river landscapes Flashcards
what is a course?
the path of the river as it flows downhill
rivers have a _____ upper course, a ______ ________ middle course and an almost ______ lower course
steep
gently sloping
flat
what does the long profile of a river show you
how the gradient of the river changes
what can rivers form as they flow down hill
channels and valleys
what does the cross profile do?
shows you what a cross section of the river looks like
what are the two types of river erosion
vertical or lateral
can vertical and lateral erosion happen at the same time?
yes but one is usually more dominant than the other
what does vertical erosion do?
- deepens the river valley and channel making it V-shaped
where is vertical erosion dominant
in the upper course of the river
what does lateral erosion do?
- widens the river channel and valley
where is lateral erosion dominant
in the middle and lower course of the valley
what are the four processes or erosion in rivers
- solution
- abrasion
- hydraulic action
- attrition
what is hydraulic action
when the force of the river water colliding with the rocks breaks rock particles away from the river channel
what is abrasion?
eroded rocks picked up by the river scrape against the channel causing it to wear away - most erosion happens by abrasion
what is attrition
eroded rocks picked up by the river crash into each-other and break into smaller fragments and the edges get rounded off - attrition causes particle size to decrease from source to mouth
what is solution ( erosion)
river water dissolves some types of rock e.g limestone and chalk
what are the 4 different types of river transportation?
- solution
- saltation
- traction
- suspension
what is traction
- large particles like boulders are pushed along the river bed by the force of the water
what is saltation
- pebble sized particles are bounced along the river bed by the force of the water
what is suspension
small particles like slit and slay are carried aloong by the water
what is solution ( transportation)
soluble material e.g limestone dissolve in the water and are carried along.
what is deposition
when a river drops the material is carrying
when does deposition occur
when the river looses velocity and energy
why does the river slow down
- volume of water falls
- amount of eroded material increases
- water is shallower e.g on teh inside of a bend
- the river reaches its mouth
where are waterfalls and gorges found
in the upper course of a river
where do waterfalls form
where a river flows over an area of hard rock followed by an area of soft rock
how are waterfalls formeed
the softer rock is eroded more than the harder rock creating a ‘step in the river’
as the water flows more the step is eroded more
eventually a ‘ steep drop’ is created which is a waterfall
what type of erosion is used to erode the soft rock in the formation of a waterfall
abrasion and hydraulic action
what does fluvial mean
another word for river
how is a gorge formed
after the formation of a water fall:
- the hard rock is undercut by erosion and becomes unsupported and eventually collapses
the collapsed rocks swirl around the foot of the waterfall and erode the soft rock by abrasion which creates a deep ‘ plunge pool’ - over time more undercutting causes more collapse. the waterfall retreats leaving a steep sided gorge
give an example of a waterfall
high force waterfall on the river tees, county durham
why are interlocking spurs created
in the upper course of the river most erosion is vertical as the river lacks the power to erode laterally so the have to wind around the hillsides that stick out into their paths.
what is the interlocking spur
the hillsides that interlock with each other as the river winds around them
where do meanders and ox-bow lakes form
in the middle to lower course of the river where the channel as both deep and shallow sections.
how are meanders formed
- the current is faster on the outside of the bend because the river channel is deeper
- the causes more erosion to happen on the outside of the bend forming river cliffs
- the current is slower on the inside because the river channel is shallower
- so eroded material is deposited on the inside of the bend creating slip-off slopes
how are ox-bow lakes formed
oxbow lakes come from meanders
- erosion on the outside bends cause them to get closer
- until there only a small amount of land between the bends called the ‘neck’
- the river breaks through the neck, usually during a flood.
