Rivers - Physical Flashcards
What places is the UK made up of?
England, scotland, nothern ireland, and wales
What is the highest mountain in the UK?
Ben Nevis, in the Grampian Mountain Range, at 1344metres high
What is relief?
The height, shape and steepness of land. The relief of an area is determined by its geology.
What is a drainage basin?
An area of land drained by a river, and its tributaries
What does long profile show?
A line showing the course of a the river from its source to its mouth where it ends, and the changes in height along its course
What is the upper course like in a Long profile diagram?
- Its gradient is steep
- V-shaped valley, steep sides,
- Narrow and shallow channel
What is the middle course like in a Long profile diagram?
- Its gradient is medium
- Gentle sloping valley sides
- Wider and deeper channel
What is the lower course like in a Long profile diagram?
- Its gradient is gentle
- Very wide almost flat valley
- Very wide and deep channel
What does a cross profile diagram show?
Represents what it would be like to walk from one side of the valley, across the channel and up the other side
What are the characteristics of a channel upstream?
- Shallow water
- Low velocity
- Low discharge
- Large bedload
- Hugh turbulence
What are the characteristics of a channel downstream?
- Deep water
- High velocity
- High discharge
- Small bedload
- Low turbulence
What is veritcal erosion?
It deepens the river channel and valley making it v-shaped. Its dominant in the upper course and movs in a downwards action
What is lateral erosion?
Widens the river valley and channel, it is dominant in the middle and lower course and moves in a sideways action
What is Hydraulic action?
The sheer force of the water breaking rock particles away from the river channel. It is most effective when the water is moving fast
What is Abrasion?
The load that is carried by the river which repeatedly hits the bed or banks dislodging particles into the flow of the river
What is Attrition?
Stones that are carried by the river, they knock into each other repeatedly and gradually become smaller and smoother.
What is Traction?
Large particles are pushed along the river bed by the force of water
What is saltation?
Sand-sized particles are bounced along the river bed in a hopping motion
What is suspension?
small sediment is held in the river
What is solution?
when the river flows over limestone or chalk, the rock is lowly dissolved. this is because it is soluble in mildly acidic water
What is Deposition?
When a river drops the eroded material its transporting.
It happens when a river slows down
What type of material is first depositied? Where is it likely to happen? And why?
- Largest material is deposited first as it is heaviest
- Likely to happen in the upper course
- as larger rocks only transport for a very short distance
Where is finer sediment carried to? Where is it mostly held? where will it be depostited? why will it be deposited there?
- Carried downstream and mostly held in suspension
- It deposits on the bed or banks where velocity is slowed by friction
Where is a large amount of deposition at? What is the terrain like?
At the river mouth where there is a gentle gradient and interaction with tides
What happens to the upper course in the cross profile change downstream?
- The river erodes its bed hydraulic action and abrasion.
- As the river travels downstream it is joined by a number of tributaries
- these increased the volume of water which gives the river energy which means more erosive power.
- this allows it to cut a much deeper channel with increased distance downstream,
What does the channel become downstream in the channel cross profile change for downstream?
- becomes wider as the gradient becomes less steep as there is less vertical erosion
What happens to the middle course in the cross profile change downstream?
Lateral erosion is dominant, this erodes the river banks which makes the channel wider
What happens in the upper course of a VALLEY cross profile change downstream?
There is a steep V-shaped cross profile
- vertical erosion by the river is important,
- creates a slope that weathered material from the valley sides can fall down.
- rivers have their source in upland areas sonthe rock is harder.
- weathering and erosion cannot have much impact and the slopes remain steep.
What happens in the middle course of a VALLEY cross profile change downstream?
- The gradient is less steep, river begins to meander and erode into valley sides
- rate of weathering also increases on the softer rocks.
- the river uses more energy on lateral erosion so not as much weathered material is removed
- this builds up the valley floor to give it a more gentle profile.
What happens in the lower course of a VALLEY cross profile change downstream?
The river is passing through low lying country.
Deposition from floods builds up the flood plain
meanders migrate.
This builds and widens the valley
Why do rivers deposit sediment? (4)
- The volume of water in the river falls
- The amount of eroded material in the water increases
- The water is shallower eg on the inside of the bend
- The river reaches its mouth
What are interlocking spurs? How are they caused? Where are they found?
- They are fingers or projections in the hillsides, that alternate from either side of the valley and project into the valley floor
- They are caused by fluvial erosion
- Found in the upper course
What do interlocking spurs have?
- A steep gradient
- Convex slopes
- Separated by a narrow valley which is taken up the river channel
- Freeze thaw weathering may occur on the slope scree
What is a waterfall?
Its is where water falls down a vertical drop in the channel
How does a waterfall form?
1) . Softer rock is eroded by hydraulic action and abrasion, more than the hard rock creating a ‘steep’ in the river
2) . As water goes over the steep it erodes more and more of the softer rock
3) . A steep drop is eventually created, which is a waterfall.
