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Geog 111 Lecture Outline: Fluvial Processes
Update: 10/8/05

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The Process of Studying Landforms

Internal Processes: building up landforms

  1. Crustal Rearrangement: Earth's dynamic crust and the consequences
  2. Vulcanism: origin and movement of molten rock
  3. Diastrophism: deformation of solid rock in the Earth's crust due to pressure from below

External Processes: breaking down landforms: forces in atmosphere + hydrosphere

Denudation: disintegration, wearing away, and removal of rock material; implies a lowering of earth's surface (via wearing away, not internal processes)

  1. Weathering: processes that break up rock at the earth's surface
    • cracks and crevices in rocks: microscopic, faults, joints
    • weathering agents: mechanical, chemical, biological

  2. Mass Wasting: processes that move fragmented rock relatively short distances down slope: falls, slides, slumps, flows, and creep

  3. Erosion: processes that move fragmented rock relatively long distances

McKnight 9.5: The Hydro Cycle

Weathering and mass wasting enhanced by presence of water: hydro cycle

But erosion is fundamentally the result of the presence of water

Fluvial Processes: any environmental processes involving the flow of water

1. Impact of Fluvial Processes on the Landscape

McKnight 16.1: Fluvial Process Photo

1a. Traditional Theory of Landform Development: The Geomorphic Cycle

McKnight 16.35a, b, c, d: Davisian Geomorphic Cycle

1b. Critique of Davisian Cycle Theory: Crustal Change and Slope Development

1c. Equilibrium Theory

Much variation in bedrock, regolith, soil around the earth: some soft, some hard

Crustal movement (vertical, horizontal) also varies: excessive uplift, minimal uplift

McKnight 16.37: Dynamic Equilibrium

Simultaneous uplift (internal forces) and denudation (external forces, primarily water)

Dynamic equilibrium rather than evolution

Both Davisian evolution and Dynamic Equilibrium theories explain some landforms

Key: geographic variations (where) in bedrock and tectonic activity vital to understand

2. Fundamental Definitions and Concepts of Fluvial Processes

McKnight 16.2: Valleys and Interfluves

2a. Valleys and Interfluves

2b. Drainage Basins - Watersheds

2c. Erosion

Weathering >> Mass wasting >>

Two basic types of erosion: by overland flow and steam flow

Erosion by Overland Flow

Beginnings of erosion: on interfluves

McKnight 16.5: Splash erosion

Erosion by Streamflow

Channeled flowing water has more ability to erode material

Erosive effectiveness

2d. Transportation: of rock particles via overland or streamflow

McKnight 16.7: Transport of particles

stream load: material carried by stream flow: three components

  1. dissolved load:

  2. suspended load:

  3. bedload:

Any stream varies in the amount of material it can transport:

Competence: measure of the particle size a stream can transport, expressed by the diameter of the largest particle that can be moved; varies with flow speed and amount

Capacity: measure of the amount of solid material a stream has the potential to transport, expressed as the volume of material passing a given point in the stream channel during a given time interval

2e. Deposition


Changes in gradient, channel widening, or change in direction

Most material deposited in sitting bodies of water: lakes, oceans

3. Stream Channels

Reiterate: fluvial processes: those that involve running water

Overland flow relatively simple

Streamflow more complicated: four characteristics of individual streams and rivers

3a. Structural Relationships

The course of a stream channel is guided and shaped by the nature and arrangement of the underlying bedrock

McKnight 16.15: Dendritic Drainage Pattern

McKnight 16.16: Trellis Drainage Pattern

McKnight 16.17: Trellis and Dendritic Drainage Patterns

McKnight 16.18: Radial Drainage Pattern

McKnight 16.19: Centripetal Drainage Pattern

3b. Channel Flow

McKnight 16.9: Friction and Streamflow

3c. Turbulence

3d. Channel Changes

McKnight 16.11: Straight and Meandering channels

Straight: uncommon and usually caused by underlying geologic structure

McKnight 16.12: Meandering Stream

Meandering: serpentine pattern

McKnight 16.13: Braided channel

4. Stream Systems

4a. Drainage Basins

McKnight 16.3: Drainage Basins

4b. Stream Orders

McKnight 16.4: Stream Order

4c. Permanence of Flow

Perennial streams: permanent, year round flow

Intermittent (ephemeral) stream: flow only part of the year

5. Shaping and Reshaping of Valleys by Fluvial Processes

Horizontal and vertical reshaping of valleys

5a. Valley Deepening

McKnight 16.21: Base Level

Limits to deepening (vertical erosion): base level

Deepening caused by hydraulic power of flowing water, prying and lifting by moving water, abrasion

Deepening most effective in upper reaches of streams: steepest slopes

McKnight 16.22: Knickpoints

McKnight 16.B: Niagara Falls

5b. Valley Widening

McKnight 16.23: Meanders and Lateral Erosion

McKnight 16.24: Valley Widening

5c. Valley Lengthening

McKnight 16.25: Headward Erosion

Headward Erosion: key location

Delta Formation: also lengthens valleys

5d. Deposition in Valleys

While valleys are deepened, widened, and lengthened over time deposition of sediments does occur

McKnight 16.29: Flood plain

McKnight 16.31: Natural Levees

Floodplain slightly higher along edges of stream channel

5e. Steam Rejuvenation

McKnight 16.33

McKnight 16.34: Entrenched Meanders

Sum: Fluvial Processes: any environmental processes involving the flow of water

1. Impact of Fluvial Processes on the Landscape

2. Fundamental Definitions and Concepts of Fluvial Processes

3. Stream Channels: Key Characteristics of individual streams and rivers

4. Stream Systems: how streams and rivers relate to each other

5. Shaping and Reshaping of Valleys by Fluvial Processes

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