Heavy Rains in Mumbai + High Tide = Mumbai Floods

After a long wait, Mumbai – the financial capital of India, witnessed continuous rain for consecutive four days from 28th June to 1st July 2019. It was raining cats and dogs across the Mumbai and extended areas of Mumbai including Kalyan, Dombivli and Navi-Mumbai. It’s been recorded that the city has received the heaviest downpour of the decade.

On 1st July, the heavy rains disrupted all train services which is also known as the Lifeline of Mumbai. Lot of trains got cancelled and delayed on all lines – Central, Western and Harbour Railway due waterlogging at various stations. The major waterlogging was on Central route between Kurla and Sion station.

Every year, we see this flooding phenomenon due to heavy rains in Mumbai. Over the years, I have been hearing and reading about the equation of heavy rains plus high tide equals to flooding in Mumbai. When it’s high tide, every news channel flashes news such as ‘A high tide of about 4.69 or 4.81 meters is expected to hit Mumbai’ or ‘ MDI predicts heavy rains and high tide’.

As this equation impacts every year the life of Mumbaikar, it was necessary for me to understand the drainage system of Mumbai. While searching for drainage system of Mumbai, I came across a detailed report on the existing situation of Storm Water Drainage Network (SWDN).

According to the report, the SWDN of Mumbai comprises of a hierarchical network of roadside surface drains, underground drains and laterals, major and minor nallahs and 186 outfall, which discharge all the surface run of into rivers and the Arabian Sea.

The report highlights, Out of the 186 outfall, there are 107 major outfalls in city, which drain to Arabian Sea directly, 4 at Mahul creek and 4 at Mahim creek. There are 29 outfalls in Western Suburbs draining directy into sea while 14 drain into Mithi river which connects to Mahim creek. In eastern suburbs 14 outfalls discharge in Thane creek while 6 discharge in Mahul creek.

There are floodgates which are used to release water into the sea during heavy rainfall. As per practice, the floodgate is closed around three hours before the high tide to prevent sea water from entering the city. It is usually opened three hours after the high tide is over, by which time the sea water recedes, as reported by DNA India in one of the articles on waterlogging in Mumbai.

In event of heavy and continues rainfall plus occurance of high tide will flood the low lying areas of the city as floodgates are closed during this period and there is no way to rain water to flow into rivers or sea. Apart from high tide, there are other reasons for waterlogging such as plastic/garbage blocking the drainage system, new constructions in the city blocking the drains, encroachment on drains and poor structural conditions.

In 1993, the Brihanmumbai Storm Water Drain (BRIMSTOWAD) project was initiated to ensure the efficient storm water drainage and to address the recurrent flooding issues. The major recommendations of this project includes remove encroachment along over the nallahs/drains, provide storm water pumping stations, improve flood gates, remove obstruction of water pipes and cables. However, most of these recommendations are yet to be implemented.

Considering the old and complex drainage network of Mumbai and reoccurence of flooding phenomenon every monsoon, it’s high time to start implementation of the not implemented recommendations of BRIMSTOWAD project and monitor till they are completed. Mumbaikars are expecting that the re-elected government will put their best people to execute the recommendations so that the equation changes to Heavy Rains in Mumbai + High Tide ≠ Mumbai Floods.

Here are some pics captured by me during this period.

References:
1. Closing of floodgate during high tide led to waterlogging in Mumbai, DNA India
2. BRIMSTOW report
3. Wikipedia – BRIMSTOW