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Channel Networks

Stream Power. Critical Power is that rate of useful energy necessary to transport the existing [sediment] loadIf more Kinetic Energy, erosion (degradation) will resultIf there is too much sediment for the available energy, deposition (aggradation) will result. Skip 233 right to 237 left, resume

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Channel Networks

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    1. Channel Networks

    2. Stream Power Critical Power is that rate of useful energy necessary to transport the existing [sediment] load If more Kinetic Energy, erosion (degradation) will result If there is too much sediment for the available energy, deposition (aggradation) will result

    3. Driving and Resisting Forces Driving forces: gravity propelling water downslope Resisting forces: friction within the fluid (water), and friction between water and the channel boundary

    4. Conservation of Mass (Continuity) The Role of Cross Section Area Mass is neither created nor destroyed Inputs = outputs Inputs and outputs for fluid flow are discharge Vel (V) x Area(A) = const. All this means is that discharge is constant, flow rate remains the same from 1 xs to the next. Unless you are in a losing/gaining reach, where inputs do not equal outputs. Water is incompressible, so the same amt of water must go through a smaller space as a bigger one. (Continuity applies to all fluid flows, even air. Continuity is not true in aerodynamics, where air flow becomes compressible when approaching Mach 1)All this means is that discharge is constant, flow rate remains the same from 1 xs to the next. Unless you are in a losing/gaining reach, where inputs do not equal outputs. Water is incompressible, so the same amt of water must go through a smaller space as a bigger one. (Continuity applies to all fluid flows, even air. Continuity is not true in aerodynamics, where air flow becomes compressible when approaching Mach 1)

    5. Gilbert’s Fluvial Process Joined John Wesley Powell survey in Utah, 1874 First suggested the concept of “graded streams” A stream’s form is defined by its ability to transport load, and that a “graded” stream condition will exist when the stream can just carry the load supplied to it “The transportation of debris by running water”, USGS Prof. Paper 86, Karl Gilbert, 1914

    7. Sediment Sources, Storage, and Yields Most sediment from creep, soil erosion, mass wasting River incision of bed-rock important after dramatic increase in elevation above sea-level Most streams transport limited: supply exceeds removal ability. = "Alluvial Streams" Most streams store sediment, only about 5 to 7 % of sediment input removed by main trunk.

    8. 6_5

    9. Active and Relict Alluvium

    10. Floodplain Morphology

    11. Fluvial Deposits

    12. Loop Cutoff and Oxbow Formation

    16. Depositional and Erosional Terraces

    17. Deltas Occur where stream hits slow water Competence nearly zero, suspended load is dropped Deposits build out into lake or sheltered sea, extending the length of the river Consists of three types of beds Topset beds - horizontal, surface delta Foreset beds - delta slope Bottomset beds – horizontal, bottom sea

    22. Colluvial Fans

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