The term ''freshet'' is most commonly used to describe a
snowmelt, an annual
high water
High Water or Highwater may refer to:
* High water, the state of tide when the water rises to its highest level.
Film and television
* Highwater (film), ''Highwater'' (film), a 2008 documentary
* ''Step Up: High Water'', a web television series
* ...
event on rivers resulting from snow and river ice melting.
Description
A spring freshet can sometimes last several weeks on large river systems, resulting in significant inundation of
flood plain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
s as the
snowpack
Snowpack is an accumulation of snow that compresses with time and melts seasonally, often at high elevation or high latitude. Snowpacks are an important water resource that feed streams and rivers as they melt, sometimes leading to flooding. Snow ...
melts in the river's
watershed. Freshets can occur with differing strength and duration depending upon the depth of the snowpack and the local average rates of warming temperatures. Deeper snowpacks which melt quickly can result in more severe
flood
A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...
ing. Late spring melts allow for faster flooding; this is because the relatively longer days and higher solar angle allow for average melting temperatures to be reached quickly, causing snow to melt rapidly. 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. Serious flooding from freshets in southern US states are more often related to rain storms of large
tropical
The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
weather systems rolling in from the
South Atlantic
The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
or
Gulf of Mexico
The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
, 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
In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to ...
is not
blocking northward movement of low pressure systems.
In the eastern part of the
continent
A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...
, annual freshets occur from the
Canadian
Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...
Taiga
Taiga or tayga ( ; , ), also known as boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches. The taiga, or boreal forest, is the world's largest land biome. In North A ...
ranging along both sides of the
Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...
then down through the heavily
forest
A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...
ed
Appalachian mountain chain
A mountain chain is a row of high mountain summits, a linear sequence of interconnected or related mountains,Whittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, p 87. . or a contiguous ridge of mountains within a larger mo ...
and
St. Lawrence valley
A valley is an elongated low area often running between hills or mountains and typically containing a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...
from Northern
Maine
Maine ( ) is a U.S. state, state in the New England region of the United States, and the northeasternmost state in the Contiguous United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Provinces and ...
and
New Brunswick
New Brunswick is a Provinces and Territories of Canada, province of Canada, bordering Quebec to the north, Nova Scotia to the east, the Gulf of Saint Lawrence to the northeast, the Bay of Fundy to the southeast, and the U.S. state of Maine to ...
into
barrier ranges in
North Carolina
North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...
and
Tennessee
Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...
.
In the western part of the continent, freshets occur throughout the generally much higher elevations of the various west coast mountain ranges that extend southward down from
Alaska
Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...
even into the northern parts of
Arizona
Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
and
New Mexico
New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
.
:''The term can also refer to the following:''
* A
flood
A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...
resulting from heavy rain or a spring thaw. Whereas heavy rain often causes a
flash flood
A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...
, a spring thaw event is generally a more incremental process, depending upon local climate and
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
.
* A stream, river or flood of
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...
which empties into the
ocean
The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...
, usually flowing through an
estuary
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...
.
* A small stream of fresh water, irrespective of its outflow.
* A pool of fresh water, according to
Samuel Johnson
Samuel Johnson ( – 13 December 1784), often called Dr Johnson, was an English writer who made lasting contributions as a poet, playwright, essayist, moralist, literary critic, sermonist, biographer, editor, and lexicographer. The ''Oxford ...
's ''
A Dictionary of the English Language
''A Dictionary of the English Language'', sometimes published as ''Johnson's Dictionary'', was published on 15 April 1755 and written by Samuel Johnson. It is among the most influential dictionary, dictionaries in the history of the English la ...
''
and followed in Thomas Sheridan's dictionary, but this might have been a misinterpretation on Johnson's part, and it is at best not a common usage.
*A controlled release of extra water into a river from a dam or other impounding structure, in additional to normal compensation flows, intended to simulate high flow events which would normally occur naturally if the river was not impounded. They are designed to aid fish migration.
Causes
Freshets are the result of the mass delivery of water to the landscape, either by
snowmelt, heavy rains, or a combination of the two. Specifically, freshets occur when this water enters streams and results in flooding and high flow conditions. When freshets occur in the winter or early spring, the frozen ground can contribute to rapid flooding. 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. Deeper snow packs with large
snow water equivalents (SWE) are capable of delivering larger quantities of water to rivers and streams, compared to smaller
snowpack
Snowpack is an accumulation of snow that compresses with time and melts seasonally, often at high elevation or high latitude. Snowpacks are an important water resource that feed streams and rivers as they melt, sometimes leading to flooding. Snow ...
s, given that they reach adequate melting temperatures. When melting temperatures are reached quickly and snowmelt is rapid, flooding can be more intense. In areas where freshets dominate the
hydrological regime, such as the
Fraser River
The Fraser River () is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain (Canada), Blackrock Mountain in the Rocky Mountains and flowing for , into the Strait of Georgia just south of the City of V ...
Basin in
British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, the timing of freshets is critical. In the Fraser River Basin, the annual freshet was observed 10 days earlier in 2006 compared to 1949. In these areas, earlier freshets can result in low flow conditions later in the summer or fall.
