Here are five ways to counter groundwater depletion in the Ganga basin

Managements of river catchments, surface waterbodies, wastewater and the agricultural sector, in addition to a water resources database can restore groundwater and improve the Ganga’s flow

By Charu Upadhyay
Published: Monday 04 April 2022
Confluence of the Alaknanda and Bhagirathi at Devprayag in Uttarakhand. Photo: iStock

Groundwater is the largest source of fresh water on Earth. It, however, remains neglected as it is out of sight and not visible like surface water resources.

The Ganga basin is one of the world’s most important and heavily exploited aquifers for groundwater. Depleting groundwater in the basin is thus a matter of grave concern. Almost 25 per cent of the world’s groundwater extraction is happening here. 

Groundwater development categories
of blocks in the Ganga basin
No. Category Number of blocks
1 Over-exploited 407
2 Critical 116
3 Semi-critical 442
4 Safe 1,884
5 Saline 3

The basin, with a density of 520 persons per square kilometre (sq km) is home to around 600 million people. The depleting water table in the basin will directly affect 40 per cent of the Indian population that depends upon it for drinking water, irrigation, ecosystem services and livelihood.

Some 407 (14.27 per cent) of a total 2,852 administrative blocks in the 11 states of the Ganga basin (Uttarakhand, Uttar Pradesh, Madhya Pradesh, Rajasthan, Haryana, Himachal Pradesh, Chhattisgarh, Jharkhand, Bihar, West Bengal and Delhi), are already under the ‘overexploited’ category.

This is according to the Dynamic groundwater Resource of India-2020.

A research published in Environmental Research Letters IOP Publishing (2021) noted that during 2002-2016, the Ganga basin lost around 226.57 ± 25.22 cubic kilometres of groundwater — about 20 times the storage capacity of the largest reservoir (Indira Sagar dam) in India.

This research supported the facts published in the journal Nature (2018) that the groundwater storage in the adjacent Ganga plain aquifer had depleted by 30 centimetres (cm) per year and the water level of the Ganga river had reduced at different points from 0.5 to 38.1 cm per year between the summers of 1999 and 2013.

The Ganga is a gaining or effluent river, as the water flow is contributed through the melting of Himalayan glaciers and baseflow of the groundwater during the non-monsoon period. An outflow of about 13.28 billion cubic metres of groundwater (2011) is estimated during the non-monsoon months as a base flow to the river.

Aquifer typologies 

The Ganga basin’s sediments are mainly derived from the erosion of the Himalayas and further redistributed and deposited by the Ganga and its tributary rivers. 

The thickness of these aquifer-forming sediments varies from 1,500-2,000 meters bgl (below ground level). The top 200 metres of the basin sediments hold about 30,000 ± 14,000 cubic kilometres of groundwater. 

Moreover, the shallow aquifers (~50 metres) in the Gangetic alluvial deposits hold about 30 per cent of the total replenishable groundwater resources of India. About 8,300 billion cubic metres of groundwater is present in the basin of which, 99 per cent is in alluvium and one per cent is in hard rock aquifer.

These aquifers were initially considered to be a single, homogeneous aquifer system. However, these can be subdivided into different typologies based on groundwater recharge, permeability, storage, groundwater chemistry and sediment types. 

The major typologies are:

  • Piedmont margin
  • Upper Ganges
  • Mid Ganges
  • Lower Ganges
  • Fluvial-influenced deltaic area of Bengal
  • Marine-influenced deltaic areas

The differences in typologies determine the quality, volume and rate of flow of groundwater from the aquifers.

Aquifer typologies in the Ganga basin

A map of the Indo-Gangetic Plain

Groundwater aquifers have two types of storage — renewable and non-renewable. Renewable storage can be easily replenished during the monsoon period in comparison to non-renewable storage. The over-extraction of these non-renewable aquifers is the major cause of the depletion of groundwater in the Ganga basin. 

Aquifer challenges

The Ganga basin is dominated by groundwater use for its water requirement despite having surface water resources like rivers, streams, lakes, etc. Human interference has increased the unsustainable exploitation of groundwater.

Multiple factors have been identified in the Ganga basin as critical challenges for groundwater aquifers’ sustainability. These include:

  • Extensive use of non-renewable groundwater
  • Climate change
  • Increase in surface temperature
  • Precipitation deficit
  • Fewer rainy days
  • Reduced river flows in the non-monsoon period
  • Frequently occurring droughts
  • Rapidly increasing population and urbanisation
  • Land use and land cover changes
  • Industrialisation
  • Indiscriminate waste (solid and liquid) and untreated sewage disposal in water resources
  • Deteriorating water quality
  • Salinisation of shallow aquifers
  • Sea water intrusion
  • Mobilisation of naturally occurring arsenic
  • Increasing nitrate concentrations
  • Improper management

These factors have further affected water and food security.

Preventing more extraction 

The Ganga basin plays a significant role in the livelihood, economic activities and socio-cultural perspectives of millions. Laws, policies and management frameworks should be reinvented and reframed to ensure water conservation and improve water security.

Here are some possible strategies for groundwater restoration and environmental flow improvement of the Ganga river.

1. River catchment management: Conservation of green corridors, restoration and rejuvenation of small rivulets and tributaries, mapping of paleochannels for potential recharge zone to store floodwater, mandatory rainwater harvesting (RWH) and artificial groundwater recharge structures in the urban areas (where groundwater is five-six metres below the surface), will subsequently contribute to groundwater and river flow. The use of dysfunctional bore wells for recharging groundwater with clean rainwater will also be a good option.

2. Surface waterbody management: Restoration of ponds, lakes and other traditional water resource structures should be an integral part of the development projects of urban and rural areas and it will substantially develop groundwater potential.

3. Wastewater management: Dual sewage system for grey water and black water and promoting reuse of the recycled water in agriculture and horticulture. Industries should also be encouraged to increase water use efficiency, effluent treatment, reuse of used water, zero liquid discharge, etc. The National Green Tribunal in its order on December 6, 2019, also directed urban local bodies and concerned departments for the treatment of 100 per cent of sewage pouring into the river.

4. Agriculture sector management: Agriculture alone consumes more than 80 per cent of groundwater in the Ganga basin. On a global scale, we are only 25-40 per cent irrigation efficient. Water-efficient irrigation systems like drip, sprinkler, avoiding water-extensive crops and use of treated wastewater for irrigation should be adopted.

5. Development of database: An open / public database on all components of water resources could help policymakers and other stakeholders in proper management and mitigation of challenges and problems.

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