Flashcards in River Landscapes Deck (70):
Describe the steps of mechanical (freeze-thaw) weathering
Water fills a crack or joint in the rock
Water freezes and the crack is widened
Repeated free-thaw action increases the size of the crack until the block of rock breaks off
Loose blocks of rock are called scree
What is chemical (acid rain) weathering?
Rainwater is slightly acidic. The acid reacts with minerals in the rocks and dissolves them. For example, granite contains feldspar, which is converted into soft clay minerals as a result of a chemical reaction with water. Acids released by vegetation speed up chemical weathering.
What is biological weathering?
When roots grow into cracks and split rocks apart
Over time the sides of a river valley become less steep as material is moved from the top to the bottom, what is this called?
What is sliding?
It is a form of mass movement where rock, weathered or eroded material or earth moves down a slope. Gravity pulls the weakened material quickly downwards.
What is slumping?
It is a form of mass movement where the river erodes the bottom of the valley slope making it steeper. Material above slides downwards, particularly if it is saturated with rain water
What is Hydraulic action?
It is a form of erosion, the force of the water on the bed and banks of the river removes material
What is attrition?
It is a form of erosion, the load that is carried by the river bumps together and wears down into smaller, smoother pieces
What is solution?
It is a form of erosion, when some rock minerals dissolved in river water (eg calcium carbonate in limestone)
What is abrasion?
It is a form of erosion where material carried by the river rubs against the bed and banks and wears them away
What is transport?
Transport is the way in which the river carries eroded material or load. There are four main types of transportation: traction, saltation, suspension and solution
What is deposition?
When the river slows down it loses energy and may drop some of its load
What is traction?
It is a form of transportation, for when large boulders are rolled along the river bed
What is suspension?
It is a form of transportation for when finer sand particles are carried along in the flow, giving a brown appearance
What is saltation?
It is a form of transportation for when smaller pebbles are bounced along the river bed, picked up then dropped as the river flow changes
What is solution? (In transportation)
For when minerals, such as chalk are dissolved in the water and carried along in the flow, although they cannot be seen
Where do rivers and the valleys they flow in change in different ways?
Between their source (where they start) and their mouth (where they join the sea)
Describe a river profile
A rivers profile shows the height and distance downstream from the rivers source to its mouth. It is a curved shaped, steeper near the source and flatter near the mouth
describe the gradient in the upper, middle and lower course
Upper - steep
Middle- less steep
Lower - shallow gradient
Describe the discharge in the up, mid, low course
Up - smaller
Mid - large
Low - very large
Describe the depth in the up, mid, low course
Shallow, deeper, deep
Describe the channel shape in the up, mid, low course
Up - narrow, steep sides
Mid - flat, steep sides
Flat floor, gently sloping sides
Describe the velocity in the up, mid, low course
Up - quite fast
Mid - fast
Low - very fast
Describe the valley profile in the up, mid, low course
Up - steep sides
Mid - flat with steep sides
Low- flat with gently sloping sides
Describe the features in the up, mid, low course
Up - waterfalls, interlocking Spurs
Mid - meanders, floodplain
Low- meanders, floodplain, levées, ox-bow lakes
Describe the sediment shape and size in the up, mid, and low course
Up - angular boulders
Mid- more rounded rocks
Low - smooth, rounded pebbles
How does the uk's water and climate have an effect on river processes ?
Causes changes to landforms and landscapes
With the impact of climate What is the erosion rate?
Erosion rate will be higher with grater discharge, so rivers in wet climates will erode more material than those in dry climates, widening and deepening river valleys and increasing the amount of eroded sediment
With the impact of climate, what is the transport rate?
The transport rates will be grater where the energy of the water is greater, so rivers in wet climates will transport more material than those in dry climates
With the impact of climate what is the amount of discharge?
The amount of discharge is affected by climate. Wetter climates mean greater discharge. Hotter temperatures mean greater evaporation so less discharge. The greeter the discharge, the height the velocity of the river
With the impact of climate what is the weathering.,
The weathering of rocks will be greater in some climates: for example, freeze-thaw weathering increase where temperatures range from just below freezing
How can increasing frequency of storms increase the risk of flood?
More periods of heavy, intense rainfall meaning more water flowing into rivers, which then overflow
How can increasing periods of hot dray weather increase the risk of flood?
It bakes the upper soli is when it does rain the water runs off the surface, it can't soak in, reaching rivers and rapidly increasing discharge
How can soil becoming impermeable during cold conditions increase the risk of flood?
Snowmelt cannot infiltrate and flows rapidly into rivers increasing flood risk
how are interlocking Spurs, waterfalls, gorges and river cliffs formed?
By erosion processes and the influence of geology in the upper course of the river
What are interlocking Spurs?
The river at its source is small and has limited energy. It flows naturally from side to side, around ridges in the valley sides called Spurs. The Spurs become interlocking with those of the other side of the valley
What are waterfalls?
Waterfalls are a common feature in the upper course of a river, where there is an increase in vertical erosion. They form where there is a layer of hard, resistant rock (the cap rock) overlaying a softer, less resistant rock
What are gorges?
Over a long period of time, the processe of undercutting and collapse is repeated and the waterfall repatriate, forming a steep-sided gorge
What is the weathering process?
Weathering is the wearing away in situ of the river valley side. There are three weathering processes common to the river valleys
How is a plunge pool formed?
Hydraulic action and abrasion
What is a floodplain?
A floodplain is the wide, flat area of land either side of a river and experiences floods when the river tops its banks
How is a flood plain shaped?
In the lower course, the river is nearing the sea and carries a huge amount of sediment (alluvium)
When the river floods,excess water spills over the. Surrounding areas urging flooding, the velocity of the river is reduced, it loses energy, and deposits sediment , forming the floodplain
The floodplain is shaped by the lateral erosion of meanders as they gradually migrate downstream and by deposition of material of the inner bends
How do levées develop?
