Rivers

Question 1

What percentage of the earths water is freshwater (+ where is that water stored)?

Answer 1

2.5% of earths water -> freshwater
68.7% is glaciers and ice sheets
30% ground water
1.3% rivers, soil moisture, lakes, atmosphere

Question 2

Define hydrological cycle

Answer 2

Continuous circulation of water in the earth-atmosphere system
Close system -> water recycled

Question 3

What are examples of stores in the hydrological system?

Answer 3

Water in atmosphere
Surface stores -> puddle, lake, river, interception (on leaves and such)
Aquifers -> permeable rocks (can hold water)
Ice and snow
Seas and oceans

Question 4

What is the hydrological cycle?

Answer 4

Evaporation:
Change of water from liquid -> gas due to heat (sun)

Condensation:
Water cools and changes from gas -> liquid (creates clouds)

Transpiration:
Plant releases water vapor from their leaves

Precipitation:
Transfer of water from atmosphere to surface (sleet, snow rain)

Percolation:
Transfer of water down into rocks/aquifers

Interception:
Leaves catch rain as it falls

Infiltration:
Water moves down from surface to soil

Question 5

What are the different types of flow?

Answer 5

Throughflow:
Movement of water through soil between groundwater store and surface

Groundwater flow:
Flow of water through rock

Evapo-transpiration:
Combined transfer of water vapor from earths surface and plants

Overland flow/surface runoff:
Water flowing across surface

Question 6

What are drainage basin?

Answer 6

Very important part of system

Drain all water which lands on earths surface
Open system
Every one has different: rock type, relief, land use, shape, size

Question 7

What are features of a drainage basin?

Answer 7

Watershed:
an area or ridge of land that separates waters flowing to different rivers, basins, or seas

Source:
the point furthest from the mouth where the river starts, this can be an upland lake, spring or glacier

Confluence:
when two rivers converge into one river

Tributary:
small river that flows into a larger river

Mouth:
where a river enters the sea/ocean and sometimes a lake

Question 8

What is drainage density?

Answer 8

A quantity that can describe the physical parameters of a drainage basin

Defined by the number of tributaries in the drainage basin
Lots -> high drainage density
Few -> low drainage density

Question 9

What are the four erosion types in a river?

Answer 9

Hydraulic action:
Force of water removing material from bed and bank

Abrasion:
Materials carried by river scrape away at bed and bank

Attrition:
Material carried by river hit each other and pieces become rounder+smoother

Corrosion (solution):
when rocks are dissolved by the slightly acidic water

Question 10

What is vertical and lateral erosion?

Answer 10

Vertical:
Dominant in upper course of rivers
Increase depth of river/valley -> erodes downward

Lateral:
Dominant in middle and lower course
Increase the width of the river/valley -> erodes sideways

Question 11

What are the 4 processes for transport?

Answer 11

Traction:
Large rocks (or material) rolled along river bed

Saltation:
Smaller material lifted by the water -> bounces

Suspension:
Lighter material carried by river flow

Solution:
Material dissolved in the water

Question 12

What is deposition?

Answer 12

When a river doesn’t have enough energy to carry material it drops them

Question 13

What causes the reduction of energy in deposition?

Answer 13

Reduced discharge (lack of precipitation, abstraction (taking water))
-> friction from river bed and banks
-> friction inside bend
-> tide influence flow at estuaries and mouths
Decreased gradient (slope)
Slower flow on the inside of a bend (shallower)
River enters sea/ocean or lake

Question 14

What are bedload and alluvium?

Answer 14

Bedload -> larger materials which are deposited first

Alluvium -> smaller materials (gravel, sand slit) which are deposited further down stream

Question 15

How does the Bradshaw model show how the characteristics of a river change as a result of erosion, transportation and deposition?

Answer 15

As you go down stream:
Increase:
Discharge
Channel width
Channel depth
Average velocity
Load quantity

Decrease:
Load particle size
Channel bed roughness
Slope angle

Question 16

What is the wetted perimeter?

Answer 16

the measure of how much water contact there is with the bed and the banks of a river

Question 17

What are river loads?

Answer 17

the total amount of sediment being transported

Question 18

What are the types of sediment in river loads?

Answer 18

Dissolved (solutes from chemical weathering of bedrock and soil) , suspended (suspended in the water) and bed load (along the bottom of the river)

Question 19

Describe the form of the river valley as a long profile

Answer 19

Shows change in gradient
Most have a concave shape
Source upland
Upper course is much rougher and steep
Middle course -> gradient decreases
Lower course -> gradient decreases and almost flat

Question 20

Describe the form of the river valley as a cross profile

Answer 20

Cross section from one bank to the other

Upper:
Shallow with steep sides
Narrow
Low velocity
Rough channel bed
Large bed load
High friction
Vertical erosion

Middle:
Deeper
Gentler sides
Wider
More velocity
Material decreases
Smoother bed
Lower friction
Lateral erosion

Lower:
Deeper
Flat
Wider
More velocity (minus mouth)
Smooth bed
Low friction
Deposition-> dominant

Question 21

Describe the shape of the valley at different points

Answer 21

Upper:
Narrow V shape (spare energy used to transport boulders -> vertical erosion)
Narrow, rough, slow flow channel
Many large boulders, turbulent waters
Mostly vertical erosion
Traction and saltation
hydraulic action, attrition and abrasion

Middle:
Deeper and wider, more of a U shape
Lots of deposits
Lateral erosion
Discharge increase -> velocity increase
Suspension

Lower:
Wide valley and large channel
Smaller rocks, smother channel
Fast flowing river
Lateral erosion

Question 22

How is a V shaped valley formed?

