Rivers Flashcards
(54 cards)
1
Q
Which physical processes help to form river landscapes?
A
(same as coasts)
2
Q
What is a meander?
What is the thalweg?
What is sinuosity?
A
meander - the bend in a river
thalweg - fastest part of a river
sinuosity - how bendy a river is
3
Q
How does the river gradient change from upper to middle to lower course?
A
steep
less steep
shallow gradient
4
Q
How does the river discharge change from upper to middle to lower course?
A
small
large
very large discharge
5
Q
How does the river depth change from upper to middle to lower course?
A
shallow - deeper - deep
6
Q
How does the river channel shape and valley profile change from upper to middle to lower course?
A
narrow, steep sides
flat, steep sides
flat floor, gently sloping sides
7
Q
How does the river velocity change from upper to middle to lower course?
A
quite fast
fast
very fast
(turbulent - laminar(2) flow)
8
Q
How do the river features change from upper to middle to lower course?
A
upper - waterfalls and interlocking spurs
middle - meanders, floodplain
lower - meanders, floodplain, levées, oxbow lakes
9
Q
What is an example of a river that shows how the river valley changes?
A
Nant Peris, North Wales
10
Q
What is a river drainage basin?
A
the area of land around a river, any water that falls in this area drains into the river
11
Q
What is the source
A
the starting point of a river - often a spring or lake
12
Q
What is a tributary?
A
a smaller stream/river that joins into a larger stream or river
13
Q
What is the mouth of a river?
A
the point where the river leaves its drainage basin and flows into the sea
14
Q
What is the confluence?
A
the point where two rivers meet
15
Q
What is the watershed of a river?
A
the boundary of a drainage basin which separates one drainage basin from another
16
Q
What is deposition?
A
when a river loses its energy and velocity so it drops the sediment
17
Q
How are meanders formed?
A
(the pool and riffle theory)
- river travels in the most energy-efficient route
- when the river moves over a pool it uses less energy where as when it goes over a riffle it will use more energy
- this means the river will avoid the riffles - eroding the bank around the riffles and forming a meander
- the thalweg continues to hit against the outer bend, forcing the river to become more sinuous and pronouncing the meander
18
Q
How does sediment size and shape vary from upper to lower course?
A
upper - larger sediments
middle - smaller sediments
lower - very small, smooth sediments
19
Q
How are oxbow lakes formed?
A
- a meander bends and its neck becomes narrower and narrower as it erodes over time
- eventually the thalweg hits across the outer bend so much that the river becomes so sinuous that it erodes through the neck as the water travels through the quickest route (abrasion and hydraulic action)
- the river now runs down straight channel, and over time deposition occurs to seal off the old meander as it becomes unused, until the meander neck completely cuts through with a horse-shoe shaped oxbow lake left behind
20
Q
What is formed on the inner and outer bend of a meander?
A
inner - point bar as lower river velocity so more deposition
outer - river cliff as more erosion
21
Q
What does the Bradshaw Model show?
A
how river gradient, velocity etc changes down a river
22
Q
How does the UK’s weather affect rivers? (3)
A
- increased storm frequency (periods of intense heavy rainfall mean more water into rivers that overflow)
- increased periods of hot/dry weather (bakes upper soil so when it does rain, the water runs straight off the surface into the river as it isn’t absorbed - increasing discharge)
- cold conditions reduce soil permeability (snowmelt cannot infiltrate and flows rapidly into rivers, increasing flood risk)
23
Q
How does the UK’s climate affect rivers? (4)
A
- erosion rate increases with discharge (so wetter climates erode more, widening and deepening river valleys and increasing amount of eroded sediment)
- transport rate increases with water energy (so more water transports more sediment - wetter conditions)
- weathering increases in certain climates e.g. freeze-thaw where temperatures range from just above and below freezing
- amount of discharge affected by climate (wetter - more discharge as less evaporation and more rainfall, more discharge means more velocity)
24
Q
How are waterfalls formed?
A
- a band of hard, more resistant rock overlies a band of soft, less resistant rock (cap rock)
- softer rock is eroded by the river at a faster rate, gradually undercutting the more resistant rock
- this continues (abrasion and hydraulic action), causing a pronounced overhang of resistant rock until it collapses due to gravity
- the height of the waterfall is increased with the formation of a plunge pool - hydraulic action and fragments of cap rock combined with high-energy currents results in abrasion
25
How are interlocking spurs formed?
1. the river at its source is small with limited energy
2. in its upper course, the river erodes vertically
3. the fastest flow of in the river channel will also naturally swing from side to side, causing maximum erosion on the outside of each bend
4. this results in lateral and vertical erosion (especially if local geology has lines of weakness e.g. joints)
5. over time a series of spurs are formed - ridges of upland sloping down to the stream on either side of the valley which are interlocking with those on the other side
26
How are gorges formed?
1. erosional processes e.g. abrasion and hydraulic action cause a waterfall to retreat
2. the undercutting/collapsing process repeats over an extended period of time, forming a steep-sided gorge
27
How are floodplains formed?
1. in the lower course, the river is nearing the sea and carries a huge amount of sediment (alluvium)
2. when the river floods, excess water spills over the surrounding area
3. during this time, river velocity is reduced, it loses energy and deposits the sediment, forming a floodplain
4. the floodplain is shaped by both the lateral erosion of meanders as they gradually migrate downstream and by the deposition of alluvium on the inner bends
28
How are levées/embarkments developed?
