3.1.3.3 River landscapes in the UK Flashcards
What is transpiration?
Tree roots absorb water and evaporate it out
What is precipitation?
Water falling to earth (snow, rain, sleet, hail)
What is infiltration?
Water penetrating ground after it has landed
What is percolation?
Water going from soil to rock underground
What is interception?
When the water lands on vegetation
What is surface run-off?
Water flowing over the surface towards river
What does the long profile of a river show?
Shows you gradient (steepness) changes over different courses
What does the cross profile of a river show?
Shows cross-section of river
What is the main process in the upper course of a river?
Erosion (wear landscape down)
What is the gradient in the upper course of a river?
Steep
What is the shape of the valley in the upper course of a river?
V-shaped valley
What is the channel like in the upper course of a river?
Shallow and narrow
What is the upper course of a river closest to?
The source of the river
What is the main process in the middle course of a river?
Transport (material)
What is the gradient in the middle course of a river?
Medium
What is the shape of the valley in the middle course of a river?
Gently sloping valley sides
What is the channel like in the middle course of a river?
Deeper and wider channel
What is the main process in the lower course of a river?
Deposition
What is the gradient in the lower course of a river?
Gentle
What is the shape of the valley in the lower course of a river?
Almost flat valley
What is the channel like in the lower course of a river?
Very wide and deep
What is the lower course of a river closest to?
The mouth of the river
What can change the cross profile of a river?
Vertical & Lateral Erosion
What does vertical erosion do to a river valley?
Deepens river valley (and channel) = makes it V-shaped
Where is vertical erosion most dominant in a river?
Upper course
Describe the process of vertical erosion
High turbulence causes rough, angular particles to be scraped along river bed = intense downwards erosion
What does lateral erosion do to a river valley?
Widens river valley (and channel) during formation of meanders
Where is lateral erosion most dominant in a river?
Middle and lower courses
Name the 4 processes of erosion
- Hydraulic action
- Abrasion
- Attrition
- Solution
What is hydraulic action?
Force of water breaks rock particles away from river channel
What is abrasion?
Eroded rocks (river’s load) scrape and rub against channel, wearing it away
What is attrition?
Eroded rock (river’s load) smash into each other and break into smaller fragments
What is solution (erosion wise)?
River water dissolves some types of rock (e.g. Chalk &
Limestone)
How does most erosion occur?
By abrasion
What happens to material the further it travels along the river?
Gets more eroded and the edges get rounded off as
rubbed together
What causes the particle size to decrease between river’s source and mouth?
Attrition
What is transportation?
Transportation is the movement of eroded material
Name the 4 methods of transportation?
- Traction
- Saltation
- Suspension
- Solution
What is traction?
Large particles like boulders are pushed along river bed by force of water
What is saltation?
Pebble-sized particles are bounced along river bed by force of water
What is suspension?
Small particles (slit & clay) are carried along by water
What is solution (transportation wise)?
Soluble materials dissolve in water and are carried along
What is deposition?
When river drops eroded material it’s transporting
When does deposition occur in a river?
Happens when river slows down (loses velocity)
Name 4 reasons why a river slows down and deposits material
- Volume in water (in river) falls
- Amount of eroded material in water increases
- Water is shallower e.g. On inside of bend
- River reaches mouth
Where are waterfalls and gorges are found in a river?
Upper Course
What process causes waterfalls and gorges to form?
Erosion
Where do waterfalls form?
Where river flows over hard rock followed by softer rock
Describe how a waterfall and gorge is formed
- Softer rock is eroded (by hydraulic action and abrasion) more than hard rock → creates ‘step’ in river
- (Steep drop created = waterfall)
- Hard rock is undercut by erosion → becomes unsupported and collapses
- Collapsed rocks are swirled around foot of waterfall → erode soft rock by abrasion → creates plunge pool
- More undercutting causes more collapses → waterfall will retreat leaving steeped gorge
What processes causes meanders to form?
Erosion and Deposition
Where do rivers develop larger bends (meanders)?
In their middle and lower courses → where there’s both shallow and deep sections in channel
Describe how a meander is formed
- Current is faster on outside of bend because river channel is deeper → less friction to slow down water
- More erosion takes place on outside of bend = forming river cliffs
- Current is slower on inside bend because river channel is shallower → more friction to slow down water
- Eroded material is deposited on inside bend = forming slip-off slopes
What types of erosion mainly take place on the outside bend of meander?
