Sunday, June 30, 2019

Groundwater Worries: Saving Pune's Hill Slopes


I wrote a short note on my Facebook page on Pune groundwater and its growing importance in response to a citizen's petition to save natural recharge areas that occur on several of Pune's hill slopes. There is a proposal for two roads (the petition mentions only one) to cut across these hills, which will result in the paving over of the recharge surface. In the picture below, the roads will be built at two levels across the slopes behind the green and yellow colored building.

 Forested Slopes of Law College Hill

Besides the threat to groundwater, there are other objections to the road, including its outdated route  and its preference for private vehicles over public transport.

Pune nature lovers and others too... do consider signing the petition and help save part of our precious remaining natural heritage.

Cross Posted from Facebook:

A couple of days ago it rained about 75 mm in central parts of Pune. If you consider a 1 area around your neighborhood, about 75 million litres of water came crashing down in a few hours. If just 2 percent of that infiltrated into the ground, about 1.5 million liters were added to our ground water resource through a 1 sq. km surface area.

Surprised that rock can hold this much water? Those who grew up swimming in the Tilak Tank of old won't be. It was fed by a natural spring. At any one time the pool held about 2.5 million liters of water. The Tilak Tank hole in the ground would have held much more, but excess water was being drained into a nullah. More recently, the Suvarnarekha building on Prabhat Road was demolished, and the builder excavated a hole for a basement. It soon filled up with ground water. It held about 5.5 million liters of water. As the builder started pumping out the water, more kept rushing in. Over a one and half year period up to 100 million liters of water was likely pumped out. All this water held under a few hundred square meter area!

Pune receives about 650 mm of rain annually. That means 260 billion liters of water falls yearly over a 400 area. How much of that is infiltrating into the ground.. 5 percent, 10 percent, 20 percent? No one knows for sure and the amount will be highly variable across a surface. But we do have an idea how much is being taken out. A recent estimate by ACWADAM, one of the leading experts on local hydrogeology, puts our annual extraction of groundwater to be 3-4 TMC, which amounts to 80-100 billion liters of water. This suggests that we are extracting more than the natural recharge, since ground water levels are beginning to dip at many places.

The Pune dam cluster collectively store 826 billion liters of water out of which 315 billion liters are allocated annually to Pune. Our increasing use of ground water at 80-100 billion liters annually, underscores the critical role ground water is beginning to play in our lives.

It is imperative that we redress the growing imbalance between extraction and natural recharge. We can do this by individual action of leaving ground uncovered around our homes, and also by protecting larger swaths of recharge areas where infiltration rates are particularly high. The Vetal - Hanuman Tekdi slopes have been identified by ACWADAM as an important natural recharge zone. They must be protected from being covered over by concrete by the proposed HCMTR and Balbharati roads.

Please sign this petition for saving Pune's tekdi slopes from being destroyed! Say no to the HCMTR and Balharati Roads.



A small addition to the above post. An earlier study by Raymond Duraiswamy and colleagues published in 2009 had identified the Hanuman (Law College) Hill slopes as potential recharge zones. The map below shows recharge potential of parts of Pune as identified using hydrogeologic criteria. The red rectangle (my addition) roughly outlines the hill slopes under threat of being paved over by roads. The study highlights an area inside the red rectangle (Table 20: Balbharati Building) as an ideal site for enhancing recharge and also points out old quarries in nearby places which could be repurposed to store runoff water for recharging the underlying aquifers. Unfortunately, some of these quarries are now being encroached by slums and also being used as dumping grounds for construction debris. 

Source: Raymond Duraiswamy, Vrishali Dumale and Usha Shetty 2009 - Geospatial mapping of potential recharge zones in parts of Pune city.

ACWADAM will be soon releasing a detailed study of the ground water situation of Pune along with maps of aquifers. I will post that information when it is made available.

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