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Rivers (Landforms (Meander (Constantly changing bend in river, Caused by…
Rivers
Landforms
Interlocking spurs
River not very powerful
Flows around 'spurs'
Waterfall
River flows over hard 'cap' rock
Forms a
step
Plunge pool
created underneath
Rock is undercut and collapses
Gorge
Valley formed by a retreating waterfall
Occasionally formed by glaciers
Meander
Constantly changing bend in river
Caused by lateral erosion & deposition
Pools
(deep) and
riffles
(shallow) formed
Thalweg
is fastest line of flow
Slip-off slope
(inside bend)
River cliff
(outside bend)
Helicoidal flow
of water
Ox-bow lake
Loop in river can be cut off
Neck
is narrowed by erosion
Meander scar
if empty
Levee
Sediment deposited when river floods
Largest load deposited first due to friction
Floodplain
Build-up of
alluvium
(deposited silt)
Wide flat river valley
Estuary
Where river meets the sea
Mix of fresh and saline water
Mudflats and salt marshes (low energy)
River Tees
Source Pennine Hills (893m)
High Force
20m drop
Whin Sill cap rock
Limestone soft rock
1200mm/y rainfall
20km wide floodplain @ Yarm
100km source to mouth
Seal Sands
Transporter Bridge & Riverside Stadium @ mouth
Changes
Load
Angular to rounded
Large to small
Few to many
Steep to gentle gradient
V-shape to wide valley
Channel
Narrow to wide
Shallow to deep
Floods
Factors
Antecedent rainfall
Soil already saturated
Extra rainfall becomes run-off
Rock type
Permeable rocks allow water to infiltrate
Impermeable rocks produce run-off
Vegetation
High vegetation intercepts water
Roots absorb water
Relief
Steep gradient means lotsa run-off
No time for infilitration
Agriculture
Furrows in fields created by tractors
Water quickly channelled
Frozen ground
Water cannot infiltrate
Surface run-off
Melting snow
Creates more surface run-off
Or melts slowly
Drainage basin
Smaller basin = less travel time = flood
Circular basin = longer lag time
Hard engineering
Dams & reservoirs
Regulates water flow
Hydro-electric power
Irrigation and water supply
Channel straightening
Artificial channel to straighten meanders
Lined with concrete
Increase speed of flow downstream
Increases bankfull capacity
Embankments
Dredging increases capacity
Soil embankments raise height
Flood relief channel
Man-made channel to bypass urban area
Excess water can flow away
Creates new wetlands
Soft engineering
Warning & preparation
Monitored by satellite
Predict and identify risks
Floodplain zoning
Restrict land use to certain locations
Low-value to high-value land
Afforestation
Establishing woodland
Trees obstruct flow of water
Roots soak up water
River restoration
Use natural processes to slow flow
E.g. meanders, wetlands
Processes
Erosion
Hydraulic action
Force of water hitting river bed and banks
Abrasion
Load carried by water repeatedly hitting bed/banks
Attrition
Stones carried by water knock against each other
Load is smaller and smoother
Solution
River dissolves limestone or chalk
Mildly acidic water
Transportation
Suspension
Light material carried by river
Traction
Large rocks roll along river bed
Solution
Minerals dissolved in water
Saltation
Small stones bounce along river bed