This might be a better question for Engineering.SE.

I know that flash flooding to the extent and intensity that is seen in the Midwest or South is more rare in the Pacific Northwest, because it was the subject of a question I asked on ES.SE. However, areal and river flooding is not uncommon in the fall and winter, such as at the Squamish River in October 2003, Stillaguamish River in March 2014 and the Thanksgiving 1990 floods.

Right now the Sumas Prairie neighbourhood of Abbotsford, BC, near the US border, is undergoing catastrophic areal and river flooding as the dikes keeping back the Nooksack River have failed. This river also flooded in the Thanksgiving 1990 floods, but I digress.

What kind of protections does the Fraser River have, particularly in the Lower Mainland (including the north and south arms)? Are there probable scenarios where the Fraser River bursts its banks and causes epic areal/river flooding in areas like Marpole, Richmond, the Fraser Foreshore area of Burnaby, or North Surrey? Or is the Lower Mainland sheltered from river flooding events and rapid snowmelt?

  • $\begingroup$ You misinterpreted the answers to your linked question. The Pacific northwest does experience flash flooding. $\endgroup$ Nov 19 '21 at 16:58
  • $\begingroup$ Your previous question asked about catastrophic flash flooding in particular. $\endgroup$
    – f.thorpe
    Nov 20 '21 at 3:03
  • $\begingroup$ Couple of comments: Yes I know that epic flash flooding can happen in the PNW, particularly with atmospheric river events combined with rapid snowmelt. what I was trying to say was, you don't see urban river flooding in New West or Surrey like the North Canadian River in May 93, May 2013 or May 2015, Arkansas River in May 84, Cumberland River in April 2010 and March 2021, Buffalo Bayou during Harvey. Even the worst case scenarios in the river valleys or the Sumas Prairie get nowhere close. $\endgroup$ Nov 23 '21 at 20:06
  • $\begingroup$ Furthermore, I was doing some research on the Sumas Prairie, and it's more nuanced than I first thought. The prairie used to be a lake, and was fed by the Nooksack River, not the Fraser River. Washington state has steadfastly refused to dredge the bottom ten metres of silt at the river, or dam the Nooksack, for decades. Nevertheless, I wonder if it's possible for a massive flood to hit the cities along the Fraser River west of Abbotsford, or if 1894 and 1948 level events are no longer possible due to various reasons. $\endgroup$ Nov 23 '21 at 20:15

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