Rivers Flashcards
What percentage of the earths water is freshwater (+ where is that water stored)?
2.5% of earths water -> freshwater
68.7% is glaciers and ice sheets
30% ground water
1.3% rivers, soil moisture, lakes, atmosphere
Define hydrological cycle
Continuous circulation of water in the earth-atmosphere system
Close system -> water recycled
What are examples of stores in the hydrological system?
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
What is the hydrological cycle?
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
What are the different types of flow?
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
What are drainage basin?
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
What are features of a drainage basin?
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
What is drainage density?
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
What are the four erosion types in a river?
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
What is vertical and lateral erosion?
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
What are the 4 processes for transport?
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
What is deposition?
When a river doesn’t have enough energy to carry material it drops them
What causes the reduction of energy in deposition?
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
What are bedload and alluvium?
Bedload -> larger materials which are deposited first
Alluvium -> smaller materials (gravel, sand slit) which are deposited further down stream
How does the Bradshaw model show how the characteristics of a river change as a result of erosion, transportation and deposition?
As you go down stream:
Increase:
Discharge
Channel width
Channel depth
Average velocity
Load quantity
Decrease:
Load particle size
Channel bed roughness
Slope angle
What is the wetted perimeter?
the measure of how much water contact there is with the bed and the banks of a river
What are river loads?
the total amount of sediment being transported
What are the types of sediment in river loads?
Dissolved (solutes from chemical weathering of bedrock and soil) , suspended (suspended in the water) and bed load (along the bottom of the river)
Describe the form of the river valley as a long profile
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
Describe the form of the river valley as a cross profile
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
Describe the shape of the valley at different points
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
How is a V shaped valley formed?
Vertical erosion -> cuts down into river bed deepens channel
Weathering and mass movement -> material from sides collapsing into river
Steep V shape
How are interlocking spurs created?
Upper course of river -> meander
Erosion on outside of bends
Upland -> interlocking spurs
How are waterfalls and gorges formed?
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)
How are potholes formed?
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
How are meanders formed?
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
How are oxbow lakes formed?
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
How are deltas formed?
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
How are floodplains and levees formed?
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
What are some hazards presented by rivers?
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
What are some opportunities presented by rivers?
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
What can be done to manage the impact of floods?
Flood prediction
hydrograph (predict river reaction to rainfall)
Lag time is most important
Short lag time and steep rising limb -> high risk of flooding
What are features of a hydrograph?
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
What factors effect lag time?
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)
What are some ways of flood management (soft engineering)?
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
What are some ways of flood management (hard engineering)?
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
What is river discharge/volume?
the volume of water flowing through a river channel; measured at any given point in cubic metres per second.
What is river velocity?
the speed at which water flows along it.
