River landscapes in the uk

course

the path of a river as it flows downhill

describe the course of a river

• A steep upper course

• A gently sloping middle course

• An almost flat lower course

what does the long profile of a river show

how the gradient changes

what do rivers form as they flow downhill

Channels and valleys

Upper course of a river:

• steep gradient

• V shaped valley

• Narrow, shallow channel

• Steep sides

middle course of a river:

• medium gradient

• Gently sloping valley sides

• Wider, deeper channel

lower course of a river:

• gentle gradient

• Very wide, almost flat valley

• Very wide, very deep channel

Source of a river

Where the river begins

Mouth of a river

where the river flows into a larger body of water

Vertical erosion

• deepens the river valley and channel making it v - shaped

• Dominant in the upper course of a river

• High turbulence causes the rough, angular particles to be scraped along the river bed - causes intense downward motion

lateral erosion

• widens the river valley and channel during the formation of meanders

• Dominant in the middle and lower courses of the river

hydraulic action

the force of the river water colliding with rocks breaks rock particles away from the river channel

abrasion

eroded rocks picked up by the river, scrape and rub against the channel - wearing it away

attrition

eroded rocks picked up by the river crash into one another and break into smaller pieces

Solution

river water dissolves some types of rock - e.g. chalk and limestone

In what course is erosion dominant in

Upper course

transportation

the movement of eroded material

what does how material is eroded depend on

velocity of the water, size of particles

Traction

Large particles like borders are pushed along the river bed by the force of the water

suspension

small particles like silt and clay are carried along by the water

Saltation

pebble sized particles are bounced along the river bed by the force of the water

solution

Soluble materials e.g. limestone dissolve in the water and are carried along

deposition

when the river drops a material its transporting

when does deposition occur

when the river loses its velocity and energy

reasons why rivers slow down and drop material

• the volume of the water falls

• The amount of eroded material increases

• The water is shallower e.g.the inside of a bend

• The river reaches its mouth

where are waterfalls and gorges found?

in the upper course of a river

how are waterfalls and gorges formed?

• A layer of hard rock and soft rock are together

• Water erodes the soft rock by hydraulic action because it is less resistant

• The water makes a plunge pool and an undercut is formed

• The hard rock is no longer supported by the soft rock eventually collapsing

• ( gorge ) - the waterfall retreats overtime and a gorge is formed

Interlocking spurs

hillsides that interlock with each other ( like a zigzag if you looked from above) as the river winds around them

how are interlocking spurs formed

• Vertical erosion deepens the river channel

• Water can’t cut through hard rock because it is too resistant so it winds around the hills

how are meanders formed?

• the current is faster on the outside of the bend because the river channel is less deeper - less friction to slow the water down

• More erosion takes place (via abrasion and hydraulic action) on the outside bend, forming river cliffs

• The current is slower on the inside of the bend because the river channel is shallower - there’s more friction

• Eroded material is deposited on the inside of the bend forming slip off slopes

aerial view of a meander

Cross section of a meander

How are ox bow lakes formed?

• erosion causes the outside bends to get closer until theres only a small bit of land left - the neck

• The river breaks through the neck - usually during a flood

• The river flows along the shortest route

• Deposition cuts off the meander

• An oxbow lake is formed

River that flooded in the Banbury flooding:

River Cherwell

date of Banbury flooding

Easter 1998

cost of damages of Banbury flooding

£12.5 million

lives lost in Banbury flooding

0

people forced to evacuate in Banbury flooding

350

What have the government done to manage the risk of flooding?

