Floodplains,Levees, Deltas, Groundwater Flashcards
What is a floodplain?
a large, realtively flat expanse of land that forms on either side of a river
area that a river floods onto when experiencing high discharge
what are floodplains composed of?
alluvium-deposits of silt and clays
why are floodplains wider in the lower course?
lateral erosion is more dominant in a river’s lower course
How are floodplains formed?
When a river has a high discharge, its able to transport a large amount of material in suspension. When a river has an exceptionally high discharge, its overflows its banks and the flood the low lying land around it. this decreases its efficiency due to increase in friction reducing its velociity forcing it to deposit its load. alluvium is fertile so floodplains are used by farmers. each time there is a flood new layers of alluvium are depositied . over time it can be wider and depth of sedimenta accretions may increase.
Levees how are they formed?
What is Groundwater?
fresh water that infiltrates or percolates the soil and is stored in pore spaces between rocks and particles of soil
Groundwater is stored in 3 zones
Saturation/phreatic zone, zone of aeration/unsaturated zone, intermittent saturation/vadose zone
explain zones in grounwater
above the impervious rock layer is zone of saturation/phreatic zone , all pore spaces are saturated with water, aquifers are found here, the upper bundary is the water table>ablove water table os zone of aeration/unsaturation where pore spaces are not saturated with water water is called soil moisture within here is capillary fring- capillary action draws groundwater out of water table into the pore spaces of sediment directly above it> capillary fringe is located in the zone of intermittent saturation or vadose zone, becomes saturated when rain fall is abundant . it is the rock layer above the water table. vadose water percolates through zone aerationin the soil before it reaches water table
Aquifer
underground formationof permable rock or loose material that store water
well
hole bored into ground from which water is obtained
artesian basin
a synclinal shaped rock structure consisting of a permable layer, the aquifer, sanwhiched between two impermeable layers of rock. the permable layer outcrops at the rim of the basin to allow rainfall to percolate into the lower part of the basin where water is largely accumulated since impermable layer prevents it from percolating further downwards.
delta
depsoitional feature found at the mouth o a riuver where the river meets the bosy of water with lower velocity. lower velocity means less energy so river will deposit load. if load is deposited faster than sea erosion a delta forms.as river enters sea the vlcoity id suddenyr reduced causing depostion. sand is deposited first and light silst and clay carried futher out.thus layers of different sediemtns are build on the sea floor until reahces the surfaceit happen on the landward side of the delta extending out
river > braided
when river flows over its own sediment a braided river is formed
distributary
ech channel in a delta
