Theme A: River Environments Flashcards
Drainage Basin:
Percipitation
Input: a rainfall, hail, sleet or snow
Drainage Basin:
Interception
Store: vegeatation/trees delay or slow down the rate at which rainfall reaches the ground
Drainage Basin:
Surface Storage
Store: water is temporarily stored on the ground’s surface
Drainage Basin:
Soil / Moisture Storage
Store: soil is capeable of holding water for a while
Drainage Basin:
Surface Runoff
Transfer: water which moves over the surface of the land
Drainage Basin:
Infiltration
Transfer: water sinking into the soil
Drainage Basin:
Through Flow
Transfer: water flowing through the soil
Drainage Basin:
Percolation
Transfer: water sinking down through the rock
Drainage Basin:
Groundwater Flow
Transfer: water flowing slowly from the rock into the river
Drainage Basin:
River Discharge
Output: water flowing away in the river
Drainage Basin:
Evapotranspiration
Output: water turning into water vapour in the air, and water turned into water vapour by plants through their leaves.
Drainage Basin Charcteristics:
Watershed
The boundary of a drainage basin which usually follows a ridge of higher ground (e.x mountains)
Drainage Basin Charcteristics:
Source
The place at which a river begins
Drainage Basin Charcteristics:
Tributary
Small rivers or streams which flow into the main river
Drainage Basin Charcteristics:
Confluence
The point at which a tributary meets the main river
Drainage Basin Charcteristics:
River Mouth
The place where a river enters/meets the sea
How a River Changes Downstream:
Gradient
- This is the steepness of the slope the river flows down
- As a river goes downstream, it gets les step
- This is because the river does more downwards erosion near the source, and more sideways erosion near the mouth
How a river changes downstream:
Depth
This is a measure from the top of the water to the river bed. As the river goes downstream, the river gets deeper. This is because the river erodes downwards as it travels.
How a river changes downstream:
Width
This is the distance from one side of the river to another. As the river goes downstream, the river gets wider, because the river erodes sideways as it travels downwards.
How a river changes downstream:
Discharge
This is the amount of water passing a point in a certain time. As the river goes downstream, the discharge increases. This is because more water flows into the river from each tributary. Water flows faster with less friction.
How a river changes downstream:
Load
This is the material a river is carrying (mud, sand, pebbles, rocks). As the river goes downstream, particles get smaller and more rounded. This is because particles knock against each other and break each other up. Sharp, angular edges get knocked off.
Name the four erosion processes carried out by a river
- Corrasion (Abrasion)
- Attrition
- Solution
4, Hydraulic Action
Describe and explain corrasion
This is the grinding of rock fragments carried by a river channel, against the bed and banks of a river. This action causes the river channel to widen and deepen. This grinding is most powerful during a flood, when large fragments of rock are carried along by a river,
Describe and explain attrition
This is the collision of rock fragments, (suspended in water) against one another. Rock particles are broken into smaller pieces and become smoother as the process continues?
Describe and explain solution - as a method of erosion
This is the process by which a river’s water chemically reacts with soluble minerals in rocks and is dissolves them.
Describe and explain hydraulic action
This is a form of mechanical weathering that is caused by the force of moving water. It can undermine riverbanks on the outside of a meander or force air into cracks within exposed rock in waterfalls such as Niagra Falls.
Describe and explain solution - as a method of transportation
Soluble minerals dissolve iin the water and are carried in solution. This is a chemical change affecting rocks such as limestone and chalk, and may result in discoloured water. For example; the rivers of the Mournes often appear yellow/brown as they are stained from iron coming off the surrounding peat bog.
Describe and explain suspension
The smallest load, like fine sand and clay, is held up continually within the water. This makes the water appear opaque. Some rivers carry huge quantities of suspended material.
Describe and explain saltation
This is the bouncing of medium-sized load, like small pebbles and stones, along the river bed.
Describe and explain traction
This is the rolling of large rocks along the river bed. This requires a lot of energy. Load carried in this way is called bed load. The largest bed load will only be moved like this in time of severe flooding.
When is deposition likely?
Deposition likely if:
- the river enters a lake or sea, slowing its flow
- the river floods onto its floodplain, where it flows very slowly
- there is an area of shallow water, slowing the rivers flow
- the load is increased suddenly, for example, after a landslide
Discuss the formation of a waterfall
- A waterfall is formed when a layer of hard rock overlies a layer of softr rock
- The river erodes the soft rock easily, so there is a step in the river bed. Eventually this becomes deeper, making a waterfall
- Hydraulic action and abrasion make a plunge pool at the bottom of a waterfall
- More erosion undercuts the hard rock, leaving it hanging over the plunge pool
- The overhanging hard rock falls into the plunge pool, and the position of the waterfall moves backwards
Discuss the formation of a meander
- A meander is a bend in a river caused by erosion.
- On the outside of the bend you will find the fastest flow of water because there is little to no FRICTION
- As the fastest flow goes downstream, it erodes and creates a river cliff.
