Despite its shrinking greens, Delhi has significant tree diversity. Pradip Krishen, a naturalist, author and filmmaker, identifies around 250 tree species in the concrete jungle, in his book titled Trees of Delhi published in 2007. But these trees do not have the breathing room they need as the Public Works Department's pavement tiling projects enclose trees completely in concrete.
Unable to spread their roots, the trees do not last long enough and also weaken the footpath. Wide scale concretisation of footpaths and spaces around the houses also reduces groundwater recharge. Not only are the trees put to strain but also the rainwater heads off as stormwater through the drains instead of seeping into the ground. The drying up of groundwater affects the trees and strains their growth. Stormwater drains overflow leading to urban floods and waterlogging. Often during flash floods, the water has to be pumped out mechanically.
The traditional approach towards this problem focuses not on recharging groundwater but on dealing with urban floods and on designing stormwater systems. The government spends crores creating bigger drains and desilting the existing ones before monsoons so more stormwater can be carried away.
Considering that urbanisation cannot be reversed, can there be better designs to restrain its ill effects? There are not many examples of this in Delhi but recently, some individuals in the city have started efforts towards making water soak in naturally into the ground.
Pavements and porous tiles
A tree lover trained in social work, Padmavati Dwivedi has come to be known for her work in motivating people to protect the trees in their neighbourhoods. The first tree census in Delhi involving citizens was possible because of her non governmental organisation, Compassionate Living. But it wasn't easy. While many people were motivated by the idea of enhancing the green cover in the colony, some did not share information.
She not only keeps a record of the pavements and trees in Sarvodaya Enclave, the locality she lives in, but also knows where the rules are blatantly flouted, and reports all such cases to the authorities. Her unyielding stance may upset many but works well most of the time. From being sceptical at some point, her neighbours and the authorities have come to rely on her. While she keeps track of contractors and builders at work whenever any cementing of premises is going on, those among them who are up to the mischief of cementing their back or front yards have to keep an eye out for her. She has thus become the repository of historical information about trees in the locality and stays alert to what happened to each tree in the aftermath of a storm.
Policy and practice
The official policy (Delhi High Court order 2009 following a petition by an NGO called Kalpavriksh) states that all tree roots be provided with six feet space around them to enable them to breathe and recharge groundwater. The National Green Tribunal too had raised the issue of rampant concretisation and tiling around trees in 2013, based on a petition filed by Aditya Prasad, an environmental activist. The Ministry of Urban Development had, in 2002, issued guidelines stating that concretisation/ tiling should not be done on pavements except where there is heavy pedestrian movement. Even in that case, only porous tiles should be used.
However, "civic bodies and the PWD do not adhere to the norms", says Padmavati. "The Forest Department agrees with the norms but the Delhi Tree Authority is ineffective in circulating the rule", she says. Whenever she notices a violation, she informs the police and Forest Department. She sees to it that the concrete and tiles are dug out immediately. She believes that the focus should be on promoting the use of designs and construction materials that can imitate some elements of the hydrological cycle instead of altering it.
Many of Delhi’s alleyways need to be de-concretised and paved with porous surfacing. "The policies are in place, but civic agencies need to be geared to implement the same. That is hard to come by given the builder-government nexus, Padmavati says.
Porous surfacing at Jaipur
In nearby Jaipur an attempt has been made at porous surfacing. The city has India’s one and only porous asphalt parking lot at the Gandhinagar railway station. There is a test section here that even integrates rainwater harvesting. Prof Prithvi Kandhal who had helped the Franklin Institute of Philadelphia (USA) develop porous asphalt pavement technology for its parking lots, was able to persuade the Jaipur Development Authority to construct the parking lot in 2012. He put in a lot of effort to design and supervise its construction.
The rainwater that percolates down is stored in an underlying open-graded stone bed, which is around 225 mm thick and lets water percolate gradually into the soil below. The water lost to evaporation is minimal. The water infiltration capacity of these pavements is higher (0.8) than that of regular cropped areas (0.3).
The advantage of the design is that the rooftop rainwater harvesting systems of buildings adjacent to the parking lot can be integrated into the porous pavement. The cost is 32% higher if it allows for rainwater harvesting structures at Rs 605 per sqm for porous surfacing as against Rs 457 per sqm for conventional surfacing. The difference is just 18% in case rainwater harvesting is not integrated into the parking lot.
The design is useful for parking lots of institutional and residential areas. The problem is that of maintaining the topmost open-graded, porous asphalt section (75 mm). According to Prof Kandhal, the porous pavement constructed in the US still looks good and works well decades later. Even in India, the pavements, if maintained properly, can last more than 20 years. Generally, soil gets clogged and the recharge potential of the layer declines. This parking lot has worked efficiently during two monsoons but the Jaipur Development Authority has lost interest in maintaining it.
