Plans to prepare Wales for more frequent flooding over the next 100 years will be unveiled by the Environment Agency this month.
It starts a three-month consultation process on Friday with representatives of those most affected.
Last week heavy rain brought chaos to the UK with south and mid Wales badly affected. One teenager died in Powys.
The agency said climate change was expected to increase the flooding risk, but higher defences would not help.
Its catchment flood management plan (CFMPs) is designed to tackle the effects of flooding along river boundaries, and is supported by both the Welsh Assembly Government and the UK government.
The purpose of the plan is to look at ways of slowing down water - possibly by planting trees, changing land use and flood storage.
"In the future it will not be possible to defend everyone, everywhere, all of the time"
Environment Agency Director in Wales Chris Mills said: "Traditionally, the approach to managing flood risk has been dominated by the construction of flood defences.
"But in the future it will not be possible to defend everyone, everywhere, all of the time.
"Building higher and higher defences won't solve the problem in 100 years time.
"We have to put plans in motion now to collectively find the best solutions for dealing with increased volumes of water that will inevitably cause us problems in the future.
"We have seen over the last few days the problems that floods can cause. It is important that we look to tackle flooding now and in the future."
But there are fears that farmland in Powys might be deliberately flooded as part of the plan.
In July, Montgomeryshire AM Mick Bates, who is also chairman of the Welsh assembly's sustainability committee, said the agency had made previous attempts to flood farmland in Powys.
Badly hit
He said water flowed off hills too quickly and that caused flooding, but there are several schemes being developed to hold the water in the hills.
Last week, heavy rain led to hundreds of flood calls across south and west Wales, with the rail and road network badly hit.
In mid Wales, Louise Valerie Amanda Ferreira, 17, from Thamesmead, south-east London died when a 4X4 vehicle overturned in a swollen river near Llanwrtyd Wells.
In south Wales, a major incident was declared in Bridgend due to rising water levels in the River Ogmore, and a number of homes were evacuated due to flooding.
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