Why Indian cities flood within hours of rain

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02-07-2025

W hen the monsoon arrived in Delhi last year, it brought welcome respite from the relentless heat. But for Rahish, this comfort was short-lived.
With just a short spell of rain, the street in front of his tailoring shop in South Delhi's Tigri was waterlogged with about a foot of rainwater. It took around four hours for it to subside.
But Rahish was expecting it. After all, he had seen the pattern repeat year after year for the last 30 years. This year, the water even entered his shop and damaged some of his cloth material. 'I am still paying for the losses,' he said, as he finished the final stitches on a pair of trousers for a customer.
'The biggest problem is that there is no exit for the water that collects,' said Rahish.
Tigri is adjacent to Sangam Vihar, one of Delhi's largest unplanned colonies, where waterlogging occurs frequently.
Excess rainwater is meant to flow into the Barapullah stormwater drain here, but most of the smaller drains that connect to it are blocked with solid waste. As a result, water seeps through manholes and flows into the sewerage system under the roads.
'But since the pipes are small, very soon it starts giving out backflow,' Rahish said. When this happens, rainwater, mixed with sewerage, flows out and contributes to the waterlogging.
This is what happened last year when water entered his home in Tigri. 'We could not even use the toilet because we have an Indian-styled one, and it was covered with sewage water,' he said.
It isn't just low-income neighbourhoods like Tigri that are affected by waterlogging. During the monsoon last year, rainwater also stagnated in Defence Colony, an upscale residential colony around eight kilometres north.
'Numerous basements flooded here, and people lost about Rs 10 lakh to Rs 20 lakh worth of furniture and other things they had stored,' said Bhavreen Kandhari, a resident of the colony.
The story is a familiar one across Indian cities and towns, most of whose stormwater drains are proving inadequate for increasing bouts of heavy rainfall. Last month was Mumbai's wettest May in more than a hundred years – rains left roads waterlogged and commuters stranded, and even gushed into a newly inaugurated metro station. Media reported that the rains revealed 80 new places that were prone to flooding, and municipal corporation officials stated that they were planning to increase drainage capacities of vulnerable areas.
Similar scenes of flooding played out in Bengaluru, where three people were also killed in rain-related accidents.
While part of the reason for frequent flooding in Indian cities is the changing rainfall patterns – more rain tends to fall in shorter periods – another key factor is poor drainage. The pattern across cities is common: poorly planned expansion means that existing drains typically lack adequate capacity; and even these are poorly maintained, almost guaranteeing their failure during days of high rainfall.
In Delhi, both Defence Colony and Tigri are adjacent to the Barapullah drain. This is a naturally occurring seasonal stream that is a tributary of the Yamuna, and earlier came alive only with the monsoon, thereby acting as a natural stormwater drain. It originates from Mehrauli in south Delhi, and flows past congested homes in Chirag Dilli, the localities of Defence Colony and Jangpura, and the busy Hazrat Nizamuddin railway station, shortly after which it meets the Yamuna.
Numerous smaller, local drains constructed by the Public Works Department are connected to this natural drain – they are supposed to collect rainwater and feed it to Barapullah, which should then carry it to the Yamuna. With these smaller drains included, Barapullah has a vast catchment area – it covers 91% of South Delhi and 95% of Central Delhi.
Other stormwater drains carry out similar functions in other parts of the city – Najafgarh drains out West Delhi, while across the Yamuna, the Shahdara and Ghazipur drains carry out the same function. In all, 201 natural drains flow through Delhi.
However, Scroll 's ground reporting found that in numerous places, like Tigri, the local drains that connect to main stormwater drains are frequently blocked with solid waste, restricting the flow of water through them.
'The drains are all connected to each other, but because of such blocks the water does not reach the main drain,' said another Tigri resident Prem, pointing to a blocked drain next to the road on which a gift shop she runs is situated. She explained that the road gets waterlogged every year.
The Delhi Traffic Police has identified over 260 hotspots that face frequent waterlogging in the city. This urban flooding occurs even during short spells of rain.
In Sangam Vihar, for instance, a Centre for Science and Environment report found that with sewage lines also working as stormwater drains, flooding and sewage spillover occurs 'even in a short 15-minute rainfall episode'.
