‘We don’t want white-topped roads, as they increase waterlogging and don’t allow water to percolate’ is a common sentiment among many Bengalureans.

While drawing more and more water from Cauvery river, Bengaluru is doing little to recharge its groundwater. With the city extracting 100% of its groundwater, citizens don’t get water even after drilling down to 1,800 feet.

Yet BBMP is white-topping our roads over the existing asphalt, without structures like rain gardens or bioswales to capture stormwater. But are Bengalureans right in believing that white-topping worsens flooding? The answer is complicated.

Do white-topped roads hinder water recharge?

Hearing a PIL, the Karnataka High Court recently questioned the scientific validity of white-topping and said that tar roads make more sense for water seepage. 

But this is a common misconception: yes, concrete is impermeable, but so is asphalt. “How well water runs off the surface is a sign of a good road, whether concrete or asphalt. Roads cannot be made permeable as long as you’re ensuring safety. As soon as water seeps in, the road will become mushy and cause accidents,” said Sourabh Kumar, founder of Ecopath, an organisation working on converting industrial waste into green building materials. 

Poorly white-topped roads can worsen flooding

Though white-topped roads don’t cause flooding per se, citizens and activists say the way Bruhat Bengaluru Mahanagara Palike (BBMP) builds these increases the risk.

“With summer rains, we already see increased water runoff to the concretised sideways. The water doesn’t enter stormwater drains (SWDs) as garbage blocks the drain openings. This leaves pedestrians stuck on waterlogged footpaths,” said Abijith Ravi, resident of NR Colony where the road is white-topped.

“Since white-topping is done over asphalt roads, it raises the road level and increases flooding on the roadside,” said Parvathi Srirama from the NGO People for Environment Organisation. 

Dattatraya Devare of the NGO Bangalore Environment Trust says, “Tree pits are essential when BBMP concretises the roads and the pavements, to allow sufficient percolation to tree roots. Since white-topping increases the temperature on roads, healthy trees can keep the roads cool.”

Bengaluru has four different types of roads, all of which the BBMP has concretised to some extent:

• Arterial roads: These are high-capacity roads, often with 4-6 lanes, linking different parts of the city. Outer Ring Road, Old Airport Road and Bellary Road are examples. 
• Sub-arterial roads: These are smaller than arterial roads, but carry significant levels of traffic. Bannerghatta Road, Sarjapur Road and Indiranagar 100 Feet Road are examples.
• Collector roads: These roads connect residential streets to arterial/sub-arterial roads. They carry moderate traffic on 2-4 lanes.
• Local/residential roads: These are narrow streets within neighborhoods, with 1-2 lanes.

According to BBMP, Bengaluru has 80 arterial roads and 285 sub-arterial roads, spanning a total of 1,940 km. Lokesh M, Chief Engineer of Projects, BBMP, said they have white-topped nearly 200 km of roads. A well-done white-topped road can increase the life-span of the road with minimal maintenance. This would especially benefit the high-density arterial and sub-arterial roads.

However, currently the cons outweigh the pros due to the poor quality of work. Though BBMP says residential roads need not be concretised, many are being built poorly, impacting residents. “Roads that are just 20-25 feet wide in Koramangala 6th cross and 5th cross are white-topped unevenly with minimal space for run-off, and no tree pits. The residents struggle with flooding every monsoon,” said Jayakumar Gopalan, resident of Koramangala 6th cross. 

Several white-topped arterial and sub-arterial roads are already damaged as well. Mohankumar Nagar Road, a sub-arterial road in Mathikere, white-topped less than a decade ago, already has potholes. Madiwala underpass is uneven and starting to chip off within a decade.

In Sukhsagar road in Koramangala 5th block, the nearby manholes leak constantly. The underground sewage line here was not fixed before white-topping, and can’t be dug up now. “Every monsoon, we see cases of roadside trees falling in Koramangala. If we have no tree pits on white-topped roads for these trees to absorb water, how will they survive?” questions Jayakumar. 

“The runoff should feed the soil to keep the plants, bushes and trees alive. Roads should be designed with recharge pits to feed trees next to them,” said Vishwanath S, founder of Biome Environmental Trust. This is often the case with asphalt roads, but not white-topped roads. Hence, many trees along white-topped roads have been drying up.

