Every monsoon, Mumbai braces for the same challenge.
Heavy rain brings parts of the city to a standstill. Roads disappear under water, train services are disrupted, and neighbourhoods along rivers and the coastline are often flooded.
The reasons are well known. Rapid urbanisation, shrinking mangroves, inadequate drainage, rising sea levels, and increasingly intense spells of rainfall all play a role.
But one chapter of Mumbai’s flooding story began more than 240 years ago, when the city as we know it did not yet exist.
In the late 18th century, present-day Mumbai was a cluster of seven islands separated by tidal creeks, marshes, and mudflats. At high tide, seawater regularly swept into the low-lying areas between them, flooding farmland and making travel difficult.
As the British East India Company sought to transform Bombay into a major trading port, controlling these tides became a priority.
Their solution was the Hornby Vellard, an embankment built in 1782 to block seawater from entering one of the city’s most troublesome inlets.
The structure solved an immediate problem and paved the way for Bombay’s expansion. It also marked the beginning of a series of land reclamation projects that would gradually reshape the city’s coastline.
More than two centuries later, that transformation continues to influence conversations about why Mumbai floods and how the city can better prepare for the monsoon.
Before Mumbai became one city
It’s hard to imagine today’s Mumbai as seven separate islands, but that was once its natural geography.
In the late 18th century, what we now know as Mumbai was a group of seven islands separated by tidal creeks, marshes, and mudflats. Photograph: (The Guardian)
Colaba, Old Woman’s Island, Bombay, Mazgaon, Parel, Mahim, and Worli were divided by creeks, estuaries, salt marshes, and mangrove forests. The landscape shifted with the tides. Areas that appeared as dry land in the morning could be submerged beneath seawater just a few hours later.
For the Koli fishing communities, who had lived along this coast long before the Portuguese and the British arrived, these tidal rhythms shaped everyday life.
Fishing routes, settlements, and livelihoods depended on the movement of the sea. Mangroves protected the shoreline from erosion, while wetlands and creeks carried excess rainwater back into the Arabian Sea during the monsoon.
The British, however, saw the islands through a different lens.
Bombay had already begun to emerge as an important trading settlement, but its geography limited its growth. Moving people and goods between the islands depended on the tides. Saltwater regularly damaged farmland, and constructing roads or expanding settlements across marshy terrain was difficult.
If Bombay was to become a thriving commercial centre, the landscape itself would have to change.
The gap that flooded Bombay twice a day
The biggest obstacle lay between Worli and Mahalaxmi.
Here, a wide opening known as the Great Breach allowed seawater to rush inland during every high tide. The incoming water flooded nearby fields, damaged crops, and left large stretches of land unusable for much of the year.
Officials had tried to address the problem before, but without lasting success.
It was Governor William Hornby who decided to pursue a permanent solution. He proposed building an embankment across the breach to stop seawater from entering the low-lying land beyond it.
The plan was ambitious—and expensive.
The East India Company’s directors in London were reluctant to fund it, but Hornby pressed ahead, convinced that the long-term benefits would outweigh the costs.
Construction of the Hornby Vellard began in 1782.
A vellard was a bund, or embankment, designed to hold back the sea. Once completed, it significantly reduced tidal flooding around the Great Breach, reclaimed valuable land, and demonstrated that engineering could reshape Bombay’s natural landscape on a remarkable scale.
Their solution was the Hornby Vellard, an embankment built in 1782 to block the sea from entering one of the city’s most troublesome inlets. Photograph: (The Guardian)
More land, bigger ambitions
The success of the Hornby Vellard encouraged the British to take on even more ambitious reclamation projects across Bombay.
Over the next century, engineers built a series of causeways linking the remaining islands, including those at Mahim, Sion, and Colaba. Marshes were filled, creeks narrowed, and low-lying land reclaimed to create space for roads, housing, markets, and docks.
Slowly but steadily, the physical boundaries between the islands began to disappear.
Areas once separated by water became connected by roads and reclaimed land, allowing Bombay to expand in ways that had once seemed impossible. Railways followed, industries flourished, and the harbour grew into one of the busiest in the British Empire.
Reclamation also transformed the city’s economy.
As more land became available, Bombay gained space for cotton mills, warehouses, commercial districts, and housing. Businesses expanded, workers arrived from across the region, and the city emerged as one of India’s most important urban and commercial centres by the late 19th century.
Much of that growth would have been difficult without reshaping the coastline.