In response, the Municipal Corporation of Delhi has focused on desilting the network of stormwater drains to ensure that they function at optimum capacity. As of early July, the corporation still had to complete 25% of this work.
But experts told Scroll that while desilting is important, long-term answers to Delhi's waterlogging would involve taking into account the natural topography of the city, delinking sewage with waste water, reviving old ponds and finding alternate exit routes for rainwater that exceeds the carrying capacity of drains.
'The administration is not looking at the issue as a system,' said AK Gosain, former professor at the Indian Institute of Technology Delhi, who has worked extensively on problems of water resources engineering. Without such a holistic approach, he added, tackling individual issues through strategies such as desilting was unlikely to produce the desired results.
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D elhi sees broadly two kinds of flooding.
The first results when there is a rise in the level of the Yamuna, on whose banks Delhi is situated. When this occurs, usually in the monsoons, water from the river flows into the stormwater drains, creating a backflow into the city.
'In such cases, the irrigation and flood department shuts the gates that connect the drains to the Yamuna, so that the river's water does not go into the city,' said Rajender Ravi, founding member of the People's Resource Centre, which researches infrastructure, rivers and urban agriculture. But, he added, this also prevents water in the city from draining into the Yamuna, leading to waterlogging anyway.
Low-intensity floods of this kind, where the river does not rise above its warning level of 204 metres, occur almost every monsoon.
Occasionally, these floods can also occur at a much greater intensity. This is what happened in the 2023 monsoon, when the Yamuna flowed at a level of 208.66 metres above sea level, breaking the earlier record of 207.49 metres in 1978. The irrigation and flood control department's website notes that the city saw eight such floods between the 1960s and the 1990s.
Such floods have also occurred when water levels rise in manmade tributaries of the Yamuna. One such tributary begins in the Najafgarh lake, which is fed by the Sahibi river, a natural tributary of the Yamuna. In 1865, the British drained this large lake out to create more arable land – to do this, they created a new channel to the Yamuna, which came to be known as the Najafgarh drain. In 1967, this channel as well as the lake itself flooded.
But a far more frequent kind of flooding is the waterlogging that occurs within localities even when the Yamuna is not in spate.
These floods are primarily caused by unplanned construction as the city has expanded. 'Because of so much concretisation, there is a lot of surface flow of rainwater which is not percolating into the ground naturally, because there is no soft space for the water to enter,' said Manu Bhatnagar, who heads INTACH's natural heritage division, and has led work on rejuvenation of drains in Delhi.
He added that there was also a lot of 'poor engineering' of drainage systems – for example, the openings of several engineered drains are higher than the grounds they are supposed to drain.
A major impediment to tackling this problem is the fact that administrative authority over stormwater drains is currently spread out between ten institutions, including the flood and irrigation department, the Delhi Jal Board, municipal corporations and public works department.
The Delhi government has attempted to tackle the problem. To start with, it asked Gosain and his team at IIT Delhi to consolidate data from various government departments on the existing capacity and function of stormwater drains, and then indicate points at which there were problems. The government also asked the team to suggest possible solutions. They were to compile the information and recommendations in a drainage masterplan – the first such to be drawn up since 1978.
When the team began gathering available data, they came up against stark limitations.
In some instances, 'We found only a line was made on a GIS map,' said Gosain.
'There were no dimensions, no invert levels,' he added, referring to measurements that are essential to ascertain the capacity of the stormwater drains. 'These are the basic data that have to be used to understand why water is not being evacuated.'
The team also struggled because several departments delayed providing information to them. Gosain suggested that in some instances, team members could themselves collect data from the ground, and submit it to departments for vetting.
For the next 18 months, his team collected this data, both from the ground and from different departments, analysing the functioning of stormwater drains and identifying areas that faced the most waterlogging. They also made recommendations, such as correcting the slopes of artificial drains to prevent stagnation. In 2018, they put together a new masterplan.
But the report noted that though government departments had agreed beforehand to vet the data that the team compiled, not all departments had done so. It stated that 'It was unfortunate that various departments passed on the survey data without vetting the data properly.' Some departments, like the Delhi Development Authority, did not even send the data the team had sought.
Though the government itself was responsible for some of these shortcomings of the report, a government committee that reviewed the master plan put the master plan on hold in 2021, citing 'discrepancies in data'.
