Freshet

Freshets can occur with differing strength and duration depending upon the depth of the snowpack and the local average rates of warming temperatures.

Snowpacks at higher altitudes and in mountainous areas remain cold and tend to melt over a longer period of time and thus do not contribute to major flooding.

[1] Serious flooding from freshets in southern US states are more often related to rain storms of large tropical weather systems rolling in from the South Atlantic or Gulf of Mexico, to add their powerful heating capacity to lesser snow packs.

Tropically induced rainfall influenced quick melts can also affect snow cover to latitudes as far north as southern Canada, so long as the generally colder air mass is not blocking northward movement of low pressure systems.

This is because the meltwaters cannot easily infiltrate the frozen surface and instead run overland into rivers and streams, leading to a rapid flooding response.

Significant rainfall events can saturate the ground and lead to rapid inundation of streams,[12] as well as contributing to snowmelt by delivering energy to snowpacks through advection.

[15] In El Niño conditions, smaller freshets contribute less runoff and result in lower nutrient inputs to lakes and rivers.

This is due to multiple factors, some include, but not limited to: differentiation in species biological anatomy, previous migration patterns, mating seasons, and feeding habits.

During base flows, water entering streams comes from deep in the soil where carbon contents are lower due to microbial digestion.

During a freshet, water is more likely to run overland, where it dissolves the abundant, less degraded carbon present in the uppermost soil layers before entering streams.

High dissolved organic carbon (DOC) levels lead to a decrease in the net primary productivity of the stream by enhancing heterotrophic microbial growth.

[22][23] The Fraser River in British Columbia experiences yearly freshets fed by snowmelt in the spring and early summer.