In the days following Hurricane Katrina and the levee breaches that flooded 80 percent of New Orleans, Baton Rouge — the closest large city — sat in the crosshairs of a human tide.

New Orleans’ future seemed uncertain. Speculation was rife that greater Baton Rouge, full of evacuees and serving as a storm-recovery staging area, could become the long-term beneficiary of one of the deadliest and most costly hurricanes in U.S. history.

Mayor-President Kip Holden’s top administrator, Walter Monsour, put it plainly at the time.

“Baton Rouge is now the largest city in Louisiana, and it’s going to be for quite a while, if not permanently,” Monsour said.

While Baton Rouge leaders and others always expressed support for New Orleans’ recovery, there also was a lot of talk in the first years after the storm about long-term growth trends away from New Orleans and the coast that would benefit the capital city and the Interstate 10/12 corridor.

Ten years later, Baton Rouge and the surrounding parishes have certainly grown.

But with the hard-fought injection of $110 billion to $120 billion in federal aid, including Louisiana Road Home money, and another $40 billion in private insurance, New Orleans homes, businesses, levees and hospitals were rebuilt. The New Orleans metro area has regained most of its population and maintained its dominance as Louisiana’s largest economy and most populous metro area, census and other data show.

LSU economist James Richardson said Katrina created a short-term surge in Baton Rouge that has petered out and given way to more normal growth patterns.

“It didn’t change the fundamentals in the whole state at all, but it certainly, in the short term, created some ups and downs that we had to deal with,” he said.

But the revitalization of New Orleans and the growth of Baton Rouge since Katrina have led many civic and business leaders in both to declare that the two cities’ fates are more intertwined than ever, even if the Baton Rouge area didn’t quite grow as some predicted.

These leaders say they see unprecedented cooperation and joint marketing, along with the Houma area, of what they call a “super region.” Another group is working on plans for a commuter rail link between Baton Rouge and New Orleans. Meanwhile, amid such high-level talk, 50,000 workday drivers commute back and forth between Baton Rouge and New Orleans, according to a New Orleans Data Center analysis of census figures.

“The region has grown much closer together. The personal ties, the business ties, the sense that we’re in it together is just far stronger than it was pre-Katrina, and I think that was the lasting effect,” said Sean Reilly, the chief executive officer of Lamar Advertising who also served on the Louisiana Recovery Authority.

“The corridor between us is filling in, and it’s filling in a way that brings us even closer together as community.”

Growth and cooperation

A look at the population and economic data shows how both New Orleans and Baton Rouge have grown during the past decade.

The New Orleans metro area recouped all but 3 percent of its 1.3 million people by July 2014, though many people were redistributed toward the River Parishes and the north shore. This left Orleans Parish far from its onetime position as the state’s largest parish, census estimates say.

Meanwhile, the Baton Rouge metro area added nearly 90,000 people between July 2005 and July 2014. Along with that growth came nearly 76,000 more jobs between June 2005 and June 2015 and the addition of $3.1 billion to its total economic output between 2005 and 2013.

The economic gap between the Baton Rouge and New Orleans metro areas also narrowed between 2005 and 2013 by about $9.6 billion, but it still remained significant, according to inflation-adjusted U.S. Department of Commerce data. In 2013, the last year for which data are available, Baton Rouge had a $45.8 billion economy compared with $70.7 billion for New Orleans.

An example of the economic intermingling between the two cities is the smattering of New Orleans businesses and restaurants that have popped up in Baton Rouge since Katrina.

Take the Mexican-themed Velvet Cactus restaurant, which opened earlier this year in a building on Old Hammond Highway that once served as the temporary home of Mandina’s Restaurant, a New Orleans institution that didn’t last long in Baton Rouge.

Partner Rusty White thinks the Velvet Cactus, which started with a location in the rebuilt Lakeview neighborhood in New Orleans, will end up being a good fit in Baton Rouge. White and his partners also own the New Orleans-based The Bulldog bar chain, which opened in Baton Rouge in 2009.

A colorful place with a patio and bar, the restaurant has an aesthetic that reflects co-owner Herb Dyer’s eye for details, White said.

Some are skeptical

The growth in Baton Rouge since Katrina created that extra comfort layer necessary for the owners to make a $3.5 million investment. The Velvet Cactus’ owners also took advantage of post-Katrina tax breaks on new assets through the Gulf Opportunity Zone Act of 2005 when the restaurant opened late last year.

White, who is 46, said the restaurant’s appeal is as much about the laid-back, yet boisterous vibe as the food.

“The question here is, at the end when we plateau, or whatever that is, can this area handle it like Lakeview? And we think it can, obviously,” White said.

But others are skeptical that Baton Rouge and New Orleans have mixed so much since Katrina and say the two communities will remain distinct.

Richard Campanella, a Tulane University geographer and author of noted books about New Orleans, pointed out that the two cities, from their very beginnings, have been places apart, separated by 80 miles of mostly swamp.

One grew up as a major port, a mercantile and slave-trading center and was subjected to waves of immigration. The other was built on bluffs outside of the Mississippi River’s delta plain and on the edge of cotton-growing country.

Even after Katrina, Campanella said, people live mostly in Baton Rouge or in New Orleans, creating “barbell” population concentrations that he doesn’t think will significantly spread out anytime soon.

