Even the strongest levees and flood walls cannot be guaranteed to save New Orleans from another hurricane like Katrina, a US National Academy of Engineering panel concludes.

The existing flood protection measures are designed to protect the city from the worst flood likely in 100 years. But the panel argues that this approach is not acceptable for densely populated areas where failure of the levees, however unexpected, would be catastrophic by causing flooding that would hinder evacuation.

In addition, the New Orleans authorities need to start a programme of voluntary relocation in some neighbourhoods, the panel says. Hospitals and nursing homes should in any case be relocated away from flood-prone areas; during the Katrina evacuation some vulnerable people died.

If people refuse to move, buildings in endangered zones should be raised so their lowest floor sits above expected flood levels. This has already been applied in some hurricane-prone coastal resorts, which require homes along the shore to be elevated on posts.

Meanwhile, a court this week began hearing a lawsuit to decide whether the controversial Mississippi River Gulf Outlet built by the army’s Corps of Engineers exacerbated flooding during Katrina. In its report, the NAE panel suggests that it contributed at most a minor amount to storm surge and flood depths.