Rivers Flashcards
define abrasion
rocks carried along river wear down river bed/banks and scrape against it wearing it down
side profile
cross section of river bed
define attrition
rocks being carried by the river smash/collide together and break into smaller smoother rounder particles
dams and resevoirs
barrier built to interrupt river flow and create a water storage lake to control the discharge of a river
discharge
the quantity of water that passes a given point on a stream or river bank within a given period of time
embankments
raised banks constructed along the river; they effectively make the river deeper so it can hold more water - protects land
lateral erosion
sideways erosion by a river on the outside of a meander channel. it eventually leads to the widening of the valley and contributes to the formation of a flood plain
estuary
the tidal mouth of a river where it meets the sea; wide banks of deposited mud are exposed at low tide
flood plain zone
attempts to organise the flood defences in such a way that land is near the river and often floodss - can be used for pastoral farming, playing fields etc
flood plain
a relatively flat area forming the valley floor on either side of a river channel, which is sometimes flooded
hydrograph
a graph which shows the discharge of a river related to rainfall over a period of time
levee
embankment of sediment along bank of river - may be formed naturally by regular flooding or be built up by people to protect an area against flooding
saltation
small rocks and particles carried by river flow bounce down the river bed
soft engineering
involves the use of natural environment surrounding a river using schemes that work with the rivers natural processes
traction
large particles e.g boulders and rocks are rolled along the river bed by the force of water at times of high discharge
solution
soluble particles are dissolved in the river such as calcium carbonate (requires little energy)
channel straightening
removing meanders from the river to make the river straighter - allows it to carry more water downstream so it doesn’t build up and is less likely to flood
suspension
fine solid material (clay/sand particles) held/carried in water while the water is moving even at low discharges
traction
the rolling of boulders and pebbles along the river bed
vertical erosion
downward erosion of river bed
water table
Current upper level of saturate rock soil where no more water can be absorbed
Ground water flow
Water flowing through the rock layer parallel to the surface
Through flow
Water flowing through the soil layer parallel to the surface
Surface run off
Water flowing on top of the ground
Evaporation
Water lost from ground/vegetation surface
Transpiration
Water lost through pores in vegetation
Ground water
Water stored in rock
Perculation
water seeping deeper through the rock
Soil moisture
Water held in the soil layer
Infiltration
Water sinking into the soil/rock from the ground surface
surface storage
Water held on the ground surface e.g. puddles
interception
Water being prevented from reaching the surface ground by vegetation or trees
how does human activity affect surface run-off
tarmacking roads increases flood risk as water is infiltrated
how does human activity affect interception
deforestation stops stem flow as less water is intercepted
what is the source
the start of a river
what is confluence
where a tributary joins the main river
describe the characteristics of upper course
narrow steep
describe the characteristics of middle course
wider shallow
describe the characteristics of lower course
very wide flat
explain why the cross profile of a river channel and valley varies downstream
The cross profile of a river generally changes from being a V shaped valleys and with a narrow channel where the dominant processes are erosion. Erosion tends to be vertical (straight down into the land) and so cuts steep sided valleys.
In the middle section of the drainage basin the river starts to erode laterally. This section contains meanders and Ox bow lakes, and the river creates a flood plain often with Levees. Here, Material is deposited and erosion can also occur.
In the lower drainage basin deposition dominates as a river enters a sea or lake, the valley is at its widest and deltas and estuaries are major landforms and habitat. The river channel is especially wide here because of the increased discharge and flat channel.
