GEOG 205 second half

What is the significance of sediment in the “source to sink” context?

Sediment transport from erosion sources to deposition sinks shapes the Earth by wind, water, and ice.

Why might we organize the landscape by watershed?

Because water is the largest component of denudation on Earth today.

What insights into geomorphology do watershed properties give?

They help infer dominant processes, parent material, and resistance of the landscape.

Define “source” in geomorphology.

A location where sediment begins moving due to erosion.

Define “sink” in geomorphology.

A location where sediment stops moving and is deposited.

What is the ultimate source of sediment on Earth?

Mountains and high elevations.

What is the ultimate sink on Earth?

The ocean.

What would be an ultimate source on a planet with uniform elevation and only wind?

Areas where wind speed or surface roughness varies enough to initiate sediment movement.

What is an intermediate source?

A location where previously deposited sediment becomes mobilized again.

What is an intermediate sink?

A place where sediment temporarily deposits before being re-eroded.

What is a watershed?

A drainage basin containing all land that drains to a specific stream.

What question helps define a watershed?

If you follow a raindrop or sediment grain, where will it end up?

Why are watersheds important for sediment movement?

They collect, transport, and disperse sediment.

What contributes to watershed storage?

Snow, glaciers, wetlands, lakes, rivers, ponds, groundwater, soil moisture, and plants.

What is the watershed hierarchy?

A nested system where small watersheds combine into larger regional and continental-scale watersheds.

Define stream order.

Classification of streams based on size and position, increasing when streams of the same order join.

What order are the smallest streams?

First order.

What happens when a first-order stream joins another first-order stream?

It becomes a second-order stream.

Which streams are most common—high or low order?

Low-order streams.

What can sediment size at a river mouth indicate?

Soil development, bedrock resistance, and slope steepness in the watershed.

Fine, organic-rich sediment suggests what watershed characteristics?

More developed soils, gentler slopes, weaker parent material.

Coarse, gravel-rich sediment suggests what watershed characteristics?

Less developed soils, stronger bedrock, steeper slopes.

Define drainage density.

Total stream channel length per unit area.

What does high drainage density imply?

Weak substrate, high runoff, steep slopes.

What does low drainage density imply?

Resistant substrate, gentle slopes, high infiltration.

What influences drainage patterns?

Climate, terrain, and underlying rock structure.

Define dendritic drainage pattern.

Tree-like branching in homogeneous material with acute tributary angles.

Where does parallel drainage form?

In areas with steep slopes or elongate landforms.

Define trellis drainage.

Pattern in folded topography where short tributaries join at near 90-degree angles.

Where does radial drainage form?

Around a central elevated point like a volcano.

Define centripetal drainage.

Streams flow inward toward a central basin or depression.

Define rectangular drainage.

Streams follow jointed or faulted bedrock and make sharp bends.

Define deranged drainage.

A disrupted pattern typically caused by glaciation and low-relief landscapes.

What is fluvial geomorphology?

The study of landforms and processes created by flowing water and sediment transport.

What are fluvial forms?

Structural landform patterns ranging from watersheds to channel bedforms.

What are fluvial processes?

Erosion, transport, and deposition of sediment by flowing water.

What is hydraulic action?

Erosion caused solely by the force of flowing water.

What is abrasion in rivers?

Grinding of the stream bed by transported sediment.

When do channels form?

When water has enough erosive force to transport sediment.

What forces influence channel formation?

Gravity, planes of weakness, friction, bedforms, channel shape, and vegetation.

What is discharge (Q)?

Q = width × depth × velocity (W × D × U).

What is stream power (Ω)?

The energy available to transport sediment, calculated as ρgQS.

What controls stream power?

Fluid density, gravity, discharge, and slope.

What is steady flow?

Flow with constant velocity and depth over time.

What is unsteady flow?

Flow with velocity and depth that change over time.

What is uniform flow?

Flow with constant velocity and depth over a channel segment.

What is varied flow?

Flow where velocity and depth change along a channel.

What controls sediment transport?

Grain size and turbulence.

What is dissolved load?

Ions and solutes from chemical weathering carried invisibly in water.

What is suspended load?

Fine particles carried in the water column.

