Term
| what is the longitudinal profile of a river? |
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Definition
| a smoothly decaying curve, with steep slopes found in the headwater and low slopes found at the mouth where a river empties into a body of still water |
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Term
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Definition
the lowest elevation on the channel, the elevation that the river cannot erode below
for many rivers this is sea level but there are cases where sea level is not the baselevel (ex: lakes and regions with no external drainage to the ocean in which playas (dry lakes) provide the baelevel) |
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Term
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Definition
a river long profile with a smoothly declinging slope
the channel has adjusted its gradient to the baselevel
viewed as a sort of equilibrium profile
bumps and hollows in a river profile = transient features that call for explanation |
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Term
| how steep will a bedrock section be? |
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Definition
| bedrock is more resistant to erosion so it will be steeper (more shear stress required to erode it, hence steeper slope) |
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Term
| how will debris affect slope? |
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Definition
| it will build a step that steepens the profile (and can also create lakes) |
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Term
| where will displaements occur in a river and how will they affect the river? |
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Definition
| they occur along a fault crossed by a river and are manifested in the long profile. if the upstream side moves up relative to the downstream side, a convexity will be seen in the profile. the opposite case (upstream side moves down relative to downstream side) is likely to be erased quickly by deposition of sediment |
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Term
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Definition
short steep sections in a river channel created by resistant rock types or baselevel lowering
they migrate up the channel over time as the river works to produce a smooth profile
waterfalls are knickpoints, usually produced by a layer of erosion resistant rock |
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Term
| what dictates the downstream variations in grainsize of bed material? |
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Definition
changes in slope
on the steepest slopes, the basal shear stress is highest, and all but the largest grains are entrained and moved downstream. as the slope decreases downstream, the shear stress available to entrain sediment declines, and so does the size of the bed material |
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Term
| why does the water in a meandering channel continue in a more or less straight line even as the channel bends? |
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Definition
momentum
it sends the water against the outer edge of a bend
the water then belatedly makes the corner, rebounding off the wall and flowing down the water surface slope created by piling up
the resulting water flow pattern forms several helical rolls within the channel |
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Term
| where do water depth, velocity, and shear stress tend to be greatest? |
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Definition
| on the outside corner of a meander bed |
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Term
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Definition
| the bank of the outer edge of a bend, where erosion is concentrated |
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Term
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Definition
| where sediment is deposited on the inner edge of the bend, a region of shallow flow and low shear stress |
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Term
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Definition
| where a meander loop has become too long, a flood occurs, and the river finds the shortcut and cuts off one of the loops. this abandoned loop becomes an oxbow lake and slowly fills with sediment over time |
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Term
| what happens when flow spills out onto a floodplain and what is an overbank deposit? |
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Definition
the sediment concentration in a river channel decreases the higher the flow, and the grain size decreases as well. it is this finer grained sediment that is carried out of the channel and onto the flood plain.
overbank deposits (sediment deposited by a river outside the channel) are always finer grained than the sediment deposited in the channel
deposits closest to the channel tend to be coarser than the sediment deposited further out on the floodplain
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Term
| what is the natural levee |
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Definition
| a ridge of sandy material often found along channels |
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Term
| why do farmers like to plant in floodplains? |
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Definition
| flat land with available water and perfect texture for agriculture (fine deposits that wash up during flooding) |
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