hard engineering
involves the building of entirely artificial man made structures using various material e.g concrete or rock to reduce impacts of river processes
what is meant by fluvial processes
water processes in the river e.g erosion, transportation, deposition
where is erosion most dominant in a river
upper course
define erosion
the wearing away of material
why does the river tend to erode vertically in the upper course
discharge is smaller and the river cuts down in a bit to get to sea level
what controls the size of a rivers load
the discharge
what is the dominant process in the lower course
deposition - river flow slows down, water looses energy
why does erosion tend to be lateral in the middle course
material carried by the river erodes the banks
hydraulic action
occurs when the force of the river compresses air trapped in cracks in banks - this increased pressure weakens and gradually wears away the banks
what is material carries by the river known as
the load
name 4 erosional processes
hydraulic action
attrition
solution
abrasion
name 4 transformational processes
saltation
traction
solution
suspension
when does deposition occur in a river
The velocity of the water has slowed, thus decreasing its energy. The heaviest material that takes the most energy will be dropped first Deposition will happen when a river bursts its banks at a floodplain or when the river reaches the sea to form a delta
Describe river severn upper course
steep, narrow
waterfalls+gorges+v-shaped valleys+interlocking spurs
mainly erosion
load is large and angular
describe river severn middle course
wider, more shallow
meanders (near welshpool)
oxbow lake (near shrewsbury)
erosion and transportation
load is slightly smaller and rounder
describe river severn lower cours
very wide, flat
levees - minsterworth
floodplain - Tewksbury
estruary - severn estuary
mudflats - Chepstow
transporation and deposition
load is small and round
what is meant by land forms
a recognisable naturally formed feature on the earths surface
characteristics of interlocking spurs
hillsides which interlock with each other as the left over river channel winds around them
formation of interlocing spurs
vertical erosion in the upper course creates steep sided v-shaped valleys
rivers lack vertical erosion so wind around hillsides
formation of a GORGE /waterfall
Water runs over alternating bands of hard rock on top and soft rock beneath it.
Erosion will start to break down rocks through processes of abrasion, hydraulic action and solution.
Hydraulic action wears away the soft rock as water runs over it as it is less resistant than the hard rock above.
Overtime the water starts to undercut the hard rock.
The rock is left unsupported and as a result of its weight it collapses into the river bed.
Rocks that have fallen are either transported down the river or scrape away at the base of the river through the process of abrasion. This coupled with continuous friction of water causes a dent in the river to start to form. This is known as a plunge pool.
The erosional processes repeat and overtime the water fall retreats backwards. Once the water fall retreats a steep sided gorge is left behind
what is a meander
a bend in the river
how does a meander differ on the inside vs outside
Water moves faster around the outside of the bend as it has the most energy and due to the decreased friction of the outer bend as it is steeper there.
Therefore more eposition occurs on the inside of the bend e.g sand and shingle often forming a slip off slope
characteristics of oxbow lake
horse shoe shape
isolated from rest of river
narrow neck
formation of ox-bow lake/meander
Water flows over land, water swings to the outside of the river where there is less friction.
As the river erodes the river bank, a bend starts to occur this is known as a meander.
On the inside of the bend the flow is slower so we get deposits of sediment.
The neck of the river grows narrower.
When the neck of the river breaks through, the river will take the shortest route and take on a straight course. This lake becomes sealed off altogether as a result of deposition. This is known as an oxbow lake.
what is aluvium
nice rich fertile soil - good for farming e.g growing crops + vegetation
Formation of levee
Before a floor water is held within channel. During flood, water passes over surface and increased friction occurs resulting in slower flow.
The heaviest material is deposited first at the closest point to the river. This is because the water has not got enough energy to carry the materials.
The finer, thinner sediment is transported and deposited further away from the river.
The levee often gets higher after successive floods.
flood plain formation
As water floods further away from river banks, the sands are deposited next, then the silts and finally the lightest clays. This build up of sand, silt and clays leads to the formation of a flat piece of land either side of the river - just after the levees. Everytime the river flood deposition builds up the floodplain.
define estuaries
Where the river meets the sea. The river here is tidal and when the sea retreats the volume of wate is reduced in the estuary. When there is less water the river deposits silt to form mudflats which are an important habitat for wildlife e.g birds, plants
flood definition
an overflow of a large amount of water beyond its normal limits especially over dry land
What happened to the river severns estuary after last ice age
The melted ice caused a rise in sea level causing low sided valleys to become flooded. This caused the river channel to grow including the estuary
Name 3 human causes for flooding
urbanisation, agriculture, deforestation
Name 5 physical causes for flooding
rock type, basin size, soil saturation, relief, precipitation
Case study for floods
Cumbria floods of 2009
400mm rainfall feel within 24 hours
steep land relief = little time for infiltration
impermeable roads
deforestation
How does rock type cause flooding
Impermeable rocks do not allow water to pass through them (Eg. Clay). Therefore a river is more likely to flood. This is because water will not seep into the rock resulting more water as flowing over land into the river.
