Hundreds of thousands of Bostonians live at risk of worsening coastal flooding, the U.S. Army Corps of Engineers (USACE) states in a draft report set to be released this week outlining massive projects to defend the city’s waterfront over coming decades.

“More than 40% of our residents now live in areas at risk of coastal flooding, including some communities who are more than a mile away from the ocean,” Mayor Michelle Wu said Monday. “Without action, we risk $54 billion in damages to our homes, hospitals, businesses, roads, and other critical infrastructure by the end of the century. And that’s why over the past decade we’ve been working with our local, state, and federal partners to build a climate-ready Boston, and it’s why once again we’re turning to the U.S. Army Corps of Engineers to help us defend our city.”

The drafted Boston Coastal Storm Risk Management Feasibility Study details over 20 infrastructure projects along 16 miles of the city’s 47-mile coastline to mitigate potentially catastrophic sea level rise and coastal flooding over the coming decades, city and Army officials said Monday.

The study, commissioned to allow Boston to access a 65% federal cost-share for construction of the baseline protection infrastructure, is set to be released in full on Friday. The city and Army are seeking public feedback on the draft, before the release of a final report scheduled for 2028.

The USACE study will “drive one of the biggest investments in our waterfront, more than twice the size of the Boston Harbor cleanup,” Wu said.

Officials outlined the impact of mounting coastal flooding and sea level rise at Langone Park in the North End, built on a sea wall to help the neighborhood withstand flooding.

About one-sixth of Boston is built on filled tidelands and is in “danger of flooding due to sea-level rise and extreme weather,” the city stated. Along with about 284,000 residents in areas at risk of coastal flooding, about 20,000 buildings are at risk of severe flooding, the USACE findings show.

Neighborhoods including Dorchester, Roxbury, the South End, Back Bay, Beacon Hill, East Boston, Charlestown, and Allston are expected to feel impacts, as well as access to hospitals, the MBTA, I-93, the Mass Pike, Logan Airport, and more.

Already 24 severe storms have triggered federal or state disaster declarations in Boston since 1991, and 14 have caused major flooding.

“The reality of this is, after looking at it, doing nothing is not a viable solution,” said Lt. Col. David MacPhail, deputy commander of the USACE New England District. “We have to do something to mitigate this. Without action, the cost of public safety and economic viability from the coastal flooding will be compounded and untenable.”

The study assesses Boston’s “people, the ecosystems of the area, the property, and the critical infrastructure,” MacPhail said, and plans for interventions including seawall improvement, flood walls, berms, levees and surge barriers – a “lattice work of almost puzzle pieces” to build resilience in the 47-mile coastline.

The construction would ultimately close 20 long-term coastal flood pathways, which are inland areas that could flood during extreme weather events. These pathways were identified “by the federal government as key areas of risk that could compromise the safety and economic future of both Boston and the country at large,” city officials said.

At the same time, MacPhail added, there has been effort to “maintain the character and charm” along the Boston Harbor with elements like harbor walks, urban furniture, and other betterments.

All together, the projects are estimated to cost over $10 billion over the next few decades, not including upgrades like green spaces and outdoor recreation expected to be added in, city officials said.

If Boston takes no action, the USACE estimated, the city is projected to lose $54 billion by the end of the century – with about $4 in residents’, businesses’, and the public sector’s avoided disaster losses for every $1 invested.

One study published in the Nature Climate Change journal in June found floods that historically had a 1% chance of striking a coastline in a year are now about 12 times more likely, on average.

Wu said that the city would “have a much better idea” of cost, phasing, funding sources and more following the 2028 final study release.

The Boston Green Ribbon Commission launched a one-year study to identify funding sources for the 35% of the projects non-federal cost share.

City officials urged residents to take part in public comment on the projects from July 24 to Sept. 18, along with an upcoming series of community meetings and webinars.

“If you live or work in Boston or have an interest in Boston, we really do want to hear from you,” said Boston Chief Climate Officer Brian Swett. “Your voice can not only help us protect Boston for generations to come, but also expand your access to green spaces and recreational opportunities right here along the Boston Harbor.”

More information on the draft Coastal Storm Risk Management Feasibility Study and public comment opportunities can be found at boston.gov/flood-prevention.

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