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Physical Geography Notes: Rivers, Floods and Management

Hydrological Cycle




Factors affecting drainage basin processes
Basin size, shape and relief:
Small basin= shorter distance= shorter lag time
Circular drainage basin= shorter lag time and higher peak flow
Steep land= shorter lag time as it takes a shorter time to reach the…

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Permeable= porous (holes) or pervious (water down joints in rock)= decrease surface
runoff
Impermeable= increase surface runoff
Soil type:
Sandy soils= rapid infiltration
Clays= slower infiltration

Hjulstrom curve




The Hjulstrom curve shows the relationship between velocity and particle size. It shows the
velocities necessary for the initiation of movement; for…

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Gradient: steeper gradient means water ravels faster
Valley width/depth: smaller means water travels faster
Volume of water: more water means a higher velocity
Number of tributaries: more tributaries means a higher velocity
Amount of meanders: more meanders means a slower velocity
Meander sinuosity: curvier river means a slower velocity

Lower…

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Landforms of erosion and deposition
Waterfalls and rapids
Waterfalls and rapids occur when there is a sudden change in gradient of the river as it flows
downstream. Waterfalls are more dramatic than rapids and may be a result of:
A resistant band of rock occurring across the course of the…

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Braided channels
Braiding occurs when the river is forced to split into several channels separated by islands. It
is most likely to occur when a river has variable discharges. The banks are formed from sand
and gravel and are generally unstable and easily eroded. As a consequence, the channel
becomes…

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Oxbow lakes
Oxbow lakes are formed by both erosion and deposition. An oxbow lake is formed by the
increasing sinuosity of a river meander. Erosion is greatest on the outer bank and with
deposition on the inner bank, the neck of the meander narrows. During times of high
discharge, such…

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Floodplains
Floodplains are created as a result of erosion and deposition. They are the flat areas either
side of the river. They are composed of alluvium- river deposited slits and clays. Over time, a
floodplain becomes wider and the depth of sediment accretion increases. The width of a
floodplain is…

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Urbanisation: Urban areas have large areas of impermeable tarmac and have good
drainage systems. This increases surface runoff which reduces the lag time so
discharge in increased.
Deforestation: clearing trees and plants reduces interception and transpiration. This
increases the volume of water running to rivers so increases discharge. Loose soil…

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builds up and is dam which can cause
gradually released erosion downstream.
Channel Where meanders are Flooding and more
Straighteni removed, making the erosion may occur
river flow faster further downstream. It
ng
through a certain area. also disturbs habitats
Levees Embankments built They allow the Quite expensive. If the…

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reduces discharge and
flooding




.

Comments

Marta Kohls

Good resource, very brief, glossary could be expanded. :)

Samueldhami

Quite a few visible mistakes with these notes, please revise them ;)

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