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AS Geography > Unit 1: Rivers, floods and management > Flashcards

Unit 1: Rivers, floods and management Flashcards

1
Q

What are drainage basins separated by?

A

Watersheds

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2
Q

What are the inputs, outputs, stores and transfers in the drainage basin?

A

Inputs: Precipitation, solar energy
Outputs: Evaporation, transpiration, discharge
Stores: Puddles, rivers, lakes, soil, groundwater storage
Transfers: Infiltration, percolation, run off, throughflow

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3
Q

What are the 6 features of the drainage basin?

A 
Main river channel 
Source
Tributaries
Confluence
Watershed 
River mouth
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4
Q

Name factors affecting the amount of infiltration:

A
  • Intensity of precipitation
  • Type of slope
  • Nature of the soil
  • Depth of the water table
  • Time
  • Climate
  • Vegetation cover
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5
Q

What’s the interception store?

A

Where water is caught/intercepted by vegetation-stored temporarily

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6
Q

What’s infiltration rate?

A

The speed at which water enters into the soil- measured by the depth of the water layer (in mm) that can enter the soil in one hour

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7
Q

Name some human factors affecting infiltration:

A
  • Urbanisation
  • Deforestation
  • Afforestation
  • Agricultural land use
  • Water resource
  • Land use
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8
Q

Name some human factors affecting interception:

A
  • Deforestation
  • Urbanisation
  • Afforestation
  • Agricultural land use
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9
Q

What’s the water balance (budget)?

A

The difference between the inputs and outputs in a drainage basin.

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10
Q

What does the water budget model show?

A

The balance between the precipitation and evapotranspiration in any given month

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11
Q

What is river discharge and what is the equation for it?

A

The volume of water passing a given point at a given time, measured in cubic metres per second

Velocity (m/s) x cross sectional area (metres squared)

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12
Q

What does a storm hydrograph show?

A

How a river responds to a period of rainfall

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13
Q

What are the physical factors affecting river discharge?

A

Rainfall
Temperature
Relief
Rock Type

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14
Q

What are the human factors affecting river discharge?

A

Urbanisation
Deforestation
Afforestation

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15
Q

What are the 3 river processes?

A

Erosion
Deposition
Transportation

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16
Q

What is the equation for energy?

A

Discharge + height above sea level + gradient

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17
Q

What are the 4 types of erosion?

A

Hydraulic action
Abrasion
Attrition
Corrosion

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18
Q

What are the 4 types of transportation?

A

Traction
Saltation
Suspension
Solution

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19
Q

What is the Hjulstrom curve?

A

A graph to show the relationship between velocity and competence

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20
Q

What’s river competence?

A

The size of the sediment a river can transport

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21
Q

Deposition occurs when:

A
  • Less discharge
  • Less velocity
  • Shallow water occurs
  • Sediment capacity increases
  • River overflows
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22
Q

What type of landforms are in the upper course?

A 
V-shaped valleys 
Rapids
Waterfalls
Braided streams 
Potholes
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23
Q

What landforms are in the middle course?

A

Meanders

Oxbow lakes

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24
Q

What landforms are found in the lower course?

A

Floodplains
Levees
Deltas

25
What are the velocity variables for high velocity?
- High discharge - high hydraulic radius - Low wetted perimeter - Increase in gradient - Centripetal force
26
What's velocity determined by?
Channel shape Roughness of channel bed/banks Channel slope
27
What's channel efficiency measured by?
It's hydraulic radius
28
What's the hydraulic radius equation?
Cross sectional area ÷ wetted perimeter
29
What's the equation for cross sectional area?
Channel width x channel depth
30
What's the wetted perimeter?
The total length of the bed and banks in contact with the water
31
What is velocity like at baseflow and bankfull conditions?
Baseflow: greater frictional drag so lower velocity Bankfull: high velocity
32
How does channel roughness/bedload impact wetted perimeter (WP), hydraulic radius (HR) and velocity (V)?
Large angular bedload: greater WP,lower HR and lower V | Smoother bed: Higher V, greater HR
33
How are rapids created?
Where there is a sudden increase in gradient or where there is an area of large highly angular bedload- increases turbulence and erosion
34
How are waterfalls and gorges created?
- Occurs where hard rock overlays soft rock - Soft rock is undercut by erosion (hydraulic action and abrasion) - Overhanging hard rock collapses - Deep plunge pool develops where soft rock was before - Waterfall retreats upstream - Steep sided cutting is left as the waterfall moves back- forming a gorge
35
How are interlocking spurs created?
In areas f resistant rock, meandering streams and rivers will be incised into the landscape- forming interlocking spurs
36
How are V-Shaped valleys created?
- Vertical erosion in the river channel results in the formation of a V-shaped valley - Over time the sides of this valley are weakened by weathering processes and continued vertical erosion at the base - Mass movement of materials occurs down the valley sides, gradually creating the distinctive V-shape - This material is then gradually transported away by the river when it has enough energy
37
How are potholes created?
- Where there are depressions/fissures, large boulders may become trapped and swirled round by the current - In resistant rock, potholes require hundreds/thousands of years to form
38
How are knickpoints created?
- Each period of rejuventation that results in an incised valley floor, is marked by a knickpoint - Knickpoints are sudden increases in gradient and can be indentified as small waterfalls in the lower course
39
What are incised meanders and how are they created?
Deeper meanders | Created by renewed energy from rejuvenation that increases vertical erosion
40
What are ingrown meanders and how are they created?
- Meanders with an asymmetric profile | - Created when incision is less rapid and lateral erosion is occuring
41
What are entrenched meanders and how are they created?
- Symmetrical cross profile due to rapid uplift | - Incision is rapid and vertical erosion dominates
42
What are river terraces and how are they created?
- When an old floodplain is left suspended at a higher level - Following rejuvenation, the river vertically incises into former valley. Several stages of rejuvenation can create several terraces (think steps)
43
What is eustatic sea level change?
Caused by a change in the volume of sea water as ice caps and glaciers melt and freeze
44
What is isostatic sea level change?
Caused by the uplift and subsidence of land (post glacial rebound)
45
What are the causes of sea level rise?
- Global warming - Sea absorbs high temps and expands - Ice sheets are melting faster than snow is replacing them - Land glaciers are melting - Post glacial rebound
46
What is river rejuvenation?
When an increases in height above sea level increases the erosive power of the river. (Isostatic uplift or eustatic fall increases the height of the river above sea level)
47
What are flood embankments/levees?
Raised banks on either side of the river designed to increase bankfull level
48
What is afforestation?
Planting more trees to increase interception storage and reduce lag time
49
What is channel enlargement?
Creating a bigger channel to higher the velocity, increase efficiency and the cross sectional area of the river
50
What do sluice gates do?
Control the discharge of the river by opening and closing depending on catchment conditions
51
What are flood relief channels?
Smaller, man made channels that take extra discharge to relieve the river
52
What are storage reservoirs?
Areas that store excess water in the upper reaches of the river- expensive to build, but can provide a form of renewable energy
53
What is contour ploughing?
Ploughing the earth so the plough channels do not run directly down slopes
54
What is flood proofing?
Temporary or permanent methods that include flood proof ground walls, sandbags and sealed doors
55
What is flood abatement?
Reduces the possibility of flooding by managing land use upstream- includes afforestation, contour ploughing and reducing the amount of bare earth
56
What are intercepting channels?
Diverting the flow of the river away from settlements, agricultural land and important land uses
57
What is the removal of settlements?
Involves moving built up areas off the flood plain - rarely used
58
How do the factors affecting river discharge effect the storm hydrogaph?
- Rainfall: higher peak discharge, shorter lag time, quick rising limb - Snow melt: steep rising limb - Porous soils/permeable rock: less steep, longer rising limb/lag time - Impermeable rock/frozen ground: steeper rising limb, peak discharge reached sooner, shorter lag time - Small drainage basin: short LT, steeper RL - Summer vegetation: slow response, peak discharge lower - Deforestation: faster response, high peak discharge

AS Geography (5 decks)

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