River Enviroments Flashcards
8 factors affecting the transfer/ storage of water
- vegetation
- soil
- type of precipitation
- intensity of rainfall
- time of year
- type of rock (geology)
- land use
- topography/ relief
Describe vegetation
Vegetation increases the rate of infiltration as they intercept precipitation and reduce the amount of water that is trying to infiltrate the surface
Describe soil
Porous soils such as sandy soils allow increased infiltration. Clay soils are not porous and therefore infiltration is reduced. If the soil is hard infiltration is reduced
Describe ‘type of precipitation’
Heavy snowfalls mean that water is held in storage. When temperatures rise there will be a release of water. If temperatures rise slowly the water will have time to infiltrate and surface run-off will be reduced.
Describe ‘intensity of rainfall’
Heavy (or intense) rainfall causes the ground to become saturated quickly. Infiltration will be reduced and increased surface run-off will take place.
Describe time of year
The warmer temperatures of the summer encourage more evapotranspiration, thus lowering discharge levels in rivers. If the soil becomes hard-baked it will not allow infiltration.
Describe ‘type of rock’
Permeable rocks increase the amount of groundwater storage and groundwater flow. Permeable rocks include chalk, limestone and and sandstone. Impermeable rocks, such as granite, decrease the amount of groundwater storage and groundwater flow. This means that less water can be stored or transferred below the grounds surface and must be stored or transferred above the grounds surface
Describe ‘land use’
When urbanisation has occurred surface run-off is increased as water cannot infiltrate impermeable surfaces such as tarmac. This will lead to increased surface run-off.
Describe ‘topography/ relief’
In steeper drainage basins, less infiltration tends to occur and so surface run-off dominates and there is less water in soil store.
Describe attrition (river)
As rocks being transported/ carried within the river’s flow (suspended in the water) they knock against each other. Prices break off them and they become smaller, smoother and rounder
Describe solution/ corrosion (river)
This happens when weak acid (chemicals) in the water react with the rock and dissolves soluble minerals. This is a form of chemical erosion
Describe abrasion/ corrasion (river)
The process of grinding rock fragments, carried/transported within the rivers flow, against bed and banks. This causes lateral (makes the river wider) and vertical (makes the river deeper) erosion. The grinding is most powerful when the river is in flood, as large particles are carried by the river
Describe hydraulic action (river)
This is a form of mechanical weathering and is caused by the force of moving water. Water and air is forced into cracks in the bed and banks. This puts pressure on the river’s channel and causes pieces to break off
Characteristics of the upper course of a river (6)
- steep
- shallow
- narrow
- large angular load
- slow velocity
- small discharge
Characteristics of the middle course of a river (6)
- gentle
- deep
- wide
- sub-angular/ sub-rounded load
- fast velocity
- large discharge
Characteristics of the lower course of a river
- flat
- deepest
- very wide
- small/ well-rounded load
- fastest
- largest
What is the gradient of a valley
This refers to how steep or gentle the valley is
What is discharge
The amount of water that passes a particular point in a river at a particular time
2 examples of water falls and their location
- Niagara falls, USA and Canada
- angel falls, Venezuela
Where do waterfalls form
Where alternating layers of hard rock and soft rock are present
How does a waterfall form (6 points)
In order
- as the river passes over the less resistant soft rock it is able to erode it at a faster rate than the harder rock, so a step develops in the river bed.
- the force of hydraulic action and abrasion deepen this step until a water fall is formed.
- as the height of the waterfall increases the rivers energy also, it also increased due to an increased velocity, eventually erosion makes a deep pool under the waterfall called a plunge pool.
- undercutting of the overhanging hard rock (cap rock) occurs and it will hang over the plunge pool.
- when the cap rock becomes too unstable, the hard rock overhang will collapse and material will fall into the plunge pool, further increasing erosion by abrasion.
