Watching the river

Recent dike improvements do not make Chilliwack immune from flooding. But the water has to get a lot higher than it is now to pose a risk.

As the water continues to rise on the Fraser River, it’s hard not to think about the floods that devastated Chilliwack in the past.

But much has changed since 1948, and certainly 1894.

Even the high-water mark of 2007 presented more of a threat to the community than circumstances today.

The difference is the ongoing improvements to Chilliwack’s flood defences: It’s extensive network of dikes, and pumping stations.

That doesn’t mean the city is immune from flooding. What it does mean is that the water has to get a lot higher than it is right now to pose a risk.

River levels remained steady last week after rain and warming temperatures brought the Fraser to 4.5 metres at the Mission gauge (where Chilliwack draws its benchmark measurements).

They peaked again at 5.2 metres on Sunday and Monday as water from the upper Fraser – which prompted isolated evacuation orders in Prince George on Friday – arrived here.

That’s still below the point were Chilliwack flood response kicks in. For that to happen, the river has to reach 5.5 metres. That’s when limited flooding in areas outside the dike may occur, and the city begins making regular patrols.

The river has to reach seven meters for those dike patrols to go to 24 hours.

That’s half a metre below the level reached in the great flood of 1948, when a breach in a dike near Greendale caused massive flooding.

Since then the dikes have been built higher, they’ve been extended, and additional pumping stations have been put in place.

All this, of course, does not rule out the possibility that Chilliwack will again experience significant flooding. Most of the city, after all, is on a floodplain.

The snowpack was exceptionally high this year and as that snow melts, the water will be coming our way.

But perspective is important. As continued reports warn of rising river levels, or floods in communities upstream, understanding the capabilities of the diking system protecting Chilliwack can mean the difference between panic and preparation.