basement are encountered in this region of India, upto explored depth of 350 m. Possibilities of ground water flow across the shallow aquifer system from western high land of Tharparkar into Rann of Kachchh is very remote and otherwise, difficult to confirm, as sediments in Indian side are predominated by silty clay formation, and saturated by highly brackish / saline ground water throughout the year.

Rajasthan: The districts along the Pakistan borders in Rajasthan are SriGanga Nagar, Bikaner, Jaisalmer, Barmer. The international boundary of Indo-Pak border along the Rajasthan State is largely occupied by Thar desert. The population of Thar desert is primarily living on limited agriculture products and raising cattle and live stocks, therefore ground water utilization is limited. In general ground water occurs in unconfined to semi-confined condition in alluvium. At places Ground Water occurrs in the Thar desert is in the form of perched water aquifer at the bottom of sand dune zone with fluctuating yield controlled by annual rainfall cycle( Zaigham, 2001). In general ground water in Thar desert is brackish to saline having electrical conductivity( EC) in the range of 5000-15000 microsemens/cm. Few patches of fresh groundwater below phreatic zone have been identified in Jaisalmer –Barmer-Ganganagar district having fossil water. The Indira Gandhi Nahar Pariyojna in Indian side and other canal system prevailing from pre independence in Sindh-Punjab province of Pakistan have brought water from inter basin transfer which has created patches of fresh water aquifer and also created water logging conditions in upper reaches of command area.

Punjab:-The transboundary aquifers of Punjab state, falls in the Indus basin. The districts along the Pakistan borders in Punjab are Pathankot, Gurudaspur, Amritsar, Taran Taran, Firojpur, Fazilka. The slope of the water table is towards west and south-west. The highlands of Punjab and J&K forms major recharge areas . The confined and semi-confined aquifers are having their slope towards west. As a first approximation, ground waters of Punjab are flowing across the international boundary towards Pakistan. There is a need to assess the quantity, quality and flow path of ground water. In the Punjab side of India, groundwater development is significantly high. Ground water resources of Punjab state have been computed as on 31.03.2004, and the Replenishable ground water resources of Punjab state have been assessed to be 23.78 BCM, and the net annual draft of the state has been estimated to be 31.16 BCM. Groundwater in the state contributes more than 70% of irrigation.

Transboundary aquifers of Indo-Bangladesh border:

India and Bangladesh share the Bengal basin aquifer along the West Bengal part of India which is the largest international border with Bangladesh. In the bordering area of West Bengal (India) 96% of groundwater is being used for irrigation. However the main concern is about the large scale geogenic contamination of groundwater due to presence of Arsenic across the border. Since the shallow aquifer in Bengal basin is largely contaminated with Arsenic, therefore the drinking water augmentation is from the deeper confined aquifers. It is essential that the proper protection must be taken across the boundary to protect the deeper aquifer from contamination due to faulty design of well construction. The delta region of Bengal basin aquifer show saline groundwater at top. The Trans-boundary Bengal aquifer system may be broadly classified in to two parts, represented by two large river systems i.e Ganges & Brahmaputra river basins.

Ganges River Basin: The Ganges is the main river along with its tributaries which drains both India and Bangladesh, having its origin in the Himalayas. The districts covered by this basin in West Bengal adjoining to Bangladesh are Maldah, Murshidabad, Nadia, North and South 24 Parganas. In Indian part, Quaternary aquifer system is represented by Recent alluvium at the top and Older alluvium at further depth except in Barind Tract in Malda and West Dinajpur districts along Old Malda- Gajol -Tapan -Balurghat -Gangarampur - Bansihari sector where older alluvium is exposed at top. In recent alluvium, groundwater occurs under unconfined condition in the near surface aquifer and under semi confined to confined condition in the deeper aquifers. The thickness of the clay bed increases towards south particularly in the coastal zones. In Nadia, Murshidabad (eastern part) districts, absence of significant clay beds down to the depth of 150 m makes entire aquifer system unconfined. However, towards west, as well as towards south fairly thick and regionally extensive clays are present. The depth to water table in the area varies from 2m to 10m bgl in pre-monsoon period and from less than 2m to 5m bgl in post-monsoon period with regional flow of groundwater towards east and southeast and ultimately enters Bangladesh.

The older alluvium consist of well-oxidized, massive argillaceous formation missed with calcareous and ferruginous concretions. Groundwater in Barrind tract occurs under unconfined condition in the near surface aquifer and under semi-confined to confined condition below a blanket of 15 to 20 m thick discontinuous clay bed in the depth span of 90 m to 110 m in most of the places. Water table is moderately deep with moderately high seasonal fluctuation. Depth to water level of the unconfined aquifer varies from 5 m to 10 m bgl in both pre- and post-monsoon period with flow towards southeast.

In adjoining parts of Bangladesh, older, ‘Barind’ tract of Pleistocene age separates Brahmaputra alluvium from Recent Gangetic alluvium. This recent alluvium of Ganga-Padma-Meghna system covers the rest of Bangladesh. General trend of groundwater flow is from north to south as well as towards the inland major rivers from their vicinity (Khandakar, 2010). The Teesta Fan in Bangladesh bordering India, reflects tectonic uplift, and a southward tilting of the apical fan segment, which developed southward longitudinal hydrologic divide between Tangon and Karatoya rivers system in the country. The average gradient of groundwater level in northern area is 0.65m/km (Khandakar, 2010).