- the collapse of the cap rock causes the waterfall to retreat upstream (backwards) leaving a steep sided gorge
What are meanders
A bend in a river
Where are meanders found
In the middle course and the lower course of a river
Describe the outside bend of a meander (4)
- fast velocity
- deep
- hydraulic action and abrasion (erosion )
- undercutting to form river cliffs
Describe the inside bend of a meander (4)
- slow velocity
- deposition
- shallow
- slip-off-slope
Where are flood plains and levees formed
The lower course of a river
What is a floodplain
A flat area of land on either side of a river channel, where material is deposited due to regular flooding
What is a levee
A natural embankment on either side of a river channel that is formed due to deposition of the largest material when a river floods
Describe how floodplains and levees are formed (4)
In order
- the river channel rises and flows onto the land
- when water comes into contact with the land the waters velocity decreases and deposition occurs
- largest material is deposited beside the river channel, this creates levees
- smaller material is deposited further from the river, creating a flood plain
Describe the Somerset levels
A low-lying region in the south west of England
The 4 main rivers of the Somerset region
- the tone
- the parrett
- the axe
- the brue
The area the Somerset levels take up
650km2
What is the slope of the Somerset levels
Slope very gently to the sea
Describe the rivers in the levels (2)
- slow-moving
- prone to flooding
Date of the Somerset levels
During the winter of 2013/2014
4 physical causes of the Somerset floods
- geology and land use
- precipitation amount
- precipitation intensity
- high tides
Describe geology
The impermeable clay means that the area is naturally at risk of flooding due to low levels of percolation and groundwater storage. This means more water travelled along the surface so river discharge increased quickly
Describe land use
Grass is the predominant vegetation in the levels. This means the area has low interception levels which increases the amount of precipitation available for surface run-off
Describe precipitation amount
Southern England received 207 mm of rainfall during January 2014, this was more than twice the expected total for that month. The winter rainfall total was the highest in England since 1766. This caused the stores to fill up and more water was being carried in the river Chanel
Describe precipitation intensity
Between mid-December and early January there were six major storms and from January to mid-February there were six more. So there was little time for the saturated ground to recover
describe high tides
The Bristol Channel has the second highest tidal range in the world. High tide levels caused floodwater to back up along the rivers across the levels and moors. This was exacerbated by the river levels being higher than usual because of recent precipitation
Describe the environment agency human cause for the floods
The environment agency took over the maintenance of the rivers agency. The rivers Tone and Parrett had not been properly dredged in 20 years. This means the river channel could not hold as much water as it used to. The agency did not dredge the rivers since 1995 due to new soft engineering approach.
What did the environmental agency describe dredging (3)
Uneconomic, ineffective and causing damage to ecosystems
1 other human cause of the floods
Extra water was sent into the levels from Taunton and Bridgwater as part of a scheme where water was pumped away from these ares to protect new homes built on former flood plains. This means that the area/ rivers received even more water that in/ they could cope with and so the river flooded
And impact of the floods
Over 600 homes were flooded, 175 of which wee under flood water for several weeks
How to layout extended floods question (8) in order
- The Somerset levels are located in
- one physical cause of the flooding was
- another physical cause of the flooding was
- a human cause of the flooding was
- a second cause of the flooding was
- to conclude, many people were affected by the flooding
5 types of hard engineering
- dams/ reservoirs
- levees and embankments (flood walls)
- storage areas
- river straightening
- channel enlargement (deepening and widening)
3 positives of dams/ reservoirs
- risk of flooding is almost completely reduced
- can produce cheap and renewable hydroelectric power
- water based recreational activities
3 negatives of dams/ reservoirs
- completely changes the natural landscape and ecosystems
- major impact on environment
- extremely expensive
2 positives of levees/ embankments (flood walls)
- little impact on river
- they work, reducing amount of flooding
3 disadvantages of levees/ embankments (flood walls)
- Flood can be more destructive
- can be expensive
- high water velocity
2 positives of storage areas
- red ice amount of water flow
- effective
2 disadvantages of storage areas
- Bad for the environment
- take up a lot of space
2 positives of river straightening
- increased water velocity
- easier to build along the side of the river
2 disadvantages of river straightening
- does not always work
- does not allow fish to lay eggs (environmental impact)
3 positives of channel enlargement (deepening and widening)
- protects both sides of river
- protects natural habitat of animals
- capable of carrying more water, so transport is fast
3 disadvantages of channel enlargement
- high water velocity
- can be expensive
- requires regular maintenance
what is hard engineering
Hard engineering methods often involve using large artificial structures to control the river, blocking its natural cycle to flood and subsidence
What is soft engineering
Soft engineering methods are generally sympathetic to the natural landscape, so they tend not to damage the river for further generations
3 types of soft engineering
- Land use zoning
- afforestation
- wash lands
What is land use zoning
This is when areas most likely to be flooded are protected from urban development
What is afforestation
Planting trees in the upper course of the river in order to increase interception and reduce the risk of flash flooding
What is wash lands
There are parts of the river floodplain in the lower course into which the river can flood temporarily
2 positives of land use zoning
- allows the river to flood naturally
- cheap and easy to carry out
1 negative of land use zoning
Not suitable in built up areas
2 positives of afforestation
- helps to reduce chance of flooding
- better for natural environments
2 negatives of afforestation
- cannot prevent flooding
- only possible where there is lots of space
1 positive of wash lands
-increases friction to reduce flooding
1 negative of wash lands
-requires lots of space