How are Gorges formed?
1) . The hard rock is eventually undercut by erosion. It becomes unsupported and collapses.
2) . The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by abrasion, this creates a deep plunge pool.
3) . Over time, more undercutting causes more collapses. The waterfall will retreat leaving a steep-sided gorge.
How do Rivers shape the land?
- the river erodes downwards as boulders, stones and rock particles are bounced back and scraped along the channel bed.
- as river cuts down, the steep sides are attacked by weathering. This breaks up and loosens the soil and rock
- the loosended material slowly creaps doen the slope because of gravity and is washed into the river and carried away
- the end result is a steep sided valley that has the shape of a V
What is the formation of a ox bow lake?
1) . Meanders migrate over time across the valley floor, they may start to erode towards each other
2) . Gradually the neck of the meander narrows until it is completely broken through, usually during a flood.
3) . This forms a newer straightner channel, the old meander loops are cut off by deposition to form a ox bow lake
What is a floodplain?
A wide flat area of marshy land on either side of a river and is found in the middle and lower courses
What are the two ways floodplain could be formed?
- meanders could migrate across the floodplain due to lateral erosion, when they reach the edge of a floodplain they erode the valley side which explains why is it wide
- when the river floods it deposits silt, creating a vey flat floodplain
What is a levee?
A raised river bed found alongside a river in its lower course
What is the formation of a levee?
1) . During low flow conditions deposition takes place, raising the river bed and reducing the capacity of the channel
2) . When flooding occurs, water flows over the sides of the channel. The velocity of the river decreases quickly leading to deposition of sediment on river banks.
3) . After many floods the height of the banks can be raised forming levees
What are estuaries? What is the main process that happens in them?
Transitional zones between river and coastal environments and are affected by wave action as well as river processes.
- main river process is deposition
What is flooding?
Where the land is not normally underwater becomed inundated.
When does a river flood occur?
When a river channel can no longer hold the amount of water flowing in it. Water over tops it and floods the adjacent land - the floodplain
How does precipitation effect flooding?
Increase - Steady rainfall over a long period of time can lead to saturated soils and high river levels
How does torrential rain effect flooding?
Increase - Can lead to flash floods
How can geology effect flooding?
Increase - Impermeable rocks such as shales and clay encourage water to flow overland and into river channels.
- this speeds up water flow and makes flooding more likely
How does urbanisation effect flooding?
Increase - Building on impermeable surfaces such as tarmac roads leads to water being transferred quickly to drains and rivers and into river channels
- this rapid movement of water makes flooding more likely
How does deforestation effect flooding?
Increase- Water that falls in trees is stored in leaves and branches as it is good for their growth.
- when trees are removed, water flows more rapidly to the river
How does agriculture effect flooding?
Soil is left unused and exposed for a long period of time, this can lead to more surface run off.
- this is increased if land is ploughed up and down steep slopes as water can flow quicker along furrows.
What is drianage basin density?
Total length of all the streams in the drainage basin ➗ total area of the drainage basin
What can drainage basins store?
Rainwater either in the river channel, in lakes or in the ground. Excess water is carried back to the sea by rivers
What is river discharge?
The volume of water passing a given point in a river at any moment in time. It is measured in cucmecs
How does impermeable rock effect river discharge?
More likely to cause flooding - as it encourages water to flow over and into the channel
How does permeable rock effect river discharge?
Slow flooding down - as the rock has holes in it which will allow water to pass through
How does heavy rainfall effect river discharge?
More likely to increase flooding - Can lead to sudden flash floods as river channels cannot contain the sheer volume of water
How does prolonged rainfall effect river discharge?
Will cause flooding- as the ground will become logged with water and there are no drainage systems to store it
How do low temperatures effecf river discharge?
Will cause flooding - as if it snows then melts the excess water could over flow the rivers
- the ground could also freeze and therefore infiltration can’t occur
How do high temperatures effect river discharge?
Reduce risk of flooding- due to evaporation which means less surface water
However, the land can be hard and dry which would result in water running over ground and into the channel
How does dry weather effect river discharge?
Reduce the risk of flooding - as soil absorbs the water
However it could dry up the land too much and lead to not being able to absorb water
How does wet weather effect river discharge?
Will cause flooding - as saturated soil increase surface run off into river channel
How does gently sloping land effect river discharge?
Cause less flooding - as there is more time for water to infiltrate and go down
However, the water would still go down and could cause a flood at the bottem
How does steep sloping land effect river discharge?
Cause flooding - as water can flow down quicker
How does deforestation effect river discharge?
Cause flooding - when trees are removed much more water is available and transferred to river channels as there is no storage for the water ie leaves
How does afforestation effect river discharge?
Reduce the risk of flooding - as there are more trees to collect the water
How does urbanisation effect river discharge?
Will cause flooding - Building on floodplains allows water to be transferred quickly to drains and then the channel
What are the characteristics of an estuary?
