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Driving Force for the Hydrological Cycle in Streams | GEOL 104, Study notes of Geology

Bowling Green State University (BGSU)Geology

Material Type: Notes; Class: Earth Environments; Subject: Geology; University: Bowling Green State University; Term: Spring 2004;

Typology: Study notes

Pre 2010

Uploaded on 08/18/2009

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koofers-user-qhs 🇺🇸

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Geol 104: Streams
1
Streams
• Why study streams?
Running water is the most important
geologic agent in erosion, transportation
and deposition of sediments.
Water
– The unique physical and chemical properties of
water make it the single most important
chemical compound in defining our existence
on this planet.
– These properties include:
• Water exists in all three states (vapor, liquid and
solid) at Earth’s surface.
• Water is a polar molecule that makes it a nearly
universal solvent.
• Unlike most compounds, water expands its volume
upon freezing.
Hydrologic Cycle
• Represents the circulation of water in its
three physical states (vapor, liquid and
solid) through the Earth’s atmosphere,
hydrosphere and lithosphere.
• See figure 10.1
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Streams

  • Why study streams?

Running water is the most important geologic agent in erosion, transportation and deposition of sediments.

Water

  • The unique physical and chemical properties of water make it the single most important chemical compound in defining our existence on this planet.
  • These properties include:
    • Water exists in all three states (vapor, liquid and solid) at Earth’s surface.
    • Water is a polar molecule that makes it a nearly universal solvent.
    • Unlike most compounds, water expands its volume upon freezing.

Hydrologic Cycle

  • Represents the circulation of water in its three physical states (vapor, liquid and solid) through the Earth’s atmosphere, hydrosphere and lithosphere.
  • See figure 10.

Driving Force for Hydrologic Cycle

  • The hydrologic cycle is driven by radiant energy from the Sun and Earth’s gravity.
  • Radiant energy of the sun is converted into stored energy of water vapor through evaporation.
  • Stored energy of water vapor is converted to kinetic energy through condensation and precipitation.

Distribution of Water

  • Distribution of water in the hydrosphere: ~97% Oceans ~2% Glaciers ~0.6% Groundwater ~0.02% Streams and lakes

Terminology of Streams

  • Stream - body of surface water flowing in a confined channel (independent of size).
  • Stream channel - long narrow depression eroded by the stream into rock and sediment.
  • Stream banks are the sides of the channel.
  • Stream bed is the bottom of the channel.

Drainage

  • Drainage basin - total area drained by a stream and its tributaries
  • Drainage Pattern - can reveal information about underlying rock type and/or structure.
  • See fig. 10.

Common Drainage Patterns

  • Dendritic
    • Tree branches-like drainage pattern.
    • Common in uniformly eroded regions.
  • Rectangular
    • Tributaries have frequent right angle bends.
    • Common in regularly fractured rocks.
  • Trellis
    • Tributaries perpendicular to parallel main streams.
    • Common in folded strata of variable resistance.
  • Radial
    • Streams diverge outward like spokes of a wheel.
    • Common around composite volcanoes and domes.
  • See fig 10.

Stream Erosion, Transport and

Deposition

  • Kinetic energy of water flowing downslope performs work in the form of eroding regolith and transporting sediments.
  • Governed by stream velocity and particle size. - Velocity - the rate at which water flows.
  • See fig. 10.

Stream Velocity

  • Three factors control stream velocity:
    • Stream gradient
      • Steepness of the stream (vertical drop over a horizontal distance).
    • Discharge
      • Volume of water flowing past given point in unit time. Discharge = velocity x cross-sectional area of stream
    • Shape and roughness of channel
      • Friction between flowing water and stream channel slows velocity.

Velocity in a Stream Channel

  • In straight sections
    • Velocity is greatest near middle of channel (least friction with channel).
  • In curved sections
    • Velocity is greatest on outside of curves.
      • Cutbank -steep slope caused by erosion along outer bank of curve due to greater stream velocity.
      • Point bar - series of arcuate ridges of sand or gravel deposited on inside of curves due to lower velocity.
  • See fig. 10.

Stream Erosion Mechanisms

  • Hydraulic action
    • Ability of flowing water to lift and move rock and sediment.
  • Solution
    • Chemical dissolution minerals/rocks.
  • Abrasion
    • Wearing away of channel and grinding of sediments by friction and impact of load.

Depositional Features

  • Three types of stream deposits:
  • Channel deposits
    • Form in stream channel itself.
  • Flood plain deposits
    • Accumulation of sediments on a flood plain adjacent to the stream channel.
  • Alluvial fans and delta
    • Form where stream’s gradient rapidly decreases like when it empties into a lake or flat plain.

Channel Deposits

  • Bar - elongated bar of sediments, generally a transient feature.
  • Point bar - deposit on inside of curve in stream.
  • Mid-channel bar - sand/gravel deposit in middle of stream channel. - Braided stream - flow along many shallow, interconnected channels instead of single central channel. Form when sediment supply is greater than stream can carry (fig. 10.18).

Meandering Streams

  • Meanders - pronounced sinuous curves in stream channel (fig. 10.22). - Form by erosion on outside and deposition on inside of stream curves.
  • Oxbow lakes - form when stream meanders become cutoff during flooding (fig. 10.24).

Flood Plain Deposits

  • Flood plain - broad strip of land built up by sedimentation on either side of a stream channel.
  • Natural levees - low ridges of flood- deposited sediment that form on either side of stream channel
  • See fig. 10.

Alluvial fan and Delta Deposits

  • Delta - triangular-shaped pile of sediment that forms where stream enters a calm body of water (lake, ocean; fig. 10.30). - Distributaries - form when stream feeding a delta or fan splits into many channels.
  • Alluvial fan - triangular-shaped pile of sediments that forms where a stream enters a flat plain or valley floor (fig. 10.32).

Stream Valley Development

  • Downcutting
    • Downward erosion of stream bed.
  • Base level
    • Deepest level to which a stream can erode its bed.
    • Ultimate base level for most streams is sea level.
    • Temporary or local base levels occur where streams empty into lakes or particularly resistant rock layers.
    • See fig. 10.