Every year, we witness flooding in our large metropolises and most state capitals. Normally, Delhi is in the news for flooding due to the overflowing of the Yamuna River when large volumes of water are released from the Tajewala dam upstream. However, on June 28, 2024, we witnessed flooding from a high rainfall episode in south Delhi. What explains the frequent in-situ urban flooding in Delhi? This happened in Bengaluru and Lucknow in 2023 as well. High rainfall and climate change are undoubtedly a reality. But is it just that, or something more?
To understand the recent flooding in Delhi, let us first understand why 15 minutes of rainfall causes flooding on the Mehrauli-Badarpur road (MB Road) in south Delhi. What does this have to do with understanding Delhi’s urban stormwater management challenges and those of other cities?
Our cities, particularly our large metropolises of Bengaluru, Delhi, and Lucknow, among others, are rapidly growing, resulting in very large built-up urban landscapes with dense habitation and unplanned and informal settlements all around their periphery. As our cities’ built-up areas expand, we are witnessing unprecedented in-situ flooding from rain, as seen in our major cities.
Bengaluru has expanded from 100 square kilometers (sqkm) to 800 sqkm in the last few decades. Delhi is bursting at the seams into neighboring cities in Uttar Pradesh and Haryana. With a plethora of construction activity, paved roads, and underground construction works like basement parking and underground metro lines killing valuable aquifers, where do we expect the rainwater to go?
Each city has its own distinct watersheds and drainage areas. Delhi has three, and so does Bangalore. Determining which areas will flood should be straightforward; these will primarily be at the catchment’s lower end.
There is a pattern of urban flooding, in which rainwater flows from one part of the city to another, because no stormwater conservation measures are in place where it rains. The lack of open spaces, parks, natural lakes, and water bodies within the dense unplanned settlements adds to the difficulty.
As a result, even a short rain episode in south Delhi’s Sangam Vihar colony causes the majority of the rainwater to flow down the MB Road. Stormwater then floods the dense settlement of Dakshinpuri colony and its residential areas. It then flows into the Dakshinpuri stormwater drain, meandering through posh and affluent areas of south Delhi before entering the Barapulla main drain and eventually the Yamuna.
The extremely heavy rainfall of 230 mm on June 28 caused massive amounts of stormwater from Sangam Vihar and subsequent catchments to flow down towards their natural drainage lines. With massive new construction projects in and around Safdarjung and south Delhi, including underground metro lines and large buildings with multi-tier basements, consuming valuable aquifer recharge potential, where could rainwater be absorbed?
There was not enough time for the natural drainage system to channel all the stormwater to drain out of upscale south Delhi localities.
If we are to address our cities’ urban flooding challenges, we must first understand this aspect of in-situ urban flooding, which includes stormwater flooding from both large built-up and unplanned residential areas.
What Needs to Be Done?
The Delhi Drainage Master Plan of 2018 identified flooding hotspots of Delhi. These were all along the drainage lines and already well known. But what needs to be done to address this is not explained.
Unless rainwater conservation is first implemented in and around the farthest catchments of our city watersheds, in colonies such as Sangam Vihar, to prevent their fifteen-minute rainfall deluge from flowing where it flows, flooding downstream cannot be controlled, nor can valuable rainwater be conserved. Given the twin challenges of extreme rainfall caused by climate change and large built-up areas that have resulted in in-situ urban flooding, we must consider both water conservation and stormwater drainage in our cities.
A recent study by the Delhi-based think tank Centre for Science and Environment (CSE) of Delhi’s water supply, sanitation systems, and stormwater challenges (using the case study of Sangam Vihar) highlighted this aspect of stormwater management as part of our Global South water-sensitive cities framework.
Delhi has a total of 426.55 km of natural drainage lines and approximately 3,311.54 km of engineered stormwater drains, which are managed by 11 different agencies. Yet these seem to not work for addressing urban flooding.
The Delhi Master Plan 2041 does lip service to addressing stormwater management and conservation, stating, “New development should be made in such a way that overall runoff from the area does not increase with the proposed urbanization. For that, necessary measures in the form of ponds, parks, porous pavements, green belts, artificial lakes, or other rainwater harvesting and storage structures, etc. may be adopted.”
It does not address how this will happen, given the densification of our urban population and increasing floor area ratio ceilings within Delhi. What infrastructure and what planning are required to address urban flooding in the national capital, which has its own unique drainage pattern and dense unplanned settlements on its periphery, is not mentioned in the master plan.
Edited By Megha Chaubey (Climate Change Expert)