A “freshet” is a large rise or overflowing of a stream caused by heavy rains or melted snow, and often used to describe a spring thaw. The term can also refer to a small stream of fresh water, irrespective of its outflow. The use of the word is first found in 1596.

A spring freshet can sometimes last several weeks on large river systems, resulting in significant inundation of flood plains as the snowpack melts in the river’s watershed.

In the eastern part of North America, annual freshets occur from the Canadian Taiga ranging along the Great Lakes then down through the Appalachian mountain chain and St. Lawrence valley from Northern Maine into North Carolina and Tennessee.

In the western part of the continent, freshets occur throughout the various west coast mountain ranges that extend southward down from Alaska, even into the northern parts of Arizona and New Mexico.

In the Fraser River Basin in British Columbia, the timing of freshets is critical. Migratory fish, such as salmon and trout, are highly responsive to freshets. In low flows present at the end of freshets, fish are more likely to ascend streams (move upstream). During high flows at the peak of a freshet, fish are more likely to descend streams.

The 1997 Red River Valley Flood was the result of an exceptionally large freshet fed by large snow packs which melted in rapidly warming temperatures, inundating the frozen ground. At the peak of the flood, the Red River reached a depth of  54 feet and a maximum discharge of 4,000 cubic meters per second. This event has been referred to as “the flood of the century” in the areas impacted.

The Fraser River in BC experiences yearly freshets fed by snowmelt in the spring and early summer. The largest freshet ever experienced in the Fraser River occurred in 1894. The 1948 flood, the second largest, caused extensive damage in the lower Fraser Valley. 

In 1972, the Susquehanna River which flows into Chesapeake Bay experienced a considerably large freshet due to Tropical Storm Agnes, resulting in flooding and increased sedimentation in Chesapeake Bay.

The word “freshet” sounds to me like something small and gentle, but it obviously describes one of the most powerful forces of nature.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: