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River Systems - Runoff. Running Water. Integral part of sculpting the Earth’s surface MOST IMPORTANT AGENT OF EROSION Indirectly results in the formation of sedimentary rocks. Stream Formation. Sheetflow or Sheetwash – overland flow of water

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Running Water

  • Integral part of sculpting the Earth’s surface

  • MOST IMPORTANT AGENT OF EROSION

  • Indirectly results in the formation of sedimentary rocks


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Stream Formation

  • Sheetflow or Sheetwash – overland flow of water

  • Repeated precipitation events cause a preferential channel to form – downcutting

  • Tributaries form & the main channel continues to grow up slope – headward erosion


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Stream Morphology

  • Streams increase in length by headward erosion – erosion occurring at the beginning of the stream

  • Streams become wider through lateral erosion – mass wasting of the stream banks

  • Streams become deeper through downward erosion of the channel by abrasion of the sand and gravel



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Stream Terminology

  • Stream System – main stream plus tributaries

  • Drainage Basin – area drained by main stream and tributaries

  • Drainage Divide – area of higher elevation that divides drainage basins

  • Function of size/scale

For Example:

Kickapoo Creek

Sangamon River

Illinois River

 Mississippi River


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Stream Terminology

  • Stream System

  • Drainage Basin

  • Drainage Divide

  • Function of size/scale

Fig. 11.7



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Stream Subsystems

  • Collecting System

    • Tributaries is head water region

    • Funnel water and sediment to main channel

    • Primarily erosion and transport

  • Transporting System

    • Main tributary

    • Main process is the movement of the sediment and water

    • Erosion, transport, and deposition all occur

  • Dispersing System

    • Distributaries at mouth region

    • Primarily deposition of the sediment

    • Coarse sediment along the confluence

    • Fine particles carried further in to body of water



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Streamflow Dynamics

  • Examine the physical and hydraulic properties of the stream

  • Discharge

  • Velocity

    • Gradient

    • Channel Properties

      • Wetted Perimeter

      • Shape

      • Size

      • Roughness

  • Sediment Load


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DailyQuestion

Duplicate the chart to the right.

On the chart add lines that represent how the following properties change:

Discharge

Velocity

Cross-Section Area

Gradient

Channel Roughness

Base level

The property “drainage basin area” is provided as an example


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Discharge (Q)

  • Volume of water passing a given point over a specified length of time (length3/time), generally given in ft3/s or m3/s

  • Calculated by:

  • Where A is the cross-sectional area (length2) & v is the velocity of the water (length/time)


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Velocity

  • The speed of the water at a given point along a stream

  • Directly related to a stream’s ability to erode and transport material

  • High velocity water can carry heavier sediment

  • Is a function of

    • Gradient

    • Channel Properties

      • Wetted Perimeter

        • Shape

        • Size

        • Roughness


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Stream Gradient

  • Slope or steepness of the stream channel

  • Vertical drop (relief) of a stream over a fixed distance

  • Controls the potential energy of the water

  • Steeper the gradient – the higher the velocity, the lower the gradient – the lower the velocity

  • Meanders decrease the gradient by increasing the horizontal distance of the stream


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Wetted Perimeter

  • The area in which water touches the channel walls

  • Channel shape and size controls the wetted perimeter

  • Most efficient streams have small wetted perimeters

  • Roughness of the channel controls the frictional resistance to water movement

    • A smooth channel decreases frictional force

    • A rough channel increases frictional force


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