The deposition process, which takes takes place during flood continues until eventually embankments, made of larger, heavier sediment, are created beside the river
When flooding occurs, the heaviest material is deposited first due to the decrease in the rivers energy. This material creates natural embankments called levées
After a flood the smaller and finer sediment, or alluvium, is deposited further from the river because it requires less energy to carry it
Go and look at the diagram
On page 19
How are the landforms meanders and ox-bow lakes created?
But the interaction of deposition and erosion process in the middle and lower courses of a river
What are meanders?
In he middle course, the width, depth and volition of the river all increase. The river erodes laterally (sideways) and starts to form large bends. The bends get bigger and wider, and eventually develop into a horseshoe shape called a meander
What is a river cliff?
In the outer bend of a meander, where the current is faster, there is greater erosion. This wears away the bank creating a river cliff
What is a point bar?
On the inner bend of a meanders, where the current is slower, there is greater deposition, creating a point bar
How are ox-bow lakes formed?
Narrow Neal of meander is gradually being eroded
Water now takes the quicker route
Deposition takes place, sealing off the old meander
Meander neck has been cut through completely
Ox-bow lake left behind meander completely cut off
How can urbanisation affect rivers and change river landscapes?
Urbanisation has caused towns to grow, meaning they are fewer permeable surfaces. Water flows into the river, increasing discharge
Increasing demand for housing has led to new houses being built on floodplain so. This changes the natural landscape
River may be channelised or made to flow underground to make room for urban developments. If this happens, erosion and deposition cannot take place
How does agriculture affect rivers and change river landscapes?
Field drains can improve farmland, but quickly move water into streams and rivers, and can destroy natural wetland landscapes
Forests can be felled yo make way for farmland. Trees intercept rainfall, helping to reduce surface run-off. Removing trees means water reaches rivers more quickly
Abstracting water for irrigation reduces the flow and velocity of a river so deposition occurs rather than erosion
Ploughing fields up and down a slope can increase the amount of sediment in rivers and increase deposition
How can the industry affect rivers and change river landscapes?
Industry is a big user of water, so can reduce the amount of water in rivers, leading to less erosion
Industrial processes can pollute if chemicals or waste are spiller or dumped into them. This can destroy plants and animals and change the natural landscape
How is river flooding caused?
By a combination of physical and human factors, and has a range of physical and human effects
How does the rainfall intensity affect flooding?
A lot of rainfall over a short period of time prevents soil infiltration,
How does geology affect flooding?
Rocks like granite are impermeable, so water is unable to percolate from thin soil above
How does snowmelt affect flooding?
At spring time warmer temperatures will melt snow creating more water
How do drainage basins affect flooding?
Steep-sided valleys or a lot of rebut arises means the water enters the river system quicker
What happens after rainfall intensity,geology, snowmelt or drainage basins has affected flooding?
Excess water will flow towards the river as surface run-off (overland flow) or groundwater
Then water will reach the river channel more quickly and force the level or river to rise above the bank level of river to rise above the bank level. Flooding can then occur
What are the physical effects of floods?
Physical effects include landslides, soil erosion, loss of natural habitats, contamination of water supplies
What are the human effects of floods?
Human effects include death, disease, damage to property, insurance claims, loss of livelihoods,moss of crops and farm animals, disruption to transport
What is hard and soft engineering used for?
To help protect river landscapes from flooding
What does hard engineering involve?
It involves building structures as a defence against flooding
What are dams and reservoirs? Name advantages and disadvantages
They are barriers constructed to hold back water in artificial lakes
Advantages: you can store large volumes of water until needed, and they are long lasting; can be used to generate hydro-electric power (HEP)
Disadvantages: expensive to build, sediment can build up in reservoirs
Landscape impact - the natural river valley landscape is flooded
What is channelisation? Name advantages and disadvantages
Channelisation is deepening or widening the river channel
Advantage: it allows water to flow more quickly from areas of flood risk
Disadvantages: visually unattractive, and more water is taken downstream, increasing the flood risk to other settlements
Landscape impact - replaces the natural meanders and floodplain with an artificial channel
What is soft engineering?
It uses natural processes to reduce the impacts of river flooding
What is floodplain zoning? Name advantages and disadvantages
Floodplain zoning prevents development in areas most prone to flooding next to rivers
Advantages: reduces number of homes at risk of flooding, and allows infiltration so surface run-off takes place and flooding is reduces
Disadvantage: restricts the growth of settlements
Landscape impact - persevere the natural floodplain
What are washlands? Name advantages and disadvantages
Washlands are areas next to rivers that are deliberately flooded to avoid flooding residential or important agricultural areas
Advantages: creates an area for floodwater to go
All natural river processes such as deposition
Disadvantage: might limit the use of land
Landscape impact - preserves the natural floodplain landscapes in the mid and lower river courses
How was the river Dee formed?
The source of the river Dee is in Ddualt, an upland area in snowdonia, north wales,
Here annual precipitation is high
The Dee flows south-easterly, eroding this heavily glaciated upland landscapes formed of igneous and metamorphic rocks
Near Chester the river meanders across a wide floodplain, eroding softer sedimentary rocks and depositing sediments
A section is artificially straightened, giving a man-made landscape
Further position occurs to form the Wirral estuarine landscape
What human factors caused changes to the river Dee?
1732-1736, channelisation of 8km improved navigation, increasing discharge and velocity and creating an artificial landscape
Under the river Dee regulation scheme a series of reservoirs was built eg Llyn Celyn
Early embankments were built along the middle course to protect agricultural land and properties, preventing further development of the floodplain landscape