Rivers Flashcards
(59 cards)
1
Q
When was the Boscastle flood?
A
- 16the August 2004
2
Q
What are the causes of the Boscastle flood
A
- 8 inches of rain in 5-6 hours
- high temperatures/high rainfall
- V shaped valley
- 2 main rivers (Jordan and Valency) confluence
- impermeable rock
- narrow funnel
- saturated soil- groundwater table full
- trees cut down by the river- less interception
- failed to cut down down trees upstream which led to debris in river
3
Q
Effects/ impacts of Boscastle flood
A
- 0 deaths
- 8 minor injuries
- 4 buildings destroyed
- 150 cars wrecked
- 100+ people rescued
- 58 flooded properties
- £50million in cost/damage/loss of income
4
Q
Responses to Boscaslte flood
A
- Everyone rescued
- search + rescue
- temporary shelter- local leisure centre
- 8 helicopters- assisted
5
Q
In rivers where does deposition occur?
A
on the inside bend
6
Q
In rivers where does erosion occur?
A
on the outside bend
7
Q
What landforms are found in the upper course?
A
- v-shaped valleys
- waterfalls
- rapids
- gorges
- interlocking spurs
8
Q
What landforms are found in the middle course?
A
- meanders
- oxbow lakes
9
Q
What landforms are found in the lower course?
A
- floodplains
- levees
10
Q
What is a drainage basin?
A
- an area of land where water collects and flows into a common outlet, such as a river or a lake
11
Q
What is a watershed
A
the boundary of the drainage basin
12
Q
What are the hard engineering strategies for flood management?
A
- dams and reservoirs
- embankments/ levees
- straightening channels
- flood relief channels
13
Q
What are the soft engineering strategies for flood management?
A
- river restoration
- afforestation
- floodplain zoning
- flood warnings
14
Q
What is the purpose of dams and reservoirs?
A
- controls the river flow by blocking the river and letting water in a controlled way
15
Q
What are the advantages of dams and reservoirs for flood management?
A
- multi-purpose can be used for energy production (hydroelectric) and water storage as well as flood control
- provides opportunities for recreation: water sports, fishing
16
Q
What are the disadvantages of dams and reservoirs for flood management?
A
- expensive
- loss of farmland and homes due to reservoir creation
- displacement of people
- affects in ecosystems- can affect fish breeding
- reservoir silts up over time
17
Q
What is the purpose of embankments/levees?
A
Artificially raise the banks of the river, increasing channel capacity
18
Q
What are the advantages of embankments/levees?
A
- increased river capacity means it is less likely to flood
- new river bank creates habitats
19
Q
What are the disadvantages of embankments/levees?
A
- expensive
- visually unattractive
- may fail and lead to more serious flooding
20
Q
What is the purpose of straightening channels?
A
- removes meanders allowing water to flow quicker
21
Q
What are the advantages of straightening channels?
A
- speeds up the movement of water over a short distance
- allows easy navigation for boats
22
Q
What are the disadvantages of straightening channels?
A
- may increase flood risk downstream as the river discharge reaches those areas quicker
- expensive
- affects river ecosystems due to changes in velocity
23
Q
What is the purpose of flood relief channels?
A
- channels built to allow excess water to flow around high value areas
24
Q
What are the advantages of flood relief channels?
A
- effective in reducing the flood risk in hight value areas
- new habitats may be created
- insurance costs may be reduced for people living nearby
25
What are the disadvantages of flood relief channels?
- expensive
- regular maintenance is needed
- disruption to existing habitats
- can be visually unattractive
26
What is the purpose of river restoration?
- restores the river to its natural state with meanders and wetland areas
27
What are the advantages of river restoration?
- increases number of habitats
- restores wetland areas
- slows down water flow reducing flooding downstream
28
What are the disadvantages of river restoration?
- expensive to construct the new channels
- some areas will flood
29
What is the purpose of floodplain zoning?
- restricts land use in areas that are at high risk of flooding and ensures high value buildings are not in floodplain prone areas
30
What are the advantages of floodplain zoning?
- low cost
- conserves habitats on floodplains and wetlands
31
What are the disadvantages of floodplain zoning?
- Restricts areas where houses can be built and may impact on economic development
- can only happen in places where development has not already happened
32
What is the purpose of afforestation for flood management?
- planting of trees to increase interception and infiltration
- trees also use up large quantities of water
33
What are the advantages of afforestation?
- inexpensive
- absorbs and stores CO2
- slows down water transfer, increasing lag time
34
What are the disadvantages of afforestation?
