Fluvial Processes and Erosion

Fluvial Processes

• Water flows from higher to lower elevations.

### Rainsplash Erosion

• Rain drops displace and scatter soil downslope.

Sheet Erosion

• Runoff channels erode surface soils and sediments.
• Occurs when precipitation exceeds infiltration rate.

### Vegetation and Erosion

• Vegetation intercepts and slows rain, reducing erosion.
• Roots bind soil, increasing stability.

River System

• Trunk: The main part of a river system (e.g., Mississippi River).
• Tributary: Smaller streams that feed into the trunk.
• Drainage Basin/Watershed: The entire network of trunk and tributaries, encompassing the area where water flows into a specific river system.

Denudation

• The overall lowering of landscape elevation due to weathering and erosion.

### River Discharge (Streamflow)

• The volume of water passing a given point in a river per unit of time.

### Erosion by Rivers

• Hydraulic Action: The force of water dislodging and cracking rock material from the valley floor and walls.
• Abrasion: Mechanical erosion caused by rocks and sediment carried by the river scraping against the valley floor and walls.
• Attrition: Rocks and sediments collide and break down into smaller pieces.
• Corrosion/Dissolution: Rocks and minerals are dissolved by water (solution).

River Sediment Load

• Consists of dissolved load (not depicted in the notes), suspended load, and bed load.

### River Sediment Transportation

• Dissolved Load: Material dissolved in the water.
• Suspended Load: Fine particles carried within the water column.
• Bed Load: Larger particles that roll, bounce, or slide along the river bed.

### River Sediment Characteristics

• Transport Capacity: The maximum amount of sediment a stream can carry at a given discharge.
• Competence: The largest particle size a stream can set in motion.

### Sediment Yield

• The mass of sediment leaving a stream basin per year.

River Sediment Characteristics: Mississippi River

• High transport capacity.
• Medium competence.

Stream Power

• A stream's ability to do work, such as moving sediments.
• Increases with discharge and slope.

Base Level

• The lowest elevation to which a river can erode.
• Ultimate Base Level: Sea level.
• Local Base Level: Elevation of nearby lakes, trunks, etc.

Erosion by Rivers: Incision

• Downward erosion of stream beds.

Deposition by Rivers: Aggradation

• Sediment accumulation that raises the level of a river valley's bed.

Delta

• A fan-shaped deposit of sediment formed when a stream reaches a coast or lake, slows down, and deposits its sediment.

Alluvial Fan

• A fan-shaped deposit of sediment formed when stream power reduces after leaving a confined valley.
• Often associated with seasonal streams.

### Factors Influencing Stream Erosion

• Climate Change: Changes in precipitation and temperature affect streamflow, vegetation, and overall erosion rates.
• Lithology: Different rock types have varying resistances to weathering and erosion, leading to different slopes and erosion rates.
• Geologic Structure: Folds, faults, and rock layers control landscape features and impact stream erosion, creating features such as hogbacks, cuestas, ridges, valleys, domes, and plateaus.

### Drainage Density

• Total length of stream channels in a given area of a drainage basin.
• Higher drainage density indicates a higher erosion rate.

Drainage Patterns

• Radial: Streams radiating outward from a central high point (mountain peak, volcano peak).
• Annular: Streams circling a high point, separated by ridges.
• Trellis: Streams following parallel layers of sloped/folded sedimentary rocks and resistant ridges.
• Rectangular: Streams with right angles, often associated with faults.
• Dendritic: Streams resembling a tree's branching structure, typically found on gently sloping, uniform rock bodies, the most common pattern.

Superimposed Stream

• A stream maintaining its course regardless of underlying geologic structure.
• Forms on horizontal surface beds overlaying folded/faulted rock.
• Indicates that the structural change predates the stream.

Antecedent Stream

• A stream that predates the ridge it erodes, formed as the ridge is lifted by tectonic activity.
• Indicates that the stream predates the structural change.

Stream Piracy

• The capture of a segment of one stream by another, often due to erosional processes.

Flood

• Bankfull: Stream fills its largest channel size, frequent, less damage.
• Overbank: Stream overflows its channel, infrequent, more damage.

Recurrence Interval

• The average time between floods of a given magnitude in a given place.

Landscape Evolution Theories

• William Davis (1850-1934): Uplift occurs followed by erosion and downward slope movement.
• Cycle of Erosion: A series of stages in landscape development:
  • Young: Deep channels and large plateaus.
  • Mature: More extensive channels, steep slopes.
  • Old: Relatively flat plain (peneplain).
• Walther Penck (1888-1923): Uplift and weathering occur simultaneously, slopes weather backward rather than downward.
• Slope Decline (Davis) vs. Slope Retreat (Penck): Two different theories about how slopes evolve.

Factors that Influence Stream Erosion

• Climate Change: Impacts precipitation and temperature, affecting streamflow, vegetation, and erosion rates.
• Lithology: Different rock types have varying resistances to weathering and erosion, leading to different slopes and erosion rates.
• Geologic Structure: Controls landscape features and impacts stream erosion, creating features like hogbacks, cuestas, ridges, valleys, domes, and plateaus.

Explore the intricate relationships between water flow and erosion with this quiz on fluvial processes. Understand key concepts like rainsplash erosion, sheet erosion, and the importance of vegetation in stabilizing soil. Test your knowledge about river systems and their components.