GEY 101 - Introductory Geology: Exploring Planet Earth
Running Water - Chapter 10

The Hydrologic Cycle -- You should know that the amount of water on the earth is relatively constant, and therefore water is recycled from the oceans to the atmosphere, to streams and back. This is called the Hydrologic Cycle. 1) Water evaporates from rivers, lakes and oceans, and is transpired by plants. 2) It forms clouds and falls as rain and snow (precipitation). Some precipitation falls in the ocean. Some falls on the land. 3) Part of the water that falls on the land evaporates, back into the atmosphere. Part seeps into the soil and travels through rock aquifers as groundwater (infiltration); some of which soaks into plants and then is released into the atmosphere called transpiration. Part runs over the earth's surface as runoff in streams and rivers.

Runoff -- when it rains, water fills the pores in soil. The rate at which rain can fall and still soak into a soil is the infiltration capacity. Originally the water flows as thin sheets (sheet flow), but then it begins to cut gullies and flows as channelized flow.

The flow in channels can be characterized as laminar or turbulent flow. Almost all streams have turbulent flow.

Streams include all different sizes, Rivers, creeks, gullies, rills, brooks and others.

  1. stream - channelized flow of water
  2. energy
    1. gradient = vertical/horizontal (fig. 10.5)
    2. channel shape (fig. 10.5)
    3. channel roughness
    4. vegetation

Gradient -- is the slope of a stream.

Velocity -- the rate at which the water moves.

Discharge -- is the amount of water flowing down a stream and is expressed in gallons per minute or cubic meters per second.

discharge(m3/s) = channel width (m) x channel depth (m) x velocity(m/s)

Longitudinal Profile

Base level -- figure 10.8 Graded streams -- Streams sill erode until they reach the maximum amount of material they can transport. This creates a balance or equilibrium between stream gradient and erosion. That is called a stream's grade. Changing any factor related to the stream can cause deposition or erosion.

For example, if the stream begins to flow faster, it cuts a deeper channel and erodes more sediment, thus flattening its slope until erosion and deposition are in balance.

Stream Erosion - streams erode rocks by abrasion and by hydraulic action -- high energy

  1. hydraulic action
  2. abrasion -- e.g. pothole -- rounded depressions (fig 10.11)
  3. solution

Transport -- Streams carry both water and sediment to the oceans -- variable energy
Settling Velocity -- speed where a particle falls thru a still fluid

  1. mechanisms
    1. bed load - rolling or saltation
    2. suspended load
    3. dissolved load
Ions are carried as dissolved load. Clay particles float in the water as suspended load. The clay settles out when the river reaches a swamp or lake and stops flowing. Sand and gravel bounce and roll across the bottom or bed of the stream as bed load (Saltation).
  1. measurement
    1. Competence -- measures the largest clast a stream can carry
    2. Capacity -- measures the total amount of sediment a stream can carry

Deposition - low energy

Sorting -- mechanism by which solid particles of various sizes are separated

Alluvium -- well sorted material deposited by a stream

Channel deposits Streams consist of channels, levees and floodplains. The channels have beds and banks. Braided Streams -- When rivers carry lots of sand and gravel, their banks are easily eroded and rivers are wide and flat (braided stream). Channels are separated by bars Floodplain -- Part of the valley that covered during a flood.
Erosional
Depositional
 Created in the process are:

Delta - stream meet calm water (usually ocean)

Evolution of the Mississippi delta can be found on p. 282-283

Alluvial fan - abrupt change in gradient (usually on land)

Stream Valleys -- Streams flow through valleys that they have carved (Playfair's Law).

Narrow Valleys are associated with:

Wide valleys are associated with: Valleys have valley walls, and valley floors Stream Terraces may line valley walls Incised Meanders -- mark where meandering streams have cut new canyons when the land around them was uplifted.

Drainage Basins the region that contributes water to a stream.

Divide -- Imaginary line where the drainage basin of one stream is separated from another (fig 10.30 and 10.31).

Drainage Patterns -- the pattern of tributary streams in a drainage basin.

Headward Erosion -- lengthening a stream by extending the head of its valley upslope (fig 10.33).

Stream Piracy -- the diversion of the drainage of one stream because of the headward erosion of another stream.

Wind Gaps -- abandoned water gaps form when the stream that cut the notch has its course changed by piracy ( fig 10.34).

Water Gaps -- steep-walled notch followed by the river through the structure (fig 10.35).

Types of Flooding

Flood Control

Questions

  1. What is the Hydrologic Cycle?
  2. What are the processes where water is moved through the cycle?
  3. How is running water important?
  4. What is sheet flow?
  5. What does Infiltration Capacity depend on?
  6. What are the two types of flow (compare and contrast)?
  7. How is stream velocity determined?
  8. What determines the amount of erosion and/or transportation of sediments?
  9. What are the parts of a stream?
  10. What is base level and how is it accomplished?
  11. What is a graded stream?
  12. Potholes represent what is the evolution of a stream?
  13. How are sediments transported?
  14. What determines the amount and size a stream can hold?
  15. What are the parts of channel deposits?
  16. What are the characteristics of floodplain deposits?
  17. What are the differences between an alluvial fan and a delta?
  18. What are the characteristics of deltas?
  19. How are narrow and wide valleys defined in terms of running water?
  20. Describe the characteristics of a wide valley?
  21. How are incised meanders and terraces formed?
  22. What is a divide?
  23. What types of drainage patterns are there?
  24. How do headward erosion, stream piracy, and water gaps work?
  25. What are the different types of floods?
  26. What are the ways to mitigate flooding?

Vocabulary

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