Freshets may also occur due to rainfall events. Significant rainfall events can saturate the ground and lead to rapid inundation of streams, as well as contributing to snowmelt by delivering energy to snowpacks through
advection
In the fields of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is a ...
. In the tropics, tropical storms and
cyclones
In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an ant ...
can lead to freshet events.
Ecology
The magnitude of freshets depends on snow accumulation and temperature. Smaller freshets have been associated with
El Niño
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
conditions, where the milder conditions lead to lower snow accumulations. The opposite is true under
La Niña
LA most frequently refers to Los Angeles, the second most populous city in the United States of America.
La, LA, or L.A. may also refer to:
Arts and entertainment Music
*La (musical note), or A, the sixth note
*"L.A.", a song by Elliott Smit ...
conditions. Runoff from freshets is a major contributor of nutrients to lakes. In
La Niña
LA most frequently refers to Los Angeles, the second most populous city in the United States of America.
La, LA, or L.A. may also refer to:
Arts and entertainment Music
*La (musical note), or A, the sixth note
*"L.A.", a song by Elliott Smit ...
conditions with stronger freshets, higher runoff, and high nutrient inputs, more positive
ecological indicator
Ecological indicators are used to communicate information about ecosystems and the impact human activity has on ecosystems to groups such as the public or government policy makers. Ecosystems are complex and ecological indicators can help describe ...
species (
Arcellacea) are present in lakes, indicating lower levels of ecological stress.
In
El Niño
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
conditions, smaller freshets contribute less runoff and result in lower nutrient inputs to lakes and rivers. In these conditions, fewer positive ecological indicator species are present.
Migratory fish, such as
salmon
Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...
and
trout
Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...
, 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. There are some species of fish that are less effected from freshets than others. Goby ''Pomatoschistus''ssp for example, show similar patterns of migration and recover in population abundance and distribution after/during freshet conditions.
The benthic-estuarine species seem to better cope with freshets, some have even showed an attraction effect due to the extent of estuarine cues. Some species are affected by the consequences of freshets more than others. 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.
Biogeochemical Impacts
Freshets are often associated with high levels of
dissolved organic carbon (DOC) in streams and rivers. 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. Freshets have also been linked to compressing salinity gradients, increasing turbidity, and in the most intense conditions of freshets they have decreased oxygen levels.
Artificial freshets have also been correlated with changes in migration patterns of adult Atlantic salmon. A study was conducted in southern Norway which showed significant alterations in migration distances. Comparing the data from pre-freshet, during freshet, and post-freshet the mean migration distances per hour of the salmon showed significant differences.
Freshets may cause catastrophic changes to society, specifically in the economy and agriculture of populated environments. The floods caused by high waters from the rivers have been documented to destroy historical monuments, destroy ecosystems as well as pose a great threat to any life living near the freshet event, including human life. The research of predicting the changes of water levels due to freshets have become a large topic in the scientific community due to prior and future catastrophic events.
History

The 1997
Red River Valley Flood was the result of an exceptionally large freshet fed by large snow accumulations which melted due to rapidly warming temperatures, producing large volumes of meltwater which inundated the frozen ground. At the peak of the flood, the Red River reached a depth of and a maximum
discharge of . This event has been referred to as “the flood of the century” in the areas impacted.
The
Fraser River
The Fraser River () is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain (Canada), Blackrock Mountain in the Rocky Mountains and flowing for , into the Strait of Georgia just south of the City of V ...
in
British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
experiences yearly freshets fed by snowmelt in the spring and early summer. The largest freshet ever experienced in the Fraser River occurred in 1894 and resulted in an estimated peak
discharge of and a peak height of at
Hope, BC.
However, due to the low population this flood had a minor impact compared to the second largest flood in 1948, which had a peak discharge of and a peak height of at Hope, BC.
The 1948 flood caused extensive damage in the lower
Fraser Valley and cost 20 million dollars at the time.

In 1972, the
Susquehanna River
The Susquehanna River ( ; Unami language, Lenape: ) is a major river located in the Mid-Atlantic (United States), Mid-Atlantic region of the United States, crossing three lower Northeastern United States, Northeast states (New York, Pennsylvani ...
which flows into
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula, including parts of the Ea ...
experienced a considerably large freshet due to
Tropical Storm Agnes, resulting in flooding and increased
sedimentation
Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...
in Chesapeake Bay. At the peak of the flood on June 24, 1972, the instantaneous peak flow was greater than , and at the mouth of the river, the concentration of
suspended solids
Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration ...
was greater than 10,000 milligrams per liter.
In southwestern Japan the Ohashi River runs between two brackish-water lagoons. In this river Ammonia "beccarii" forma 1 (a benthic foraminiferan) has been found to colonize these waters depending on seasonal changes in the ecosystem. These organisms have been studied prior and post freshet events, and have been found to recover even when their habitat has been diminished by physical disturbances. The freshets in winter or early spring cause rapid flooding. The water abundance due to the melting of snow cannot easily infiltrate the frozen surface and run into nearby rivers, in this study the Ohashi River. Many of the organisms in this river have evolved to overcome the effects of the freshets
See also
*
Wajū
References
External links
* {{Commons category-inline
"Freshet"at
Answers.com
Flood
Bodies of water
Hydrology