When Washington Square Park in North Beach reopens on Wednesday, the changes on view will be subtle.

The central lawn now slopes toward Columbus Avenue with gravitational ease to prevent the muddy bogs that long plagued the park. The kidney-shaped walkway is clad in concrete, not asphalt. Rustic cobbles line the walkway. Small touches like these.

Which for a crossroads cherished by so many people is pretty much the point.

San Francisco’s square that isn’t a square, host to a statue of Ben Franklin rather than George Washington, is an official city landmark. More to the point, it’s an integral aspect of what makes North Beach and Telegraph Hill such enduring attractions: the cosmopolitan nonchalance, where low-slung buildings crowd the streets while Coit Tower and Ss. Peter & Paul Church look down.

Lawrence Halprin understood this in 1957, when the landscape architect who wasn’t yet a legend conceived a master plan that was followed by a design of restrained civic elegance, trees and shrubs lining a sunny green with an ease that proved to be an ideal fit for North Beach’s beatnik heyday.

A similarly light touch defines the $3 million upgrade that has kept Washington Square fenced off since June.

Other San Francisco parks have been given total makeovers in the recent past, with landscape architecture firms designing such successes as South Park and Lafayette Park. Washington Square’s playground and restrooms were redone a few years ago as well.

But the protected status of the landscaped portion of the park ruled out any major revamps — rightly — and the design work was kept in-house.

“The main thing is to ensure that the space works well,” said Kelli Rudnick, project manager for the city’s Recreation and Parks Department. “But we also wanted to make a more cohesive place in terms of design, while keeping the texture and quality that people expect.”

Most of the budget was consumed by features we don’t see, such as the replacement of drainage pipes and watering systems. Six to 9 inches of soil beneath the lawn were replaced, since the old dirt was compacted beyond redemption by decades of intensive use.

Details like this explain why the makeover is billed as a “water conservation project.” If all goes well, annual water consumption should fall from 3.3 million to 1.1 million gallons. No longer will low spots near Union Street resemble seasonal marshes.

Rec and Parks, teaming with the Department of Public Works, smartly used the project to do other upgrades that serve the square well.

The entryways from Filbert and Union streets now are marked by basalt tiles. Dense shrubbery inside the park at the Filbert opening was replaced by softer plantings such as lavender.

All the wooden benches look as they did in the 1950s — some because they’re the (repainted) originals, while others are replicas that replace various models installed in subsequent decades.

Another welcome visual touch: Cobblestones are used far more extensively than before. In most cases, they’re raised several inches along planting beds as a surface-level aesthetic touch to mark borders.

This being San Francisco — and the ever-protective Telegraph Hill/North Beach neighborhood in particular — there was no shortage of second-guessers during the project’s gestation.

One set of opponents filed a lawsuit challenging the project, saying it exceeded repairs that the city earlier had said were needed and that the use of concrete rather than asphalt violated the square’s historic status.

The health of each tree marked for replacement because of age was the subject of repeated diagnoses. An arborist was on hand when piping was replaced near the roots of sycamores, stone pines and other old friends.

Black metal posts and chains along the planting beds — intended mostly to keep out dogs — were replaced late in the design process by ropes and wooden posts, in part because of design quibbles from a handful of neighbors.

In terms of aesthetics, I can go either way. But the wooden posts aren’t set in concrete. We’ll see how long they survive.

What counts is the larger picture. One of San Francisco’s oldest parks, both a cultural treasure and an urbane oasis, received the sensitive fine-tuning that it deserves. Even if people who visit in coming years don’t notice the alterations, they’ll know that they want to come back.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron