The term freshet is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting.
The term freshet is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting.
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. 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 flooding. 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. [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.
In the eastern part of the continent, annual freshets occur from the Canadian Taiga ranging along both sides of the Great Lakes then down through the heavily forested Appalachian mountain chain and St. Lawrence valley from Northern Maine and New Brunswick into barrier ranges in North Carolina and Tennessee.
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 even into the northern parts of Arizona and New Mexico.
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. [9] Deeper snow packs with large snow water equivalents (SWE) are capable of delivering larger quantities of water to rivers and streams, compared to smaller snowpacks, given that they reach adequate melting temperatures. When melting temperatures are reached quickly and snowmelt is rapid, flooding can be more intense. [10] In areas where freshets dominate the hydrological regime, such as the Fraser River Basin in British Columbia, the timing of freshets is critical. In the Fraser River Basin, the annual freshet was observed 10 days earlier in 2006 compared to 1949. [11] 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, [12] as well as contributing to snowmelt by delivering energy to snowpacks through advection. [13] In the tropics, tropical storms and cyclones can lead to freshet events. [14]
The magnitude of freshets depends on snow accumulation and temperature. Smaller freshets have been associated with El Niño conditions, where the milder conditions lead to lower snow accumulations. The opposite is true under La Niña conditions. Runoff from freshets is a major contributor of nutrients to lakes. In La Niña conditions with stronger freshets, higher runoff, and high nutrient inputs, more positive ecological indicator species (Arcellacea) are present in lakes, indicating lower levels of ecological stress. [15] In El Niño 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. [15]
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. [16] There are some species of fish that are less effected from freshets than others. Goby Pomatoschistusssp for example, show similar patterns of migration and recover in population abundance and distribution after/during freshet conditions. [17] 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. [18]
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. [19] [20] Freshets have also been linked to compressing salinity gradients, increasing turbidity, and in the most intense conditions of freshets they have decreased oxygen levels. [17]
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. [18]
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. [21] 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.
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 16.46 metres (54.0 ft) and a maximum discharge of 4,000 cubic metres per second (140,000 cu ft/s). This event has been referred to as “the flood of the century” in the areas impacted. [22] [23]
The Fraser River in British Columbia 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 17,000 cubic metres per second (600,000 cu ft/s) and a peak height of 11.75 metres (38.5 ft) at Hope, BC. [24] 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 15,200 cubic metres per second (540,000 cu ft/s) and a peak height of 10.97 metres (36.0 ft) at Hope, BC. [24] The 1948 flood caused extensive damage in the lower Fraser Valley and cost 20 million dollars at the time. [25]
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. At the peak of the flood on June 24, 1972, the instantaneous peak flow was greater than 32,000 cubic metres per second (1,100,000 cu ft/s), and at the mouth of the river, the concentration of suspended solids was greater than 10,000 milligrams per liter. [26]
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 [27]
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.
A flood is an overflow of water 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 concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding. Examples for human changes are land use changes such as deforestation and removal of wetlands, changes in waterway course or flood controls such as with levees. Global environmental issues also influence causes of floods, namely climate change which causes an intensification of the water cycle and sea level rise. For example, climate change makes extreme weather events more frequent and stronger. This leads to more intense floods and increased flood risk.
The Fraser River is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain in the Rocky Mountains and flowing for 1,375 kilometres (854 mi), into the Strait of Georgia just south of the City of Vancouver. The river's annual discharge at its mouth is 112 cubic kilometres (27 cu mi) or 3,550 cubic metres per second (125,000 cu ft/s), and each year it discharges about 20 million tons of sediment into the ocean.
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 or snow flowing over ice sheets or snowfields. Flash floods may also occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam, as occurred before the Johnstown Flood of 1889. Flash floods are distinguished from regular floods by having a timescale of fewer than six hours between rainfall and the onset of flooding.
The Snowy River is a major river in south-eastern Australia. It originates on the slopes of Mount Kosciuszko, Australia's highest mainland peak, draining the eastern slopes of the Snowy Mountains in New South Wales, before flowing through the Alpine National Park and the Snowy River National Park in Victoria and emptying into Bass Strait.
A jökulhlaup is a type of glacial outburst flood. It is an Icelandic term that has been adopted in glaciological terminology in many languages. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland, which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir.
