Rivers KO Flashcards
Upper course channel characteristics
Narrow and shallow. Likely to have
large rocks in it. Water flow is
turbulent and speed is variable.
Where water is shallow there will
be friction and so slow flow.
Where water is deeper flow will be
quick.
Upper course valley characteristics
Steep sided. V
shaped.
Upper course processes
Vertical erosion is
dominant.
Upper course landforms
Interlocking spurs. V
shaped valleys.
Waterfalls. Gorges.
Middle course channel characteristics
The river channel here is wider and
deeper as tributaries have added
additional water. Flow is faster
than in the upper course as there
is less friction between the water
and the river bed and banks.
Middle course valley characteristics
Wide. Gently sloping.
Middle course processes
Lateral (sideways)
erosion,
transportation and
deposition.
Middle course landforms
Meanders. Ox-bow
lakes.
Lower course channel characteristics
River is deepest and widest in this
section. Flow will slow because the
river meets the sea.
Lower course valley characteristics
Very wide. Very
gently sloping.
Lower course processes
Deposition
Lower course Landforms
Meanders, Estuaries.
Levees. Deltas.
Waterfalls and gorges: location and how they form
Found mostly in upper course of river or where upper course becomes middle course.
1. hard rock overlays soft rock
2. a break or gap in the hard rock layer allows the softer rock to be eroded more quickly
forming a drop
3. The drop means that erosion happens more quickly. A plunge pool is formed
4. the water undercuts the hard rock creating an overhang
5. the overhang collapses and the waterfall moves upstream
6. repeated movement upstream forms a gorge (a narrow steep-sided valley
Meanders and oxbow lakes: location and how they form
Found mostly in lowland areas in the middle course of a river
1. on a bend the river flows more quickly on the outside then it does on the inside
2. This causes erosion on the outside of the bend and deposition on the inside of the
bend.
3. The bend becomes exaggerated forming a meander.
4. over time the neck of the meander is eroded
5. The meander is cut by erosion and sealed off by deposition. The river is now flowing
in a much straighter line.
6. The old sealed off meander has become an oxbow lake.
Floodplains: location and how they form
When a river floods in the lower course, it deposits very fine sediment (silt). Layer after
layer builds up to form a thick deposit of silt across a very flat wide valley.
The floodplain is made wider due to large meanders that wind across the floodplain.
Levees: location and how they form
When a river floods, the speed of the river decreases = less energy = deposition.
* Heavier, coarser sand and small stones are deposited first next to the river bank.
* Lighter silt/mud is deposited further across the floodplain.
* Over time the height of the banks are raised by a buildup of coarser sand
deposits = levees.
Factors affecting flood risk: Urbanisation
Human factors:
Building on the flood plain creates artificial impermeable surfaces (concrete, tarmac
etc.). water moves quickly into drains and sewers and then into the river. The river
cannot cope with all the water and so floods.
Factors affecting flood risk: Deforestation
Human factors:
Trees slow down the movement of water in to the river. They intercept the rain and
store some on their leaves from where it is evaporated. Trees also use some of the
water to grow. When trees are removed much more water makes its way to the river
making a flood more likely.
Factors affecting flood risk: Agriculture
Human factors:
Farming leads to more surface runoff as the fields are often left empty (especially in
winter when heavy rain is more likely). More surface runoff means the river has to cope
with more water, which means floods are more likely.
Factors affecting flood risk: Precipitation
Physical factors:
Sudden heavy rainfall can cause flash floods as the river channels cannot cope with the
amount of water flowing into them.
Steady rainfall over a number of days can also lead to floods as the river becomes full.
Factors affecting flood risk: Geology
Physical factors:
Impermeable rocks mean that the water cannot soak into the ground, it therefore gets
to the river more quickly making flooding more likely
Factors affecting flood risk: Steep slopes
Physical factors:
Steep slopes mean that the water falling as rain gets to the rivers much more quickly,
this makes flooding more likely.
Ways to reduce flood risk: Dams and reservoir EXPLANATION
Hard engineering:
Used to regulate river flow and reduce the risk of flooding. The flow of water can be
stopped during periods of heavy rainfall. The water is stored in a reservoir so that the
river does not flood downstream.
Ways to reduce flood risk: Dams and reservoir POSITIVES
+ Effective, long lifespan, used for irrigation, water supply, recreation and HEP.
Ways to reduce flood risk: Dams and reservoir NEGATIVES
- Expensive, damage habitats, people have to relocate due to flooding.
Ways to reduce flood risk: Channel straightening EXPLANATION
Hard engineering:
Rivers are straightened by cutting through meanders to create a straight river channel.
This speeds up the flow of water along the river.
Ways to reduce flood risk: Channel straightening POSITIVES
+ Effective as water does not have time to build up, long lifespan.