Abrasion & hydraulic action
What happens to a meander as it gets larger over time?
Turns into an ox-bow lake
How are ox-bow lakes formed?
- Erosion causes outside bends to get closer until there’s only a small bit of land left between the bend (called the neck)
- The river breaks through this land, usually during a flood, and the river flows along the shortest course
- Deposition eventually cuts off meander forming an ox-box lake
Explain why some rivers wind around interlocking spurs
- In upper course of river most of erosion is vertically downwards (creates steep-sided, V-shaped valleys)
- Rivers aren’t powerful enough to erode laterally (sideways) ∴ have to wind around the high hillsides that stick out their paths on either side
- Hillsides that interlock with each other as river winds around them are called interlocking spurs
Name 3 landforms that are formed in the lower course of a river due to deposition
- Flood plains
- Estuaries
- Levees
What are flood plains?
Is wide valley floor on either side of river which gets flooded (occasionally)
How can flood plains be built up (mention 2 ways)?
- When river floods on flood plain → water slows down and deposits eroded material that it’s transporting → builds up flood pain (makes it higher)
- Deposition that happens on slip-off slopes of meanders also builds up flood plain
How can a flood plain be made wider?
Meanders migrate across flood plain making it wider
What happens to the valley when meanders migrate downstream?
They flatten out the valley floor
What are estuaries?
Tidal areas found at mouth of a river, where it meets the sea
What does it mean if water is tidal?
River level rises and falls each day
How roughly are estuaries formed?
- Water floods over banks of river carrying silt and sand onto valley floor
- As tide reaches its highest point, water is moving very slowly so sediment is deposited
- Over time, more and more mud builds up, creating large mudflats e.g. the Severn estuary
What happens when the tide is low on a estuary?
The wide, muddy banks are exposed
What are levees?
Natural embankments (raised bits) along edges of river channel
How are levees formed?
- During flood, eroded material is deposited over whole flood plain
- Heaviest material is deposited closest to river channel → because it gets dropped first when river slows down
- Over time, deposited material builds up → creating levees along edge of channel
When does flooding happen?
When level of river gets so high it spills over its banks
What happens a river floods?
River level increases = discharge increases (high discharge = more water in channel)
What is river discharge?
The volume of water that flows in a river per second
What is river discharge measured in?
Cumecs - cubic meters per second (m^3/s)
What do hydrographs show?
Show how the discharge at a certain point in a river changes over time in relation to rainfall
What is peak discharge?
The highest discharge in the period of time you’re looking at
What is lag time?
The delay between peak rainfall and peak discharge?
What is rising limb?
The increase in river discharge as rainwater flows into the river
What is falling limb?
The decrease in river discharge as the river returns to its normal level
Why does lag time happen?
Because most rainwater doesn’t land directly in the river channel - there’s a decay as rainwater gets to the channel
How does rainwater get to the river channel (name 3 ways)?
- By flowing quickly overland (called surface run-off or just runoff)
- By soaking into the ground (called infiltration)
- By flowing slowly underground
Name 3 physical factors that can increase discharge and cause flooding
- Prolonged & heavy rainfall
- Geology (rock type)
- Relief (change in height of the land)
Name 2 human factors that can increase discharge and cause flooding
- Building on land e.g with concrete
- Removing trees
How can prolonged & heavy rainfall cause flooding?
Long period of rain = soil becomes saturated → further rainfall can’t infiltrate = increases runoff into rivers → increases discharge quickly = flooding more likely
How can geology cause flooding?
Clay soils and some rocks (e.g. Granite, shale) are impermeable (don’t allow infiltration)
→ discharge increases quickly = cause flooding
How can the relief cause flooding?
If river in steep-sided valley = water will reach river much faster → because water flows more quickly on steeper slopes
→ Discharge increases rapidly = increase flood risk
How can building on land cause flooding?
- Buildings made from impermeable materials (e.g. Concrete) + are surrounded by roads made from tarmac (impermeable)
- Impermeable surfaces increase runoff + drains quickly take runoff to rivers → discharge increases quickly = greater risk of flooding
How can removing trees cause flooding?
- Trees intercept rainwater on their leaves, then evaporates & also take up water from ground and store it
- Cutting them down increases volume of water that reaches river → increases discharge = makes flooding more likely
What is the aim of hard engineering strategies?
