Physical Geography Rivers Notes AS Level

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  • Created on: 24-05-13 09:57
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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 river
Tides and storm surges:
High tides and strong winds= increased river levels
Drainage density:
Number of surface streams
More streams= longer lag time
Types of precipitation:
Prolonged rainfall= long period of heavy rainfall
Intense storms= rainfall intensity may be greater than infiltration therefore rapid rises
in river levels
Snowfall= heavy snowfall= water held in storage and river levels drops
Very cold= hard land= increased surface levels
Very hot= hard ground= increased surface levels
Land use:
Vegetation= intercept rainfall and store moisture before use its evaporated back up.
In winter deciduous trees shed leaves so less taken up by leaves and more by roots
Urbanisation= water cannot infiltrate due to impermeable surfaces
Rock type:

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Permeable= porous (holes) or pervious (water down joints in rock)= decrease surface
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 development; and the area where
transportation will continue to occur once movement has initiated.…read more

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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 Course Middle Course Upper Course
Landforms Landforms Landforms
Small waterfalls Rapids Large meanders
Rapids Small meanders Levees
Potholes Small floodplain Floodplain
Large boulders
Uneven, steep river
Processes Processes Processes
Hydraulic action Attrition Reduced erosion…read more

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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.…read more

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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 very wide in relation to its depth.…read more

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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 as floods, the river cuts through this neck and the new cut eventually
becomes the main channel and the former channel is sealed off by deposition, thus forming
an oxbow lake.…read more

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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 determined by the amount of meander migration and lateral erosion that has
taken place.…read more

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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 is
also carried to rivers, raising the river bed.
Physical factors
Sparse vegetation: Little rainfall intercepted, increasing the amount of water reaching
the river which increases discharge.…read more

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Channel Where meanders are Flooding and more
Straighteni removed, making the erosion may occur
river flow faster further downstream. It
through a certain area. also disturbs habitats
Levees Embankments built They allow the Quite expensive. If the
along rivers so it can floodplain behind it to levees are breached
hold more water be built on there is also a risk of
without overflowing. severe flooding.…read more

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Marta Kohls

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


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

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