More than 300,000 homes and billions of dollars of infrastructure could be affected by a major flood in the Lower Mainland because our dikes haven’t been built to withstand more severe flooding caused by climate change, reports and experts say.

A $500,000 push is under way to assess how bad the damage could be and where is vulnerable – the first step to unifying a fragmented Lower Mainland flood management strategy, said David Marshall of the Fraser Basin Council.

“To me, this the most critical issue that the Lower Mainland will face in the next 15-20 years,” Marshall told CTV News.

There are some 1,100 kilometres of dikes in B.C., with 600 kilometres in the Lower Mainland. Much of that was built through a federal and provincial program in the decades after a devastating flood in 1949, which washed away 2,000 homes.

In the late 1990s and 2000, cuts at the federal and provincial levels left municipalities in charge of the infrastructure, making B.C. one of the few jurisdictions worldwide without a region-wide flood authority, said flood consultant Tamsin Lyle.

“I would argue that we are extremely under-resourced when it comes to flood hazard,” Lyle said.

Some municipalities are aware of the flood risk and are actively investing in new equipment to protect their citizens, like North Vancouver, she said.

But others lack basic tools like flood maps, which can estimate where the biggest damage is likely to be, and require changes in new buildings in the area.

The disorganization becomes a huge problem now because flood risk has changed since the time those dikes were built, said Lyle.

Climate change models suggest that floods will be more severe and more frequent, putting pressure on the river dike system.

On top of that, sea level will rise, authorities say, with the City of Vancouver mandating that buildings must be prepared for flooding as much as 4.6 meters above sea level.

That means that even cities farther inland have to deal with the threat of a higher sea level, said Dana Soong of the City of Coquitlam.

“The current weather forecasts look at a sea level rise of meters,” he said. “We have to prepare for that.”

Lyle looks to the Calgary floods in 2013 to show off a worst-case scenario. In that flood, damages were estimated at more than $5 billion. Vancouver’s could be worse as it has a larger population with a larger river, as well as dangers from the coast.

The Fraser Basin Council’s Marshall says his organization has stepped in to unite the province, the federal government, 25 municipalities and other regional interests such as railway companies and pipeline company Kinder Morgan.

The non-profit has raised $500,000 to conduct a detailed study of the risks in the Lower Mainland, run through likely flood scenarios, and determine how best to allocate scarce resources to protect citizens, Marshall said.

That study will be finished at the end of the year, he said, and then the next job will be to figure out how to build the infrastructure required, he said.