Sourabh adds that tree pits contribute to less than 1% of recharge, but are essential to keep the trees alive. Soil and trees on the roadside also absorb runoff and reduce waterlogging.

“If people see more cases of flooding because of poorly white-topped roads, they will believe that roads have a role in percolation. It’s the responsibility of the government to construct quality roads,” said Hari Prasad HK, senior research associate at Well Labs, an NGO that designs solutions for land and water issues.

Currently, the third and fourth phase of white-topping is going on in Bengaluru at the cost of Rs 2,000 crore.

Recharge pits possible in drains along white-topped roads

BBMP’s 2010 SWD master plan proposed recharge structures in drains, and in 2011-12 BBMP allocated Rs 30 crore for the same. However, as per a 2021 report by Comptroller and Auditor General of India, BBMP did not execute many items in the master plan, including recharge pits. 

“Local organisations and MLAs took initiative to make recharge pits along asphalt roads in parts of Malleshwaram, Jayanagar, JP Nagar, and Koramangala,” added Vishwanath. He pointed out that installing recharge pits in the drains along asphalt roads is difficult compared to the recently white-topped roads, where both the drain and road are revamped simultaneously.

BBMP officials claim they have now started adding recharge pits in SWDs. “We are also trying to adopt bioswales in a pilot project,” said Lokesh, adding that he can’t reveal more details as the project is in the initial stages.

“By clearing silt and placing recharge pits every 100 metres, about 20% of the groundwater can be recharged,” said K Radhakrishna Pradeep, lead for environment and climate action projects at the NGO United Way Bengaluru. 

Pavements concretised due to garbage dumping: BBMP

“Charandi (SWD) is always associated with sewage and garbage. Most people don’t know that it is supposed to carry clean rainwater, and not dump garbage in it,” said Hari.

“We are concretising pavements and footpaths because people dump garbage in and around these, which causes rodent issues. Rodents then destroy the permeable cobblestones of footpaths and pavements,” said Lokesh from BBMP.

But government agencies themselves seem to be allowing the charandi treatment by ignoring the sewage entry into drains from industrial and residential premises. In this context, Vishwanath says, it’s good the city lacks recharge pits that would directly recharge the polluted drain water into aquifers. “There’s a lot of incidental pollution from the roads – grease, oil, fumes – that settle as silt and dust, especially in major arterial roads. This water should be taken to the lakes for treatment and then only sent for aquifer recharge.”

However, SWD treatment at the entry point of lakes is still at the early stages. “We don’t have one grade A lake (water fit for drinking) in Bengaluru,” said Hari. 

BBMP has given an Annual Maintenance Contract (AMC) to clean all rajakaluves (major drains) in the city every three months. Lokesh claims the smaller drains are “self-cleaning”. BBMP pourakarmikas are supposed to regularly clean the opening points to these drains. But this is not happening in many areas such as Koramangala, Hebbal and Yeshwanthpur, resulting in waterlogging.

Ineffective rainwater harvesting contributes to flooding

Water experts and BBMP say the huge amounts of runoff from the dysfunctional rainwater harvesting (RWH) systems of houses and apartments contribute to urban flooding.

“Sixty per cent of the city is private institutions and residential houses, 15% contain parks and the remaining 25% are roads. Despite mandatory RWH, if 60% does not recharge groundwater, the rest cannot completely compensate for it,” said Vishwanath. 

Read more: Digging a borewell in Bengaluru? Here’s a guide to groundwater extraction rules

“Flooding in the city would reduce by 80% if the residential houses and private institutions utilise RWH effectively,” pointed out Radhakrishna. 

“We don’t have aquifer mapping for Bengaluru. So we will not know which aquifer will recharge which area. So, it’s important to educate people to practice groundwater recharging so that they will benefit from it somewhere someday,” said Hari. 

Permeable walkways in other locations

Though roads themselves can’t be made more permeable, certain technologies can be used to improve water percolation in walkways in other premises.

For example, the product GridMats, by the social impact initiative Pothole Raja, is an eco-friendly road and flooring solution. It uses recycled plastic waste to make a honeycomb-shaped base on walkways, which is then filled with gravel to allow percolation.

Surya Narayana Bhatta, head of finance and project management at Pothole Raja, says this technology can be adopted in farmlands, parking lots, and roads within school and office premises, increasing the land available for water percolation. 

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• Three diverse communities, one goal: Beating water scarcity in Bengaluru