At the same time, altering the landscape also changed the way water moved through the islands. The effects were not immediate, but they laid the groundwork for challenges that would become more apparent as the city continued to grow.
What changed when the sea was pushed back?
The Hornby Vellard was built to solve a specific problem, and by most accounts, it achieved exactly that.
It reduced tidal flooding around the Great Breach and created land that could be used first for farming and, later, for development.
But it also altered a landscape that had evolved over centuries.
Before reclamation, seawater flowed freely through creeks and marshes. Mangroves and wetlands absorbed excess rain during the monsoon before gradually releasing it back into the sea. Together, these natural systems worked with the tides, helping the islands cope with seasonal flooding.
As Bombay expanded through the 19th and 20th centuries, many of these natural buffers gradually disappeared.
Marshes were filled to make way for neighbourhoods, roads, and railway lines. Several creeks became narrower or were cut off altogether. Rivers that once spread naturally across floodplains during heavy rain found themselves hemmed in by development.
Each project served the needs of a growing city. Collectively, however, they left less room for water to flow.
This is why historians and urban planners are careful not to draw a direct line between the Hornby Vellard and Mumbai’s flooding today.
The embankment was the first major intervention, but it was only one part of a much larger transformation. Over the next two centuries, successive reclamation projects, expanding infrastructure, and rapid urban growth continued to reshape the landscape.
The Mumbai we know today is the result of hundreds of decisions taken over generations, with each one adding another layer to the city’s evolving relationship with water.
Why does Mumbai flood today?
Mumbai’s flooding is rarely caused by a single factor.
During the monsoon, heavy rain often coincides with high tide. When that happens, stormwater cannot drain into the sea as quickly as it should. If the drainage system is already under pressure, water begins to collect on roads, railway tracks, and in low-lying neighbourhoods.
During the monsoon, heavy rain often coincides with high tide. Photograph: (CNN)
The city’s geography makes the situation even more challenging.
Much of present-day Mumbai stands on reclaimed land that was once made up of marshes, mudflats, creeks, and tidal inlets. Over the years, wetlands have shrunk, mangroves have been cleared in several areas, and rivers such as the Mithi have been narrowed or encroached upon.
At the same time, rapid urbanisation has replaced open ground with concrete, reducing the amount of rainwater that can seep into the soil. Instead, large volumes of runoff flow directly into drains that were designed for a much smaller city.
Climate change has added another layer of complexity.
Scientists have observed an increase in short bursts of extremely heavy rainfall along India’s west coast. When large amounts of rain fall within a few hours instead of being spread across an entire day, even well-designed drainage systems can struggle to cope.
In Mumbai, where millions of people live on a narrow strip of reclaimed land bordered by the sea, the effects are felt almost immediately.
The devastating floods of 26 July 2005 brought these vulnerabilities into sharp focus.
Nearly 944 millimetres of rain fell within 24 hours—one of the highest single-day rainfall totals ever recorded in India. The downpour coincided with high tide, preventing floodwaters from draining into the Arabian Sea.
Train services came to a halt. Roads became impassable. Thousands of people were stranded overnight.
More than 400 people lost their lives across the Mumbai Metropolitan Region.
The disaster prompted planners and policymakers to take a fresh look at the city’s drainage network, rivers, and the cumulative impact of decades of rapid and often unplanned development.
Can the city prepare for the future?
Since the 2005 floods, Mumbai has invested in improving its stormwater drainage system.
Authorities have also taken steps to protect some mangrove areas and expand flood-management projects. Yet many experts believe engineering solutions alone will not be enough.
Increasingly, wetlands, mangroves, and floodplains are being recognised as critical infrastructure rather than vacant land waiting to be developed.
Mangroves help reduce the force of storm surges. Wetlands temporarily store excess rainwater during heavy downpours. Rivers need enough space to carry floodwaters safely to the sea.
Protecting these natural systems can be just as important as building larger drains or installing more pumping stations.
The debate over Mumbai’s future therefore extends far beyond a single embankment built in the 18th century.
Concrete has replaced open ground, reducing the amount of rainwater that can soak into the soil. Photograph: (CNN)
It is about how a growing coastal city can continue to develop while respecting the natural landscape on which it was built.
Every new road, housing project, or transport corridor must contend with a geography that was once shaped by tides, creeks, wetlands, and mangroves.
That balance between development and ecology will play a crucial role in determining how well Mumbai adapts to increasingly intense monsoons in the years ahead.
