The maps were intended to show how rising sea levels threaten some of Miami-Dade County’s most vital facilities.

If they prove anywhere close to accurate, the fate of three major sewage plants would represent only the tip of a hulking, hugely expensive iceberg of concerns for South Florida.

Drawn up by climate scientists as part of an environmental lawsuit, the maps indicate the plants in coastal South Miami-Dade, North Miami and Virginia Key would remain dry in coming decades. But they’d be reduced to shrinking islands as high tides flood land, streets and neighborhoods nearby. It could happen faster than experts predicted only a few years ago — with a damaging two-foot rise potentially coming in less than 50 years, not the next century.

The sobering scenarios were filed last month in federal court by Biscayne Bay Waterkeeper, a clean-water advocacy group challenging Miami-Dade’s $1.5 billion plan to repair the county’s aging, spill-plagued sewage system. The Water and Sewer Department has drawn up the proposal, called a “consent decree,’’ under the pressure of a U.S. Environmental Protection Agency lawsuit and threat of millions of dollars in potential fines.

Critics contend it has a gaping hole: It ignores looming sea-rise that both county and EPA planning policies acknowledge poses trouble, potentially deep trouble, for a region in line to feel the earliest effects of climate change. Miami-Dade endorsed a pioneering four-county compact that calls for adapting roads and buildings for climate change. Last year, the EPA released two reports promoting “climate ready” utilities.

Yet after 10 months of negotiations between agencies, the sewer plan doesn’t contain a word about dealing with flooding tides or the sort of storm surge that devastated the Northeast during Hurricane Sandy. No calls for sea walls, elevated separating tanks, stronger casks for pressurized liquid chlorine or other “armoring” measures.

University of Miami geology professor Harold Wanless, one of five experts from UM, Florida International University and Florida Atlantic University retained by Waterkeeper, hopes the data will open the eyes of regulators before a deal is sealed. That could happen in the next few months, with any agreement subject to approval by county commissioners and a federal judge.

“At some point, and I hope it’s this year, Miami-Dade government and everybody has to start truly recognizing that we’re in for it, that this is coming,’’ Wanless said.

$206 million project

When it does, it’s clear there will be a lot more to worry about than sewage plants.

Brian Soden, a UM professor of atmospheric science, said many communities and residents will be facing difficult, costly decisions.

Miami Beach last year approved a $206 million overhaul of an aging drainage system increasingly compromised by rising seas. Just another foot of sea-rise, possible within 20 years, could worsen high-tide street flooding there. It also would inundate much of coastal South Miami-Dade, leaving a sewage plant adjacent to the dump called Mount Trashmore, as well as Turkey Point nuclear power plant, virtual islands.

“If you look at downtown Miami, where all the new places have gone up, all the new condominiums, the billions going in there, those places are at some of the lowest levels,’’ Soden said. “It’s a broader impact all of South Florida is going to be facing sooner or later. Right now, a lot of people are choosing not to look at it.’’