Fluvial Processes Part I

Many a calm river begins as a turbulent waterfall, yet none hurtles and foams all the way to the sea. —Mikhail Lermontov

1 The Fluvial Processes  The Impact of Fluvial Processes on the Landscape  Streams and Stream Systems  Stream Channels  Structural Relationships  The Shaping and Reshaping of Valleys  Floodplains  Stream Rejuvenation  Theories of Landform Development

2  The Impact of Fluvial Processes on the Landscape • Fluvial processes involve running water. • Running water is Earth’s most important external agent. • Ubiquitous (everywhere except in Antarctica)

Gorge carved by the Green River, northeastern Utah.

3  Streams and Stream Systems • Stream Flow and Overland Flow – Stream flow – channeled movement of water along a valley bottom – Overland flow – unchanneled down slope movement of surface water • Valleys and Interfluves – Valley – drainage system of channeled (stream) flow • Valley bottom and valley walls – Interfluve – No clearly established channeled flow • High area between valleys • Overland flow

4 Valleys and interfluves. Valleys normally have clear-cut drainage systems; interfluves do not. 5 • Drainage Basins Divides of sub-basins – Valley bottom – Valley sides – Interfluves that drain toward the valley – Drainage divides • Main stream basin • Tributary sub-basins

Divide of main drainage basin

6 – Hierarchy of Drainage Basins • Larger basins include a hierarchy of smaller tributary basins.

Mississippi

Missouri

N. Platte

Platte

Laramie

7 – Stream Orders • First-order stream – Smallest stream, has no tributaries • Second-order – Begins at confluence of 1st order streams • Third-order – Begins at confluence of 2nd order streams • Etc.

8 • Fluvial Erosion and Deposition Animation (Stream Sediment Movement) – Erosion by Overland Flow • Splash erosion and sheet wash • Rill and gully erosion

Top of slope Splash erosion and sheet wash

Rills

Gully

Bottom of slope 9 – Erosion by Stream Flow • Volume of flow • Abrasion of streambed • Chemical weathering of channel • Turbulence of flow • Flow speed

10 – Transportation • Load • Types of load • Competence and capacity

Three types of stream load

11 – Deposition • Alluvium – Sorted/stratified deposits – Smooth, rounded particles • Cause: Decrease in flow speed • Stream Flow Variability – Floods – periods of peak stream flow • Erode upper portions of valleys. • Form vast floodplains in lower parts of valleys. – Perennial stream – Ephemeral or Intermittent stream

12  Stream Channels • Channel Flow – Friction – Turbulence

13 • Stream Channel Patterns (4 types) – Straight channels (uncommon) • Short sections of a channel • Eventually take on sinuous characteristics due to scouring and filling.

14 – Sinuous Channels • Common • Steep gradients • Gentle gradients

15 – Meandering Channels • Tightly curved loops • Abandoned channels • Where land is flat, such as large floodplains

16 – Braided Channels • Heavily loaded stream • Gentle gradient slows flow speed. • Slow moving stream chokes channel with alluvium. • Sand and gravel bar deposits divide (braid) the stream.

17  Structural Relationships • Consequent Streams – Stream flow and channel development is in response to the initial slope of the land. • Subsequent Streams – Streams that develop along zones of structural weakness in bedrock. – Often trend at right angles to other channels.

18 • Antecedent Streams – Slow uplift interrupts drainage pattern. – Stream erodes downward and maintains its course. – A deep gorge forms.

19 • Superimposed Streams – Originally streams flow on a high sequence of land. – The original stream’s pattern erodes down into the underlying sequence of rocks of a different structure. – The pattern is unaffected by the structure; that is, streams maintain their pattern in the new sequence of rocks.

20 • Stream Drainage Patterns (Reflect underlying geologic structure or topography.) – Dendritic Drainage Pattern • Most common drainage pattern • Tree-like • Underlying structure does not control the pattern. – Nearly horizontal strata

21 – Trellis Drainage Pattern • Alternating bands of tilted hard and soft rocks • Long parallel streams cut into soft rocks. • Parallel streams are jointed by short, right-angled segments.

22 West Virginia has both trellis and dendritic patterns. Trellis Dendritic

23 – Radial Drainage Pattern • Streams drain from a mountain peak or volcano.

24 – Centripetal Drainage Pattern • Streams converge into a basin.

25 – Annular Drainage Pattern • Streams converge into a basin.

26 Maverick Spring Dome WY