HT Monsoon audit: A spot check of stormwater drains

With the stormwater drains (both underground drains and nullahs) that help flush out floodwater during the rains not effective enough, their upgrading still remains a major concern for the city. Its inefficiency results in submerged low-lying areas during heavy downpour.

Following the 2005 deluge, several recommendations made by the Chitale Committee (appointed to look into the reasons behind the floods) are yet to be accomplished by the implementing body, the Brihanmumbai Municipal Corporation (BMC). The nullahs carry rainwater into the sea, making it a prime area for pre-monsoon work.

Desilting is a crucial aspect of monsoon preparedness as it leads to better flow of water accumulated in these stormwater drains. According to BMC data, there are 276.02km of different major and minor drains in the city. The BMC has claimed to have desilted more than 80% of all drains. The entire stretch of stormwater drains includes the Mithi River, an important natural stormwater drain.

Every year, the BMC divides the desilting work into three phases —pre-monsoon, during monsoon and post-monsoon work. In the past two years, the BMC is changing its methodology of cleaning these drains. For this year, the BMC has aimed to complete 70% of its nullah-cleaning work before monsoon, 15% during monsoon and rest of the work post monsoon. However, last year it was 60% before monsoon, 20% during monsoon and rest after monsoon. Apart from desilting, regular work of widening, maintenance and operations of drains is carried out.

Last year, areas around several major drains faced waterlogging during heavy downpour as the drains started overflowing. There were complaints that even areas around Mithi River at BKC faced serious waterlogging issues last monsoon. Mithi, one of the important major drains in the city, is being rejuvenated by the BMC. The natural stormwater drain had played a major role in the 2005 deluge. Under the Mithi River rejuvenation project, BMC will be carrying out work to clean the river and decontaminate it in four phases at ₹671 crore. The first phase, involving the installation of a treatment plant, is expected to be completed in two years.

Why does flooding occur every year?

Uncleaned stormwater drains, dumping of debris and other waste, encroachments alongside the drains and pending widening of drains, are the most common reasons pointed out by experts behind flooding. After the 2005 deluge, some of the recommendations of the Chitale committee involved renovation, augmentation of old stormwater drains, widening of nullahs, removing encroachments, providing service roads on either side of the drains, separation of sewage from stormwater drains.

As HT visited some pre-monsoon cleaning spots with experts, panellists pointed out several mistakes that the BMC has been doing. We inspected three crucial spots — Everard Nagar, Irla Nullah at Vile Parle and the Mithi River stretch at CST Road near Kurla-BKC. Firstly, most of the bigger drains have seemingly lost its slope, which is required to easily carry the accumulated water into the sea. The slope has been lost owing to uncleaned heavy silting over a long period. Apart from this, poor maintenance of retaining walls and excavated silt left unattended also result in the obstruction to the flow of the nullah. Charles Simoes, an expert on the HT panel, said, “Walls of nullahs must be cleared of all vegetations and roots, and corroded reinforcement must be treated or replaced. This will help in smoothening of walls to avoid any obstruction to the flow. Also, the civic body needs to change its methodology for cleaning these drains. There needs to be a dumper vehicle, while desilting is being carried out, so the excavated silt is directly dumped into the vehicle and taken to the dumping sites.”

What is BMC doing about it?

With several irregularities in desilting work reported in the past years, the BMC has started looking upon other options to prevent major drains from further clogging. In 2017, the BMC had decided to cover few major drains by acrylic sheets to prevent dumping of garbage in drains. They had selected specific spots in Kandivli to implement this project on a pilot basis. As of now, the BMC is framing a policy guideline to implement this project across the city.

Last year, the stormwater drains (SWD) department decided to deploy robots in several major drains to ensure end-to-end cleaning is done. Former civic chief Ajoy Mehta directed SWD to submit a list of drains with complications. The drains that were selected for deploying robots were notorious spots, where there were serious complications faced while desilting, even with mechanical force.

In the island city, most stormwater drains are underground and there are barely any open drains. A senior civic official from the SWD department said, “These underground drains are large and have a greater carrying capacity. However, there are some underground drains that are smaller and prone to clogging every year. Sometimes it is difficult to send in robots to clean these drains.”

For this monsoon, new BMC chief Praveen Pardeshi announced that localities found dumping garbage in drains despite several warnings will have to face disconnection of water supply. Until now, this is one of the most stringent decisions made by the BMC to prevent garbage dumping in drains.

Apart from this, widening of drains and installing trash brooms among other works are ongoing this year. While trash brooms are used to collect floating garbage in the drains, widening of drains is expected to help increase the water-carrying capacity of drains to increase the water-receding time. The widening also involves removal of encroachments along the drains that facilitate garbage and sewage dumping directly into the drains. While nullahs are supposed to be stormwater drains that carry water into the rivers or the sea, Mumbai’s nullahs double up as gutters and carry sewage from toilets of households constructed on its banks, experts said. Suresh Patankar, the other panel expert, said,“Complications of stormwater drains are completely different from what they were before owing to the growing population. There is an urgent need for the BMC to enhance their methodology of desilting. Also, the BMC should focus upon separating the sewage from entering the drains.”