The scale of the long-term devastation inflicted on New Orleans has been revealed by the 2010 US census, which found that the city's population has collapsed by almost a third over the past decade.

Figures released this week show that there are 343,839 residents of New Orleans, down 29% from the previous count of 485,000 in 2000. The current population is also substantially depleted from the 455,000 people believed to have been living in the city just before hurricane Katrina struck in August 2005.

The powerful storm overpowered the city's levees and caused flooding that forced about 200,000 residents to flee.

Families relocated to makeshift camps elsewhere in Louisiana, Texas and Mississippi. No one knows what has happened to those people — the census records current location but does not show the movement of individuals between counts — but it is evident that many have never returned.

The detailed breakdown of the figures underline the enormous structural and demographic changes that the hurricane has imposed on New Orleans into the longer term. The first shift that leaps out is that the city's racial composition has altered dramatically.

Before Katrina, New Orleans was famously an overwhelmingly black city, with African Americans making up 67% of the population. That figure has dropped to 60% in the 2010 census, which reveals 118,000 fewer black residents.

That is likely to skew the dynamics of New Orleans in subtle and less subtle ways. The city last year elected its first white mayor since 1978, though Mitch Landrieu won the ballot with the support of 64% of the black voters.

Landrieu put a brave face on the census results. He said: "Our progress has always been much bigger than a population number. Over five years after Hurricane Katrina, our story is one of redemption and resurrection."

While the black population has declined, the white population has crept up to 30%, and there has been an increase in the Hispanic presence too, a result of the influx of workers needed for the city's reconstruction.

One of the most worrying statistics shows almost 60,000 fewer children in the city than in 2000, a drop of about 44%. New Orleans has always prided itself in its youthful vibrant culture, but that figure suggests its long-term vitality may be in doubt.

Within the confines of New Orleans, the poorer, blacker parts of the city, notably on the east side, have been devastated, with sharply depleted populations and entire neighbourhoods such as the Lower Ninth Ward that remain largely boarded up.

By contrast, the whiter, richer western districts of New Orleans stretching out towards Baton Rouge have proved to be relatively successful in regaining their strength.