Fluvial processes

weathering, mass movement, erosion, transportation

weathering

decomposition of rocks in situ

types of weathering

physical

chemical

biological

physical/freeze thaw

water freezes & expands

thaws & pressure on rock is released

water freezes

process continues

chemical/carbonation/solution

carbonic acid naturally occurs in rainwater

reacts chemically with rocks

slowly dissolves them

biological (trees)

roots wedge into cracks

tree grows & roots force rock apart

biological

decomposition of dead organic material releases _____ and CO2 and leads to chemical weathering

acids

Rockfall

on cliffs & produces rocky outcrops

Slide/slump

water soaks into ground

heavy ground above triggers slide

Flow

on steep tropical hills & volcanic slopes

lots of water

Creep

slow & continuous

fine material moves

Erosion

wearing away of material by a moving force.

Moving force

wind/ running water

Hydraulic action

force of water against bed & banks

Attrition

load bumps against each other

Abrasion

load thrown against bed & banks

Corrosion/solution

acids in water slowly dissolve bed & banks

Traction

large boulders roll

Saltation

sand hops

Suspension

fine silts carried by water

Solution

material dissolved in water

River efficiency

ability of a river channel to move water & sediment

85% of a river’s energy is used overcoming ______

friction

Hydraulic radius

proportion of water in channel cross-section in contact with bed & banks

Wetted perimeter

length of bed and banks in contact with river (m)

Hydraulic radius calculation

cross sectional area / wetted perimeter

Large WP = more friction = ______ efficient

less