Answer 22

Vertical erosion -> cuts down into river bed deepens channel
Weathering and mass movement -> material from sides collapsing into river
Steep V shape

Question 23

How are interlocking spurs created?

Answer 23

Upper course of river -> meander
Erosion on outside of bends
Upland -> interlocking spurs

Question 24

How are waterfalls and gorges formed?

Answer 24

Formed where there is a drop in the river bed from one level to another
Drop-> change in hardness of rock (hard on soft)
Mainly hydraulic action and abrasion

Process:
Soft rock erodes quicker, undercuts harder rock and creates steep drop-off (and pool at bottom)
Creation of overhang of hard rock -> collapses
Over hang -> pool and increases abrasion and pool is deeper
Cycle (cliff retreated creates steep gorge)

Question 25

How are potholes formed?

Answer 25

weakness or crack or fault line is exposed
Abrasion or hydraulic action erodes the fault
-> pothole

Many become bigger and merge -> river bed lowered due to vertical erosion

Question 26

How are meanders formed?

Answer 26

Fastest water -> outside of river bend -> creates river cliff -> collapse and edge moves out

Slowest water -> inside of river bend -> deposition (slip off slope) -> meander migrates

Question 27

How are oxbow lakes formed?

Answer 27

Size of meanders increase
Erosion on outside -> meander neck (the bend)
Flood -> river cut through neck of meander and form a straight line
Flow at entry and exit -> slower -> deposition
Cut off meander -> oxbow lake

Question 28

How are deltas formed?

Answer 28

River enters large body of water -> deposition
If there is no tidal current (calm water needed), deposition will form deltas
Fine material deposited can block the channel
River divided into smaller channels called distributaries

Buildup breaks through surface-> delta

Question 29

How are floodplains and levees formed?

Answer 29

Floodplains → flat expanses of land either side of the river (prone to flooding)
The migration of meanders -> formation of floodplain

High discharge-> overflow the bank -> flood floodplains -> material deposited across the floodplain and height increase-> heaviest material despotism closest to river=levees

Question 30

What are some hazards presented by rivers?

Answer 30

Flooding and erosion
Natural (rain, landslides, snow melting, storm surges)
Human (urbanisation, deforestation, dams and bridges, climate change)

Erosion causes flooding

Hazards:
Floodwater-> spread disease, breeding ground for mosquitos, bacteria
Death and injuries
Infrastructure damaged
Erosion -> lose of land and housing
Destruction of crops

Question 31

What are some opportunities presented by rivers?

Answer 31

Silt deposit-> rich in minerals and nutrients (good soil)
River -> food source
Floodplains -> good for construction and transport networks
Water -> irrigation
Tourism
Electricity
Transport goods and people

Question 32

What can be done to manage the impact of floods?

Answer 32

Flood prediction
hydrograph (predict river reaction to rainfall)
Lag time is most important
Short lag time and steep rising limb -> high risk of flooding

Question 33

What are features of a hydrograph?

Answer 33

Base flow -> normal amount
Peak rainfall -> highest rainfall
Rising limb -> increase in rive discharge
Peak discharge -> high level of discharge
Lag time -> different between peak rainfall and discharge
Recessional limb-> river discharge returning to base flow

Question 34

What factors effect lag time?

Answer 34

HUMAN:
Deforestation (less interception and infiltration)
Urbanisation (concrete and tarmac)
Agriculture (bare soil and ploughing)
Climate change (rising global temps and etc)

PHYSICAL:
Relief (steep slopes reduce infiltration)
Rock type (impermeable rocks)
Soil (frozen, saturated, or compacted soil)
Weather (prolonged or heavy rainfall or snow)
Seasonal variations (higher temps melt snow, etc)
Drainage density (more tributaries, more flood)
Vegetation (little -> more flood)

Question 35

What are some ways of flood management (soft engineering)?

Answer 35

River restoration (stabilisé banks, connecting floodplains)
Wetland conservation (place of excess water)
Catchment management plans (asses risk and create outline)
Flood plain zoning (only certain uses for floodplain)
Afforestation (planting vegetation)

Soft engineering:
Minimises damage
Works with environment

Question 36

What are some ways of flood management (hard engineering)?

Answer 36

Dams and reservoirs (amount of discharged controlled)
Embankments of levees (increase capacity of river)
Straightened channels (flows quicker in vulnerable areas)
Flood relief channels (water flow out of main channel)
Spillways or overflow channels (excess water from main channel)

Hard engineering:
Building structures or changing the river channel

Question 37

What is river discharge/volume?

Answer 37

the volume of water flowing through a river channel; measured at any given point in cubic metres per second.

Question 38

What is river velocity?

Answer 38

the speed at which water flows along it.