User:Waterdragonfly/Stream bed: Difference between revisions
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A '''streambed''' or '''stream bed''' is the bottom of a [[stream]] or [[river]] ([[bathymetry]]) and is confined within a [[Stream channel|channel]], or the banks (sides) of the waterway.<sup>[1]</sup> Usually, the bed is kept clear of terrestrial [[vegetation]] and instead supports different types of aquatic vegetation ([[Aquatic plant]]), depending on the type of streambed material and water velocity. The nature of any stream bed is always a function of the flow dynamics and the local geologic materials. A streambed is usually a mix of particle sizes which depends on the water velocity and the materials introduced from upstream and from the watershed. Particles can be from very fine silts and clays to large cobbles and boulders ([[Grain size]]). Particles get sorted to different parts of a streambed as water velocity changes. In general, sands move most easily, and particles become harder to move as they increase in size. Silts and clays, although smaller than sands, can stick together, making them harder to move along the streambed<ref name=":0">{{Cite book |last=Allan |first=David |title=Stream Ecology: Structure and Function of Running Waters |publisher=Springer |year=2009 |isbn=9781402055829 |edition=2nd |location=Dordrecht, The Netherlands |pages={{!}}pages=36-41 |language=en}}</ref>. |
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The lateral confines or channel margins are known as the stream [[Bank (geography)|banks]] or riverbanks. A [[flood]] occurs when a stream overflows its banks and flows onto its [[flood plain]]. As a general rule, the bed is the bottom of the [[Stream channel|channel]], and the banks are the sides of the waterway.<ref name=":0" /> Usually, the bed is kept clear of terrestrial [[vegetation]], whereas the banks are subjected to water flow only during unusual or perhaps infrequent high-water stages and therefore might support terrestrial vegetation some or much of the time. |
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The intensity and frequency of both drought and rain events are expected to increase with climate change<ref>{{Cite journal |last=Blöschl |first=Günter |last2=Hall |first2=Julia |last3=Viglione |first3=Alberto |last4=Perdigão |first4=Rui A. P. |last5=Parajka |first5=Juraj |last6=Merz |first6=Bruno |last7=Lun |first7=David |last8=Arheimer |first8=Berit |last9=Aronica |first9=Giuseppe T. |last10=Bilibashi |first10=Ardian |last11=Boháč |first11=Miloň |last12=Bonacci |first12=Ognjen |last13=Borga |first13=Marco |last14=Čanjevac |first14=Ivan |last15=Castellarin |first15=Attilio |date=2019 |title=Changing climate both increases and decreases European river floods |url=https://www.nature.com/articles/s41586-019-1495-6 |journal=Nature |language=en |volume=573 |issue=7772 |pages=108–111 |doi=10.1038/s41586-019-1495-6 |issn=1476-4687}}</ref> <ref>{{Cite journal |last=Marsooli |first=Reza |last2=Lin |first2=Ning |last3=Emanuel |first3=Kerry |last4=Feng |first4=Kairui |date=2019-08-22 |title=Climate change exacerbates hurricane flood hazards along US Atlantic and Gulf Coasts in spatially varying patterns |url=https://www.nature.com/articles/s41467-019-11755-z |journal=Nature Communications |language=en |volume=10 |issue=1 |pages=3785 |doi=10.1038/s41467-019-11755-z |issn=2041-1723 |pmc=PMC6706450 |pmid=31439853}}</ref>. Where natural conditions of either [[grassland]] or [[forest]] ameliorate peak flows, streambeds should remain more stable and exhibit minimal scour. They should retain rich organic matter and, therefore continue to support a rich biota.([[River ecosystem|River ecosystem)]] Where conditions produce unnatural levels of runoff, such as occurs in urban areas with high levels of [[Impervious surface]], the stream beds will exhibit a greater amount of scour, often down to bedrock and banks may be undercut causing [[bank erosion]]. This process greatly increases watershed erosion and results in thinner soils upslope from the stream bed, as the channel adjusts to the increase in flow. |
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The nature of any stream bed is always a function of the flow dynamics and the local geologic materials. With small streams in [[Mesophyte|mesophytic]] regions, the nature of the stream bed is strongly responsive to conditions of [[Precipitation (meteorology)|precipitation]] [[Surface runoff|runoff]]. |
The nature of any stream bed is always a function of the flow dynamics and the local geologic materials. With small streams in [[Mesophyte|mesophytic]] regions, the nature of the stream bed is strongly responsive to conditions of [[Precipitation (meteorology)|precipitation]] [[Surface runoff|runoff]]. The stream bed is very complex in terms of erosion. [[Sediment]] is transported, eroded and deposited on the stream bed<ref>{{Cite journal |last1=Garcia |first1=Marcelo |last2=Parker |first2=Gary |year=1991 |title=Entrainment of Bed Sediment into Suspension |journal=Journal of Hydraulic Engineering |language=en |volume=117 |issue=4 |pages=414–435 |doi=10.1061/(asce)0733-9429(1991)117:4(414)}}</ref> as the water flows downstream. Sediment is usually deposited on the inside of curves and eroded on the outside of stream curves.<ref name=":0" /> FIND OR CREATE DIAGRAM |
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The majority of sediment washed out in higher flows is "near-threshold" sediment that has been deposited during normal flow and only needs a slightly higher flow to become mobile again. This shows that the stream bed is left mostly unchanged in size and shape over time.<ref name="Phillips&Jerolmack2016">{{cite journal |last1=Phillips |first1=Colin B. |last2=Jerolmack |first2=Douglas J. |year=2016 |title=Self-organization of river channels as a critical filter on climate signals |journal=Science |volume=352 |issue=6286 |pages=694–697 |bibcode=2016Sci...352..694P |doi=10.1126/science.aad3348 |pmid=27151865 |doi-access=free}}</ref> |