Prof Kandhal says that for recharging groundwater, architects and town planners would have to incorporate rainwater harvesting techniques and design porous pavements. This technology can significantly use the surface runoff water from roads and parking lots for recharging groundwater in urban areas. But only if maintained well.
This article was originally published on India Water Portal.
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Unable to spread their roots, the trees do not last long enough and also weaken the footpath. Wide scale concretisation of footpaths and spaces around the houses also reduces groundwater recharge. Not only are the trees put to strain but also the rainwater heads off as stormwater through the drains instead of seeping into the ground. The drying up of groundwater affects the trees and strains their growth. Stormwater drains overflow leading to urban floods and waterlogging. Often during flash floods, the water has to be pumped out mechanically.
The traditional approach towards this problem focuses not on recharging groundwater but on dealing with urban floods and on designing stormwater systems. The government spends crores creating bigger drains and desilting the existing ones before monsoons so more stormwater can be carried away.
Considering that urbanisation cannot be reversed, can there be better designs to restrain its ill effects? There are not many examples of this in Delhi but recently, some individuals in the city have started efforts towards making water soak in naturally into the ground.
Pavements and porous tiles
A tree lover trained in social work, Padmavati Dwivedi has come to be known for her work in motivating people to protect the trees in their neighbourhoods. The first tree census in Delhi involving citizens was possible because of her non governmental organisation, Compassionate Living. But it wasn't easy. While many people were motivated by the idea of enhancing the green cover in the colony, some did not share information.
She not only keeps a record of the pavements and trees in Sarvodaya Enclave, the locality she lives in, but also knows where the rules are blatantly flouted, and reports all such cases to the authorities. Her unyielding stance may upset many but works well most of the time. From being sceptical at some point, her neighbours and the authorities have come to rely on her. While she keeps track of contractors and builders at work whenever any cementing of premises is going on, those among them who are up to the mischief of cementing their back or front yards have to keep an eye out for her. She has thus become the repository of historical information about trees in the locality and stays alert to what happened to each tree in the aftermath of a storm.
Policy and practice
The official policy (Delhi High Court order 2009 following a petition by an NGO called Kalpavriksh) states that all tree roots be provided with six feet space around them to enable them to breathe and recharge groundwater. The National Green Tribunal too had raised the issue of rampant concretisation and tiling around trees in 2013, based on a petition filed by Aditya Prasad, an environmental activist. The Ministry of Urban Development had, in 2002, issued guidelines stating that concretisation/ tiling should not be done on pavements except where there is heavy pedestrian movement. Even in that case, only porous tiles should be used.
However, "civic bodies and the PWD do not adhere to the norms", says Padmavati. "The Forest Department agrees with the norms but the Delhi Tree Authority is ineffective in circulating the rule", she says. Whenever she notices a violation, she informs the police and Forest Department. She sees to it that the concrete and tiles are dug out immediately. She believes that the focus should be on promoting the use of designs and construction materials that can imitate some elements of the hydrological cycle instead of altering it.
Many of Delhi’s alleyways need to be de-concretised and paved with porous surfacing. "The policies are in place, but civic agencies need to be geared to implement the same. That is hard to come by given the builder-government nexus, Padmavati says.
Porous surfacing at Jaipur
In nearby Jaipur an attempt has been made at porous surfacing. The city has India’s one and only porous asphalt parking lot at the Gandhinagar railway station. There is a test section here that even integrates rainwater harvesting. Prof Prithvi Kandhal who had helped the Franklin Institute of Philadelphia (USA) develop porous asphalt pavement technology for its parking lots, was able to persuade the Jaipur Development Authority to construct the parking lot in 2012. He put in a lot of effort to design and supervise its construction.
The rainwater that percolates down is stored in an underlying open-graded stone bed, which is around 225 mm thick and lets water percolate gradually into the soil below. The water lost to evaporation is minimal. The water infiltration capacity of these pavements is higher (0.8) than that of regular cropped areas (0.3).
The advantage of the design is that the rooftop rainwater harvesting systems of buildings adjacent to the parking lot can be integrated into the porous pavement. The cost is 32% higher if it allows for rainwater harvesting structures at Rs 605 per sqm for porous surfacing as against Rs 457 per sqm for conventional surfacing. The difference is just 18% in case rainwater harvesting is not integrated into the parking lot.
The design is useful for parking lots of institutional and residential areas. The problem is that of maintaining the topmost open-graded, porous asphalt section (75 mm). According to Prof Kandhal, the porous pavement constructed in the US still looks good and works well decades later. Even in India, the pavements, if maintained properly, can last more than 20 years. Generally, soil gets clogged and the recharge potential of the layer declines. This parking lot has worked efficiently during two monsoons but the Jaipur Development Authority has lost interest in maintaining it.
Prof Kandhal says that for recharging groundwater, architects and town planners would have to incorporate rainwater harvesting techniques and design porous pavements. This technology can significantly use the surface runoff water from roads and parking lots for recharging groundwater in urban areas. But only if maintained well.
This article was originally published on India Water Portal.