The Byrd Polar and Climate Research Center (BPCRC) is a polar, alpine, and climate research center at Ohio State University founded in 1960.
A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a jökulhlaup. The dam can consist of glacier ice or a terminal moraine. Failure can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, volcanic eruptions under the ice, or massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.
Surface runoff is the unconfined flow of water over the ground surface, in contrast to channel runoff. It occurs when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes.
In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many parts of the world, in some cases contributing high fractions of the annual runoff in a watershed. Predicting snowmelt runoff from a drainage basin may be a part of designing water control projects. Rapid snowmelt can cause flooding. If the snowmelt is then frozen, very dangerous conditions and accidents can occur, introducing the need for salt to melt the ice.
Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found during early spring when snow packs and frozen rivers melt with rising temperatures, and in the ablation zone of glaciers where the rate of snow cover is reducing. Meltwater can be produced during volcanic eruptions, in a similar way in which the more dangerous lahars form. It can also be produced by the heat generated by the flow itself.
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. Snowpacks provide water to down-slope communities for drinking and agriculture. High-latitude or high-elevation snowpacks contribute mass to glaciers in their accumulation zones, where annual snow deposition exceeds annual melting.
A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long, large streams are usually called rivers, while smaller, less voluminous and more intermittent streams are known as streamlets, brooks or creeks.
A river is a natural freshwater stream that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it runs out of water, or only flow during certain seasons. Rivers are regulated by the water cycle, the processes by which water moves around the Earth. Water first enters rivers through precipitation, whether from the runoff of water down a slope, the melting of glaciers or snow, or seepage from aquifers beneath the surface of the Earth.
A water year is a term commonly used in hydrology to describe a time period of 12 months for which precipitation totals are measured. Its beginning differs from the calendar year because part of the precipitation that falls in late autumn and winter accumulates as snow and does not drain until the following spring or summer's snowmelt. The goal is to ensure that as much as possible of the surface runoff during the water year is attributable to the precipitation during the same water year.
The flash flood guidance system (FFGS) was designed and developed by the Hydrologic Research Center, a non-profit public-benefit corporation located in San Diego, CA, US, for use by meteorological and hydrologic forecasters throughout the world. The primary purpose of the FFGS is to provide operational forecasters and disaster management agencies with real-time information pertaining to the threat of small-scale flash flooding throughout a specified region.
A glacier stream is a channelized area that is formed by a glacier in which liquid water accumulates and flows. Glacial streams are also commonly referred to as "glacier stream" or/and "glacial meltwater stream". The movement of the water is influenced and directed by gravity and the melting of ice. The melting of ice forms different types of glacial streams such as supraglacial, englacial, subglacial and proglacial streams. Water enters supraglacial streams that sit at the top of the glacier via filtering through snow in the accumulation zone and forming slush pools at the FIRN zone. The water accumulates on top of the glacier in supraglacial lakes and into supraglacial stream channels. The meltwater then flows through various different streams either entering inside the glacier into englacial channels or under the glacier into subglacial channels. Finally, the water leaves the glacier through proglacial streams or lakes. Proglacial streams do not only act as the terminus point but can also receive meltwater. Glacial streams can play a significant role in energy exchange and in the transport of meltwater and sediment.
Snow science addresses how snow forms, its distribution, and processes affecting how snowpacks change over time. Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world. The study includes physical properties of the material as it changes, bulk properties of in-place snow packs, and the aggregate properties of regions with snow cover. In doing so, they employ on-the-ground physical measurement techniques to establish ground truth and remote sensing techniques to develop understanding of snow-related processes over large areas.
Climate change in Utah encompasses the effects of climate change, attributed to man-made increases in atmospheric carbon dioxide, in the U.S. state of Utah.
The 1997 California New Years Floods resulted from a series of winter storms, from December 26 to January 3 of 1997, fed with tropical moisture by an atmospheric river. It impacted Northern California, resulting in some of the most devastating flooding since the Great Flood of 1862. Similarly to the 1862 event, the flooding was a combined effect of heavy rainfall and excessive snowmelt of the relatively large early-season Sierra Nevada snowpack. The resulting flooding in the Central Valley and other low-lying areas forced over 120,000 people from their homes and caused over $2 billion in property damage alone. 48 out of California's 58 counties were declared disaster areas with many streamflow gauge stations in these areas recording return intervals of over 100 years. It would take months for the worst-hit areas to recover fully.
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