On Tuesday, Mayor Michael Bloomberg announced a much-anticipated $20 billion plan to bolster the city’s defenses ahead of another storm like Sandy — to create, in the words of his administration, “A Stronger, More Resilient New York.” It includes more than 250 recommendations — everything from levees, floodwalls and storm barriers to updated building codes and utility upgrades.

Mayor Michael Bloomberg reveals his ambitious sea-rise defense plan before a friendly audience Tuesday at the Brooklyn Navy Yard. Photo: Spencer T. Tucker

Though $20 billion is an expensive — and still theoretical — price tag, the city already has about $15 billion available in its own capital bank account and from federal aid. But even with the finances taken care of, and assuming support from future mayors, other obstacles remain. Shepherding through proposals will require collaboration between city departments, state and federal agencies, and outside companies and consultants. It will involve an array of planning and approval processes on all levels of government. In short, it will involve a lot of bureaucracy.

One major player is the U.S. Army Corps of Engineers, the federal agency that oversees projects on the nation’s waters. When Sandy hit, the Army Corps showed up to help clear out floodwaters and clean up debris. It appears in many of the projects outlined in Bloomberg’s plan, including proposals to study the potential for dunes in the Rockaways, breakwaters around Great Kills Harbor and wetlands in Howard Beach. Many of the projects included in the plan — like beach restoration in Coney Island and the Rockaways and studies of New York Harbor and Staten Island — were in the works even before Sandy hit.

The partnership between the city and the Army Corps is mediated through a higher power. Congress has the final say on which projects the Army Corps takes on, which means the city has to take any new proposals there. In general, Congress approves any new projects as line items the Water Resources Development Act, which is renewed every seven years or so, according to Army Corps spokesman Chris Gardner. There may, however, be opportunity for a more streamlined process if the city comes forward with Sandy-related projects, Gardner said.

The mayor’s plan also calls for extensive collaboration with Consolidated Edison on efforts to protect substations and generally stormproof its electrical system, which covers the entire city except for the Rockaways. Two weeks ago, city representatives filed testimony with the state’s utility regulator raising strong objections to the company’s own plans for protecting its infrastructure, saying they do “not appear to be supported by any substantive analysis.”

The Bloomberg administration may have an easier time moving forward with the handful of agenda items that involve the state Department of Environmental Conservation, tasked with protecting New York’s natural resources. The regional office that oversees New York City is currently headed by Venetia Lannon, a former vice president from the New York City Economic Development Corporation.

E-mails obtained by The New York World show that Lannon is still friendly with her former colleagues, sometimes stepping in to help projects speed through DEC’s approval and permitting processes.

“This came through in record time!” wrote EDC vice president Kay Zias in an e-mail to Lannon last August about an approval to reclassify dredged waste as construction fill. “Thanks VERY much, Venetia, for prioritizing the review. The material will help keep the DSNY mitigation project on schedule and solvent!”

In the mayor’s plan, the city and state agencies would work together to identify areas for new ferry landing barges and explore ways to use dredged material to protect the southwest Brooklyn coastline.

Since Sandy hit, Mayor Bloomberg and Gov. Andrew Cuomo have presented differing visions for how best to move forward on resilience measures — Bloomberg stressing efforts to rebuild, Cuomo allowing more opportunities to abandon vulnerable coastlines. But the city and state will have to work together to move forward, said Ronald Shiffman, a former member of the City Planning Commission and co-founder of the Pratt Center for Community Development.

“They need to sit and talk to each other and they need to talk to each other in a way that is transparent,” he said.

Shiffman recommends that the city allow for innovation and flexibility, possibly letting developers take immediate measures to help prepare for storms — like raising electrical outlets higher in flood-prone areas — before going through extensive building-code reform processes.

“We do need to be able to move quickly,” he said.

The mayor’s plan is based in part on new findings from the New York City Panel on Climate Change, which show that risks are even greater than they were when the panel first published its data four years ago. By the 2050s, sea levels could rise more than 2.5 feet, the city could have three times as many days that hit 90 degrees or higher as it did previously, and the number of days with more than two inches of rainfall could jump to five, compared to three in the last century.