Brahmaputra River Basin: In Indian part, Quaternery aquifer system is represented by the alluviums of 'Terai' which is made up of permeable sand, gravel and some pebbles interfringering with relatively impermeable silt and silty clay, unconformably lying over tertiary Shiwalik Group. Districts covered by this basin in West Bengal adjoining to Bangladesh are Coochbehar, Jalpaiguri, Uttar and Dakshin Dinajpur. The regional flow of groundwater is towards south. In adjoining parts of Bangladesh, major lithological units of the aquifer systems are unconsolidated piedmont alluvial sediments deposited by rivers draining from the foothills of the Himalayas (Khandakar, 2010).

Megahalaya & Tripura :- In the Meghalaya part of India-Bangladesh border, the East Khasi & Jaintiahill districts are having consolidated sedimentary aquifer across the border which have cavernous and fracture porosity and medium to good yield. The Indo-Bangladesh border area of Tripura is broadly occupied by semi-consolidated sedimentary formations .The valley area is having groundwater potential between 10-150 m₃/hr. The Artesian condition are found in pockets across the border and are largely developed.

Transbounary aquifer of Indo-Nepal border :

The Indo-Nepal border aquifer is laid down in the Gangetic plain alluvium running across the border of Uttarakhand, Uttar Pradesh and Bihar States of India. Groundwater development in Uttar Pradesh & Bihar is under safe category . It is largely recharged from the Bhabar zone of the Himalayan foot hills, which is partly in the Nepal. Bhabar zone is generally permeable and unconfined in nature. Coarse sand, gravel, pebble and cobble constitute the Bhabhar zone and consists mostly of reworked sediments from the Siwalik rocks. Terai zone is separated by spring line from Bhabar zone and consists of alternating layers of sand, silt, clay and gravel deposits of varying thickness (Khan & Tater, 2006). The Tarai belt along with Indo-Nepal border is known for its artesian condition especially for auto flowing wells, which forms extensive and prolific aquifers. The auto-flow discharge found along the Bihar-Nepal Border is upto 18 m³/hr which is significant energy saving features for ground water resources development. It is construed that ground water development in Tarai zone in last few decade has lowered the peizometric head. Thus the Indo-Nepal transboundary aquifer management across the border is important for saving auto flowing condition. In general ground water flow is toward south moving towards India from Nepal border. The Upper Siwalik conglomerate is a potential aquifer unit intermittently found in Siwalik rocks across the border.

Transboundary Aquifers of Indo-China, Indo-Bhutan and Indo- Myanmar Border

Indo-China: The Indo-China international border is running through J&K, Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh of India and is conspicuously separated by the Himalayan range. The terrain is extremely difficult and is characterised by high altitude land and valleys. The area is largely occupied by semi-consolidated to consolidated sedimentary and crystalline rocks. At many places, the area is covered with snow and glaciers, which is important for groundwater recharge. Groundwater draft is limited across the border due to scanty population, sloping topography and low yielding aquifers in the area.

Indo-Bhutan:- The Indo-Bhutan border area along Assam is largely covered by alluvial aquifer and is extension of the Bhabar –Tarai zone with moderate to high yield potentials (150-200 m³/hr).

Indo-Myanmar:- The Indo-Myanmar border is predominantly covered by semi-consolidated Tertiary formations. The area is difficult to approach and is having low ground water yield potential for its development.

SUM UP

Transboundary aquifers are significant for the food and drinking water security in coming future in the Indian sub continent. The broad recommendations for the management of Transboundary aquifers pertaining to the Indian Sub-continents are as follows:-

- The transboundary aquifer systems of Punjab and West Bengal are under stress due to overexploitation and contamination, which need prioritized attention.
- The retrieving glaciers due to the possible impact of climate change can be significant for change in recharge behavior of transboundary Indo-gangetic alluvial aquifers system, which need special emphasis.
- Indo-Pak transboundry aquifer of arid region contained fossil fresh groundwater need protection as precious drinking water resource.
- Proper identification of transboundary aquifer and its characterization has to be ensured.
- There is a need is to assess and quantify the flows as well as study the chemical quality of the water flowing across the countries

REFERENCES
- Khandakar M. A. T. (2010) Setting Stage of Cooperation Between Bangladesh and India for Transboundary Aquifers; Proc. of Transboundary Aquifers: Challenges and New Directions UNESCO-IAH-UNEP Conference, Paris, 6-8 December 2010.
- S.K.Sharma, 2009, Transboundary Aquifer System of Indian Sub-Continent, Technical Papers;Workshop on Transboundary Aquifer Systems by CGWB, MOWR, New Delhi , 23rd March 2009
- Siddhi Pratap Khan and Pratap Singh Tater, 2006, Hydrogeology and Groundwater Resources of Nepal. Workshop on the Role of Environmental Performance Verification for Safe Water in Nepal,(ICIMOD),Kathmandu, Nepal, 30th November and 1st December, 2006
- Nayyer Alam Zaigham, 2002: Strategic Sustainable Development Of Groundwater In Thar Desert Of Pakistan, Sciencevision,Vol.7,No3&4, P 61-74.
- CGWB, 2001, Hydrogeology And Deep Ground Water Exploration In Ganga Basin.
- G Ram Mohan Rao, Arun Kumar & P R Gupte ( 1993), Hydrogeology of a part of Great Rann of Kachchh, Gujarat, CGWB, WCR Report.

S.C.Dhiman
Chairman, Central Ground Water Board, Faridabad
S.K.Jain
Scientist-D, Central Ground Water Board, Faridabad