User:AvOsero/Freshet

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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. 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. 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.

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 16.46 m and a maximum discharge of 140,000 cuft/s. This event has been referred to as “the flood of the century” in the areas impacted.

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 m3/s and a peak height of 11.75 m 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 15,200 m3/s and a peak height of 10.97 m 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 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 32000 m3/s, and at the mouth of the river, the concentration of suspended solids 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 has been found to habitate these waters dependent 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 diminshed 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 froxen surface and run into nearby rivers, in this study the Ohashi River. The many of the organisms in this river have evolved to overcome the effects of the freshets

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 an increase in the net primary productivity of the stream by enhancing 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.

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