MUMBAI, India — As this city prepared recently to inaugurate a shiny new bridge that officials promise will ease Mumbai’s chronic traffic jams, Dilip da Cunha was peering at the underbelly of the city’s waterways and drainage systems.
Taking two visitors on a tour of the busy causeway where the city’s befouled Mithi River meets the Arabian Sea near the new bridge, the Bandra-Worli Sea Link, he pointed out a small clump of trees nearby under which several men were defecating.
The trees represented one of the last remaining species of the mangroves that once dominated the ecology of Mumbai, India’s financial capital and its most populous city. Over the decades, most of the wetlands of the Mithi River estuary that were home to such trees have given way to highways, slums, office buildings and apartment towers.
While the mangroves’ retreat has provided valuable acreage for Mumbai’s growth, Mr. da Cunha, who is one half of a husband-and-wife team that recently finished an exhaustive study of the city’s landscape, said their disappearance, along with the degradation of the city’s waterways, has made the city increasingly vulnerable to flooding during the monsoons.
“At some point there were many species of mangroves here, and they must have made this a fantastic wetland,” he said. “We have reduced these mangroves to almost a single species that have survived with the bad waters, the sewage that is around.”
In the summer of 2005, a few weeks before Hurricane Katrina devastated New Orleans and parts of Mississippi, Mumbai received a record 37 inches of rain in 24 hours during high tide. Approximately 900 people died in those floods in the city and surrounding areas.
While Mumbai has spent millions on its drainage system since then, last week an overnight rain about one-tenth as severe as the 2005 downpour brought traffic and suburban trains in many parts of the city to a crawl during the morning rush hour.
Inspired by the 2005 floods, Mr. da Cunha and his wife, Anuradha Mathur, who teach design and landscape architecture at the University of Pennsylvania, have spent the last two and a half years studying Mumbai and its uneasy relationship with water. They recently released their findings and 12 proposals for making the city more resilient to floods in the form of a museum exhibit and a book, both titled “Soak: Mumbai in an Estuary.”
They have documented the current state of the city’s waterways and mangroves and collected a trove of historical maps, images and documents dating back hundreds of years. They previously did similar, though less comprehensive, work on the Mississippi River and Bangalore.
Their findings show that a series of natural features like mangrove swamps and interconnected creeks once protected and shaped Mumbai, just as the bygone swamps of the Mississippi River delta once protected New Orleans. But those defenses were weakened over the years, dating to the days of British rule, as swamps were filled in, land was reclaimed from the sea and creeks were narrowed or diverted.
The historical maps and documents show little appreciation for those long-lost natural features. Most old maps make no mention of swamps, which were often labeled simply as “badlands.” There are few images of the trees and plants that made up these areas.
Moreover, boundaries between land and sea were never drawn as they existed during the monsoon, when the wetlands of the estuary expanded, only as they stood during the summer or winter. “The monsoon was seen as foul weather,” Ms. Mathur said. And “all of the planning is based on fair weather maps.”
Ms. Mathur and Mr. da Cunha, who both grew up in India but met in San Francisco, said they set out on their work in part to provide an alternative interpretation of Mumbai — to have it be recast as an estuary where salt and fresh water coexist rather than as an island that has to be protected from the water.
“We are sort of trying to find ways to visualize these complex landscapes,” Mr. da Cunha said.
Yet they also seem realistic and do not advocate returning the city to an earlier, more idyllic landscape. They propose a series of projects that, they say, would alter and tilt the landscape in ways that could reduce or contain flooding during the monsoon without displacing its vibrant population and commerce.
For instance, they advocate that maidans, or empty fields, often used as playgrounds or fairgrounds should be redesigned so they can hold flood waters during storms and connect streams to one another. They also recommend creating more passages to the sea for the Mithi River, which currently has only one outlet. Another proposal recommends creating and widening ditches that could serve as green belts in fair weather but would carry rainwater and surging saltwater from the sea in the west to outlets in the east.
Ms. Mathur, Mr. da Cunha and partners like the Asia Society have been able to enlist the help of powerful and influential backers for their work. One of them, the chief minister of Maharashtra State, of which Mumbai is the capital, spoke at the public opening of their exhibit and made the prestigious National Gallery of Modern Art available to house their work.
But it is unclear how much weight officials will give to their ideas, which are a world apart from city and state plans to use more traditional flood control approaches like pumping stations and river dredging. The chief minister, Ashok Chavan, who exerts significant control over the local government, praised the exhibit as educational but did not speak about any of its proposals.
Still, Ms. Mathur and Mr. da Cunha are hopeful that their ideas will have some lasting impact. Members of a wealthy family recently asked how they could help. They plan to ask the patron to provide the prize money for a competition in which engineers would design prototypes of one their proposals: toilet barges for the poor who live near the water. The barges would be equipped with technology to treat the sewage and perhaps turn it into energy.
Ms. Mathur said the barges could even dock under the new Bandra-Worli bridge when they are full and treating their cargo.