'Unexpected' is a relative term in this case. I remember the same area flooding back around 1990. The Sumas Prairie is a recent construct. Circa 1924 Sumas l

'Unexpected' is a relative term in this case. I remember the same area flooding back around 1990. The Sumas Prairie is a recent construct. Circa 1924 Sumas lake (seasonal lake to be sure) was drained for farmland and the area experiences flooding on this scale in something like a 35 year period - So, not even a 50 year or 100 yr weather conditions (or sequence of weather events). Since the 1990 flood there have been efforts to improve the ability to withstand known current weather events, but that proceeds at the bureaucratic pace you might expect when dealing with municipal/provincial/federal/indigenous governing bodies.