To reduce risk of flooding occurring
What are hard engineering strategies?
Man-made structures built to control flow of rivers and reducing flooding
Name 4 examples of hard engineering
- Dams and Reservoirs
- Channel Straightening
- Embankments
- Flood Relief Channels
What are dams and reservoirs and where they located?
- Dams (huge walls) are built across rivers - usually in upper course
- Reservoir (artificial lake) formed behind the dam
What do dams and reservoirs aim to do?
Reduce discharge
Name 2 benefits of using dams and reservoir
- Reservoirs store water (especially during prolonged/heavy rain) = reducing risk of flooding
- Water in reservoir can be used as drinking water + generate hydroelectric power
Name 3 disadvantages of using dams and reservoir
- Dams are very expensive
- Creating reservoir can flood existing settlements
- Eroded material is deposited in reservoir and not along river’s natural course = farmland can become less fertile
What is channel straightening?
River’s course is straightened - meanders are cut out by building artificial straight channels
What is the aim of channel straightening?
To increase velocity
Name a benefit of straightening a channel
Water moves out of area more quickly (doesn’t have to travel as far) = reducing flooding
Name 2 disadvantages of straightening a channel
- Flooding may happened downstream - as water is carried there faster
- More erosion downstream = water’s flowing faster
What are embankments?
Raised walls built along river banks
Name a benefit of using embankments
River can hold more water = flood less frequently → protecting buildings on flood plain
Name 2 disadvantages of using embankments
- Quite expensive
- Risk of severe flooding if water rises about level of embankments OR if they break
What is the aim of using embankments?
To increase the capacity
What are flood relief channels?
Channels built that divert water around important areas OR take it elsewhere if river’s water level get too high
What is the aim of flood relief channels?
To reduce discharge
Name 2 benefits of using flood relief channels
- Flooding prevented because river discharge is reduced
- Gates on flood relief channels → release of water can be controlled
Name 2 disadvantages of using flood relief channels
- Increased discharge where relief channels rejoins river/joins another river = cause flooding
- Water level gets too high for relief channels = could flood
What is the aim of soft engineering strategies?
To reduce effects of flooding
What is soft engineering?
Scheme set up using knowledge of rivers and its processes to reduce effects of flooding
Name 5 soft engineering strategies
- Flood warnings
- Preparation
- Flood plain zoning
- River restoration
- Planting trees
What are flood warnings?
Environmental Agency warns people about possible floods through TV, radios, newspapers, internet
Name a benefit of using flood warnings
Impact of flooding is reduced → warnings give time to move possessions upstairs + put sandbags in position and to evacuate
Name 2 disadvantages of using flood warnings
- Warning don’t stop a flood
- People may not hear/have access to warnings
What is preparation? Give 2 examples
- Plans made (what do in flood) like keep items (torches and blankets in handy place)
- Buildings are modified to reduce damage from flooding
Name 2 benefits of preparing for a flood
- Impact of flooding is reduced = buildings less damaged + people know what to do
- People less likely to worry about threat of floods
Name 2 disadvantages of preparing for a flood
- Expensive to modify buildings
- Doesn’t guarantee safety from flood + give people false sense of security
What is flood plain zoning?
Restrictions prevent building on areas (of flood plain) that’s likely to flood
Name 2 benefits of using flood plain zoning
- Impact of flooding is reduced → no damage to buildings
- Risk of flooding is reduced → impermeable surfaces aren’t created (e.g. Buildings)
Name 2 disadvantages of using flood plain zoning
- Expansion of an urban area is limited if there aren’t other suitable building sites
- It’s no help areas that have already been built on
What is river restoration?
Making river more natural e.g. Removing man-made levees so flood plain can flood naturally
Name 2 benefits of using river restoration
- Less risk of flooding downstream - discharged is reduced
- Little maintenance needed as river is left its natural sate + better habitats for wildlife
Name a disadvantage of using river restoration
Local flood risk can increase, especially if nothing’s done to prevent major flooding
Explain how planting trees can help reduce the effects of flooding
Planting trees in river valley = increases interception of rainwater + increase lag time
Name 2 benefits of planting trees
- Discharge and flood risk are reduced
- Vegetation reduces soil erosion + provides habitats for wildlife
Name a disadvantage of planting trees
Less land available for farming
