Protests in Chinatown against the city’s drive to build a “jailscraper” there are A fresh warning that this “replace Rikers” scheme is an utterly misbegotten boondoggle.

The bid to build four new borough-based jails and then close Rikers Island is years behind schedule, with costs ballooning by the billions.

The Chinatown project sits atop the old Collect Pond; construction will require massive pumping and drainage, at risk of sinking the surrounding ground and endangering other buildings.

More important, this whole scheme is nuts: The problems at Rikers stem from mismanagement and forgone maintenance — not from the location, which in fact is ideal, since no civilian wants a jail in the ‘hood.

Yes, the existing jails on Rikers are crumbling, but the island has plenty of space to build new jails on site, if that’s cheaper than repairs and modernization.

Building jails in the boroughs is a stealth bid to put a hard, too-low cap on how many people the city can keep locked up, no matter how bad crime gets.

The planned four-borough jails will hold at absolute most a total of 4,200 inmates; over 6,500 are now in detention citywide, and that’s historically low.

The progressives are aiming to make New York City a place where it’s almost impossible to get arrested, because there won’t be anywhere to put you.

“Replace Rikers” is of a piece with the no-bail law, the de-facto decriminalization of shoplifting, the war on stop-and-frisk and public-housing “vertical patrols” and the non-prosecution of fare beating.

It’s obscene to let existing jails rot while the city burns $16 billion — a sum sure to grow — on “replacements” that can’t do the job, which makes it illegal to actually shut Rikers down.

The sooner the city’s leaders admit the insanity of this plan, the sooner they can turn to truly giving Gotham modern jails — on Rikers Island, which is simply irreplaceable when it come to public safety.