UGA GEOG1111 Chapter 10

Base level: the level below which a stream cannot erode its valley.

Imaginary surfaces extending inland from sea level.

Local Base-level: river, lake, resistant strata

Drainage basins are the unit we use when we describe river systems. It’s the bowl that an entire river system drains.

Overland flow: thin sheet of water flowing downslope. Either go into the basin, or fill rills (tiny channels)

A primary feature of a drainage basin is its drainage density

Drainage density is determined by dividing the total length of all stream channels in the basin by the area of the basin.

The drainage pattern is the arrangement of channels in an area: f(x) if topography, slope, geology, & climate

Dendritic drainage: gradual slope | Parallel drainage: steeper slope

Radial drainage: found around mountains & volcanoes

Rectangular drainage: Associated with really jointed geology, channels flow along joints

Trellis stream drainage occurs in folded landscapes

Steeper gradient in headwaters region, as you move down to the mouth of the river, the gradient decreases. Elevation change over a distance becomes less and less. (decreasing exponentially)

Erosion, transportation, and deposition effects fluvial landscapes.

Sediment carried by a stream is known as the sediment load.

Sediment load consists of multiple different types – it’s a function of topography. Steeper the channel, greater the erosion, the greater the suspended material in the stream channel.

Competence – the ability to move particles of a specific size. The greater the energy, the greater the competence. Some streams can only pick up silt and clay because of low energy, others with more energy can pick of sand and stuff.

Capacity – total amount of sediment the stream can transport.

Bed load – material that is too large & too heavy to be dragged along the streambed.

Solution – all the salt dissolved within the water

Traction: pushing/rolling large materials on the floor. Saltation: bouncing along the channel

Meandering streams: found on floodplains, much less steep gradient, much less energy.

Area with greatest velocity tends to be the deepest point.

The location of the deepest point will move over time.

Cutbank – where the river does a turn, usually a steep wall above the river

Point bar: across from cutbank, usually just sandy with no water

Oxbow lake – isolated lake which is no longer connected to the main channel

Every time a river floods, it creates natural levees, where the banks of the river increases in elevation, meaning the next flood needs slightly more water to spill over the channel.

Alluvial terraces – step-like paired at similar elevations

Deltas – mouth of river reaches base-level à decrease in velocity à sediments deposited

Types of deltas: braided (excess sediment), arcuate (arc-like), and estuarine (seawater & freshwater)

Hydrographs: Stream height over time.

Base-flow: dry season, low water flow

Peak-flow: precip event in water shed, function of the amount, location, and duration of event

Urbanization hastens peak flow

Coastal Geomorphology

Ocean absorbs CO2 from the atmosphere, forms carbonic avid, and reduces ocean pH. Current Ocean pH is 8.1 (slightly alkaline). pH could decrease by 0.4 to 0.5 by the end of the century (5x change in acidity)

Changes in sea level expose a range of coastal landforms to tidal and wave processes. The quantity of ice locked up in ice sheets can increase & decrease and result in sea level changes accordingly.

If Antarctica and Greenland became ice-free, sea level would rise at least 65m worldwide.

WIND

Eolian means wind. Eolian processes include erosion, transportation, and deposition (from wind).

Because air is denser than water, wind is unable to move materials as effectively as water.

Over time, wind can do enormous work

Wind is most effective at picking of sand, as opposed to larger materials

Deflation – Removing and lifting individual loose particles.

Abrasion – Grinding rock surfaces by “sandblasting”, all the sand erodes bigger things

Deflation blows away non-cohesive loose sediment. Leads to desert pavements (concentration of large rock pavements)

Protects underlying surface from further erosion.

Blowout depressions – removal of loose sediment leading to shallow basins

Abrasion: sandblasting by wind-blown grains

Pitted, grooved or polished with aerodynamic shaped (prevailing wind direction)

Ventifact – rock that bears evidence of wind sculping (erosion)

Yardang – rocks exposed to abrasion over long periods of time; appear pitted, fluted, polished.

Eolian Transportation:

Wind à drag (frictional force); fluid

Saltation: transport of grains along ground, aerodynamic lift, bounce and impact.

Surface creep: impact of grains pushing other larger particles forward

Mitigation of beach erosion: stabilizing native plants, sand fences, walkways

Ripples: smallest features shaped by individual saltating grains

Dune: accumulation of sand, shaped by wind

Live dunes: bare of vegetation, dynamic

Fixed dunes: inactive, covered in vegetations

Windward side: gently sloping | leeward side: steeper (slipface)

Angle of repose: steepest angle at which slope is stable (30-34 degrees)

Avalanche slope: constant addition of sand allows it to tumble down from the crest & migrate

Dunes vary in shape and size depending on directional variability & strength of the wind, the sand supply, and the presence of vegetation.

Barchan dune: concentric circles, horn pointed down, found in areas with constant wind and limited sand

Parabolic dune: opposite of Barchan, Crescent-shaped dune with opening end facing upwind, vegetation is stabilizing the sand and creates a parabolic shape

Transverse dune: Long, sinuous dune with asymmetrical ridge and only one slipface. Just a bunch of straight lines