Physical Flashcards
attrition
rocks that bash together to become smaller
solution
a chemical reaction that dissolves rocks
abrasion
rocks hurled at the base of a cliff to break pieces apart or scraped against the banks and bed of a river
hydraulic action
water enters cracks in the cliff or river bank, air compresses, causing the crack to expand
solution
minerals dissolve in water and are carried along
suspension
sediment is carried along in the flow of the water
saltation
pebbles that bounce along the river bed
traction
boulders that roll along the river by the force of the flowing river
deposition
when the sea or river loses energy, it drops the sand, rock particles and pebbles it has been carrying.
precipitation
moisture falling from clouds as rain, snow or hail
interception
vegetation prevents water reaching the ground
surface runoff
water flowing over the surfaces of the land into rivers
infiltration
water absorbed into the soil from the ground
transpiration
water loss through leaves and plants
physical causes of flooding
- prolonged heavy rainfall causes soil to become saturated leading runoff
- relief - steep sided valleys channels water to flow quickly into rivers causing greater discharge
- impermeable rocks causes surface runoff to increase river discharge
human causes of flooding
tarmac and concrete are impermeable this prevents infiltration and causes surface runoff
upper course of river
Near the source, the river flows over steep gradient from the hill this gives the river a lot of energy, so it will erode the riverbed vertically to form narrow valleys
middle course of river
Here the gradient gets gentler, so the water has less energy and moves more slowly. The river will begin to erode laterally making the river wider
lower course of the river
Near the rivers mouth, the river widens further and becomes flatter. Material transported is deposited
Formation of waterfall
- river flows over alternative types of rocks
- river erodes soft rock faster creating a step
- further hydraulic action and abrasion form a plunge pool beneath
- hard rock above is undercut leaving cap rock which collapses providing more material for erosion
- waterfall retreats leaving steep sided gorge
formation of floodplains and levees
When a river floods, fine silt is deposited on the valley floor, closer to the rivers banks, the heavier materials build up to form natural levees.
formation of ox bow lakes
- erosion of outer bank forms rover cliff. Deposition inner bank forms slip off slope
- further hydraulic action and abrasion of outer banks, neck gets smaller
- erosion breaks through neck, so river takes the fastest route, redirecting flow.
- evaporation and deposition cuts off main channel leaving an oxbow lake
soft engineering
afforestation - plant trees to soak up rainwater, reduces flood risk
demountable flood barriers - put in place when warning raised
managed flooding - naturally let areas flood, protect settlements
hard engineering
straightening channel - increases velocity to remove flood water
artificial levees - heightens river so flood water is contained
deepening or widening river - to increase capacity for a flood