IF BOSTON IS going to avert the most catastrophic impacts of projected sea level rise this century, it needs to get building.

A new landmark draft plan set to be released this week from the US Army Corps of Engineers in partnership with the city recommends 20 specific projects to shore up the most flood-prone parts of Boston.

Some 20,000 buildings and 40 percent of the city — more than a quarter-million residents — at risk of flooding are depending on it.

“Today marks a major milestone in Boston’s fight to protect our city from climate change,” Mayor Michelle Wu said at a press conference along the waterfront in the North End. “This study … will give us the clearest picture we’ve ever had of how rising seas and stronger storms threaten our neighborhoods, and importantly, the report also will lay out a plan for Boston to become the greener, healthier, more resilient city our residents deserve.”

The draft plan is set to act as a roadmap for how New England’s largest city, one-sixth of which is built on filled tidelands, can navigate the more than four feet of sea level rise the Army Corps projects will hit Boston by 2090 as the world continues to warm. It’s also a glimmer of cooperation between the federal government under President Trump and a deep-blue city in a state with a Democratic trifecta in what has otherwise seen a souring relationship.

If all goes to script and the draft plan for Boston — which has an estimated price tag of $10 billion — is finalized in roughly its current form, in the years and decades ahead, new floodwalls up to nine feet high could dot the edges of the harbor in Charlestown, the North End, and South Boston. Levees could be built at Pattens Cove, Tenean Beach, and Pope John Paul II Park in Dorchester. And floodgates could go up right outside Logan Airport in East Boston.

There’s a key sweetener, too: Boston can pass up to 65 percent of the tab on to the federal government for the construction of the infrastructure that the Army Corps recommends to protect the city from flooding.

Delivering the final study to Congress in two years from now — which will mark a six-year process that kicked off in 2022 — is just the first step. Federal lawmakers will need to appropriate money to fund the suite of flood control projects every two years, requiring Boston to continue to make the case and compete with other cities for funding.

The plan comes as Massachusetts is hitting a critical crossroads with respect to the adverse economic consequences of flooding around the state, from rising insurance costs to lost property value for homeowners and businesses. That’s now prompting state officials to consider more sweeping and potentially contentious reforms, including a voluntary buyout program now under discussion and efforts to require property owners to disclose their flood risk and prior flooding history.

“I always like to bring the perspective that we are protecting people,” Gabriela Coletta Zapata, a city councilor who represents East Boston, Charlestown, and parts of the downtown waterfront, said at Monday’s press conference. “These are folks. These are lives. This is decades of memories of folks living in one place that are at risk. And this investment in climate resilience is more about just seawalls and infrastructure. It’s about protecting them.”

The Army Corps estimates that the cost of closing Boston’s floodways through these 20 projects located along 16 miles of the city’s 47-mile coastline is $10 billion for the baseline infrastructure alone — which doesn’t include upgrades city officials said they would want in order to improve public access to Boston Harbor and integrate the infrastructure into parks and public spaces on the water.

On a statewide basis, a study released last year from Gov. Maura Healey’s administration found that between $90 billion and $130 billion will be needed in resilience investments through 2050.

The cost of inaction, though, is far greater. Boston could otherwise experience $54 billion in losses by the end of the century, if nothing is done, according to the draft plan. Key regional assets like Logan Airport, hospitals, I-93, I-90, and rail stations remain highly vulnerable. Neighborhoods more than a mile from the ocean could experience severe flooding in the next 25 years.

And the prospect of significant buy-in from the federal government further helps take the financial sting out of the billions of dollars necessary to close Boston’s most vulnerable points where water can spill onto land and snake its way through streets.

Yet even if Congress appropriates the full 65 percent of the funding needed for the projects, how Boston pays for the rest under constrained state and local budgets is an open question.

Boston’s Green Ribbon Commission has embarked on finding some of the answers, hiring a consultant team last month to develop a coastal resilience financial blueprint that will identify financing options from public and private sources to support the 35 percent the federal government won’t cover. Brian Swett, Boston’s climate chief, stressed to reporters last week that Boston taxpayers alone wouldn’t need to shoulder the burden — the private sector, the state, and the Massachusetts Bay Transportation Authority would all be expected to chip in, too.

The Army Corps will be accepting public comment on the draft report through September 18 once it is released in full on Friday. But there are already early signs that some stakeholders will want changes.

Conservation Law Foundation said in a statement Monday that it wants to see an approach that better reflects “years of community planning” and prioritizes nature-based solutions, like salt marsh restorations and open spaces.

Top city officials don’t necessarily disagree: Wu said that Boston has stepped up its efforts around permeable pavements and improving tree canopy, while Swett pointed to a “living” seawall that’s attracted new species and led the Boston Harbor to become a fishing hotspot.

Long before the new draft plan from the Army Corps, Boston has been working to improve its resilience in the face of rising seas and more extreme weather events. Fourteen of the 24 severe storms in Boston that triggered disaster declarations since 1991 have caused major flooding.

The city has touted a slew of projects along the waterfront either in the works or completed over the past decade designed to mitigate flood risk.

But with Boston mostly dodging the worst of the devastating consequences of some of the biggest storms in recent years, the scope of what needs to be done to insulate the city’s residents and economy from rising seas is much broader than what’s been accomplished to date — and in need of more financial muscle.

Hurricane Sandy, which battered the Northeast in 2012 with historic flooding and led to at least 43 deaths in the New York area, is what underscores the urgency of the moment for Swett.

“In Boston, we missed a massive cataclysmic flooding event not by 500 miles, but by five hours,” he said. “If that same storm, that same trajectory, had hit at our high tide, we would have had the worst flooding in Boston. That was that ‘A-ha’ moment.”