Own Knowledge - Rivers Flashcards
types of weathering
physical - freeze thaw
chemical - acid rain
biological - roots of plants
types of mass movement
sliding
rock fall
slumping
types of erosion
hydraulic action - sheer force of the water
abrasion - material carried by the river being rubbing against banks and bed of the channel, wearing it away
solution - minerals dissolve into water - slightly acidic - dissolve rocks
attrition - sediment particles collide with each other - rounder and smaller
types of transportation
traction - rolling along river bed
saltation - bounce over eachother on the river bed
suspension - the water flow carries silt and clay-sized particles
solution - river water dissolves some minerals
how do interlocking spurs form
- upper course
- erode downwards
- flow around the hardest parts of the rocks
how do waterfalls form
- band of hard more resistant rock lies over a band of soft rock
- river erodes less resistant rock at a faster rate - undercutting it
- eroded by hydraulic action and abrasion
- hard rock overhangs
- hard rock falls under force of gravity
- falling rocks cause erosion of the river bed and the formation of PLUNGE POOL
- gorge forms as waterfall retreats = soft rocks eroded and hard collapses - gorges form in hard rock where vertical erosion is dominant
how do meanders form
- found in flood plain
- highest velocity on outside of the bend - lateral erosion
- forms a RIVER CLIFF
- inside of bend - velocity less - deposition
- forming a POINT BAR
how do oxbow lakes form
- rivers erode outside of bend fastest
- narrows the neck
- eventually erodes through neck
- new river by passes the meander
- dries up leaving an oxbow lake
how is a flood plain formed
- formed by both erosion and deposition
- lateral erosion on outside of bends of meanders means they MIGRATE across valley floor + erode Vally sides = valley floor becoming wide and flat
- during floods - flood water spreads across valley floor + deposit fine sediments called ALLUVIUM as it loses energy - flat land
how do levees form
- natural embankments of sediment on either side of a river
- during a flood water come out of channel and lose velocity
- deposits the larger + heavier material first on its bank
- repeated flooding causes these banks to get higher - forming levees
how do deltas form
- when rivers meet another body of watet eg. ocean - loses velocity + deposits sediment
- if river deposits faster than it erodes = sediment builds up in a fan-shaped DELTA
how does width change from source to mouth
- increases
how does depth change from source to mouth
increases
how does velocity change from source to mouth
increases
how does discharge change from source to mouth
increases
how does gradient change from source to mouth
decreases
how does channel roughness change from source to mouth
becomes smoother = less friction
how does sediment size change from source to mouth
becomes smaller + rounder
define lag time
the difference between peak rainfall and peak discharge
flashy hydrograph
- steeper rising limb
- short lag time
- higher peak discharge
subdued hydrograph
- gentler rising limb
- longer lag time
- lower peak discharge
how does drainage size and shape affect hydrograph
- small, elongated = higher discharge
- circular = lower discharge
bridging points on river severn
Shrewsbury
antecedent conditions - river severn 2007
140mm - highest in 100 years
why is the risk of flooding increasing
- increasing population = building on floodplains
- changes to land use = urban development creates more impermeable surfaces
- changes to weather patterns = climate change
Tewksbury damage
- 4800 homes affected
- each home had estimated repair cost of 20,000 - 30,000 pounds
- local council - 140,000 pounds
who is responsible for managing the risk of flooding
environment agency
how does the environment agency reduce chance of flooding
catchment management = rating the risk of properties
hard + soft engineering
hard engineering strategies
- flood walls
- embankments
- flood barriers
building infrastructure to overcome challenges
advantages and disadvantages of embankments
- high banks built on or near a river / man made levees
advantages
- stop water from spreading into areas where it could cause problems - eg. settlements
- they can be earth and grass - which blend into environment
disadvantage
- flood may go over the embankments
- can burst under pressure, causing even greater damage
advantages and disadvantages of flood walls
artificial barriers designed to raise the height of river banks
advantages
- increases capacity + prevent water from spreading
disadvantages
- expensive to build
- may cause flooding downstream
- ugly
advantages and disadvantages of demountable flood barriers
a temporary structure that is only installed when needed
advantages
- put up and taken down when needed
- prevent so much ugliness
disadvantages
- may not be installed in time
advantages and disadvantages of permanent flood barriers
flood gates built near the river mouth to prevent a storm surge form flooding
advantages
- gates can be closed when a high surge is forecasted
- able to protect large areas
disadvantage
- high cost
- ugly
examples of soft engineering
- flood plain retention
- river restoration
working with nature to encourage natural processes
advantages and disadvantages of flood plain retention
strategies to maintain rivers original flood plain = allowing rivers to flood and intentionally allowing areas of floodplain to build up - this slows down the river flow reaching areas of economic importance + planting trees
advantages
- slow waters down
- recover a rivers natural sedimentation process - helps the soil more efficient at storing water
disadvantage
- may require a change in land use - eg. a change in farmland
advantages and disadvantages of river restoration
restoring a river to its natural course of meanders to slow rivers down + remove impermeable surfaces and replace with natural materials to promote infiltration
advantages
- more attractive for recreation
- create natural habitats which benefit wildlife
disadvantages
- changes in land use