how does land relief cause flooding
Steep slopes allow for water sun over the land quickly, leaving little time for water to seep into the soil. Therefore mor water enters the river channels
how does basin size cause flooding
When a river basin is large it is able to store more water, however if it is small it has an increased risk of flooding as it cannot carry as much and so will overflow.
how does urbanisation cause flooding
Building in areas at risk from flooding. Areas are made from impermeable rock (tarmac) which means water runs over the roads into drains and then into the river channel
how does soil saturation cause flooding
When soil can no longer absorb any more water it becomes over saturated and causes flow of water over land.
how does deforestation cause flooding
Trees take up water, therefore if we cut down trees areas will have less trees to uptake the water. Therefore it is rabidly transferred into the river channels.
how does precipitation cause flooding
Torrential rainstorms can lead to sudden flash floods as river channels cannot contain the volume of water falling into them
how does agriculture cause flooding
In arable farming, soil is left unused and exposed to the elements for periods of time. This can lead to more surface runoff.
Name 5 hard engineering river management strategies
Channel straightening
Embankments
Flood relief channel
Damns/Reservoirs
key terms in hydrograph
rising limb
peak discharge (highest recorded discharge following a rainfall event)
falling limb
lag time - the time difference between peak rainfall and peak discharge
Damns/reservoirs management strategy
A dam is a large concrete barrier built across a river to hold back its flow. This causes the valley behind the dam to flood, creating an artificial lake called a reservoir. This controls the amount of water downstream. Water is released in a controlled manner through gates in the dam. If water releases are carefully controlled and monitored, there should be no flooding downstream.
pros;
electricity
attracts tourists
cons;
expensive
disrupts habitats
damns trap sediment
could release green house gases
channel straightening management strategy
Channel straightening is when a meandering section of a river is engineered to create a widened, straightened and deepened course. By doing this, it can carry more water and reduce flood risk. This usually happens on low-lying areas that are highly at risk from flooding
pros;
more water held in channel
decrease flood risk
cons;
needs to be dredged frequently
increases flood risk downstream
embankments management strategy
Embankments are raised river banks. By raising these banks, more water is contained in the channel. This reduces the flood risk. An embankment is made by bulldozers moving huge mounds of impermeable soil on to the river banks to build up their height.
Some embankments are lined with concrete.
pros;
reduce flood risk
cons;
river less attractive recreational purposes
flood relief channel strategy
Flood relief is when another channel is built to deliberately move water away from human settlements during times of high discharge. It is essentially a back-up channel for a river that frequently floods.
pros;
diverts water
cons;
dependent on flood severity
may cause flooding downstream
name 3 soft engineering flood management strategies
Flood plain zoning, afforestation, river restoration
define soft engineering strategies
mitigating risk of flooding river whilst working with the natural environment to not disruptive
define flood watch
Flooding of low-lying land and roads is expected. People should be prepared and watch river levels.
define flood warning
There is a threat to homes and businesses. People should move items of value to upper floods and to turn off electricity and water
define severe flood warning
Extreme danger to life and property is expected. People should stay in the upper floors and turn off electricity and water. People are also informed to leave property
how does river restoration work
It is reverting a river back to how it was before hard engineering. Meanders may be put back in and the river may be dredged to create more space in the channel.
how does flood plain zoning work
Land is divided up into 4 flood risk areas by an environmental agency. low value land use is encouragedh near to the river and high value land away. however overtime erosion may cause the river to advance near urban settlements.
how does afforestation work
Trees are planted near the river to collect (intercept rainfall) precipitation instead of it going into the river and slows down rate of water infiltrating soil - reducing surface run off. Plant soil is fertile and stabilized and the roots of trees reduce river erosion.
two key words to use in writing to describe time and space
temporally
spatially
