Mapping Pune’s aquifers

Groundwater use has doubled in Pune. Comprehensive mapping of groundwater resources and better management and governance is the need of the hour.
Groundwater, an exploited resource (Image Source: India Water Portal) Groundwater, an exploited resource (Image Source: India Water Portal)

Pune continues to face a water crisis every summer despite having sufficient water, thanks to its geographical location and plentiful natural water assets. While enough of its water needs are taken care of by water supply from the Khadakwasla dam, the use of groundwater to meet the needs of the population continues to increase.

However, the relative invisibility of groundwater, the lack of information on available groundwater resources and the amount of groundwater being extracted, limits a complete understanding of the available water resources. This further restricts opportunities for proper planning and management of groundwater resources to deal with the future water crises.

A study “Pune’s aquifers: Some early insights from a strategic hydrogeological appraisal’ by Advanced Centre for Water Resources Development and Management (ACWADAM) an organisation working on groundwater issues, attempts to fill this gap by:

•    Conducting a detailed hydrological investigation of Pune city by mapping Pune’s aquifers and their characteristics
•    Providing an estimation of the quantities of groundwater extracted in the city of Pune
•    Developing a framework for better management of groundwater resources in the city

What lies beneath

Pune city is underlain by basalt layers (commonly known as Deccan Traps) formed from molten hot lava that occur as horizontal layers stacked one above the other. These layers are as thick as a few metres to hundreds of metres. The basalt layers occur in two forms - the vesicular and compact variety.

Vesicular formations can hold water in the form of ‘unconfined’ aquifers when they are up to 10 metres thick. Their water holding capacities depend upon the intensity of weathering, fracturing and jointing. These processes create open spaces or gaps within the rock, for storage and movement of ground water. The compact portions of basalt which occur below vesicular formations normally do not hold water, but when weathered, fractured and jointed, they have the potential to store water to form aquifers in ‘confined’ conditions.

Vesicular layers can be recharged from the surface above, but effective recharge can take place only upto 15 to 20 metres below the surface. Water from these unconfined aquifers is extracted from dug wells that usually tap this layer. Water from deep confined aquifers is extracted through bore wells and is difficult to recharge directly from the surface above due to the confining layer. Borewells can be effectively recharged only from specific areas where the confining layer ends.

Pune has five aquifers exposed over a topographic profile of nearly 250 metres. These aquifers are visible on the surface in different parts of the city and constitute the shallow unconfined aquifers that are accessed through dug wells. Other aquifers found at deeper levels in basalt units represent confined aquifers that are tapped by deeper bore wells. Pune’s groundwater is of moderate hardness, but does contain worrying biological contamination in the form of high bacteriological and E coli counts that vary spatially as well as temporally and can threaten the health of the population.

Groundwater dependency and recharge 

Peri urban areas of Pune such as Aundh, Baner, Pashan, Sinhagad road, Wadgaonsheri and Dhayari are the most dependent on groundwater.

The natural groundwater recharge and discharge areas for Pune city include those lying east of Dhankawadi, while the others include the western part occupying the ridge between Kothrud and Pashan and the - ARAI hill – Vetal tekdi – Chatushringi – Bavdhan – MIT college ridge. Smaller recharge areas can also be found in the Aundh-Baner-Pashan ridge line, Range Hills and Viman nagar, close to Pune airport.

Groundwater extraction in the city

Groundwater extraction in Pune city has doubled in the last nine years, from over 2 TMC in 2011 to nearly 4 TMC in 2018-19. This means that the city needs an annual recharge of 35% of its average normal precipitation, if current levels of extraction are to be sustained, according to the report.

Groundwater in the city is tapped by dug wells, bore wells and springs, but the well yields have been declining at a rapid rate. For example, evidence shows that while the number of wells in Maharashtra have increased ten times since the 1960s, the yield per well has been dropping since the 1990s.

In the 1960s, wells were shallow and did not fully penetrate the aquifer. Most of the groundwater was hand-drawn or bullock-drawn. Today, electric powered deep-well submersibles and solar powered pumps can extract water at much higher rates. Groundwater has become more divided as the number of wells have increased, turning basalt aquifers into ‘common pool resources’.

How to ensure sustainability of groundwater resources

The report identifies a threefold strategy to ensure sustainability of Pune’s  groundwater resources:

•    Planning for a comprehensive application of the practice of Managed Aquifer Recharge (MAR) in the city. These can include larger public recharge systems along with point-source systems that include injection recharge at strategic locations. The public recharge systems must be based on the main recharge zones identified for each of the five aquifers in the city.
•    Protecting the natural recharge zones that connect watersheds to Pune’s aquifers
•    Setting up a robust practice of groundwater management complimented by a groundwater governance framework for the city by sharpening the aquifer mapping exercise, and by catalysing Participatory Groundwater Management.

The report can be accessed here

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