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Sunday, September 27, 2020

Explained: Why flooding is a problem for Gurgaon every monsoon

Following heavy rains, Gurgaon on Wednesday found itself submerged. Among the worst affected stretches were the Narsinghpur-Khandsa stretch, Golf Course road and seven of the 11 underpasses in the city.

Written by Sakshi Dayal , Edited by Explained Desk | Gurgaon | Updated: August 22, 2020 7:57:02 am
Gurgaon, Gurgaon news, Gurgaon waterlogging, Gurgaon floods, Gurgaon rains, Gurgaon weather forecast, Indian ExpressAn underpass was submerged, with fire tenders deployed to pump out water. (Express Photo: Praveen Khanna)

How much rainfall did Gurgaon receive on Wednesday?

As per figures released by the district administration, Gurgaon received 23 mm rainfall in the 24 hours ending 8.30 am Wednesday, with another 95 mm between 8.30 am and 11 am. This, officials say, is “six to seven times” the usual amount of rain received by the city. As a point of comparison, in 2016, 52 mm rainfall wreaked havoc, leading to waterlogging in several parts and causing traffic jams that left several people stranded on the roads for more than six hours.

Which parts of Gurgaon were most impacted by the rain?

Officials say the entire city was impacted; there was waterlogging across Gurgaon. Among the worst affected stretches, however, were the Narsinghpur-Khandsa stretch, the Golf Course road, and seven of the 11 underpasses in the city. The DLF Phase 1 underpass on Golf Course road was exceptionally unfortunate, with rainwater collecting almost till its roof.

Why was the impact particularly bad on the DLF Phase 1 underpass?

The location of the underpass itself leads to the structure being vulnerable, with runoff water from the Aravalli Hills travelling down through the Phase 1 area and filling the underpass. Since the structure is located at a level below the main drainage network of the city, DLF has constructed a concrete rainwater harvesting chamber into which any rainwater is meant to flow. In the event of this filling up, three pumps located in the underpass are meant to be activated, pumping the water up to the main drainage network. On Wednesday, however, once the chamber filled up and the pumps were activated, the water, instead of flowing into the drainage network, experienced a backflow, making it impossible to pump it out.

In several other parts of the city, officials said, a similar backflow occurred, making it impossible to clear the water.

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Gurgaon, Gurgaon news, Gurgaon waterlogging, Gurgaon floods, Gurgaon rains, Gurgaon weather forecast, Indian Express An aerial view of Gurgaon on Wednesday.

What was the reason for this backflow of water?

Rainwater normally flows into the Badshahpur drain, which then carries this to the Najafgarh drain. On Wednesday, the unusually heavy rainfall led to the Badshahpur drain flowing at full capacity, leading to it overflowing and making it impossible for the rainwater to be pumped out.

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Why is waterlogging an issue in Gurgaon every year?

As it is located at the foothills of the Aravallis, Gurgaon is at a disadvantage. Until the 1980s, the city had natural “jheels” through which rainwater would flow. Due to rapid urbanisation in the late 90s and early 2000s, however, several structures were built on top of, or in the route of these jheels, blocking the natural course of the water.

Further, a lot of concretisation took place on the Badshahpur drain itself — the main drainage system — with this encroachment further limiting the capacity of the drain. In several new sectors of the city, a drainage system is yet to be constructed and connected to the main drainage system of Gurgaon.

Gurgaon, Gurgaon news, Gurgaon waterlogging, Gurgaon floods, Gurgaon rains, Gurgaon weather forecast, Indian Express Trucks submerged in Gurgaon on Wednesday.

What is being done to resolve the waterlogging problem in Gurgaon?

In 2016, a project was announced to expand the Badshahpur drain at Khandsa village, a 600 metre stretch where its width reduces from 30 metres to 10 metres. Most of the work on this has been done, but some still remains due to litigation over structures that need to be removed. A comprehensive drainage project for the city has also been approved by the state government which will focus on arresting rainwater from high level areas by draining them out through creeks. In addition to this, the administration is also looking to develop 20 check dams in the Aravallis to check the flow of water down into the city.

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