River Landscapes in the UK Section C (P1) Flashcards
This is one of the optional topics for 'Physical landscapes of the UK' topic. You have a choice between two of glacial landscapes, coastal landscapes or river landscapes. If you are unsure, ask your class teacher.
Define ‘long profile’?
The change in the gradient of the river course from the upper course to the lower course.
What is a ‘cross profile’?
A cross section of the river - this shows a ‘slice’ of the river valley and channel
What is a V-Shaped valley?
A valley with steep sides and a narrow bottom that has been formed by erosion
What is a tributary?
A smaller river or stream flowing into a larger river
What is a confluence?
The point where two rivers meet
Define ‘load’
The amount of material carried by a river
What is ‘sediment’?
Material such as sand and clay that is carried by a river
What are the characteristics of the upper course of a river?
- Steep gradient
- Narrow v-shaped valley
- Narrow/shallow river
- Large angular sediment load
- Mostly erosion taking place
What are the characteristics of the middle course of a river?
- Shallower gradient
- Asymmetrical valley cross section
- Deeper river
- Smaller/rounded load
- Balance between erosion and transportation taking place
What are the characteristics of the lower course of a river?
- Very low gradient
- U-shaped valley
- Wide/deep river
- Small suspended load
- Mostly deposition taking place
Define ‘erosion’?
The wearing away of rock by the natural processes of rivers, ice, wind and sea
Name the 4 processes of river erosion
- Abrasion
- Attrition
- Hydraulic Action
- Solution
Define ‘hydraulic action’
Fast flowing water pushes air into cracks and the force of this causes the banks to break up over time
Define ‘abrasion’
Sand and pebbles are dragged along the river bed, wearing it away
Define ‘attrition’
Rocks and stones wear each other away as they knock together
Define ‘solution’ (erosion)
Rocks such as limestone are dissolved in acid rainwater
Define ‘transportation’?
The movement of eroded material by natural processes such as wind, rivers and sea
Name the 4 processes of river transportation
- Traction
- Saltation
- Suspension
- Solution
Define ‘traction’
Big boulders and stones are rolled and dragged along the river bed
Define ‘saltation’
Stones and pebbles bounce along the river bed
Define ‘suspension’
Smaller particles and stones (e.g. sand and silt) are carried along in the rivers flow.
Define ‘solution’
Some material is dissolved into the river water and transported this way
What does ‘deposition’ mean?
When a river drops the sediment that it is carrying
Why will a river deposit its load?
- Drier weather (less water so less energy)
- River slows in speed (less speed so less energy e.g. inside bend of a river)
- River floods (water onto the flood plain and deposits layers fine silt and clay [this is known as alluvium] which is fertile and good for farming)
Name the river landforms formed by erosion
- Waterfalls
- Gorges
- Interlocking spurs
Name the river landforms formed by erosion and deposition
- Meanders
- Ox-bow lakes
Name landforms created by deposition
- Floodplains
- Levees
Name the landforms found in the upper course of a river valley
- Waterfalls
- Gorges
- Interlocking Spurs
- Rapids
What is a waterfall?
A vertical fall of water where the course of a river is interrupted by a steep drop in the land it is flowing over
How does a waterfall form?
- Water flows over harder rock followed by softer rock
- The softer rock underneath the harder rock will erode over time (hydraulic action and abrasion) creating a step in the river
- The hard rock is undercut by erosion.
- Eventually the hard rock will collapse as it is now unsupported creating a deep plunge pool.
- The process will continue over time creating a steep sided gorge
What is a gorge?
A steep-sided cut through the landscape formed over thousands of years by a retreating waterfall
What is a plunge pool?
The area of deep water at the bottom of a waterfall, formed by hydraulic action and the grinding of rocks and pebbles
What are ‘interlocking spurs’?
Interlocking’ hillsides that look like a ‘zip’ formation.
How are interlocking spurs formed?
In the upper course, rivers aren’t powerful enough to erode laterally, so they wind around the hillsides creating a zig-zag shaped flow.
Name the landforms found in the middle course of the river
- Meanders
- Ox-bow lakes
Define ‘helical flow’?
The corkscrew pattern of flow found in a river
What is the thalweg?