It was only this April that the Public Works Department announced that by June this year, it would finalise a detailed project report for the drainage masterplan.
Gosain hinted that he was disappointed with the delay in implementing his team's solutions, 'We prepared this huge scientific database,' he said. 'It is possible to reduce the extent of flooding by implementing the recommendations made by our study and accepted by the government, as long as they do it with proper intent and effort.'
A mong the major measures that the government undertakes each year to try and tackle flooding is the desilting of stormwater drains.
In May, across Delhi, workers with large spades were seen entering manholes and clearing wet mud from the manmade drains. Along the larger natural drains, like Barapullah, large bulldozers did the same work. This work, typically done before the monsoon, is aimed at increasing the capacity of the drains.
But experts pointed out that poor planning has made it impossible for desilting to be carried out to the extent needed. Specifically, in many areas of the city, long stretches of these drains have been covered over in ways that leave them inaccessible. 'When we were analysing the data and preparing the master plan, we found many stretches of drains around 1 km to 2 km, where there is no access to the drain and desilting is not possible,' said Gosain.
'Stormwater drains are only supposed to be covered temporarily so as to gain access whenever required,' he added. 'But now, most are permanent. Unless you break them you won't know if the drain is silted or not.'
In Defence Colony, the Delhi Development Authority covered large portions of Kushak drain – a part of the Barapullah drain – to create a park. Kandhari said that residents had raised their voices 'for years to not cover the drain since it prevented routine inspection, desilting and maintenance which caused silt to build up, stagnate, and lead to foul odour'.
This year, the Municipal Corporation of Delhi is attempting to rectify this mistake. An official told Scroll that they had broken large rectangular tracts of the covered portions of this drain so that bulldozers could scoop out silt.
'It is such a waste of resources,' said Kandhari, who recorded a drone video along the Kushak drain where these bulldozers can be seen at work.
Kushak Drain Saga ⬇️ #DefenceColony
*Started covering: 2009
*Stalled: 2013
*Abandoned: 2014
* @rsuri54 moved NGT: 2015 → SC twice over→ Yamuna Committee (till 2021)
*2025: Back to NGT
Citizens suffer for decades while absurd decisions go unchecked.
Video as on 2/6/25 ⬇️ pic.twitter.com/abzwQvHmZh
— Bhavreen Kandhari (@BhavreenMK) June 3, 2025
It was not only residents who opposed this work. In 2015, the National Green Tribunal noted that work of covering drains had begun in Defence Colony and other parts of south Delhi, but that this would have 'very adverse impacts upon the environment and ecology of Delhi'. It added, 'This would result in more flooding, explosion of diseases and clogging of drains.'
Many smaller drains within colonies have also been covered, such as with footpaths, or with extensions of shops.
'In most of the colonies, rooftop water is connected to the sewer line, which is not designed to get the stormwater,' said Gosain.
Elsewhere, drains have temporary coverings. In Tigri for example, Prem pointed to a few shops that had covered the naalas running outside their shops with cemented slabs, but ensured that they had iron handles that would allow them to be lifted. But allowing this access has not helped residents.
'These can be opened,' she said. 'If the MCD comes tomorrow to clean these drains, no one will say no. But they should at least come.'
It was not just silt that hindered the flow of water in the drains. Prem also pointed towards a cave-like cemented structure on one side of Tigri's market – this was an opening to a stormwater drain, towards which the ground around was intended to slope, so that water would flow into it.
The opening to this drain had not been cleaned for years, she said. It was choked with plastic packets and other waste, and had no water in it. During rains, too, residents said, this drain did not carry any water at all.
W hile in many places, rainwater enters the sewer system and causes floods, elsewhere, sewerage is directly released into stormwater drains, polluting them and choking their capacity.
On an early June morning, a portion of the Barapullah flowing in Chirag Dilli was a muddy green channel with plastic waste and cloth material on its banks. But experts noted that up to the monsoon period, which typically begins at the end of June, the drain should technically be empty.
'Over a period of time as urbanisation surrounded them, stormwater drains have been used as a substitute to sewer systems,' INTACH's Bhatnagar said. 'Earlier in the non-monsoon period there was never any flow. Now around the year the flow is there and that is basically sewerage.'
