Louisiana’s $50 billion coastal restoration plan comes with two slight problems.

It is not guaranteed to work, and we don’t have the $50 billion.

The scientific challenge has been compared to the one faced by NASA when it was shooting for the moon. Lobbying Congress for the requisite funds, meanwhile, may be like reaching for the stars.

Still, the cost of shifting Mississippi mud and sand to the evanescent wetlands is not set in stone. It would be quite easy to spend much more, such is the scale of the loss, but some restoration is better than none, and the state does have a few bucks in the erosion kitty. By the time BP is assessed its multibillion-dollar fines over the Deepwater Horizon spill, there should be enough money to sustain hopes that great swathes of the state may be preserved from the waves.

There are apparently two ways of doing so. One, tried and trusted, is to pump slurry into subsiding marshes and shrinking barrier islands. But nature is washing land away much more quickly than we can shore it up, and slurry pipelines merely provide a temporary solution.

The other is to mimic the natural processes that formed the delta by liberating the water and sediment that used to replenish the wetlands before the river was by encased by levees. Diversion projects won’t come cheap, but they should keep creating new land so long as the sediment flows down the river.

They do not, however, offer entirely firm hope for the future. The computer models are evidently encouraging, but hydrology is not easily tamed. It’s almost like cutting off one head only to have two more appear elsewhere. As one researcher studying sediment levels said, “Anything you take out or put in will have an effect on the rest of the river.”

The benefits of diversion also must be weighed against any adverse impact on fisheries or the shipping and energy industries. Coastal restoration will take us into much new territory.

Louisiana is estimated to run out of restoration money in 10 years, and it seems unlikely that we will undo enough of the damage unless Congress is prepared to bet, to the tune of many billions, that we have the science right.

That the preservation of Louisiana is vital to the long-term national interest has been blindingly obvious for years, but members of Congress may be too focused on the next election to fret about what will happen to the economy down the road if New Orleans is left teetering on the Gulf Coast.

Without effective intervention, Louisiana, having already lost 2,000 square miles, could lose almost as much again in 50 years. Half of America’s refineries and oil pipelines would be underwater, and, 70 years from now, with New Orleans exposed to the Gulf elements, the port could face frequent shutdowns costing $300 million a day.

So posterity needs us to find a fix, but Congress may be more inclined to ask what posterity ever did for us. Another question on Capitol Hill may be what Louisiana is prepared to do for itself, when reams of studies have attributed about one-third of wetlands loss to oil and gas companies that failed to honor their obligation to repair the damage caused by their canals and pipelines. The lawsuit filed by a New Orleans-area Flood Protection Authority might yield billions for coastal restoration, but Louisiana politicians always have been in cahoots with energy companies and Gov. Bobby Jindal, and legislators remain determined to block it.

Meanwhile, Louisiana is sinking faster than most of the planet, as climate change causes the seas to rise. Man-made climate change has its doubters in and outside Congress, but nobody who has laid eyes on the coastal zone can doubt that cataclysmic forces are at work. If this is not the greatest scientific challenge, it must be the most elaborate hoax since the moon shot.

James Gill’s email address is jgill@theadvocate.com.