Overflow flood ways on the Mississippi River are in the news as flood waters are directed into overflow routes to ease flooding at other sites. A natural overflow route is located in northwest Whatcom on the Nooksack River. During large floods, part of the Nooksack River spills into the much smaller Sumas River and flows north into Canada and on to the Fraser River.
Nooksack River with overflow route shown by the long arrow directed to the northwest
Nooksack River overflow route between the two small towns of Everson and Nooksack
The Canadians on the north side of the border are never very thrilled with part of the Nooksack River flooding the Sumas Valley which is a former lake bed so the flood waters cover a large area. The border town of Sumas is deeply flooded as well during these big floods.
The area where flood waters exit the Nooksack has been reduced by a levee in Everson. That levy combined with the widening of the bridge span has reduced frequency of flooding upstream of Everson, but may be causing more frequent downstream flooding. A good reason for coordinating flood plans and development planning.
Bridge at Everson and the Nooksack River
The overflow route has been planned for flood water including flow. The road between Everson has been designed to be overtopped by flowing water.
Everson-Sumas overflow route looking east. Flood water approaches from the right.
Over flow route looking west. The shoulder slope is paved so road shoulder is not eroded.