What controls suspended load movement?

Settling velocity, grain density, grain shape, and water density.

What is bedload?

Sediment moved by rolling, sliding, or bouncing along the bed.

What is saltation?

Sediment lifted briefly by turbulence and then dropped back onto the bed.

When does sediment begin moving?

When critical bottom shear stress is exceeded.

What happens if shear stress is frequently exceeded?

Sediment remains mobile.

What happens if shear stress is only exceeded during extreme events?

Sediment moves mainly during floods or storms.

What happens if shear stress is never exceeded?

Sediment is deposited.

What are channel planforms?

Channel patterns shaped by biophysical conditions.

What is the equation for estimating sediment transport?

Qs = CoQ

In the sediment transport equation, what does Co represent?

Concentration of suspended sediment (mg L⁻¹)

In the sediment transport equation, what does Q represent?

Discharge (m³ s⁻¹)

Calculate sediment transport for the Fraser River given Co = 186 mg L⁻¹ and Q = 3500 m³ s⁻¹.

651,000 mg/s (or 651 g/s)

What happens to geomorphic processes from headwaters to large river corridors?

They change progressively along the fluvial continuum.

What results from changes in geomorphic processes across a fluvial continuum?

Clear changes in channel shape and form.

What characterizes the source/high altitude zone in the fluvial continuum?

Steeper slopes and headwater conditions.

In the lower altitude/basal zone (2a), what limits channel sinuosity?

Vegetation constraints.

What is characteristic of the lower altitude/basal zone (2b)?

Greater sinuosity and meandering.

What characterizes the alluvial fan, delta, or terminus zone (3)?

Low slope and lower energy.

What controls channel patterns?

Sediment transport load, width-depth ratio, and channel stability.

Name the four main fluvial planform types.

Straight, Meandering, Braided, Anastomosed/Anabranching.

Why are straight channels rare in nature?

Sinuosity is usually limited only by strong biophysical constraints.

Where do natural straight channels typically occur?

Steeper slopes and headwaters.

How are most straight channels created?

Artificial channelization.

What defines a meandering channel?

One main winding channel.

In meandering rivers, where does deposition occur?

At the point of minimum velocity.

In meandering rivers, where does erosion occur?

At the point of maximum velocity.

What landforms result from cutoffs in meandering rivers?

Oxbow lakes.

What is a cut bank?

The outer bank of a meander where erosion is greatest.

What is a pool in a meandering channel?

A deep area with tranquil water during baseflow.

What is a riffle?

A shallow, fast-moving, turbulent section of the channel.

What is the thalweg?

The deepest continuous pathway through a channel.

What do riffle-pool or step-pool sequences represent?

Longitudinal profiles through the channel thalweg.

What does the sinuosity ratio describe?

How “bendy” a channel is, calculated as channel length divided by valley straight-line distance.

What defines a braided channel?

Two or more channels separated by unstable bars.

Why are braided channels unstable?

Bars and channels frequently shift after flow events.

What type of banks do braided rivers typically have?

Easily erodible banks.

What initiates braiding?

Local deposition in the channel center causing flow divergence and deceleration.

How does flow deflection contribute to braiding?

Increases bank erosion, causing further divergence and deposition.

What can local deposition do to slope downstream?

Increase it and promote more braiding.

What defines an anastomosing river?

Two or more distinct, stable channels separated by vegetated islands.

How does lateral migration in anastomosing rivers compare to meandering or braided rivers?

Much lower lateral change.

What type of hydrologic regime is typical of anastomosing systems?

Flood-dominated regimes.

What is a floodplain?

A flat strip of land beside a river formed by the stream under its current hydrologic regime.

What are alluvial fans and deltas examples of?

Fluvial depositional landforms.

What is aeolian geomorphology the study of?

The study of erosion, transport, and deposition by wind.

Aeolian processes occur most commonly in what environments?

Deserts and arid regions.

What percentage of Earth’s land surface is desert?

About 33%.

What percentage of Earth’s land surface is covered by sand?

About 20%.

Why is wind a less potent erosional agent than water?

Because air has lower density and viscosity than water.

What limits wind action as an erosional agent?

Vegetation and soil moisture.