THE FLOOD risk in Wales is being grossly underestimated and is putting lives and property at risk, according to a world renowned rivers expert.

Prof Mark Macklin, the head of the River Dynamics and Hydrology Research Group at the University of Aberystwyth warns that existing flood defences may not be adequate because the Natural Resources Wales are failing to use all available data to predict the risks on tonight’s Week In Week Out programme.

Prof Macklin leads a team of researchers who have discovered historical geological markers across the UK which show evidence of much larger and more frequent floods than those which have been measured by NRW gauges over the last 50 years in Welsh rivers.

He believes more historical data should be used to help calculate risks and warn communities of the likelihood of future flooding.

He said: “We had in the late 18th century floods which were 20, 30 per cent larger than the instrumental record. If we go back further than that to the last three and a half thousand years where we have long sedimentary records we have floods that were perhaps 20 per cent larger than that as well.

"So we’re actually looking at flood magnitudes that may be approaching in some areas, the Upper Severn as parts of mid Wales where flood magnitudes could be anywhere 20 to 40 per cent higher than what we’ve seen in the post 1980 period.”

Prof Macklin has been studying the sedimentation and geological flood rock deposits for over 30 years in the UK and across the world. His methodology is already being used to assess risks in New Zealand and the US.

He believes urgent action is needed.

“We will need to rethink and re-map our flood plains to look at changing flood risks. If we don’t, we’re going to put more properties and livelihoods at risk”.

Natural Resources Wales says it doesn’t accept that their flood maps are underestimating Wales’ flood risk. However they are aware of Prof Macklin’s work and are considering a pilot study to see if they can use the data in their modelling.

Week in Week Out: Flooding - Are you as safe as you think? will be on BBC One Wales tonight (Monday, 29 February 29) at 10.40pm and on BBC iPlayer.