• roads have been built higher up - so flooding wont disrupt traffic

• Embankments and flood walls have been constructed outside businesses and houses of importance

• A pumping station to pump any flood water out of the town

• Flood water storage - gates can be closed if weather reports show a risk of high rainfall, water will be gradually released downstream to avoid sudden flooding

social effects from the flooding

• uninsured houses are at risk because homeowners lose everything and must pay for repairs themselves

Environmental effects from the flooding

• During construction of the flood water storage, heavy machinery damaged the nearby vegetation

• Soil was removed from areas surrounding Banbury to make enbankments - disrupts habitats and wildlife

• (Positive) New biodiversity plan increases vegetation to reduce risk of flooding - will improve the environment

economic effects from the flooding

• construction work cost £18.5 million

• Construction jobs were created in the process, as well as some jobs to maintain biodiversity plan

• Storage scheme has saved £100 million in avoiding damages

river discharge

volume of water flowing in a river per second - measured in cumecs (cubic metres per second - m³/s)

What do hydrographs show

how the discharge at a certain point in a river changes over time in relation to rainfall

• peak discharge : the highest discharge in the period of time you’re looking at

• Lag time : the delay between peak rainfall and peak discharge

• Rising limb : increase in river discharge as rainwater flows into the river

• Falling limb : decrease in river discharge as the river returns to its normal level

how does heavy rainfall affect flood risk

Heavy water means that the water arrives too quickly to infiltrate - a lot of surface runoff which increases discharge

how does rock type affect flood risk?

clay soils and some rocks e.g. granite is impermeable - surface runoff is increasd

How does prolonged rainfall affect flood risk

prolonged rainfall can’t saturate the soil - further rainfall can’t saturate, runoff is increased

how does relief (changes in land height) affect flood risk

• if a river is in a steep sided valley water will reach the river channel quicker because it will travel down the steeper slopes faster - rapidly increases discharge

Engineering

reduce the risk of flooding or its effects

hard engineering

Man made structures built to control the flow of rivers and reduce flooding

Dams and reservoirs

• dams are barriers built across the river - usually in the upper course

• A reservoir (Artificial lake) is formed behind the dam

benefits of dams and reservoirs

• reservoirs store water (e.g. after heavy rain), control water flow, and prevent floods downstream

• Can be used to generate hydroelectric power

Disadvantages of dams and reservoirs

• very expensive

• Can flood existing settlements

• Material is deposited in the reservoir - farmland downstream can become less fertile

channel straightening

meanders are removed by building straighter, artificial channels

benefits of channel straightening

• water leaves the area faster rather than building up so flood risk is lower

disadvantages of channel straightening

• Flooding may happen downstream instead

• Faster moving water may cause more erosion downstream

Embankments

Raised walls are built along river banks

Benefits of embankments

river can hold more water - floods are less frequent

disadvantages of embankments

• expensive

• Risk of severe flooding if water rises above level of embankments or if they break

Flood relief channels

channels are built to divert water around built up areas e.g infrastructure or to divert excess water from a river if the levels get too high

benefits of flood relief channels

gates on the channels mean that the release of water can be controlled - reduces flood risk

disadvantages of flood relief channels

• increases discharge where the relief channels rejoins the river or another river - will cause flooding

soft engineering

schemes set up using knowledge of a river and its processes to reduce the effects of flooding

flood warnings and preparation

• Environmental agency issues flood warnings through media

• Buildings are modified to minimise flood damage

• Residents can prepare sandbags and flood boards prior to floods

advantages of flood warnings and preparation

• warnings give people time to move possessions or evacuate - reduces the impact of flooding

disadvantages of flood warning and preparation

• doesnt prevent floods

• Some people may not have access to the warnings

• Modifying buildings is expensive

• Doesn’t guarantee safety from a flood

Flood plain zoning

restrictions prevent buildings on a parts of a flood plain that are likely to be affected by a flood

Advantages of flood plain zoning

• flood risk is reduced - fewer impermeable surfaces are created

• impact of floodings are reduces - no buildings at risk of damage

Disadvantages of flood plain zoning

• cant help in an area with existing buildings

Planting trees

increases interception of rain water (and lag time)

adv of planting trees

• discharge and flood risk decrease

• vegetation reduces soil erosion in the valley

• provides better habitats for wildlife

Disadvantages of planting trees

• less land is available for farming

river restoration

making the rive rmore natural - e.g. removing man made levees so that the flood plain can flood naturally

adv of river restoration

• discharge is reduced - less risk of flooding downstream

• little maintenance needed

• better habitats for wildlife

disadvantages of river restoration

local flood risk can increase