💧Rivers Flashcards
What is a river drainage basin?
The area drained by a river and it’s tributaries
What is watershed?
The area of high land surrounding the river drainage basin
What are tributaries?
Small streams that feed into the main river
What is the mouth?
Where a river meets the sea or a lake
What is the source?
Where the river begins, high up in the mountains
What is a confluence?
The point where 2 or more tributaries meet together
What is the channel?
The main body of the river in which the water flows
What is erosion?
The wearing away of the land by the river
What is deposition?
The depositing (dumping) of material carried by the river
What are the 3 parts of a river?
The upper, middle and lower course
What type of erosion happens in the upper course?
Vertical erosion
What type of erosion happens in the lower course?
Lateral erosion
What are some features of a river in the upper course?
Waterfalls
Vertical erosion
Narrow V shaped valley
Rapids and large boulders
Fast flowing
Tributaries
The source of the river is found here
What shape is the upper course?
A narrow v shaped valley
What are some features of the middle course of a river?
Wide floodplains
River starts to meander
River starts to slow down
Gorges can be found here
Oxbow lakes
Raised banks caused by flooding are called leeves
What is the shape of the middle course?
Wider, less steep u shaped valley
What begins to happen in the middle course?
Meandering and slower speed
Where is the river at its slowest?
The lower course
What are some features of a river at its lower course?
River is at its slowest
Lateral erosion
Very wide flat valley
Industry and ports are found here
Large meanders
Sand and alluvium deposited
Where are industry and ports found on a river?
Lower course
What is the shape of a river at its lower course?
Very wide, flat valley
What are the 4 main processes of erosion?
- Hydraulic action
- Corrasion/Abrasion
- Attrition
- Solution/Corrosion
What is hydraulic action?
The sheer force of the water hitting the banks and river bed
What is corrasion/abrasion?
This is the process by which the bed and banks are worn down by the river load. The river throws there particles against the bed and banks, sometimes at high velocity
What is attrition?
Material (the load) carried by the river bump into each other and so are smoothed and broken down into smaller particles
What is solution/ corrosion?
This is the chemical reaction of river water. The acids in the water slowly dissolve the bed and banks, particularly limestone
What are the 4 main factors that affect the rate of river erosion?
- Gradient
- Rock resistance
- Discharge
- Velocity
What is discharge?
The amount of water in a river
How does discharge affect the rate of river erosion?
Erosion increases if the discharge increases. The more water in a river the more power it has. Therefore rivers have more power when they are full/in flood
How does the gradient affect the rate of river erosion?
A steeper gradient results in the river water being pulled by gravity, cutting down and eroding the channel. Rivers are steepest in their upper course
How does rock resistance affect the rate of river erosion?
Less resistant, softer rock erodes more quickly- for example, limestone is easily eroded- harder rocks such as igneous rocks are difficult to erode
How does velocity affect the rate of river erosion?
Erosion rate increases as velocity increases- more load can be carried and therefore more erosion occurs.
What is bedload?
The material carried by a river as it moves
How does bedload enter the river channel?
Falling in or attrition via erosion
Why does the bedload get smaller downstream?
Attrition
Where is the most material transported?
The lower course since it’s bigger so it can carry more
What can a river carry?
Rivers can on,y carry so much load depending on their energy
What is the rivers capacity?
The maximum volume of load that a river can carry at a specific point in its course
What is the rivers competence?
The biggest sized particle that a river can carry at a specific point
What are the 4 transportation processes?
- Traction
- Saltation
- Suspension
- Solution
What is traction?
The largest rocks in the river are slowly rolled along the bottom of the river by the force of the water. This primarily occurs in the upper reaches of the river
What is saltation?
Smaller rocks are bounced along the river bed. This occurs in the upper and middle sections of the river in general
What is suspension?
The water carries smaller particles of material. This process occurs throughout the course of the river, but increases the closer you get to the mouth of the river
What is solution?
Material is dissolved within the water and carries along by it. Primarily this occurs in the middle and lower reaches of the river.
What is solution?
Material is dissolved within the water and carries along by it. Primarily this occurs in the middle and lower reaches of the river.
What is deposition?
Simply dropping the material. It’s occurs regularly along the riverbed, but also at a range of other particular points
When does deposition occur?