During the rains, since stormwater drains are already carrying sewage, they have limited capacity to take on excess rainwater.
A court-appointed Yamuna Monitoring Committee flagged this problem in 2020 – it found that sewage was mixing with stormwater in 144 places in the city. The IIT Delhi Master plan found that at least 50% of the capital territory does not have access to the engineered sewer system, and that 'sewage generated from these areas is inevitably discharged into the storm water system', which leads to 'overflows and sluggish movement of the storm water within the drainage network'.
Not just sewage, even industrial waste flows in these drains. When the Yamuna Monitoring Committee did a random survey of industries in Bawana and Narela between 2019 and 2020, they found that 29 industries were discharging their wastewater into stormwater drains.
The National Green Tribunal also issued directions to the Delhi Jal Board in 2015, 2017 and 2019 to ensure that stormwater drains do not carry sewage. In 2017, the board claimed that it had indeed stopped the entry of sewage into 11 out of 17 drains where it had been mixing with stormwater. But upon ground verification, the committee found that a number of these drains were still carrying sewage.
The Municipal Corporation of Delhi official agreed that sewage and industrial waste continues to flow into nalas. 'But that is anyway the responsibility of Delhi Jal Board,' he said.
Scroll emailed Delhi government authorities, seeking their responses to criticisms of poor planning and management of the the city's stormwater drain system. This story will be updated if they respond.
I n some parts of Delhi, the Public Works Department has proposed that it will lay drains of a larger width to prevent waterlogging. But experts argue that this would not be practical because it would entail digging up large parts of the city.
'The other option we have is to use and rejuvenate all the existing waterbodies, induce infiltration through rainwater harvesting, create retention storages in the city to reduce the stormwater and flooding to some extent,' said Gosain.
Indeed, in the master plan, Gosain and his team created simulations based on the data of slopes and drains they collected, to see if waterbodies in Delhi could naturally absorb the rainwater run-off. After mapping existing lakes and ponds in the three major drainage basins – Najafgarh, Barapullah, and Trans Yamuna – they found that waterbodies 'could store a considerable volume' of water.
In Budhela, an urban village in south-west Delhi, residents explained that up till about two decades ago, an old pond or johad, played exactly this role. 'This is where we used to take cows and goats for a swim, and we would swim ourselves,' said Ramniwas, a resident of the village. He explained that the natural incline of the area was such that during rains, runoff from the interiors of the densely laid streets of Budhela would flow into this rainfed lake. The village is part of the Najafgarh drainage basin, and the main Najafgarh drain flows less than a kilometre from Budhela.
But in 2002, Delhi Development Authority acquired the pond from the gram sabha and handed it over to Delhi government's cultural wing to develop a building to host cultural events. To make the ground stable, the Delhi government filled the pond completely in the years following it.
'Since that time, we have started seeing waterlogging issues in a few of our streets like this one,' said another resident Harmohan, as we walked on a street adjacent to the boundary of the pond.
Budhela's waterlogged street in the rains has also presented a health hazard – Harmohan explained that numerous mosquitoes breed on the still water, raising the risk of diseases spreading among residents.
It was only in late 2023 that the construction of the building began on the land where the pond had been. In 2024, a resident challenged the project in the Delhi High Court, arguing that the court had set precedent in 2013, when it directed the Delhi Development Authority to cancel all allotments of land on waterbodies wherever the land was still vacant – the court had also ordered the authority to revive these water bodies.
This March, the Delhi High Court stayed the construction of the building.
When Scroll visited the johad on a hot June morning, a half constructed two-storey building stood in the depression of the dry pond. 'We want the pond to be used as a pond, so that it can be used for the village residents,' said Ramniwas.
Experts also suggest other methods to tackle excess water that do not rely on stormwater drains – though they cautioned that the authorities had delayed acting on the problem. 'Public parks also might have certain depressed areas where the stormwater can collect and recharge acquifers,' said Bhatnagar. He explained that rainwater being collected from roofs in homes around those localities could be directed into these depressions, rather than into into stormwater drains.
For now, residents are unsure of how much the desilting work in the city will help during the monsoon. Tigri's Rahish said that he had been writing to different authorities for years to pay attention to the waterlogging in their locality, but that nothing had changed. 'When it rains, the water stops, our lives stop for a few hours,' he said.