Rivers Flashcards
Water facts
A drop of water may spend over 3000 years in the ocean before evaporating into the air.
A drop of water spends 9 days in the atmosphere before falling back to Earth.
An amazing 96.5% of all water is stored as salt water in the oceans. Just 0.001% is stored in the atmosphere and 0.0002% is stored in the worlds rivers.
Throughflow
Is when water in the soil moves down hill
Drainage basin
The area of land drained by a river where the water cycle takes place.
A drainage basin is an area of land that is drained by a river and its tributaries. Precipitation falling within the basin finds its way into streams and rivers that flow towards the sea. The drainage basin system is part of the hydrological cycle.
Precipitation
Is any form of liquid or solid water particles that fall from the atmosphere and reach the surface of the Earth.
Condensation
The process of water vapour turning to a liquid as it is cooled.
Infiltration
When water soaks into the soil.
Percolation
When water moves vertically through the soil and rock
Channel flow
Is the flow of water through in a river
Groundwater flow
Is when the water in a rock flows downhill.
Transpiration
Evaporation water is heated by the sun and turns into water vapour
Surface runoff
When water flows overground(on top of land)
Interception
When water droplets collect on trees or plants.
Surface storage
When water lies on the ground as puddles or lakes.
Soil moisture
Water stored in the soil.
An increase in rainfall?
Surface storage would increase.
A decrease in rainfall?
Decrease in surface storage because the water would evaporate.
A lot of snow which melted very quickly?
Lot of surface storage because the water would melt on the surface there would also be infiltrated and moisture.
Long winter with temperatures below freezing for several weeks?
The ground would freeze and there would probably be more overground flow since it wouldn’t be able to go underground.
Warm day following several days of heavy snowfall?
There would be less snow since a lot of snow would melt and then evaporate into the atmosphere.
A very hot long dry summer?
Not much surface storage or surface runoff since a lot of the water on the ground would’ve evaporated into the atmosphere.
what do all rivers flow in?
bowl-shaped depressions or basins
inputs
water entering the system
transfers/flows
the movement of water through the system
stores
water stored in the system
outputs
water leaving the system
watershed basin
the outer edge of a drainage basin
upper course
higher upland areas, with mountains
upper
source:
start of the river, always begins in high upland areas like mountains
upper
v-shaped river valley:
a deep river valley shaped like a V, formed by erosion
upper
tributaries:
a small river that joins a larger river
upper
confluence:
where tributaries join each other to form larger river channels, where two rivers join
upper
gorge:
narrow, steep-sided river valley
middle course
the river becomes less steep and becomes more of a gentle gradient, erosion, water increasing, the river channel has widened probably due to lateral erosion, meanders and ox-box lakes will form
middle
river channel:
a landform that contains a river at the bottom of the valley
middle
main river channel:
the river will go from being in more upland areas to more gentler river slope areas
middle
meander:
a winding curve or bend of a river
lower course
wider river channel, deposition due to sand deposits
lower
floodplain land:
the river meets the flattest area of land
lower
estuary:
a broad flooded valley where a river joins the sea
lower
mouth:
the river at the end of the journey just before it meets the sea in flat lowland areas
How does a cross profile of a river change as you go downstream.
The river channel becomes wider and deeper, with the valley becoming wider and flatter.
Sides become less steep compared with the V-shape upstream
In reality there are many variations
The changes downstream are due to the amount of water flowing in the river. As tributaries flow into the main channel from other parts of the drainage basin the river becomes bigger. With more water there is more energy and more ability to erode making the channel further wider and deeper
The changes in the cross profile are due to this channel erosion broadening and flattening the base of the valley.
Together with weathering and mass movement, these processes make the sides of the valley less steep
Erosion process
Erosion is the process of water wearing away the land. The river erodes as it carries materials in its water. The more energy the river has, the faster it can erode.
Transportation process
The sediments(load) are transported. Transportation is the process of water carrying rocks and sediment downstream. The material a river transports is called it’s load. The size and total amount of load that can be carried will depend on the river’s state of flow – its velocity. The more energy a river has, the larger the load it can carry. After a rainstorm in high-flow rivers often look very muddy because they are flowing fast and transporting a large amount of sediment. At low flow, when the rivers are usually clearer, very little sediment is being transported.