- On the inside of the meander bend you will find the slowest flow of water. It is not able to transport its load due to its slow flow.
- This deposition creates a slip-off slope.
- Eventually, the outside bends will further erode and merge to create an oxbow lake.
- The inside bends of the meander are cut off.
- They are now called an oxbow cut off lane.
Discuss the formation of levees and floodplains
- Flat land either side of the river will be covered in water if the river bursts its banks: this is callled a floodplain.
- When the water slows down, it looses energy. This means it will deposit a load (sediment) which is fertile.
- The heavier, larger particles are deposited first, building up on the river bank, while smaller particles can be carried along the floodplain.
- This means that over time the river banks will build up into long mounds called levees made of the larger particles.
Name and locate the river which you have studied in the British Isles
Name: River Parret
Location: Somerset Levels, South West England
Explain the HUMAN CAUSES of why the river you have studied flooded
- Rivers had not been dredged properly in 20 years, so they were full of silt and could not hold the water.
- Houses were build in Taunton and Bridgewater nearby, so that water drains quickly from the impermeable surfaces, and arrives quickly in the rievr, making the river more likely to flood. It was also pumped away from these areas to protect homes built on former floodplains.
Explain the PHYSCIAL CAUSES of why the river you have studied flooded
- Low lying land, with grassy vegetation, doesn’t intercept much rain, and the impermeable clay which doesn’t soak up the water. This leads to an increase in surface runoff.
- Severe weather storms in December/January in Southern England during 2013/2014, giving 207mm of rain in January, more than twice of what was expected, and the highest since 1910.
- High tides caused the water in the river to back up into the River Parret, so floodwater could not leave this area.
Discuss the positive Impacts of Flooding on PEOPLE
- Replenishes drinking water supplies, especially wells
- Provides sediment that naturally fertilises the soils of the floodplain
- Countries rely on floods to help crops grow
- Can encourage innovative solutions in future building design, such as building houses on stilts to avoid floodwater, or tiling all gorund floor walls and floors to facilitate easy clean-up after flooding.
Discuss the negative Impacts of Flooding on PEOPLE
- Spreads waterborne diseases such as cholera
- People and animals can be made homeless or even drown
- Buildings and infrastructure can be damaged or destroyed
- Crops grown on fertile floodplains can be washed away in a flash flood
- Can increase house insurance costs for home owners, or even make it impossible for them to ensure the home at all
Discuss the positive Impacts of Flooding on the ENVIRONMENT
- Fish benefit as they an breed in the standing floodwater
- In dry areas, floods bring relief from drought, providing drinking water for wild animals
Discuss the negative Impacts of Flooding on the ENVIRONMENT
- Flooding can wash chemicals or sewage into the local rivers and so pollute them
- Wild animals may drown or lose their habitat during a flood
Flood Mamagement Methods:
Dams
Allow water to be stored rather than surging downstream and causing floods there, they can also be used for water supply, hydro-electricity and recreation
Flood Mamagement Methods:
Flood Walls
Walls built beside rivers that are likely to flood in urban areas - they take up less space than levees
Flood Mamagement Methods:
Levees
These make the river banks higher so more water can be held in the channel
Flood Mamagement Methods:
Straightening and Deepening of the River
Water flows faster in a straight and deeper river so it leaves the area without causing problems
Flood Mamagement Methods:
Washlands
Parts of the floodplain, often used as pasture in the summer, that can be allowed to flood in the winter - one form of flood storage
Flood Mamagement Methods:
Land Use Zoning
Land that is at the highest risk of flooding is not used for flooding, but used for playing fields or for pasture
Flood Mamagement Methods:
Afforestation
Trees take up water by their roots and reduce the amount of water that reaches the river, so it is less likely to flood
Name all HARD ENGINEERING river management methods
- Dams
- Flood Walls
- Levees
- Straightening and Deepening of the River
Name all SOFT ENGINEERING river management methods
- Washlands
- Land Use Zoning
- Afforestation
Name and locate a river that you have studied outside of the British Isles
Name: The River Mississippi
Location: USA
Engineering Method Used in the River Mississippi:
Levees
Short description
Is it sustainable?
The levees have been built at 15m high for 3,000km along the river
Sustainable? - Yes
Engineering Method Used in the River Mississippi:
Dams
Short description
Is it sustainable?
Over 100 dams were built along tributaries
Sustainable? - Yes
Engineering Method Used in the River Mississippi:
Straightening and Deepening of the River
Short description
Is it sustainable?
Engineers cut through meanders to straighten 1750km of channel, to make the river flow faster
Sustainable? - No
Engineering Method Used in the River Mississippi:
Afforestation
Short description
Is it sustainable?
Afforestation in the Tennessee Valley - teh trees absorbed the water
Sustainable? - Yes
Engineering Method Used in the River Mississippi:
Land Use Zoning
Short description
Is it sustainable?
Houses near the river were bought and then demolished, and areas of the floodplainare turned into green spaces
Sustainable? - Yes