- It may have high tidal range
- It may be very wide
- It will have mudflats that are visible at low tides
- It may have tidal bores - which are huge waves that funnel up the river
Where is Banbury located?
In the Cotswold Hills, about 50km north of oxford.
Much of the town is on the flood plain of the river Cherwell, a tributary of the River Thames
The population is 45,000
Why was a flood management scheme needed in Banbury?
Has a history of flood
- 1998&2007 = devastating flood affects included the railway station submerging, roads closed, more than 150homes and businesses were flooded, £12.5 million damage
What is the first of three features in the Banbury flood storage reservoir?
A 2.9km earth embankment- built parallel to the M40 motorway to create a flood storage area; it holds 3 million cubic meters of water. Reduces flooding
What is the second of three features in the Banbury flood storage reservoir?
The A361 road - the road plus improvements to the drainage basin has helped to prevent flooding
What is the last of three features in the Banbury flood storage reservoir?
Flow control structures- specially designed openings that control the rate of flow downstream towards Banbury.
Any excess water backs up behind filling up the reservoir rather than continuing towards Banbury.
What type of strategy is Dams and Reservoirs? What can they do?
- Hard engineering strategy
- Dams are barriers which trap water in a lake (reservoir). Water can be released in a controlled way.
- they are often multipurpose and can be used for recreation, H.E.P, water supply and flood prevention
What are the issues/costs/benefits of dams and reservoirs?
Issues - often controversial people lose land and may have to move if the valley floods
Costs - very expensive to build
Benefits - can provide renewable energy, store water for when levels are low, effective at controlling water flow eg Elan Valley Dam
What type of engineering is Channel straightening? What does it do?
Hard engineering
- meanders are cut off to form a straight channel which may be lined with concrete
What are the issues/costs/benefits of channel straightening?
Issues - can lead to flooding, it can be unattractive, needs maintaining
Benefits - speeds up water flow to reduce flooding in an area eg River Derwent
What type of engineering is Embankments? What do they do?
Hard engineering
- they are man made levees
What are the issues/costs/benefits of Embankments?
Issues - if made of concrete blocks can make it look unattractive
Benefits - allows river channels to hold up more water eg River Trent
What type of engineering is Flood relief channel? What does it do?
Hard engineering
- a man made river built to bypass an urban area
What are the issues/costs/benefits of a flood relief channel?
Costs - expensive to build
Benefits - during high flow, sluice gate allows water from the river to enter the relief channel to reduce flooding
- can create recreational opportunities
What is flood plain zoning?
- soft engineering
Restricts different land uses to certain locations on the floodplain
What are the issues/costs/benefits of flood plain zoning?
Issues - Difficult to implement, farmers may be inconvenienced
Cost- Doesn’t cost to implement,
Benefits- reduces risk to high value land uses e.g. Hospitals
What is wetland and flood storage areas?
- soft engineering
Fields of grassy areas that are allowed to flood
What are the issues/costs/benefits of wetland and flood storage areas?
Issues- Land cannot be used for anything else
Benefits- Reduces flooding elsewhere, creates wildlife habitat
What is preparation for floods?
- soft engineering
River levels and weather are monitored by the environment agency who issue warnings
What are the issues/costs/benefits of preparation for floods?
Issues/cost - Cost of running Environment agency, insurance may increase and house prices decrease
Benefits- Reduce damage by taking action
Emergency service will also be prepared
What is afforestation?
Tree planting
What are the issues/costs/benefits of tree planting?
Issues- Cost of trees, planting and maintenance
Benefits- Trees intercept rainfall and slows down transfer of water to the river channel
What are the social benefits for people in the banbury scheme?
- Road A362 - will be open during a flood to avoid disrupting people’s lives
- reduced levels of anxiety and depression through fear of flooding
What are the environmental benefits for people in the banbury scheme?
- a new biodiversity action plan habitat has been created with ponds, trees and hedgerows
- part of the floodplain will deliberately allowed to flood if levels are high
what are the economic benefits in the Banbury scheme?
- cost of scheme was about £18.5 million
- donors included environment agency and Cherwell district
where is the river tees?
its an important river in the north east of England. its source is in the pennine hills near cross fell
how has high force waterfall and gorge been formed
- its located close to forest in Teesdale in the river’s upper course
- it has formed due to a resistant band of ingenious rock, its hard to erode this tough rock which has formed a step in the long profile of the river -> high force waterfall
- as the river plunges over the waterfall, it undercuts the weaker limestone forming an overhang. is eventually collapses and the waterfall retreats upstream to form a gorge.
what are pools and riffles?
- where streams carry coarse sediment they may develop alternating sequence of shallow, fast flowing sections called riffles, they develop between meander bends where a drop in velocity has led to deposition of coarser sediment.
- the deeper, slower-moving sections called pools, they develop close to the outside bend of the meander.