Deposition definitions and processes
Deposition is the processes where material being transported by a river is dropped. Deposition of sediment occurs when river decreases velocity. It no longer has enough energy to erode or transport sediment so the load is deposited. Sediment is deposited on the river bed and the banks and at the river’s mouth
Larger sediment tend to be deposited first in the upper course of the river. They are only transported very short distances, mostly by traction, during periods of very high-flow
Finer sediment is carried further downstream, mostly held in suspension. This material will be deposited on the river bed or the banks, where velocity is slowed by friction
Dissolved material stays in the water, it will end up in the sea or lake.
Summarise what happens to the processes as you move down the river:
Erosion occurs in the upper course which causes v-shaped valleys and waterfalls to form. There are four types of erosion: abrasion, attrition, hydraulic action and solution. In the middle course, erosion, deposition and transportation occur. There are four types of transportation which are suspension, traction, solution and saltation. Deposition mostly occurs in the lower course of the river. Deposition occurs when a river decreases velocity.
Rivers long profile
Erosion is the main process in the upper course
Both erosion and deposition occur in the rivers middle course
Deposition wins out in the lower course as it loses energy
The river valley, in cross section
In the upper course, the river erodes downwards. The result is a v-shaped valley.
Now the banks are being eroded, so the channel is getting wider. A floodplain forms, where the river floods time after time.
River courses
Upper course - mostly erosion landforms e.g. waterfalls
Middle course - mostly erosion and deposition landforms e.g. meanders and transportation
Lower course - mostly deposition landforms e.g. levees
Why are histograms useful in geography?
Histograms are useful in geography because they help us to compare the quantity or frequency of categories in a data set and they are easy to draw and interpret.
6 rules for histograms
- There are no gaps between the bars because histograms display continuous data.
- The categories have to be plotted along the x-axis
- The y acid represents the number of things(e.g. pieces of sediment) in each category
- Label the x and y axis
- Give the graph a title
- Plot a single bar for each category on the graph
How to interpret histograms
- look for obvious peaks
- look for any odd bars
- compare with other histograms
Landform
Anything that has been created through physical processes e.g. beaches are formed by the process deposition.
V - shaped valley formation
A small stream will naturally follow small depressions in the landscape.
Over time, weathering and gravity wear away the steep valley sides, forcing material into the stream, which it uses to cut the valley steeper.
As the small stream flows down steeply, the bed load will erode downwards and scrape away the bottom of the channel (vertical erosion).
This vertical erosion deepens the valley, making the sides steeper and exposed.
What are interlocking spurs?
Interlocking spurs are slopes that form either side of the valley.
How are interlocking spurs formed?
They are formed because at this stage of the river it small in width. Its main work is eroding the channel vertically and has no energy to do anything else so the river uses the easiest course rather than eroding the slopes.
Waterfalls
Warterfalls occur when there’s a sudden change in the composition of a rock from a resistant to a softer rock. The river erodes the weaker rock more quickly than the more resistant rock. The resistant rock is undercut creating an overhang.
headward erosion
waterfall retreating
What happens to the harder rock in a waterfall?
The harder rock can’t take the weight and collapses.
undercutting of softer rock
waterfalls
undercutting of softer rock by hydraulic action and abrasion creating an overhang.
What is a gorge?
A gorge is a narrow steep sided valley that is usually found immediately downstream from a waterfall.
How is a gorge formed?
Gorge formed by a retreat due to headward erosion.
Plunge pool
A deep area of water at the base of a waterfall.
Where are meanders?
In the middle and lower course.
Meander formation
Where a river meets layers of hard and soft rock. When it meets hard rock it moves around it.
Meander
A bend in the river
The inside bend
The slowest and where the mist deposition occurs = slip off slopes
Outside bend
has more erosion as it has a high velocity = river cliff
Is the outside bend or the inside bend steeper?
Deeper on the outside bend because of erosion, shallower on the inside bend due to deposition because of decreased velocity.
Oxbow lake
In the lower course of the river meander bends become even more extreme and gradually the neck of the meander narrows eventually forming distinctive features known as ox-bow lakes.
Deposition
The processes where material being transported by a river is deposited.
