Deep trenches — several metres wide — are now being dug near key foothills across the city, to hold the water running off slopes. Officials said the pits will be filled with natural purification and filtration units, using sand, brick and stone.
What’s more, the trenches, according to PMC’s plans, will also prevent surface runoff from inundating major roads near the foothills.
“So, along with recharging groundwater, the pits will stop critical routes from being flooded during the monsoon,” a PMC official said, adding that PMC has already started a survey to identify areas where rainwater runoff from hilltops and slopes reach roads.
The trenching project, a collaboration between the PMC’s roads and drainage departments, also relies on important drainage surveys that were conducted by a private agency to divert rainwater.
A decade ago, the agency had identified 234 nullahs with a combined length of 362 kilometres that had the capacity to take runoff away from roads and residential areas. The agency had also found locations where the nullahs had been encroached, leaving the city with a goldmine of information on how to prevent urban flooding.
Another survey followed in 2016, which identified flood-prone locations. PMC officials said the new trench project combines data from the two surveys, to determine how best to conserve and divert rainwater. Among major areas earmarked for the project are Fergusson College Road, Canal Road (near SNDT campus) and SB Road. Civic officials said work on a trench has already started near the Fergusson College ground. It’s expected to ease flooding on FC Road and JM Road.
“PMC will earmark private and municipal land where rainwater harvesting can be carried out,” said Shridhar Yeolekar, an executive engineer from PMC’s drainage department.
Other possible locations for the new project include areas near Law College Road, Kothrud, Taljai Hill, Vetal Hill and Katraj.
“This is also about spreading awareness on rainwater harvesting. The trenches will help increase groundwater levels,” said a senior official from the roads department.
Pune is in desperate need of a recharged groundwater table. A recent report on aquifers by the Advanced Centre for Water Resources Development and Management (ACWADAM) had said that the city has permanently lost at least three million cubic metre or three billion litres of groundwater storage capacity due to construction.
Shashank Deshpande, a retired senior geologist from the Groundwater Surveys and Development Agency, said PMC’s trench project is on the right track, as long as it uses the right technique at the best locations. “Government-recognised techniques suchas continuous contour trenches should be used for better results. Moreover, factors such as the availability of aquifers should be considered before finalising a site, for best outcomes,” Deshpande said.
According to the ACWADAM report, Pune city has nine main unconfined aquifer systems.
In addition to this, there are 19 unconfined aquifers at higher elevations represented by the hillocks and ridges, particularly in the south and west of the city.
The report stated that protecting these recharge zones would primarily mean a “no-compromise protection” of catchments in three main watershed clusters: the Kothrud-Vetal hill-Chatushringi-Pashan-Bavdhanrange; Vishrantwadi-Vimannagar highland zone; Dhankawadi-Yewalewadi-Katraj range. The study found that some of the natural groundwater recharge and discharge areas for Pune city were situated east of the Dhankawadi area, while the other was in the western part, occupying the ridge that lies between Kothrud and Pashan.
Himanshu Kulkarni, former executive director and currently scientist (Emeritus) of ACWADAM said: “PMC’s trenching initiative is good. But, it should, at the same time, ensure stormwater drains have adequate capacity. Steps are also needed to revive natural streams, which will help in discharge of rainwater runoff in a natural way. ”
How countries are already tapping their ‘invisible water’
Invisible water’ is water hidden in soil moisture, plants and the atmosphere. Increasing these reservoirs will prove to be important for cities. For example, 90% of South Korea’s total water assets are ‘invisible’, which is why the country is retaining more plants and cutting down on surfaces that rebuff rainwater. In Singapore, nearly 86% of the population lives in high-rise buildings, where large rooftop collection points store water for toilet flushing and other household needs
Why ‘sponge cities’ are the future
‘Sponge cities’ are those with abundant natural areas having trees, lakes and parks, all of which absorb rain and prevent flooding. Experts believe ‘sponge cities’ may be able to handle the rise in rainfall global warming is set to bring. Globally in 2020, there were 26% more storms than the annual average of 102 events and 23% more floods than the annual average of 163. Pune, with its many hills and wide open spaces, could be turned into a sponge city, one that can absorb (and save) this additional rainfall