When the water in river channel no longer has the sufficient energy to move the material
What are 3 places that deposition occurs?
- Inner bend of meander
- Floodplain
- River mouth
Why does deposition occur on the inner bend of a meander?
The river flow is slowest here, which means it doesn’t have enough energy and deposits it
Why does deposition occur on a floodplain?
When a river floods, the water on the floodplain becomes still and has no energy so deposition occurs
Why does deposition occur at the river mouth?
The flow of the water is at its slowest, so has little to no energy and deposition occurs
Why do upper-course landforms have a steep sided v shaped valley?
The landscape is eroded by vertical erosion- the river cuts downwards into the landscape
What is an interlocking spur?
Hard resistant rock
How is a v shaped valley formed? (4 stages)
By vertical erosion
1. The river erodes downwards as boulders, stones and rock particles are bounced and scraped along the channel bed (saltation and traction)
2. As the river cuts vertically downwards, the steep sides are attacked by weathering. This breaks up and loosens the soil and rock.
3. The loosened material slowly creeps down the slope because of gravity or is washed into the river by rainwater. The river begins begins to transport it away.
4. The end result is a steep sided valley that has the shape of a letter ‘v’.
When does differential erosion occur?
In waterfalls, the hard rock and soft rock are in parrallel bands which erode at different speeds.
What is differential erosion?
Eroding at different speeds.
How is a plunge pool created?
Hydraulic action and abrasion
How is a waterfall formed?
When a river flows over layers of hard rock and soft rock.
1. The soft rock starts to erode overtime, through abrasion and hydraulic action leaving an overhanging platform of hard rock.
2. The hard rocks in the plunge pool begin to wear away through attrition and the pool becomes deeper
3. The hard rock eventually becomes weak and collapses.
4. Overtime the waterfall retreats creating a vertically sided gorge
What are the key features of a meander?
Helicoidal flow
Thalweg
What is thalweg?
The fastest flow of the river, this the middle of a straight river.
What is helicordal flow?
The water in a river flows in a spiral, a little like a corkscrew.
What does helicordal flow cause?
A variation in the velocity across the river channel
What does the variation in river flow mean?
Some parts of the river experimce erosion, whilst others experience an increase in deposition
Where do we find meanders on a rivers course?
On the middle course, because the river is now wider and deeper
We don’t find them on the lower course
How does erosion occur on meanders?
The water on the outside bend of the meander is moving quickly meaning it has more energy to erode the river bank
How does deposition occurs in a meander?
On the inside the water flows slower, so less energy and deposition occurs as the river drops its load
What is the cross sectional area?
A Slice through the river that shows the bed and banks
How is Cross Sectional Area calculated?
Multiplying the width of the river by the average depth
How is discharge measured ?
Multiplying the CSA by the velocity
What is vertical erosion?
Eroding the bed as it moves downwards
What is lateral erosion?
Eroding the banks as it moves sideways
What are the 5 risks of the experiment?
- Slices, trips and falls
- Weather issues
- Issues with wildlife and animals
- Medical issues
- Traffic accidents: bus and in the road
What are the 3 sampling techniques?
- Systematic
- Stratified
- Random
What is systematic sampling?
This involves identifying sites which are roughly equidistant from each other. It reduces the likelihood of bias but it is possible to miss important locations
What is stratified sampling?
Involves selecting specific locations to collect data. This may be when you think a change might occur. It does lead to bias, but it also means that specific and likely important data can be collected
What is random sampling?
This is where sites/ samples are chosen totally randomly. It involves no bias, but it may be unrepresentative of the whole of the area/place investigated.
What is an oxbow lake?
A horse shoe or semi-circular area that represents the former course of a meander
How is an oxbow lake formed? (4 stages)
- The meander is formed naturally but gets bigger because of the erosion (hydraulic action and abrasion) of the river banks
- As the fastest flow is on the outside bend of the meander, the outside of the meander gets eroded quickly. This makes the neck more narrow and the river is separated only by a small piece of land.
- When the water levels are high the river had enough energy to push through the small piece of land to make an easier course, producing a meander cut off. This often happens in times of flood (more powerful).
- The small piece of land is broken through and then the river starts off once again in a straight channel leaving the bend isolated from the rest of the river. This is known as an oxbow lake. The lake often dries up as it is no longer supplied with river water.