1. flooding occurs, the heaviest material is deposited first due to the decrease in river energy, this material makes natural embarkments called levees on the very edge of the river
2. the smaller sediment/alluvium is deposited further from the river as it requires less energy to carry it
3. this results in the natural banks getting steeper over time and forming levees
29
Which human activities and changes in land use have affected rivers? (3)
1. urbanisation
2. agriculture
3. industry
30
How has urbanisation affected rivers? (3)
1. caused towns to grow, meaning fewer permeable surfaces so water flows into rivers, increasing discharge
2. demand for housing means they are built on flood plains, changing natural landscape
3. rivers are channelised or made to flow underground to make room for development, meaning erosion and deposition cannot take place
31
How has agriculture affected rivers? (4)
1. field drains can improve farmland but move water into streams and rivers and can destroy natural wetland landscapes
2. forests are felled to make room for farmland, meaning less trees can intercept rainfall and reduce surface run off
3. abstracting water for irrigation reduces the flow and velocity, so deposition occurs rather than erosion
4/ ploughing fields up and down a slope increases the amount of sediment in rivers - increasing deposition
32
How has industry affected rivers? (2)
1. big user of water, reduces discharge and so leads to less erosion
2. industrial processes pollute rivers if chemicals/waste is spilled into them - destroys plants and animals and changes the natural landscape
33
What are the physical causes of river flooding? (4)
1. rainfall intensity
2. geology
3. snowmelt
4. drainage basin
(all lead to excess water flowing into rivers as surface run-off or groundwater)
34
How does rainfall intensity cause river flooding?
a lot of rainfall occurs over a short time which prevents soil infiltration - so excess water flows to the river as surface run-off - increasing channel flow rapidly so the river rises above bank level
35
How does geology cause river flooding?
rocks like granite are impermeable so water cannot percolate through the thin soil layer above
36
How does snowmelt cause river flooding?
warmer temperatures in spring time will melt the snow creating more surface run-off
37
How do drainage basins cause river flooding?
steep-sided valleys or a lot of tributaries mean that water enters the river system more quickly so the area is more susceptible to flooding
38
What are the human effects of river flooding?
include death, disease, damage to property, insurance claims, loss of livelihoods, loss of crops and farm animals, disruption to transport
39
What are the physical effects of river flooding?
landslides, soil erosion, loss of natural habitats, contamination of water supplies
40
How does a hydrograph work?
shows how a river responds to a rainstorm
rising limb - rapid rise in discharge after a period of heavy rainfall
lag time - the difference in time between peak rainfall and peak discharge - the shorter the lag time, the greater risk of flooding
falling limb - decrease in discharge as the river returns to normal
41
What hard engineering techniques are being used on rivers? (3)
1. dams
2. reservoirs
3. channelisation
42
What soft engineering techniques are being used on rivers? (2)
1. flood plain zoning
| 2. washlands
43
What are dams/reservoirs and how can they lead to change in river landscapes?
- barriers constructed to hold back water in artificial lakes
- natural river valley landscape becomes flooded
44
What are the advantages and disadvantages of using dams/reservoirs as a river management technique?
advantages: store large volumes of water until needed, long-lasting and can be used to generate hydro-electric power
disadvantages: expensive to build and sediment builds up in reservoirs
45
What is channelisation and how can it lead to change in river landscapes?
- deepening and widening the river channel
| - replaces natural meanders and floodplain with an artificial channel
46
What are the advantages and disadvantages of using channelisation as a river management technique?
advantages: allows water to flow more quickly away from areas of flood risk
disadvantages: visually unattractive, more water is taken downstream which may increase the flood risk
47
What is floodplain zoning and how can it lead to change in river landscapes?
- prevents development in areas prone to flooding near rivers
- preserves the natural floodplain
48
What are the advantages and disadvantages of using floodplain zoning as a river management technique?
advantages: reduces number of homes at risk of flooding, allows infiltration
disadvantages: restricts the growth of settlements
49
What is a washland and how can it lead to change in river landscapes?
- an area next to a river that is deliberately flooded to avoid flooding of other areas (e.g. residential or important agricultural areas)
- preserves the natural floodplain landscapes in mid/lower river courses
50
What are the advantages and disadvantages of using washlands as a river management technique?
advantages: creates an area for floodwater to go, allows natural river processes e.g. deposition
disadvantages: might limit land use
51
Where is my river casestudy?
River Dee, Wales
52
How was the the River Dee formed?
1. source is Dduallt - upland area of Snowdonia
2. here, annual precipitation is very high
3. the Dee flows south-easterly, eroding the heavily glaciated upland landscape (igneous/metamorphic)
4. river meanders across a wide floodplain near Cheshire, eroding softer sedimentary rock and depositing sediment
5. a section is artificially straightened, giving a man-made landscape
6. further deposition occurs to form the Wirral estuarine landscape
53
What are the most influential human factors that caused change on the River Dee? (3)
1. 1732-36 channelisation of 8km - improved navigation/discharge/velocity and created an artificial landscape
2. River Dee Regulation Scheme built a series of reservoirs e.g. Llyn Celyn
3. earth embarkments built along the middle course to protect agriculture/properties and prevented further development of the floodplain landscape
54
What are the most influential physical factors that caused change on the River Dee? (3)
1. floodplain landscape (Holt-Worthenbury) has meanders, alluvium and river terrace deposits formed by active erosion and deposition - causing change in river course
2. sea level rise in the Dee Estuary will destroy the estuary landscape
3. if sea levels rise by 1m by 2100, coastal landscapes will replace salt/freshwater marsh landscapes
