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 .