“Sure, you have Gonzales and Prairieville kind of trickling toward New Orleans, and Kenner and LaPlace trickling toward Baton Rouge, but generally there’s a thin stretch of concrete on piers connecting the two cities, and that has a way of keeping them culturally apart even as it keeps them physically apart,” he said.

‘This is home’

It’s difficult to say how many of the thousands who arrived in Baton Rouge after the storm ended up relocating permanently. But some found a home there.

Myra Engrum, 60, wound up in Baton Rouge in the months after Katrina and stayed, finding her spiritual home at the New Hope Baptist Church on Greenwell Springs Road.

One recent Thursday night, Engrum and more than 35 other choir members at New Hope Baptist belted out, “There’s a bright side somewhere,” while a few children occupied themselves in mostly empty pews. With overlapping harmonies from different sections of the choir, the “bright side” chorus filled the church’s high, wood-paneled roof.

Engrum, a former New Orleanian who is now raising the 9-year-old son of her deceased daughter in her adopted city, finds herself in a comfortable niche in Baton Rouge, just like her front-row place in the choir.

“This is home,” she said.

Engrum is one of probably thousands who have remained in the Baton Rouge area and not returned to New Orleans in the decade since Katrina. An army of social science researchers and demographers have studied who has gone back to New Orleans, but solid numbers on precisely who and how many people have remained in Baton Rouge are lacking, experts said.

A 2014 analysis of annual census surveys, for instance, showed in the first year after Katrina that 12 percent of the New Orleans residents who had not returned lived somewhere else in Louisiana.

Troy Blanchard, a demographer and associate dean of the LSU College of Humanities and Social Sciences, said the methods used by the census and other sources are not designed to handle the population fluidity that followed Katrina.

One estimate, based on U.S. Centers for Disease Control and Prevention data, was pulled together by Elizabeth Fussell, a former Tulane population researcher who lived through Katrina and is now at Brown University in Rhode Island.

Her analysis shows that of the scores or hundreds of thousands who may have evacuated to East Baton Rouge Parish temporarily around the late August storm, the parish ultimately saw a population spike of about 17,500 people at the end of 2005 — a number that’s close to other estimates.

“There was a significant and permanent gain between 2005 and 2006 that is certainly due to Katrina evacuees,” Fussell wrote in an email.

More leave than arrive

Since then, though, the parish has seen more leaving than arriving virtually every year, though it is not clear from the data who they are, where they are going or why they are leaving — whether Katrina evacuees or existing residents moving to the suburbs, Fussell and others said.

Natural growth from births has overcome this regular loss of people from outmigration, so the overall population in East Baton Rouge has continued to increase since the 2005 spike — but on the more gradual trajectory seen before the storm, Fussell’s analysis shows.

“From these data, it is impossible to differentiate Katrina evacuees from everyone else in the population,” she said.

What the social science research has turned up is that a variety of factors have typically melded to prevent some people from returning. Others made a more active choice to move.

Consider Joe and Peggy Geraci, who had lived in heavily damaged St. Bernard Parish.

With flood insurance and the help of a U.S. Small Business Administration loan, the Geracis bought a house in Denham Springs after the storm, relocating along with most of their extended family.

Livingston and nearby Ascension parishes were growing Baton Rouge suburbs before Katrina. Both saw a rush of people after the storm and have continued to grow despite the economic slowdown a few years ago.

Sixty percent of the nearly 90,000 people added to the Baton Rouge metro area since 2005 live in Livingston and Ascension parishes. Almost all of the rest, 36 percent, live in East Baton Rouge, census data say.

As in other parts of the Florida Parishes, where former St. Bernard neighbors and family members have moved together into the same areas, the Geracis’ Willow Pointe neighborhood is home to several members of Peggy Geraci’s extended family. One of her daughters, her husband and their 8-year-old child also live in nearby Watson.

Joe, 71, is retired, while Peggy, 64, is nearing retirement. They’ve had their difficulties, recently dealing with the death of Peggy’s son, but they say they are satisfied to stay in the Baton Rouge area.

Joe said he saw immediate similarities between Chalmette and Denham Springs and has not felt the desire to move back. Peggy, who said she briefly considered moving back a few years after the storm, is happy being near her family. Still, she continues to feel a connection to a place and people who largely are no longer there.

“Like I say, ‘This is home now,’ and it is, but I kind of feel like there is always a part of me that will feel like Chalmette was home,” she said.

A promise to stay

Engrum, whose apartment off Read Boulevard in New Orleans East was swamped by floodwaters, said it was too emotional for her to go back. She had no interest in saving her belongings, she said.

Her daughter died shortly after Engrum’s grandchild was born nearly a year after Katrina, and Engrum promised her daughter to raise the boy, Jeremiah Dixon, in Baton Rouge.

There have been struggles and successes, and help has come from unexpected places.

The aptly named Higher Ground Outreach Church in Baton Rouge gave her and her daughter shelter for a month in the weeks after Katrina.

Assistance from Catholic Charities in Baton Rouge, where she worked for a time, and later AARP helped her get on her feet and find work. She does field work nearly 30 hours per week for a national opinion research company, which allows her to be home for Jeremiah after school.

Engrum was able to buy her first home and win legal custody of Jeremiah.

She and Jeremiah also have found fellowship at New Hope church, which is attended by several other former New Orleanians displaced by Katrina.

“When we get to the end, when we get to places where we have a lot of difficulty, you know, I must say, my faith in the Lord and the people that are around me, they will show up,” she said.

Follow David J. Mitchell on Twitter, @NewsieDave.