Warning of homes and lives in greater flood danger
Lives and homes are in danger because the flood risk in Wales is being underestimated, according to a rivers expert.
Aberystwyth University's Prof Mark Macklin said magnitudes could be 40% greater than planned for in some areas.
He told BBC Wales Natural Resources Wales (NRW) is failing to use all historical data to predict the risks.
A NRW spokesman said its flood maps were not underestimating the problem but it was considering using the data.
Prof Macklin, who heads the university's river dynamics and hydrology research group, questioned why NRW uses river gauges from the past 50 years only to predict flood risk.
He told Week In Week Out his researchers had found "evidence of much larger and more frequent floods" in the 18th century, which were between 20% and 30% larger.
Among areas most at risk, Prof Macklin said parts of the upper River Severn in Powys could see flood magnitudes between 20% and 40% greater than what had been experienced since 1980.
"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," he said.
Despite £7m being spent on new flood defences in Llanrwst in Conwy Valley, residents on Conway Terrace had their properties flooded on Boxing Day 2015 when a temporary dam was not put up in time.
An NRW spokesman said while it did not accept its flood maps were underestimating the risks, it was aware of Prof Macklin's work and was considering a pilot study to see if it could use the data in its modelling.
- Week In Week Out is on BBC One Wales at 22:40 on Monday, 29 February.