Unit 1C – River Landscapes in the UK
Cross Profile
The shape of the river channel. Shown as a
cross-section.
Long Profile
Shows how gradient changes downstream.
Erosion
The process of wearing away rock. There are
four types: abrasion, attrition, hydraulic action,
solution.
Abrasion
The rocks carried by the river scrape and rub
against the channel wearing it away. Most
erosion in a river is done by abrasion.
Attrition
The rocks carried by the river bash into one
another and break into smaller fragments. The
edges get rounded off as they rub together. The
further the rock travels the more eroded it gets
so attrition causes the bed load to get smaller
downstream.
Traction
Large rocks being rolled along the bed by the
force of the water as they are too heavy for the
water to lift.
Saltation
Pebble sized particles are bounded along the
river bed. This happens when the rivers velocity
changes – when it is fast it can carry the rocks,
when it slows down it drops the rocks.
Suspension
Small particles are carried along in the water
without being dropped.
Solution
Soluble materials are dissolved in the water and
carried along.
Deposition
This is when a river drops the material it is
carrying. This happens when the river slows
down for example: when the discharge falls, the
amount of bed load increases, the water is
shallower, the river reaches the mouth.
Hydraulic Action
Water forces its way into cracks in the bank of
the river, making these cracks bigger and
breaking bits off.
Helicoidal
Flow
A cork-screw like flow of water in a meander.
Vertical Erosion
Erosion that makes the river deeper – mainly by
abrasion as the rocks are rolled along the
bottom of the river by traction. It’s dominant in
the upper course.
Sediment
Load
The amount of material (rocks, sand, silt etc.)
that the river is carrying.
Discharge
The volume of water in a river. Measured in
cumecs (m3/s) or cubic meters per second.
Storm
Hydrograph
A graph to show how the discharge in a river
changes in response to a rainfall event. It is
shown over a set period of time usually hours
or days.
Estuary
A large river mouth which experiences high and
low tide. At low tide mudflats are visible.
Lateral Erosion
Erosion that makes the river wider – mainly by
abrasion and hydraulic action. It’s dominant in
the middle and lower courses.
Transportation
The movement of eroded material. There are
four types of transportation: traction, saltation,
suspension, solution.
Unit 1C – River Landscapes in the UK
How a river changes downstream
The long profile and cross profile changes as you go
downstream. It has three distinct (clear) parts the
upper, middle and lower course.
River Tees Examples
Upper Course:
Source – Cross Fell
High Force Waterfall
Middle Course:
Town of Yarm has
meanders
Lower Course:
Middlesbrough –
estuary and port.
Unit 1C – River Landscapes in the UK
Landforms of Erosion (Upper Course)
Waterfalls, gorges, v-shaped valleys and
interlocking spurs are all found in the
upper course and are caused by erosion.
V-shaped valleys are created as the river
has a low velocity and so energy,
therefore moves rocks by traction, this
creates abrasion on the bed leading to
vertical erosion making the river deeper
but not wider. This creates the steep Vshape.
Interlocking spurs are hillsides that
interlock with each other (like a zip if you
were looking from above). The river
doesn’t have the energy to erode laterally
so they have to wind around the hard
hillsides that stick out into their path.
Unit 1C – River Landscapes in the UK
Landforms of erosion and deposition (middle
course)
Meanders and ox-bow lakes are found in the middle
course. They are produced by lateral erosion and
deposition.
Meander Formation
1) Water is fastest on the outside bend of the river.
This causes this bank to erode through lateral
erosion. This creates a steep bank called a river cliff.
2) On the opposite bank (the inside bend) the river
is shallower and so the water is travelling slower.
This leads to deposition. This builds up a beach
called a slip-off slope.
3) Helicoidal flow is the spiralling of water in the
middle of the river. This will move eroded material
from the outside bank to the inside bank. Making
the river cliff steeper and the slip-off slope bigger.
4) Overtime the meanders will get bigger and will
move across the valley floor. They sometimes create
ox-bow lakes.