When does deposition occur?
Deposition occurs when a river loses energy.
This can be when a river enters a shallow area (this could be when it floods and comes into contact with a floodplain) towards its mouth where it meets another body of water.
Oxbow lakes formation
As erosion continues, the neck of the meander is worn away. It gets narrower and narrower.
Then, during flooding the river takes a shortcut straight across the neck.
Soon the loop of the meander gets sealed off. It turns into an oxbow lake.
In time the lake will get covered with weeds and fill with soil and disappear.
Lower course landform
Floodplains
The flat land beside a river.
Forms when a river floods, deposits a lot of sediment making the land very fertile.
Can also be formed by large looping meanders.
Lower course landforms
Levees
Levees are raised river banks.
They are formed naturally by deposition in a flood.
OR
Artificially to hold more water and reduce flood risk.
Lower course landforms
Deltas
When a river reaches a lake/sea the water slows down and loses the power to carry sediment.
Sediment is deposited at the mouth of a river.
Some rivers drop so much sediment that waves and tides can’t carry it all away, it builds up in layers forming a delta.
The Nile delta in Egypt.
Lower Course Landforms
Estuaries
An area where a freshwater river or stream meets an ocean (saltwater).
The water is tidal - rises and falls each day.
Deposition is the key process and helps it to build a mud flat.
long profile
a long profile is a line representing the river from its source to its mouth
cross profile
a cross profile shows a cross section of a rivers channel and valley at a certain point
upper course landforms
v-shaped valleys
interlocking spurs
waterfalls
gorges
middle course landforms
meanders
oxbow lake
lower course landforms
estuaries delta floodplains levees mud flats
braided river
a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, aits or eyots
river disharge
River discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second (cumecs).
load
everything the river carries
bedload
whats carried along the floor of the river
Physical Causes of Flooding:
- heavy rain
- impermeable rock (water can’t soak through/ be taken in/percolate
- tributaries
- hard dry soil (rain can’t infiltrate)
- steep slopes
- saturated soil(impossible to take in more water)
- snow melting
Causes of flooding:
steep sides
If the surrounding land is steep/ mountainous then water will flow down the sides (and end up in the river) faster.
Causes of flooding:
dry soil
If the weather has been hot/dry the ground gets ‘baked’ and the rain can’t soak in very quickly. So it flows overground to the river.
Causes of Flooding:
Building on or near floodplains
We often build on or near to the floodplain. The rain can’t soak through the surfaces (e.g. concrete) and instead gets to the river faster through drains.
Causes of Flooding:
saturated soil
If there has been a lot of rain over a period of time the ground gets ‘saturated’ and can’t hold any more water.
Causes of Flooding:
cutting down trees
Trees catch rainwater(interception). When we chop them down, we prevent this from happening. Water then ends up in the river faster.
Causes of Flooding:
impermeable rock
The type of rock is important. Some are permeable and let water through, others are impermeable and don’t.
Causes of Flooding:
heavy rainfall
Heavy rainfall. Quite simply too much water ends up in the river causing the river to burst its banks.
Causes of Flooding:
snow melting
When snow starts to melt, a large volume of water finds its way to the river.
Human Causes of Flooding:
- cutting trees(can’t soak water, interception), deforestation
- concrete floors(not able to soak water)
- building on or near a drainage basin and floodplains(water can’t infiltrate)
SEEP
Social, Environmental, Economic, Political
When does flooding occur?
Flooding occurs when rivers discharge is greater Han the discharge it was designed to carry.
Hard Engineering:
Hard engineering involves using man-made structures to prevent or control natural processes from taking place.
Dam and Reservoirs
How it works?
Negative Impacts (cost):
Postive Impacts:
- When rainfall is high water is stored in a reservoir, behind a dam. This means water that would have once flowed downstream and flooded a town is now held and slowly released(decreasing discharge).
- Large areas of land have to be flooded to make way for a reservoir meaning many people would have to be be moved from their homes. Vey expensive. £1 billion per dam.
- They can have multiple purposes, for example many dams don’t just stop flooding they can also be used to generate power or store water in periods of water or draught.
Channel Straightening
How it works?