What is an estuary?
The tidal part of a river where freshwater from a river merges with salt water from the sea
How are levees formed?
As water slows, competence and capacity decrease resulting in deposition when flooding, the largest and heaviest materials are deposited first nearest to the river bank and the lighter materials get delisted on the flood plain making fertile land for farming
How are natural levees good?
Make fertile land for farming
What are artificial levees?
A flood defence to increase maximum volume of water the channel can take and reduce the likelihood of flooding
How are deltas formed?
Form at the mouth where river meets sea
Here river slows down and deposits its load, start of delta is flat as heavy material (sand and silt) is deposited first nearest to
Further out to sea in deeper water the lighter materail(clay and sand) is deposited leading to a sudden drop off
What does infiltration mean?
Water soaks into a permeable surface
What does permeable mean?
Water can infiltrate (soak into) a permeable surface
What is surface run off?
Water flows over the impermeable surfaces- it cannot infiltrate
What is interception?
Water is caught on the leaves of vegetation
How much rain is approximately caught on vegetation thanks to interception?
≈70%
What does impermeable mean?
Water cannot infiltrate (soak into) an impermeable surfaces eg. Concrete/ tarmac
High or Low flood risk: Impermeable surfaces
Why?
High
No infiltration so more surface run off
Get to river faster
High or Low flood risk: Permeable surfaces
Why?
Low
Water can infiltrate
Less surface run off so ground water
High or Low flood risk: Heavy rain
Why?
High
More water
High or Low flood risk: Light rain
Why?
Low
Less water
High or Low flood risk: Forest and trees
Why?
Low
Interception so less water infiltrates into soil resulting in less surface run off and less chance of saturated soil
High or Low flood risk: Little or no vegetation
Why?
High
No trees to infiltrate so soil can become saturated resulting in surface water run off
High or Low flood risk: Steep valley sides
Why?
High
Flows downhill with gravity so no time to infiltrate
Lots of surface run off Get
High or Low flood risk: Saturated soil
Why?
High
Soil become impermeable so becomes surface run off and
High or Low flood risk: Frozen ground
Why?
High
Impermeable
High or Low flood risk: Buildings and Roads/ urban setting
Why?
High
Impermeable
High or Low flood risk: Countryside/ rural environment
Why?
Low
Permeable surfaces (soil) and interception (trees) mean less surface run off
What are storm hydrographs?
A graph showing The relationship between precipitation and discharge
The shorter the lag time…
The steeper the rising limb and greater the flood risk
The longer the lag time….
Gentler the rising limb and the lower the flood risk
On a storm hydrograph, what is the rising limb?
The effects of precipitation reaching the river
On a storm hydrograph, what is the falling limb?
Some rainfall reaching the river but in decreasing amounts, the river is returning to normal base flow
On a storm hydrograph, what is lag time?
The difference between the time of heaviest peak rainfall and the peak discharge
On a storm hydrograph, what is the peak discharge?
The maximum level/ volume of water in a river
What is hard engineering?
Involve man made structures which are used to prevent or control natural processes form taking place
Is hard engineering expensive?
Yes
What is hard engineering used for?
Protecting expensive property or land
What are some costs of hard engineering?
Financial
Negative impacts on the environment and peoples lives
eg. Ugly Appearance/ disruption to daily life/ huge building work?
What are some benefits of hard engineering?
Financial savings by preventing flooding
Environmental improvements
Long term?
Explain the flood prevention method of artificial concrete levees:
Concrete walls built along flood prone stretches of river
Raises height of banks, higher amount of water in river reducing flood risk
Positives of artificial concrete levees:
Long lasting
Effective
Disadvantages of artificial concrete levees:
Ugly
£8000 per metre
Explain the flood prevention method of artificial sandbags levees:
Used to raise height of river so more water can be held prevent flood risk
Benefits of sandbag levees
Cheap
Better for environment
Reusable
Disadvantages of artificial sandbag levees:
Temporary
Ugly
Explain the flood prevention method of flood relief/ overflow channels:
Artificial channels close to the real channel, at times of flood they act as overflow channels which water is obeyed to.