- and then the river flows along the shortest course
- deposition eventually cuts off the meander forming an ox-bow lake
- ox-bow lakes eventually dry up back into land
what is a flood plain
a flood plain is the wide valley floor on either side of a river which occasionally floods
what happens when a river floods
the water slows down, loses energy and deposits the material that its transporting which builds up the flood plain
what are leeves
they are natural embankments along the edge of a river channel
how are levees formed
- during a flood, eroded material is deposited onto a floodplain
- the Heaviest material is deposited closest to the channel because it gets dropped first when the river loses energy
- over time the deposited material builds up creating levees along the edge of a channel
where are estuaries found
at the mouths of rivers
how are mud flats formed
- at river mouths
- the water is tidal so the river level rises and falls each day
- when the river floods over the banks of the river it carries silt and and sand onto the valley floor
- as the tide reaches the highest point water moves slowly so the river has little energy and deposits sediment
- over time more sediment builds up creating large mudflats
what are estuaries
estuaries are tidal areas where the river meets the sea
what is the name of the river in the river landscape case study
River tees
what are the land forms on river tees
interlocking spur - Calderon snout
source - cross fell in The pennies
water fall - high force
what are the land forms in the middle of the river tees
Barnard castle - river meanders
what land forms are at the end of the river tees
seal sands - estuary
what is river discharge
the volume of water flowing in a river per second mesured in cumers
what do hydrographs show
they plot the river discharge aftera storm
what are the different parts of a flood hydrograph
- peak discharge
- lag time
- rising limb
- falling limb
- base flow
what is the peak discharge in a hydrograph
- the highest point of discharge
what is the lag time in a hydrograph
the delay between the peak rainfall and the peak discharge
what is the rising limb in a hydrograph
the increase in river discharge as rainwater flows into the river
what is the falling limb in a hydrograph
the decrease in river discharge as rainwater flows into the river
how does flooding occur
when a rivers level rises so much that it spills over the banks
why does lag time occur in hydrographs
becuase most rainwater doesnt land directly in the river channe. it flows quickly overland or soaks into the ground and flows to the channel
what are some physical factors that affect flood risk
- heavy rainfall
- geology
- relief
- prolonged rainfall
how does heavy rainfall affect flood risk
the water arrives too quickly to infiltrate, so theres alot of surface runoff which increases discharge
how does geology affect flood risk
some rocks eg. granite + clay soils are impermeable and dont allow infiltration so surface run off is icrease
what is surface run off
when preciptation runs off the landscape
who does prolonged rainfall affect flood risk
prolonged rainfall can saturate the soil as there is more time. but any further rain fall cant infiltrate which increases surface run off
how does relief affect flood risk
if the river is on a steep sided valley water will reach the river quicker as it can flow faster down steep slopes which rapidly increases discharge.
what are human factors that affect flood risk
- urbanisation + buildings
- removing trees
- climate change + burning fossil fuels
how does urbanisation and buildings affect flood risk
buildings and roads are often made from impermeable rock like concrete + tarmac so water cant infiltrate + increases surface run off
man made rains also send water directly to river which increases discharge
how does removing trees affect flood risk
- trees intercept water on their leaves which then evaporates
- trees take in and store water from the ground
so cutting them down increase amount of water going to river
how does climate change affect flood risk.
- people burn more fossil fuels that make the atmosphere warmer. the warmer atmosphere can hold more moisture so when it releases it there is heavier rainfall
what is the difference between hard engineering and soft engineering
hard - man-made structures built to control flow of rivers and reduce flooding
soft- using the knowledge of rivers to reduce the effects of flooding
what are different methods of hard engineering to reduce the risk of flooding.
- dams and reservoirs
- channel straightening
- embankments
- flood relief channels
what are dams + reservoirs
dams - dams are barriers built across rivers
reservoirs - artificial lake that is formed behind the dam
what are the benefits of using dams and reservoirs in reducing the risks of flooding?
- store water after heavy rain
- controls water flow and prevents floods down stream
- can be used to generate hydroelectric power
what are the disadvantages of using dams and reservoirs in reducing the risks of flooding?
- dams are expensive to build
- creating a reservoir can flood existing settlements
- material is deposited into reservoir instead of along the rivers course so farmland downstream can be less fertile
what is channel straightening
meanders are removed by building straighter artificial channels
what are the advantages of channel straightening in reducing the risks of flooding?
water leaves area more quickly rather than building up so flood risk is flower
what are the disadvantages of channel straightening in reducing the risks of flooding?