The line of fastest flow in a river
What is a meander?
A pronounced bend in a river
What is an ox-bow lake?
A horse-shoe shaped lake shaped that is formed when a river bend is cut off from the main river and becomes isolated
Explain how an ox-bow lake forms
- The fastest flow of water is on the outside bend of the river
- This results in erosion. The outside bends move closer together as the meander neck becomes narrower.
- When there is a very high discharge, the river cuts across the neck and takes a straight course. The former meander is left as a horseshoe shaped ox-bow lake.
Name the landforms found in the lower course of a river valley?
- Wide floodplain
- Levees
- Deltas
- Estuaries
What is a floodplain?
A flat area either side of a river which floods when the river overflows
What are mudflats?
Flat coastal areas formed when mud is deposited by rivers and coasts
What is a levée?
River embankments found along the river banks
How is a levée formed?
- The river channels get shallower during low flow conditions, causing deposition on the river bed.
- This means that the river cannot hold as much water as before as the river bed has risen.
- During a flood, sediment is deposited on the river banks; depositing coarser (heavier) sediment nearer to the river and finer sediment further away.
Define ‘river discharge’
The amount of water flowing in a river at any one point
List the factors affecting river discharge?
- Rock and soil type
- Land use
- Rainfall
- Weather conditions
- Relief
How can you recognise the upper course of a river on an OS map?
- Contour lines are close together
- River crosses lots of contour lines
- Narrow river (thin blue line)
- Spot heights are high numbers
How can you recognise the lower course of a river on an OS map?
- Limited contours or very wide contours (land is flat)
- Wide river that is meandering
- Spot heights are low numbers
Name an example of a river valley in the UK
River Severn
How can you recognise a V-shaped valley on an OS map?
V-shaped contours point uphill and river crosses the middle of the V-shaped contours
Where is the River Severn?
In the North West of Wales
Where is the mouth of the River Severn?
Bristol channel, western super mare
Where is the source of the River Severn?
Plynlimon Hills
Name 4 physical causes of flooding?
- Heavy/Prolonged precipitation
- Snowmelt
- Relief (steep slopes)
- Geology
Name 3 human causes of flooding?
- Urbanisation
- Deforestation
- Agriculture
What is a hydrograph?
A graph showing how a river responds to a storm, showing the rainfall and discharge over time
What is a ‘flashy’ hydrograph?
A hydrograph with a short lag time and a high peak discharge
What is a ‘flat’ hydrograph?
A hydrograph with a long lag time and a low peak discharge
How is river discharge measured?
Cubic metres per second (cumecs)
Which factors influence the shape of a flood hydrograph?
- Basin size
- Drainage density
- Rock type
- Land use
- Relief
- Rainfall intensity
What is ‘lag time’?
The time between peak rainfall and peak discharge on a hydrograph
What is antecedent rainfall?
The amount of rain that has already fallen prior to a specific event
Define ‘interception’
Leaves and tree branches catch rainfall and prevent it from running into the river
Define ‘infiltration’
Rain that soaks into the top layers of the soil and rock below
What is impermeable rock?
Rock which water is not able to flow through
What is permeable rock?
Rock which water is able to flow through
Define surface run off?
Water runs over the top of ground which is very hard (i.e. baked soil or concrete) or very wet (saturated) ground.
Surface run off occurs when no water can infiltrate into the ground.
What is hard engineering?
Building structures to deal with natural hazards, such as dams to prevent flooding
Name a range of hard engineering stategies used to manage river flooding?
- Reservoirs and dams
- Channel straightening
- Embankments
- Flood relief channels
What is soft engineering?
Soft engineering involves adapting to natural hazards and working with nature to limit damage. For example, planting trees to limit flood risk.
Name a range of soft engineering strategies used to manage river flooding?
- Afforestation
- Land use zoning
- River restoration
- Wetland restoration
- Flood warnings
How do dams regulate water flow?
During periods of high rainfall, water is stored in the dam.
Water is released when rainfall is low.
Why is building dams controversial?
- They are very expensive
- Land is flooded to create the reservoir
- People are relocated to make way for the dam
What are the benefits of dams?
- They are multi purpose - so they can be used to generate HEP as well as manage river flow.
