Streams and Rivers
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Streams and Rivers
• Powerful agents of erosion, transport and
deposition
River long profile
Source
Upper
course
Middle
course
Lower
course
Mouth
River features
Source
Upper
course
Middle
course
Lower
course
Mouth
River stages
River valley
• Grey Mare’s Tail
River long profile
• Upper Course
– Young Stream
• Steep gradient
• Small volume
• Fast moving (average flow rate similar to lower
course)
• Narrow valley
• Erodes downward
River long profile
• Middle course
– Mature stream
• Gradient decreases
• Volume increases
• Speed decreases
• Valley widens
• Erodes sideways
• Some meanders
River long profile
• Lower course
– Flood plain
• Flat gradient
• Large volume
• Slow moving
• Wide valley
• Desposition dominant
• Meanders
River Basin Framework
• Water and sediments transported through
catchments
River Beginnings:
• Streams
– Perennial or ephemeral
(episodic flow)
• Water flow on bare fields
– rills Æ gullies
River Flows
• One-way flow systems, trend downstream
towards
– decreasing river slope
– increasing depth
– increasing water volume
– increasing discharge rate
– decreasing turbulence
River Transport
• water loses energy when:
– decreased gradient
– channel widens
– meanders
– volume decreases (e.g. after flood)
• when river has insufficient energy to transport
load, deposition occurs
River Flow
• Fastest flowing part of a river
– at middle top away from bed and banks
• River at low water
– has less energy because it is smaller
– uses more of its energy to overcome friction
• River at high water
– river flows faster
– more energy to erode and transport
Meandering Stream
Meander
Development of Meander
Flow
direction
Time
River Forth, Stirling
Braiding
• River with low energy
• Channel bars grows upstream
• Vegetation grows
• Increases sediment trapping
• Channel shifting via runnel enlargement across
alluvial islands
• Existing channels get blocked off by deposition at
upper ends
Flood Plain Deposition
• When river bursts banks
• Coarsest material nearest the channel
Deltas
• form as river loses energy Æ deposition.
• distributaries
Alluvial Fans
• Occur at boundaries between steep
hills/mountains and lowland areas
• Sudden energy drop Æ deposition
Delta
• Nile - satellite photo
• North Sannox, Arran