- flooding may happen downstream instead
- faster moving water may cause more erosion downstream
what are the advantages of enbankments in reducing the risks of flooding?
river can hold more water so floods are less frequent
what are enbankments
flood managment
raised walls built along river banks
what are the disadvantages of embankments in reducing the risks of flooding?
- expensive
-if they break or water rises above there is a severe risk of flooding
what are flood relief channels
channels are built to divert water around built up areas or to divert excess water if river levels are too high
what are the advantages of flood relief channels in reducing the risks of flooding?
- gates on the channels mean that release of water is controlled
what are the disadvantages of flood relief channels in reducing the risks of flooding?
increased discharge where relief channel rejoins teh river
what are the different types of soft engineering in reducing the risks of flooding?
- flood warning and preperation
- flood plain zoning
- planting trees
- river restoration
what is flood warning and preparation
- environment agency issue flood warning through TV or radio etc
- buildings are modified to minimise damage]
- sandbags + flood boards prior to floods
what are the advantages of flood warning and preparation in reducing the risks of flooding?
- give people time to prepare and place sandbags and move possessions upstairs
what are the disadvantages of flood warning and preparation in reducing the risks of flooding?
- doesn’t prevent floods
-modifying buildings are expensive - doesn’t guarantee safety - false sense of security
what is flood plain zoning
restrictions that prevent building on parts of the flood plain that are likely to get flooded
what are the advantages of flood plain zoning in reducing the risks of flooding?
flood risk reduced as there are fewer impermeable surfaces
- impact reduced as no buildings to damage
what are the disadvantages of flood plain zoning in reducing the risks of flooding?
- expansion of an urban area is limited
- cant help in areas with existing buildings
how does planting trees reduce the affects of flooding
– trees intercept water on their leaves which then evaporates
- trees take in and store water from the ground
what are the advantages of planting trees in reducing the risks of flooding?
- flood risk + discharge decreases
what are the disadvantages of planting trees in reducing the risks of flooding?
- less land for farming
what is river restoration
making the river more natural by removing man made structure e.g leeves so the flood plain can flood naturally
what are the advantages of river restoration in reducing the risks of flooding?
- discharge is reduced so less risk of water flowing down stream
- little maintenance is needed + more habitats for wildlife
what are the disadvantages of river restoration in reducing the risks of flooding?
- local flood risks can increase
why was a flood management scheme need in oxfard?
- oxford sits at the confluence of the river Thames and river cherwell - the proxminity of these river channels means oxfard is prone to flooding
- the floods restricted people access to work + services
- prevented tourists vising historic centre
- damaged the local economy
what happened in 2007 in oxfard
- intense flooding + flash floods
- over 250 homes had to be evacuated
-A420 road was flooded for 100 metres
what was the Oxford flood management scheme called and when was it created
oxford flood alleviation scheme
2014
what are the different parts of the Oxford flood alleviation scheme?
- span 5km
- includes hard + soft engineering
- creating embankments + flood walls using excavated material
- creating areas of woodland + floodplain meadow to decrease peak discharge
- increasing water storage in an existing bypass channel.
what are the social issues of the Oxford flood alleviation scheme?
positive + negitive
- compulsory purchase orders were send to landowners whose land was need to widen the flood plain - some people did not want to sell their land
- construction disrupt residents lives - noise pollution
- improve public footpaths
- residents will feel more confident that their homes wont flood
what are the economic issues of the Oxfard flooding allevation scheme?
positive + negitive
- cost over 150 million pounds in total
- homes + businesses will be better protected so less risk of expensive damage.
what are the enviromental issues of the Oxfard flooding allevation scheme?
- 2000 trees and 2 hectres of grassland removed. they will be replanated but will take a while for vegitation to grow back
- scheme will create over 20 hectares of new riverside habitats improving biodiveristy.
Where does the River Tees flow?
from the pennine hills to the northen sea
what is the soft rock and hard rock on the high force waterfall in the river tees
soft: limestone
hard: dolerite