- can increase acidity in the soil
- loss of farmland
35
What is the purpose of flood warnings
- monitoring of rivers to provide people with warnings when flooding may occur
36
what are the advantages of flood warnings?
- helps people to prepare to evacuate if needed
- less expensive than hard engineering
37
What are the disadvantages of flood warnings?
- expensive to set up monitoring equipment
- people may not takewarnings seriously
38
What are the human factors which increase the risk of flooding?
- deforestation
- urbanisation
- agriculture
- climate change
39
What are the physical factors which increase the risk of flooding?
- relief
- rock type
- soil
- weather
- seasonal variations
- drainage density
- vegetation
40
What impact does deforestation have on increased flooding?
- lack of trees reduces interception and infiltration- increasing overland flow
41
What impact does urbanisation have on increased flooding?
- impermeable concrete and tarmac causes increased overland flow
- water flows into the drains reaching the river rapidly
42
What impact does agriculture have on increased flooding?
Bare soil and ploughing increases overland flow, especially where ploughing is downslope
43
What impact does climate change have on increased flooding?
Rising global temperatures may increase storm frequency and intensities
44
What impact does relief have on increased flooding?
Steep slopes reduce infiltration and increase overland flow
45
What impact does rock type have on increased flooding?
Impermeable rocks reduce percolation and increase overland flow
46
What impact does soil have on increased flooding?
- frozen, saturated or compact soil reduces infiltration and increases overland flow
- some soil types such as clay reduce infiltration and increase overland flow
47
What impact does weather have on increased flooding?
- heavy or prolonged rainfall means that the rate at which water reaches the surface exceeds the infiltration rate leading to increased overland flow
- after a period of snow, rising temperatures can cause rapid melting, which increases overland flow
48
What impact does vegetation have on increased flooding?
- where there is little natural vegetation there is reduced interception leading to increased overland flow
49
How are interlocking spurs formed?
- formed in the upper course of a river, where vertical erosion creates a v-shaped valley
50
How are waterfalls formed?
- Waterfalls form where there is a change from hard to soft rock under the river
- Hydraulic action and abrasion are the main erosional processes
- The soft rock erodes quicker, creating a ‘step’ in the river
- This step is eroded more and more until a steep drop is eventually created
- The hard rock is undercut by erosion, becomes unsupported and collapses
- The collapsed rock swirls around at the bottom and creates a ‘plunge pool’ via abrasion
- Over time more undercutting causes more collapses, the waterfall retreats leaving steep sided gorges
51
How are v-shaped valleys formed?
- Vertical erosion takes place
- this cuts down into the river bed and deepens the river channel
- weathering and mass movement leads to material from the valley side’s collapsing into the river
52
How are meanders formed?
- The faster moving water is on the outside bend where the river is deeper- less friction to slow the water down- more energy in the water
- So erosion takes place on the outside of the bend, undercutting the riverbank forming a river cliff
- The slower moving water is on the inside bend where the river is shallower- more friction- less energy
- So deposition occurs, due to lack of energy, on the inside bend, forming slip-off slopes
- Over time the result or this erosion and deposition means that the meanders gradually change shape and migrate across the floodplain
53
How are oxbow lakes formed?
- A meander is a winding bend in a river, which over time due to erosion and deposition, gradually changes
- The neck of the meander narrows due to lateral erosion on opposite sides of the meander bend
- The meander neck is broken through, usually during high flood conditions
- The river now flows along the shorter route, by-passing the old meander
- Deposition occurs at the edges of the new straight section, cutting off the old meander
- This old meander now forms an ox-bow lake, separated from the main river
- Gradually the ox-bow lake silts up to form marshland
54
What is a flood plain?
The wide, flat expanses of land either side of the river, which occasionally floods
55
How are floodplains created?
- When rivers flood, the water slows down, loses energy and deposits the material that its transporting, this builds up the flood plain
56
What are levees?
- natural embankments along the edges of a river channel
57
How are levees formed?
- during a flood, eroded material is deposited over the whole flood plain
- but the heaviest material is deposited closest to the river channel as it is dropped first when the river slows down and loses energy
- over time the deposited material builds up, creating levees along the edges of the channel
58
What is an estuary?
- where the river meets the sea
- large deposits of sediment form mudflats and salt marshes
- these are the result of high tides bringing sediment which is mixed with the sediment carried by the river
59
How are mudflats and salt marshes formed in an estuary?
- the deposited sediment from the tide and river builds up in layers to form mudflats which rise above the water surface
- vegetation begins to grow on the mudflats to form salt marshes