Negative Impacts (cost):
Positive Impacts:
- cutting through meanders to create a straight channel, this speeds up the flow of water along the river
- £4700 per metre. Disrupts wildlife. Unnatural. May increase flood risk further downstream.
- speeds flow and prevents the banks from collapsing
Embankments
How it works?
Negative Impacts (cost):
Positive Impacts:
- A raised riverbank. Raising the level of a river bank allows the river channel to hold more stare before flooding occurs.
- They are made of concrete which some people may think is too expensive, stops water seeping into the ground, doesn’t look natural and can cause worse flooding if it isn’t properly maintained.. £1152 per metre
- Prevents the flooding of valuable property. Mud dredged from the river can be used and it is more sustainable and looks more natural. Helps the river hold more water.
Flood Relief Channels
How it works?
Negative Impacts (costs):
Positive Impacts:
- Excessive water flows away into the flood relief channel and reduces the threat of flooding.
- £12,000 per metre. Requires regular maintenance.
- Reduces flood risks. New habitats of aquatic life. Bypass urban and high-value life.
Soft engineering
Involves adapting to a river and working with natural processes, it is cheaper but less effective than hard engineering. It doesn’t involve building artificial structures.
Aims to reduce/slow the movement of water.
Trees
Advantages:
Disadvantages:
- Planting trees in order to intercept rainfall and prevent it from reaching the river, thus reducing the flood risk. Also creates new habitats for wildlife and is very cheap.
- Cheap and creates nee wildlife. Better for the environment.
- Takes up space. Not 100% sustainable/reliable.
River Restoration
Advantages:
Disadvantages:
- Where the course of river has been change artificially, river restoration can return to its original course. Uses the natural processes and features of a river e.g. meanders and wetlands to slow down river flow and reduce the likelihood of a major flood.
- Keeps rivers natural. Doesn’t add concrete or artificial structure. Creates more channel space.
- Lengthy process. Not sustainable.
Flood warnings and preparations
Advantages:
Disadvantages:
- Flood warnings and preparations: river and river basins are remotely monitored using satellites and computer technology. Instruments check rainfall and check river levels. Computer models used to predict discharges and identify areas at risk from flooding.
- Keeps areas alert and gives people enough time to protect themselves or move.
- Not 100% reliable. Doesn’t stop or reduce flood risk.
Floodplain Zoning
Advantages:
Disadvantages:
- Floodplain zoning restricts different land uses to certain locations on floodplains. Areas close to the river and at risk from the flooding can be kept clear of high value land uses such as housing and industry. Instead these areas can be used for pasture, parkland, playing fields etc. Reduces losses caused by flooding. Can be difficult to implement on floodplains that have already been developed causing prices to fall.
- Keeps expensive property safe in low flood risk areas. Makes use of areas by river safety. Causes land price to fall. Difficult to implement on developed floodplains.
Where does deposition occur?
- Where the river becomes shallower and friction increases
- When the river meets a slow moving body of water like the sea and slows down
- When the river floods and moves across floodplains
- Where the river changes it’s course and an area of the river is cut off from the moving water.
Type of Erosion
Abrasion
sand and stones scrape the bed and banks like sandpaper, and wear them away
Type of Erosion
Attrition
when stones carried by the river knock against each other, gradually making the stones smaller and more rounded
Type of Erosion
Hydraulic Action
in a fast-flowing river, water is forced into cracks in the bank, over time it breaks up the bank by compressing the air and breaking up the particles.
Type of Erosion
Solution
Water dissolves soluble minerals from the bed and banks. This helps to break them up. / When the river flows over limestone or chalk, the rock is slowly dissolved. This is because it is soluble in mildly acidic water.
Type of Erosion
Vertical erosion
gravity pulling the water down that starts to erode on the bottom of the hill creating a v-shaped valley.
Type of Erosion
Interlocking spur
when the river erodes around the softer rock moving around the harder rock.
Type of Erosion
Lateral Erosion
erosion of the banks rather than the beds
Type of Transportation
Suspension
fine, light materials carried along by the river
Type of transportation
Traction
large boulders and rocks are rolled along the river bed
Type of Transportation
Solution
minerals are dissolved in the water, this is a chemical change
Type of transportation
Saltation
small pebbles and stones are bounced along the river bed