- They are affective holding back water in times of potential flood
- They are long lasting
Most dam schemes are multi-purpose. What are their main functions?
- Flood prevention
- Irrigation
- Water supply
- Hydro-electric power generation
- Recreation e.g. sailing
What is channel straightening?
Cutting through meanders to create a straight channel to speed up water flow
What are the advantages of channel straightening?
It moves water out of an area quickly as water passes through a straight channel quicker than a meandering channel.
Why is channel straightening problematic?
It may increase the risk of flooding further downstream
What are river embankments?
Raised riverbanks which allow the river channel to hold more water and prevent flooding
What are the advantages of river embankments?
Embankments increase the volume of water that the river can hold, reducing the risk of flooding.
What are the problems with embankments?
Not always effective. Water can rise above the embankments, causing flooding.
What are flood relief channels?
A man-made river channel constructed to by-pass an urban area
What are the benefits of flood relief channels?
River discharge can be controlled by using gates to control water levels.
What are the disadvantages of flood relief channels?
Increased levels of flooding could occur where the diverted water re-enters the river.
How does floodplain zoning work?
- It restricts different land uses to certain locations on the floodplain.
- Expensive/important landuses are placed further away from the river e.g. housing and industry
- Low value uses are placed close to the river e.g. pasture and parkland.
What are the advantages of flood plain zoning?
Consideration into the landuse around the river is taken which means concrete surfaces are not used, reducing impermeable surfaces close to river. Less damage occurs as important facilities are located futher away.
What are the disadvantages of flood plain zoning?
It limits the uses of land closes to a river.
It is almost impossible to use flood plain zoning on land that has already been built on.
What is river restoration?
Making the river more natural. For example:
- When rivers have previously been artificially starightened they are returned to their original course.
- Removing levees so that the river floods naturally
The purpose of this is to prevent flooding further downstream.
What are the benefits of river restoration?
- Less risk of flooding downstream
- Limited maintenance needed
- Creates habitats for birds
What are the problems with river restoration?
- Flooding can increase
- Major floods are more likely unless planning takes place.
How does afforestation help manage river flooding?
Planting trees to intercept and absorb water reduces surface run off.
Who issues flood warnings in England and Wales?
The Environment Agency
What are the 3 levels of flood warnings?
- Flood Watch
- Flood Warning
- Severe Flood Warning
What would people be encouraged to do by the Environment Agency to prepare for a flood?
- Plan what to do eg. move possessions upstairs
- Use flood gates to prevent water entering their property
- Use sandbags to keep floodwater away from buildings
Name a example of a flood management scheme in the UK
Banbury on the river Cherwell
Why does the town of Banbury need a flood management scheme?
the town was destroyed in 1998 and has been flooded again since.
caused £12.5 million in damage
350 people forced to evacuate however no one died.
What was done to manage flooding in Banbury?
- Road A361 has been raised - prevents floods from disrupting traffic
- Afforestation in local towns near to the river and the storage sights - this increases the intake of water through infiltration to reduce the risk of flash flooding.
- Improved existing flood defences - embankments and flood walls have been constructed near areas or importance.
- Flood water storage and gates set up - can hold up to 1200 Olympic size swimming pools of water and the gates can closed if high rainfall is forecast to prevent flash flooding.
- A pumping station has been built - this pumps any flood water away from the town.
Describe the social issues (+ and -) arising from the Banbury flood management scheme
+ Local people less worried about the risk.
+ new foot paths and parks to improve QoL
+ reduced traffic disruption
Describe the economic issues (+ and -) arising from the Banbury flood management scheme
-/+ 441 houses and 73 commercial properties are protected.
-/+ property value increase due to the decrease in risk.
- Cost of the scheme was £18.5million
- Frontier park, an industrial estate, may still flood.
Describe the environmental issues (+ and -) arising from the Morpeth flood management scheme
+ The Biodiversity Action Plan (BAP) has resulted in planting trees and hedgerows and constructing ponds.
+ The reservoir provides a temporary habitat for waterbirds.
+ Part of the floodplain will be left to flood if river levels get too high.
- The concrete apertures are unnatural in the landscape.
- Around 100,000 tonnes of earth were required to make the embankment resulting in some habitat destruction.