The majority of sediment washed out in higher flows is "near-threshold" sediment that has been deposited during normal flow and only needs a slightly higher flow to become mobile again. This shows that the stream bed is left mostly unchanged in size and shape over time.<ref name="Phillips&Jerolmack2016">{{cite journal |last1=Phillips |first1=Colin B. |last2=Jerolmack |first2=Douglas J. |year=2016 |title=Self-organization of river channels as a critical filter on climate signals |journal=Science |volume=352 |issue=6286 |pages=694–697 |bibcode=2016Sci...352..694P |doi=10.1126/science.aad3348 |pmid=27151865 |doi-access=free}}</ref> |
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=== References === |
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Where conditions produce unnatural levels of runoff, such as occurs in urban areas with high levels of [[Impervious surface]], the stream beds will exhibit a greater amount of scour, often down to bedrock and banks may be undercut causing [[bank erosion]]. This process greatly increases watershed erosion and results in thinner soils upslope from the stream bed, as the channel adjusts to the increase in flow. |
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=== Refer<ref name=":0">{{Cite book |last=Allan |first=David |title=Stream Ecology: Structure and Function of Running Waters |publisher=Springer |year=2009 |isbn=9781402055829 |edition=2nd |location=Dordrecht, The Netherlands |pages={{!}}pages=36-41 |language=en}}</ref>ences === |
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A streambed or stream bed is the bottom of a stream or river (bathymetry) and is confined within a channel, or the banks (sides) of the waterway.[1] Usually, the bed is kept clear of terrestrial vegetation and instead supports different types of aquatic vegetation (Aquatic plant), depending on the type of streambed material and water velocity. The nature of any stream bed is always a function of the flow dynamics and the local geologic materials. A streambed is usually a mix of particle sizes which depends on the water velocity and the materials introduced from upstream and from the watershed. Particles can be from very fine silts and clays to large cobbles and boulders (Grain size). Particles get sorted to different parts of a streambed as water velocity changes. In general, sands move most easily, and particles become harder to move as they increase in size. Silts and clays, although smaller than sands, can stick together, making them harder to move along the streambed[1].
The intensity and frequency of both drought and rain events are expected to increase with climate change[2] [3]. Where natural conditions of either grassland or forest ameliorate peak flows, streambeds should remain more stable and exhibit minimal scour. They should retain rich organic matter and, therefore continue to support a rich biota.(River ecosystem) Where conditions produce unnatural levels of runoff, such as occurs in urban areas with high levels of Impervious surface, the stream beds will exhibit a greater amount of scour, often down to bedrock and banks may be undercut causing bank erosion. This process greatly increases watershed erosion and results in thinner soils upslope from the stream bed, as the channel adjusts to the increase in flow.
The nature of any stream bed is always a function of the flow dynamics and the local geologic materials. With small streams in mesophytic regions, the nature of the stream bed is strongly responsive to conditions of precipitation runoff. The stream bed is very complex in terms of erosion. Sediment is transported, eroded and deposited on the stream bed[4] as the water flows downstream. Sediment is usually deposited on the inside of curves and eroded on the outside of stream curves.[1] FIND OR CREATE DIAGRAM
The majority of sediment washed out in higher flows is "near-threshold" sediment that has been deposited during normal flow and only needs a slightly higher flow to become mobile again. This shows that the stream bed is left mostly unchanged in size and shape over time.[5]
References
- ^ a b Allan, David (2009). Stream Ecology: Structure and Function of Running Waters (2nd ed.). Dordrecht, The Netherlands: Springer. pp. |pages=36-41. ISBN 9781402055829.
- ^ Blöschl, Günter; Hall, Julia; Viglione, Alberto; Perdigão, Rui A. P.; Parajka, Juraj; Merz, Bruno; Lun, David; Arheimer, Berit; Aronica, Giuseppe T.; Bilibashi, Ardian; Boháč, Miloň; Bonacci, Ognjen; Borga, Marco; Čanjevac, Ivan; Castellarin, Attilio (2019). "Changing climate both increases and decreases European river floods". Nature. 573 (7772): 108–111. doi:10.1038/s41586-019-1495-6. ISSN 1476-4687.
- ^ Marsooli, Reza; Lin, Ning; Emanuel, Kerry; Feng, Kairui (2019-08-22). "Climate change exacerbates hurricane flood hazards along US Atlantic and Gulf Coasts in spatially varying patterns". Nature Communications. 10 (1): 3785. doi:10.1038/s41467-019-11755-z. ISSN 2041-1723. PMC 6706450. PMID 31439853.
{{cite journal}}: CS1 maint: PMC format (link) - ^ Garcia, Marcelo; Parker, Gary (1991). "Entrainment of Bed Sediment into Suspension". Journal of Hydraulic Engineering. 117 (4): 414–435. doi:10.1061/(asce)0733-9429(1991)117:4(414).
- ^ Phillips, Colin B.; Jerolmack, Douglas J. (2016). "Self-organization of river channels as a critical filter on climate signals". Science. 352 (6286): 694–697. Bibcode:2016Sci...352..694P. doi:10.1126/science.aad3348. PMID 27151865.