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[RalphH]

Big long solid rock canyon = hydro-logically a young river structure with high velocity at the canyon terminus   + it's historically has much wider flow swings on a regular basis than the Chilliwack.

[clarki]

https://vancouversun.com/news/local-news/u-s-officials-consider-plan-that-would-send-nooksack-river-overflow-into-canada
This could get interesting..
Then what is Abbotsford’s response? Build a dyke along 0 Ave to deflect the floodwaters back into the US?

[Fish Assassin]

Not a neighbourly thing to be doing.

[dcajaxs]

just shows that in the U.S. they are moving ahead with doing something about it to mitigate future events.

As the article states studies have been done here but nothing has come of it yet year after year. My frustration sits with the fact that the dyke in abbotsford failed and followed by a 100 meter breach.  If no breach had occured how much less of a disaster would it have been? Whos responsible for the breach in the dyke?

[DanTfisherman]

This is tricky.
From what I understand, the breach took place at the first, lowest spot on the dyke the flooding waters came to where the water could initially trickle over.  As that trickle increased, the volume and velocity of that water increased, increasing erosion at that spot rapidly, until all the water previously held back ripped through that one opening and expanded it to become that 100 meter gash.

So yes, people will look to learn and will build a higher dyke.  But as time goes on and the miles of dyke age and wear, and people forget the past, there will always be one spot a bit lower, and thus weaker and succeptable to erosion.  It could be a spot where the soil depresses and sinks over time.  It could be some unknowing or unsuspecting man made damage.  It could be a grassfire at some time down the line.  It could be cattle or other wildlife somehow impacting the dyke, It could be a freak thunderstorm where pounding rain one time causes some minor, barely noticed erosion, it could be consistent foot traffic in one area of the dyke, it could be an earthquake causes some minor structural issues.  We are talking possibly 50 to 100 years of planning and ongoing consistent monitoring.  We as a species have such a short memory that after 40 years of monitoring and nothing happening to the dyke, the next generation will forget the past, question the expenses, and thus fail to see the logic of continuing on-going expensive efforts.  You can see that this is what happened with the last flood committee that was formed after the 1990 flood.
"After the last significant Nooksack flood in 1990, a cross-border group was created to come up with a mitigation plan. It went dormant in 2011 and was only recently resurrected."

The issue then becomes under the new US plan, there will be increased water heading this way.  Who can make accurate predictions on how all these floodwaters coalescing at a intense flood event will act and how high the water will get.  What I do know is that in the future such events, if the US follows through with their plan, that dyke will need to hold back a larger volume of water, and if it does fail and break through an even taller dyke, imagine how much water will instantly rush through and how big that gash will be next time.

Dano