3 basins, 18,000 km of drains: What’s Delhi’s ambitious plan to flood-proof city

This year, the infamous flood zone under Minto railway bridge did not see waterlogging despite unusually heavy monsoon rainfall, thanks to local drainage fixes and the use of multiple high-capacity pumps. But several other areas across the Capital continued to face the same problems that they have grappled with for years now.

The interlocking web of Delhi’s stormwater drains, with a network length of more than 18,000 km, is managed by eight different government agencies that has inevitably led to inefficiencies and mismanagement.

Poor infrastructure, inadequate maintenance, rampant encroachment, civic neglect, and insufficient desilting have further diminished the capacity and effectiveness of the drainage system. On September 19, Union Minister for Housing and Urban Affairs Manohar Lal unveiled a Rs 57,000 crore Delhi Drainage Master Plan 2025, a 30-year solution for urban flooding that aims to reduce instances of waterlogging and flooding by 50% in the next five years.

The plan for revamp

The new Drainage Master Plan is a comprehensive, first-of-its-kind roadmap in almost a half century that takes into account a wide range of factors and offers agency-wise solutions to each problem.

Based on a classification done by IIT-Delhi in 2018, the new master plan has divided the city into three drainage basins — Najafgarh, Barapullah, and Trans-Yamuna — which are divided further into sub-basins.

Private consultants studied factors including the reasons for waterlogging and delay in the draining of surface water runoffs, rainfall distribution, and the disposal and reuse of stormwater. They suggested solutions and made recommendations, which have been included in the plan.

A hydraulic study, based on the movement of water on the surface, was carried out at locations across the three basins to identify areas at high risk of flooding.

Rainfall analysis is an important component of the plan. At the request of the Public Works Department, the Design Storm Unit of the India Meteorological Department’s (IMD) Hydromet Division carried out a comprehensive study on the Intensity Duration Frequency (IDF) curve for the Palam station, the plan states.

The IDF curve shows the relationship between average rainfall intensity, its duration, and frequency of occurrence. It helps to estimate the probability and characteristics of extreme rainfall events for specific return periods, and is used in the designing of hydrological structures such as drainage systems and dams.

The study analysed rainfall data from 1993 to 2023 and mapped it against the existing design of the city’s stormwater drainage systems. The plan has taken into account projected rainfall trends up to 2054.

Challenges & solutions

GRADIENT & GRAVITY: The Aravalli hills and associated outcrops ensure that stormwater is directed mainly towards lower elevations to the east. The area to the east of the Yamuna, on the other hand, was originally part of the river’s floodplain, and is low-lying.

In the low-lying areas, the flow of stormwater is impeded further because of irregular drain sections, improper gradients, and choked or closed drains, officials said. Disposal of solid waste, silt, and construction and demolition debris reduces the carrying capacity of drains, several of which flow in from outside the state.

CLIMATE CHANGE: Changes in climate patterns have meant that the intensity of rainfall events have in recent times often exceeded the designed capacity of stormwater drains, officials said. The rainfall study has shown an 11% increase in average rainfall intensity — typically measured in mm of rain per hour — from 1994 to 2023; an increase in intensity of another 11% is projected over the period until 2054. The plan focuses on increasing the carrying capacity of the drains.

PARKS AND DRAINS: A major suggestion in the plan is to link water bodies with drains to improve their flood-handling capacity. Integrating with DDA’s Master Plan 2041, the drainage plan suggests the development of green areas of 46 parks owned by DDA, which have potential for diverting stormwater. Feasibility reports for 27 of these parks are already available.

“Facilitating the improvement of the groundwater table by providing rain harvesting systems is a key objective of the project,” a senior PWD official said.

The road ahead

In the first phase of implementation of the project — planned from 2025-26 to 2026-27 — the government is aiming at critical flood control, including rehabilitation work for priority flood locations such as Minto Bridge, ITO, Mathura Road, Drain Number 14, Barapullah Drain, Drain Number 12, M B Road, and DDU Marg. Remodelling and upgradation of the drainage infrastructure to “eliminate flooding in the basin” is also on the cards.

However, the detailed project report (DPR) is yet to receive final approval from the Delhi government, and work on the ground is likely to be delayed.

“PWD has sent the cabinet note to the minister for his approval, following which it will be forwarded to departments like Finance for their comments. Once their objections, if any, are addressed, the note will be placed before the cabinet. The tendering process will start after cabinet approval is received,” a senior official working closely on the project said. Also, officials said that a city court has recently asked the government to include a sewerage plan in the Drainage Master Plan, which will require some modifications to the project.

“The court has directed that instead of re-developing stormwater drains and sewage drains separately, work should be executed parallely as part of one plan, so that future conflicts may be avoided and crucial issues may be addressed,” the PWD official said.

“The current plan focuses on the stormwater drain network, but the situation of sewer drains in the city is perhaps worse,” the official said.

Officials also flagged potential implementation challenges such as ensuring inter-departmental coordination, managing conflicts with existing infrastructure, adapting to changes in urban development patterns, and accommodating evolving climate patterns and extreme weather events.

From the homepage

Pakistani ‘person of interest’ arrested recently was in touch with Sonam Wangchuk, sent reports across border, claims Ladakh DGP

IAS officer removed for ‘administrative reasons’ after technical glitches at PM’s Rajasthan rally

Five killed, one critical as Thar crashes into divider on Delhi-Jaipur Expressway