Made form concrete they mean that the main river doesn’t overflow
Benefits of flood relief / overflow channels:
Long term
Effective
Costs of the flood relief/ overflow channels:
£5000 per metre
Effects on the environment
Explain the flood prevention method of straightening the rivers course:
A new channel is dug which makes river flow faster and removes flood water more quickly
Positives of straightening the rivers course:
Effective
Long term
Costs of straightening the rivers course:
Time consuming
Very expensive (£10000 per metre)
Environmental damage
Explain the flood prevention method of dams and reservoirs:
Can be built in the upper course, holing water in a reservoir being the dam so the release of staff can be controlled to reduce risk of flooding.
The reservoir’s usually flood a huge area
Benefits of dams and reservoirs:
Hydroelectric power
Very effective
Long term
Disadvantages of dams and reservoirs:
Very expensive (£5-25 billion)
Long time to build
Damage to environment
What are 5 flood prevention schemes? (Hard engineering)
Concrete artificial levees
Sandbag artificial levees
Flood relief/ overflow channels
Straightening the river course
Dams and reservoirs
What is soft engineering?
Trying to slow after getting to the river and prepare for the likely impacts of flooding. It doesn’t involve building artificial structure and therefore has less effect on the environment
What are 4 examples of soft engineering?
- Afforestation
- Flood plain zoning
- Flood warning and preparation
- Water restoration
What is afforestation?
Planting shelter belts of trees across slopes and woodland in floodplains to intercept the water and avoid it reaching the river
What are some benefits of afforestation?
More carbon dioxide absorbed
Increases biodiversity
Decreases water downstream
Cheap
Creates new habitats
What are some costs of afforestation?
Loss of potential grazing land
Changed appearance as countryside is wooded rather than open grass and arguably more artificial looking and less aesthetically pleasing
What is flood plain zoning?
Where land unit a river valley is used in such a way to minimise impact of flooding by categorising the flood risk zones which are then used to guide building decisions
What are some benefits of flood plain zoning?
Amount of impermeable surfaces is decreased by restricting building on the active flood plain
Low cost
Protects floodplain creating a green space
Traditional water meadows by a river are protected by from development
Difficult to get planning permission on the floodplain
What are some costs of floodplain zoning?
Limited impact on UK cities as they have already been sprawled on the floodplain
Housing shortage in the UK restricting building increases the problem and thus house prices
Habitats are destroyed due to increased building on other green sites
What is flood warning and preparation?
The environmental agency carrying out action plans for areas at risk
Specific roles are given to emergency services, the armed forces and voluntary groups
What are some benefits of flood warning and preparation?
Cheap
Makes people feel more secure and safe
Can protect valuables earlier
Ensuring safety without investing in high cost hard engineering
What are some costs of flood warning and preparation?
Doesn’t help people living in areas prone to flooding
Clear up operations are distressing
Insurance costs increase
Only effective if people listen and take action
——> education is needed and not everyone has access to or listens to the media or internet
What is river restoration?
Removing hard engineering from a river in order to restore it back to its natural channel
What are some benefits of river restoration?
Creates wetland habitats and increases biodiversity
Increased water storage areas reduce the risk of flooding downstream
Aesthetically pleasing
What are some costs of river restoration?
Not always the most effective or practical strategy
Possible loss of agricultural land and flooding of crops near the river
Can be expensive
Why does Tewkesbury flood? (3)
- Built on a floodplain so flat
- Close to the river
- Next to a confluence where the Avon and the Severn meet so it receives more water
What happened in Tewkesburys past?
2007 flood
Over a 5 day period, 5 inches of rain fell
What were the effects and impacts of the 2007 flood?
All roads were cut off —> inaccessible
5000 homes and 400 businesses flooded
Power station under threat —> Power off with no heating
Water contaminated with sewage —> dependent on bottled water
Stranded in own homes
Months to return to normal life
What were some methods that have been used to protect Tewkesbury from flooding?
- People were given sandbags
- Ditches were cleared so water can flow easier (£10 000)
- Village flood relief ditch scheme (£51 000)
- Upgrade to a flood pumping station (£47 000)
What was the soft response to Tewkesbury’s flooding and why is it good?
The county council produced an exhaustive guide on what to do in a flood, given yearly to inhabitants
—> The cost is low, only needed yearly
—> Huge benefits, everyone knows what to do
