Stream Ecology: River Structure and Hydrology

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Stream Ecology River Structure and Hydrology

• Unit 1 Module 4, Lectures 1

2
Objectives

• Students will able to
• describe how evaporation and precipitation
  influence river formation.
• diagram the distribution of water on Earth.
• define and provide examples of a watershed.
• diagram stream networks and drainages.
• explain how a meandering stream can form an oxbow
  lake.
• predict riffle and pool formation in a stream
  segment.

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Module 4 introduces students to

• Lecture1
• The Importance of Rivers
• The Hydrologic Cycle
• Watersheds as a concept
• Geomorphology
• watersheds and drainage networks
• channel morphology
• habitat scales

• Lecture 2
• Hydrology
• flow and discharge
• storm and annual hydrographs
• flood probability
• sediment transport and deposition

4
Importance of rivers

• Rivers
• Provide water and nutrients for agriculture
• Provide habitat to diverse flora and fauna
• Provide routes for commerce
• Provide recreation
• Provide electricity

5
Natural watercourses

• Existence depends on
• Availability of surface water
• A channel in the ground
• An inclined surface

6
Lotic systems

• Four dimensions
• Longitudinal
• Lateral
• Vertical
• Time

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Variation in time and space

• The shape, size and content of a river are
  constantly changing, forming a close and mutual
  interdependence between the river and the land it
  traverses.

www.aquatic.uoguelph.ca/rivers/chintro.htm
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Effect of climate

• Rivers are very dependent on climate and their
  characteristics are closely related to the
  precipitation and evaporation regimes in their
  drainage areas.
• Three types
• Perennial or permanent rivers
• Periodic rivers
• Episodic rivers

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The hydrologic cycle
10
Distribution of water on earth
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What is a watershed?
12
What is a watershed?
13
Spatial scale Stream segments
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Stream networks or drainages
15
Stream order

• A method of classifying or ordering the hierarchy
  of natural channels.
• Strahler (1957) is the most widely used system.
• Stream order correlates well with drainage area,
  but is also regionally controlled by topography
  geology.

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Spatial scale Segment system
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Stream corridor and channel morphology
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Cross section of a channel
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Floodplain
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Meandering rivers
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Sinuosity Gradient and substrate

• Small meanders
• high gradient
• coarse substrates

• Big meanders
• low gradient
• fine substrates

22
Braided channel

• Braided Pattern high slope high stream power
  coarse bed materials

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An oxbow lake
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Spatial scale Reach system
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Riffles, pools, and cascades

• Riffles and pools alternate in somewhat
  predictable patterns

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Pool - riffle sequence

• Riffle to riffle 5 - 7 channel widths