The plan crafted by Miami Beach’s engineering consultant, CDM Smith, is intended to address sea level rise for just 20 years.

Environmentalists and other critics said that relatively short window, at least in terms of climate change impacts, seemed intended to minimize costs. But Mike Schmidt, a vice president with CDM Smith, said projects could be altered to account for faster or higher rises. More or larger pumps, for instance, could be added to force storm water out against the higher pressures of rising sea levels.

Much of Miami Beach’s drainage system dates back to the 1940s and there is limited data about how many outfalls were designed to remain above high tide or for how long. But an analysis performed by Coastal Systems International, another contractor assisting in the project, showed the ends of the drain pipes are spending more time submerged, with the mean high water elevation creeping up by about 1.68 inches over the last 14 years. The plan, which still must be approved by the Miami Beach Commission, is designed to handle another six inches by 2030

Beckmann, the public works director, said the city only needed to two pumps for stormwater when he started 11 years.

“Right now, we have 17 and we’ll probably call for another 14,’’ he said.

Schmidt said rainfall still accounts for 95 percent of the flooding in Miami Beach but in century or two, the city could be more like New Orleans, sitting below sea level with its safety dependent on sea walls and pumps. “Eventually, if the projections are true, you’re facing a position where the sea level rise would go above the land surface and then you’re raising critical infrastructure,’’ he said. “Your sea walls are going higher, you’re putting in locks and dams and you’re pumping almost everything.’’

For now, Miami Beach Mayor Matti Bower said her biggest concern was figuring out how to pay for the projects, saying she didn’t think it was fair for the city alone to be tackling the expense.

Normally, the city would issue a bond and raise stormwater rates to cover costs but because the drainage project is also designed to reduce environmental impacts to the bay, the city will explore options including seeking federal grants or money from other state or county agencies.

“I’m not even worried about 25 years from now because I’ll be 100 then,’’ Bower said, “but I do worry for the children and grandchildren.’’

Miami Herald staff writer David Smiley contributed to this report.