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.
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