A year after a tsunami ravaged 200 miles of coastline in Japan, the world's press is full of photographs which detail the remarkable clean-up effort.

But a Norwich professor who has just returned from the region devastated by the Tohoku earthquake and resulting tsunami has told how the country still faces a decade of clearing up the 'mountains of rubble' that still remain in some places.

Professor Paul Hunter, from the Univeristy of East Anglia's Norwich School of Medicine, was invited out by the University of Tokyo to see the impact of the tsunami – which killed thousands of people and triggered the world's worst nuclear crisis since Chernobyl – on waste water treatment plants. The professor of health protection went out on the trip to help him and his Japanese colleagues identify opportunities for possible joint research projects in the future.

He said: 'On a personal level it was incredibly distressing when you think about all the lives that were lost.

'Also being a medical specialist, seeing the totally destroyed hospitals was very hard. But I was very much impressed with how the Japanese have just got on with the reconstruction.

'They are well used to dealing with tsunamis but this was so enormous it was just overwhelming for too many of the areas. They think it was the biggest tsunami they have had in Japan for at least a thousand years.

'It will be 10 years before they have dealt with the clearing and the rebuilding will go on for decades.'

Prof Hunter said he saw mountains of rubble waiting to be sorted and then sent to landfill, as the rubble contains many valuable metals that can be reused.

Prof Hunter said the main waste water treatment plant he visited serves Sendai and while it is now able to do primary treatment and chlorination, it will not be back to full effectiveness for about four years.

This has led to concerns about the impact of inadequately treated sewage discharge to sea.

He added: 'There is a major problem with rebuilding in some areas. After the tsunami receded it took sediment with it.

'The land dropped 40 to 60 cm in many places, which makes a lot of the land below the level of high tide.

'So there are issues with building sea walls or raising land levels. Indeed, the rebuilt roads have been raised up.

'Another problem is that the rubble mountains are fermenting and are at risk of developing spontaneous fires.'

kim.briscoe@archant.co.uk