2. Erosion
Erosion: the wearing away of the bed and banks of the river
channel. There are four types of erosion that take place in a
river:
1. Corrasion: the pebbles being transported wear away the bed
and banks of the river channel.
2. Attrition: The particles are knocked about as they are
transported, and they gradually become more rounded and
reduced in size.
4. Hydraulic Action: The sheer force of the water by itself can
erode material from the bed and banks of the river channel.
3. Corrosion (Solution): some rocks such as limestone are subject to
chemical attack and slowly dissolve in the water.
3. Transportation
Transportation: the river moves material as bedload (traction or
saltation), suspended load (suspension) or dissolved load (in solution).
4. Traction: material rolled along the bed of the river.
2. Suspension: very small and light material, usually fine clay
and silt, are carried by the river.
3. Saltation: material bounced along the bed of the river.
1. Solution: some rocks such as limestone are subject to
chemical attack and slowly dissolve in the water.
4.
5. Upper valley characteristics
“V”shape valley,
vertical erosion
dominant
Interlocking spurs
Slumping and
landslides - very
active hillslopes
Terracettes formed
by soil creep
Narrow, shallow
channel, low
velocity and
discharge
Large bedload
derived from
upstream and
from valley
sides
13. Diagram shows formation of a Meander show areas of erosion (red X’s)
X
X
X
X
Outside Inside
Fast flowing water Slow flowing
More energy, so more erosion Less energy, so deposition
Wearing away of bank and
bed – undercutting
Material deposited forming
new land
River Cliff River Beach
Lateral erosion (sideways)
18. True or False
A storm hydrograph shows how a river's discharge responds following a period
of heavy rainfall
Rising Limb shows the increase in discharge on a hydrograph
The shape of a hydrograph is determined by the speed in which flood waters
are able to evaporate.
•permeable rocks and soil have a high infiltration capacity and so will not
absorb water
On a hydrograph, the flood is shown as a star above the base (normal) flow of
the river
Where more water is able to pass into the soil and travel to the river via
throughflow / groundwater flow
River discharge does not respond immediately to rainfall inputs as only a little of
the rainfall will fall directly into the channel.
The fastest route to the river is via overland flow.
The response of a river to a rainfall event can be measured in terms of the
speed of light