Ox-bow Lake Formation
A meander will eventually create a narrow neck due
to erosion of two outside bends. In a high discharge
situation like a flood the neck is eroded completely
through. The river then takes the straightest course
and deposition occurs on the new inside bend. This
blocks off the old meander which over time will dry
up and create a marsh.
Unit 1C – River Landscapes in the UK
Landforms of deposition (Lower Course)
Flood plains, levees and estuaries are landforms created by
deposition.
Flood plain formation
The flood plain is the wide and mainly flat valley floor on either
side of the river which occasionally gets flooded.
When a river floods the water slows down and deposits the
eroded material its transporting. This builds up the flood plain
(making it higher). Meanders also move across (migrate) across
the flood plain, making it wider. Most of the material deposited is
fine (small) material like silt and clay.
Levée Formation
Levées are natural embankments (raised bits) along the edges of
the river. During a flood the heaviest (and largest) material is
dropped first as it is heavier. This is deposited on the bank of the
river making the bank higher.
Estuary Formation
Estuaries are found at the mouth of a river, where it meets the
sea. The water here is tidal – the river level rises and falls each
day. Estuaries were created at the end of the last ice age when
big river valleys were flooded by rising sea levels. As the river
slows down (particularly at high tide) sediment will be deposited
(especially if the river has a high sediment load). This creates
mud flats or sand banks that can be seen at low tide.
Unit 1C – River Landscapes in the UK
Storm Hydrographs
Storm hydrographs show how rivers respond to rainfall, they have
a time axis at the bottom and two axis for rainfall in mm and
discharge in cumecs up the side. A hydrograph can either be
‘flashy’ or ‘delayed’
Flashy Hydrograph/River
Responds quickly to rainfall
with a short lag time, steep
rising limb and high peak
discharge. Generally seen in
urban areas.
Delayed Hydrograph/River
Responds slowly to rainfall with
a long lag time, gentle rising
limb and low peak discharge.
Generally seen in rural areas.
Hydrographs have several components (parts). They are:
Peak Rainfall
Highest rainfall in the time period
Peak Discharge
Highest discharge in the time period.
Lag time
The period of time between peak rainfall and
peak discharge. This happens because most
rain doesn’t land directly in the river but has
to find its way into the river.
Rising Limb
The increase in discharge after the rainfall
event.
Falling Limb
The decrease in discharge after the rainfall
event.
Bankfull
Discharge
The maximum amount of water a river can
hold. After this the river will flood.
‘Flashy’
‘Delayed’
Unit 1C – River Landscapes in the UK
Factors affecting Discharge
Various factors (things) can affect the amount of discharge in a river and how long the lag time is. If a river has a higher amount of discharge
and a short lag time it is more likely to flood.
Prolonged Rainfall
If it rains for a long period of time the soil becomes saturated (full of water). This means any
further rainfall cannot soak in (infiltrate) and so runs into the river quickly as surface runoff.
Heavy Rainfall
If the rain is too heavy the soil cannot absorb it quickly enough as infiltration takes some time.
This means the rain runs off into the river quickly as surface runoff.
Rock Type (geology)
Impermeable rock (rock that doesn’t let water through) will stop rock infiltrating into the
groundwater. Permeable rock (rock that absorbs water) allows water to infiltrate into he ground
water which takes a long time to reach the river.
Relief
Steep slops do not allow time for water to infiltrate as the water runs down them too quickly.
This leads to surface run off.
Vegetation
Vegetation absorbs water, decreasing discharge and also acts like an umbrella intercepting
(stopping) rainfall reaching the ground. This reduces discharge. Deforestation removes this
vegetation causing high discharges and short lag times.
Land Use
If an area is urbanised (a town or city) there are lots of impermeable surfaces like roads and
buildings. This means the water runs straight into drains and quickly gets into the river causing a
short lag time and a high discharge. If an area is rural there is lots of permeable soil and
vegetation decreasing lag time and reducing discharge.
Unit 1C – River Landscapes in the UK
Use knowledge of the river and Man-made structures to control the flow of rivers and
its processes to reduce flooding. reduce flooding.
