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A tow truck removes cars from floodwater in the Septima Clark Parkway after heavy rain closed roads on July 20. A 2009 project to fix flooding in the area is four years behind schedule and $30 million over budget.

On Tuesday, some members of Charleston City Council apparently learned for the first time that a massive drainage project near the Crosstown in downtown Charleston is at least $30 million over budget and four years behind schedule. It ought to serve as a warning.

The Crosstown drainage project had to be split into four phases nearly a decade ago when a federal grant fell through and city officials were forced to get more creative to fund the $154 million system of pumps and tunnels.

When city officials put the fourth and final phase out to bid, the lowest offer they got was about $30 million more than originally expected.

That’s not particularly shocking. The cost of construction tends to go up over time — witness the steadily spiraling price tag to build the rest of I-526 across James and Johns islands — so it makes sense that the original estimate from 10 years ago wouldn’t hold up today.

But again, this ought to serve as a warning that fixing Charleston’s longstanding and increasingly problematic flooding challenges is not going to be easy or straightforward.

We’ve known for a while now that the price tag for a list of identified flood prevention and mitigation needs is about $2 billion. We know how long it takes to complete a major infrastructure project.

Still, the Crosstown drainage mess suggests it’s worth keeping in mind that the $2 billion estimate — already an unthinkable sum for the city to raise without county, state and federal help — is likely to be on the low end. And the timeline to complete those urgently needed projects, even if they all got underway today, is likely to be measured in decades.

The Crosstown job, for example, dates back to 2009. It was expected to take 11 years to finish. Now it’s going to be 15.

To be sure, that drainage effort is one of Charleston’s most expensive and ambitious infrastructure projects ever. Its complexity and the need to wait on a variety of funding sources help explain the long timeline.

Coordinating multiple multimillion-dollar drainage projects across a city as large as Charleston is going to be a challenge. It’s one of the most critical tests the city has faced. Charleston officials can’t afford any major surprises when the costs are so great and the stakes are so high.

More broadly, we need to figure out why major infrastructure projects take so long and cost so much. It’s not just Charleston, of course. Building roads, bridges, subways and tunnels tends to take far longer and cost far more pretty much anywhere in the United States than it does in our peer countries.

We can’t afford that inefficiency — either in time or money, which in many cases are effectively the same.

In the extra four years it’s expected to take to finish fixing Crosstown drainage, for example, it’s likely that thoroughfare and the surrounding area will flood multiple times, snarling traffic, damaging homes, ruining vehicles and even making it more difficult for people to get to the hospital.

And those consequences pale in comparison to what will happen to the city if we can’t act fast enough as sea levels continue to rise and storms grow stronger.