Aim of session: To revise content from the topic of rivers
The Hydrological Cycle
What is happening at
points A and B? Name the
Can you identify an input, store, flow/transfer and output?
Weathering- when natural agents break up the
Can you explain- biological, freeze thaw and
chemical weathering? Use the images to help!
How does a v-shaped valley form?
1. Vertical erosion (in the form of
abrasion, hydraulic action and
solution) in the river channel results in
the formation of a steep sided valley
2. Over time the sides of this valley are
weakened by weathering processes
and continued vertical erosion at the
base of the valley
3. Gradually mass movement of
materials occurs down the valley sides,
gradually creating the distinctive v-
4. This material is then gradually
transported away by the river when
there is enough energy to do so.
How do they form?
As the river flows through the valley it is
forced to swing from side to side around
more resistant rock outcrops (spurs). As
there is little energy for lateral erosion,
the river continues to cut down vertically
flowing between spurs of higher land
creating interlocking spurs.
The sea comes up the river at the mouth. At low
tide the edges are exposed. That leaves mudflats
at the sides of the river.
Floodplain - the area of land around
a river channel which is formed
during times of flood when the
amount of water in a river exceeds
its channel capacity and deposition
of rich silt occurs. The rich silt is
Levées - a raised river bank (can
be natural features formed by
deposition or artificial
structures built to increase
channel capacity and reduce
A delta happens when a river has
lots of load. When it reaches the sea
the water flow slows down, so it
drops its load. If the waves or
currents aren’t too strong and the
land doesn’t slope to steeply , the
load builds up to make a delta. The
sediment blocks the river so it has to
divide up into lots of different
channels called distributaries. Deltas
can be different shapes, but the two
main types are birds foot
(Mississippi) and arcuate deltas
The River Thames has an estuary. This is a
wide, deep mouth. Estuaries are really
useful for shipping, so they usually have
ports and factories along them.
What are Storm Hydrographs?
Hydrographs are graphs which show river discharge (the amount of water in a river)
over a given period of time and show the response of a drainage basin and its river to a
period of rainfall.
Discharge is measured in cumecs (cubic metres per second). This can
be calculated by multiplying river velocity by channel volume at a given
point and time.
Physical causes of flooding
-Rainfall- long spells of heavy rain or melting snow means more water
in the river
-Antecedent rainfall- it has already been raining and the ground is
saturated. Water can’t infiltrate so it becomes surface run-off.
-Rock/Soil type- Permeable/Impermeable rocks and soil
-Weather- Sunshine and high temperatures increases evaporation. This
can lead to sudden, heavy downpours. After dry weather the ground
is baked hard. If there is then heavy rain, water can’t infiltrate. Frozen
ground also doesn’t all water to infiltrate. This leads to more surface
-Relief- Where slopes are steep, water doesn’t sink in as it is flowing
too fast. (Gentle slopes mean more infiltration is likely).
Human causes of flooding
-Deforestation- Trees take up water through their roots and
intercept water with their leaves. If trees are chopped down,
water reaches the ground faster and saturates it, so surface run
-Soil Erosion- Deforestation leaves soil bare. Rain washes the soil
in to rivers. This clogs the rivers up, causing them to flood.
-Farming- Ploughing the land creates vertical channels which
allow rainfall to flow straight downhill to the rivers.
Building- Concrete and tarmac surfaces are impermeable-water
flows quickly across them into drains, which flow into rivers.
Hard options tend to be more expensive and
have a greater impact on the river and the
Soft options are more ecologically sensitive.
The tables summarise the main flood