Soft engineering
Hard engineering
Definition Scheme
Dams and reservoirs
How it works
Dams (walls) are built across the rivers
creating a reservoir (artificial lake) behind it.
The water is stored in the reservoir and is
slowly released downstream by valves in the
dam.
Costs (negatives)
Expensive
Floods land behind the
dam.
Traps sediment leading
to less fertile land
downstream.
Flooding happens at
the next meander
instead.
There is more erosion.
Benefits (positives)
Reduce risk of flooding
due to storage.
Use water for drinking
or to create
hydroelectric power.
Straightening meanders
The meanders are cut out leaving a artificially
straight river. This means the water flows
faster, reducing the risk of flooding in the
bends.
Embankments
Raised walls along the river which increase the Expensive.
If it does flood the
capacity of the channel so it can hold more
flooding will be worse.
water.
Reduce risk and
frequency of flooding.
Flood relief channels
Channels are built that divert the water around
important areas or takes it elsewhere if the
river is high. This doubles the capacity of the
river as there are now two rivers instead of one
for the same amount of water.
Expensive.
Where the channel rejoins the main river
there can be flooding
due to increased
discharge.
The Environment Agency warns people at risk Will not stop a flood.
of flooding via phone, TV, radio, online. People People may not hear the
can then prepare their homes to reduce the
warnings.
damage e.g. moving things upstairs.
There will still be
damage.
Only allowing low-value land use near the river Can only be used for
like parks and car parks. Houses, hospitals and new buildings.
other high value land uses are built as far as
Cities cannot grow as
possible from a river. This means less damage much/land is wasted.
is done in a flood.
Reduces risk of
flooding.
Release of water into
channel can be
controlled.
Flood Warnings and
preparation
Flood plain zoning
Reduce risk of flooding.
Does not require
maintenance.
The impact is reduced.
Cheap.
Cheap
Creates open spaces
Creates new habitats.
Unit 1C – River Landscapes in the UK
Flood Defence Case Study – Carlisle, 5th/6th December 2015
Defences (before 2015):
Causes:
Heavy Rain – 341 mm in 24 hours. UK RECORD!
Geology – Granite and Slate which are impermeable
Vegetation – Lots of deforestation in the fells
Urbanisation – Lots of impermeable surfaces.
Major Tributes – 3 rivers – Rivers Eden, Petteril and Caldew all
meet.
10 km of flood walls around the city including in Denton Holme along
the Caldew and around Lidl. These are designed to stop a 1 in 200 year
flood.
Effects:
£500 million damage across Cumbria.
More than 1000 people evacuated, many to shelters such as at
Morton School.
West Coast Main Line closed.
Many bridges such as the Eden Bridge. This caused travel problems
in the area.
Schools flooded – Central, Trinity and Newman. Newman still shut.
2,100 houses flooded.
Many businesses shut – like the Dry Ski Slope and Tesco on
Warwick Road causing loss of money.
Responses:
Temporary Tesco store set up in car park of flooded store.
RNLI, Mountain Rescue and Army went house to house to evacuate
people.
Evacuation centres set up such as at Morton School.
Newman School moved to the old Pennie Way Site.
Cumbria Community Foundation raised over £6 million and coordinated the collection of supplies to help flood victims such as
food and clothes.
Schools like Caldew gave books and resources to schools who had
lost theirs.
Bridges have been rebuilt to make them higher and they have sides
with gaps in to allow water to pass through them without the bridges
collapsing.
The Holme Head Storage Scheme created an area of land that is
allowed to flood to store water to prevent folding downstream.
Willow Holme and Durranhill Basin pumping stations pump water away
from vulnerable areas.
Impacts of the Defences:
• Residents lives were disrupted by construction
• Only protects against a 1 in 200 year flood – didn’t work in 2015.
• Cost £38 million but reduces the costs caused by a flood as less
buildings will flood.
• The flood walls look unsightly.
• The storage areas create open space for enjoyment and a wetland
habitat for wildlife.
Social
Economic
Environmental