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.
Ways to reduce flood risk: Channel straightening NEGATIVES
- Expensive, unnatural, damage habitats, result in flooding downstream.
Ways to reduce flood risk: Embankment EXPLANATION
Hard engineering:
A raised riverbank (levee) which allows the river to channel to hold more water.
Ways to reduce flood risk: Embankment POSITIVES
+ Effective, long lifespan, can look natural if covered in vegetation
Ways to reduce flood risk: Embankment NEGATIVES
- Expensive, if concrete is used it is unnatural and unattractive.
Ways to reduce flood risk: Flood Relief Channel EXPLANATION
Hard engineering:
A man-made river channel constructed to divert water in a river channel away from
urban areas.
Ways to reduce flood risk: Flood Relief Channel POSITIVES
+ Effective as regulate river discharge (in heavy rain, relief channels are opened)
Ways to reduce flood risk: Flood Relief Channel NEGATIVES
- Expensive, can cause more flooding downstream
Ways to reduce flood risk: Afforestation EXPLANATION
Soft engineering:
Planting trees to create a woodland/forest
Ways to reduce flood risk: Afforestation NEGATIVES
- Less effective than hard engineering.
Ways to reduce flood risk: Afforestation POSITIVES
+ Trees slow down the movement of water into channels (longer lag time) = less likely to
flood. Water is stored in trees and so less in river channel. Cheap.
Ways to reduce flood risk: Wetlands POSITIVES
+ Cheap, easy to maintain, create habitats, stores water so less in river channel.
Ways to reduce flood risk: Wetlands EXPLANATION
Soft engineering:
Where land next to wetlands is left to flood.
Ways to reduce flood risk: Wetlands NEGATIVES
Short lifespan, constant maintenance, beach is closed due it is being done.
Ways to reduce flood risk: Floodplain zoning EXPLANATION
Soft engineering:
Land is allocated for different uses according to its flood risk. Land closest to the river is
used as parkland and land further from rivers is used for housing and industries.
Ways to reduce flood risk: Floodplain zoning POSITIVES
+ Doesn’t’ stop the flood but reduces overall cost as infrastructure is not destroyed.
Ways to reduce flood risk: Floodplain zoning NEGATIVES
- Flood is not stopped, is difficult to if the land has already been built on.
Ways to reduce flood risk: River restoration EXPLANATION
Soft engineering:
Ways to reduce flood risk: River restoration POSITIVES
+ Cheap, easy to maintain, creates habitats, natural.
Ways to reduce flood risk: River restoration NEGATIVES
- Flooding still occurs, less effective.
Ways to reduce flood risk: Planning and preparation EXPLANATION
Soft engineering:
Rivers are monitored to measure flood risk using satellites, instruments and computer
models. The Environmental Agency issue alarms if a flood will happen.
Soft engineering explanation
Soft engineering – using natural, environmentally friendly methods to prevent erosion.
It aims to reduce and slow down the transfer of water to the river channel to help
prevent flooding.
Ways to reduce flood risk: Planning and preparation NEGATIVES
- Flood still occurs, house prices can drop if deemed ‘at risk’
Ways to reduce flood risk: Planning and preparation POSITIVES
+ People can prepare – sandbags around home, move valuable upstairs, evacuate
Soft engineering positives
+ Often cheaper than hard engineering
Soft engineering negatives
need more maintaining and have a shorter lifespan
Hard engineering explanation
Hard engineering – using manmade, artificial structures to prevent erosion.
Hard engineering positives
+ More effective, long lasting and need less maintaining than soft engineering,
Hard engineering negatives
- however more expensive and less natural/environmentally friendly.
River Severn location
The River Severn begins in the
Cambrian mountains of Wales
and runs first east and then
south into England through
Shropshire, Worcestershire
and Gloucestershire
River Severn source
610 m above sea level at Plynlimon, in Cambrian Mountains of mid Wales.
River Severn mouth location
Severn Estuary/Bristol channel
Length of the Severn river
354km - UK’s longest river
Upper course features of the Severn river
Waterfall -
Middle course features of the Severn river
Meanders
About the Severn river estuary
The River Severn enters the sea at the Bristol
Channel. It forms a huge estuary ‐ about
3.2 km wide at Aust and 14 km wide
between Cardiff and Weston‐super‐Mare.
It has a massive tidal range of 15km
Deposition here had created extensive
mudflats as river and sea water mix and
velocity of the river is reduced
What is the river management example?
Jubilee river flood relief channel
Why was the Jubilee river built?
- The area is low-lying and contains the royal
settlement of Windsor, which attracts international
tourists. Impermeable surfaces from urban growth
have led to high flood risk. - Constructed to reduce the risk of flooding in
Windsor and Eton by diverting water from the River
Thames.
Characteristics of the Jubilee river
- Funded by the Environment Agency at a cost of £110
million. - 11.7km long and 50m wide. UK’s largest artificial
channel. - Designed to look like a natural river with meanders
and shallow reed beds. - It has five weirs (small dams) along its course.
Social issues with the jubilee river
- The overflow discharge re-enters the
Thames when the Jubilee River re-joins it
(see image right). This actually increases the
flood risk downstream at Old Windsor. This
led to severe flooding in 2014 just to protect
Windsor and Eton.
Economic issues with the Jubilee river
- Maintaining the channel is very expensive. In
2003, only a year after the channel was
opened, the weirs (see images right and
below right) were damaged by floods. - The Environment Agency have projected the
final bill of the channel to reach £330
million. Three more relief channels were
planned but can no longer be funded. - Loss of business in flood events. Business
repair costs in downstream Wraysbury alone
cost £500 million in 2014.
Environmental issues with the jubilee river
- Fields downstream were flooded in 2014,
causing damage to crops and wildlife
habitats. - The concrete weirs are ugly and disruptive
to wildlife. - Algae grows rapidly behind the weirs, which
can lead to waters in the channel becoming
hypoxic (no oxygen).
