Studied by 2 peopleupland area
pennines
lowland area
anglesey
river in uplands
river severn
river in lowlands
river thames
fluvial erosion
erosion in rivers
erosion
the wearing away of rocks by a moving agent with the materials transported away
hydraulic action
the force of the water erodes the river bed as air is forced into cracks causing mini explosions, most effective in fast flowing rivers.
abrasion
stones are thrown at the river bed and the river banks causing material to break off (sandpaper)
attrition
stones knock against each other causing pieces to break off, becoming smoother and rounder
solution
rocks like chalk or limestone are eroded by slightly acidic river water which dissolves it
vertical erosion
downward erosion which deepens the river
lateral erosion
sideward erosion which widens the river channel
fluvial transport
process which the river carries its load
transport
sediment carried within a river
Load
load varies in size, from large boulders in the upper course to small sediment in the lower course
load mainly comes from weathered material that has rolled down hillside into the river and from the eroded bed and banks of the river
solution
minerals are dissolved in the water and carried along in the water
suspension
fine, light materials are carried along on the surface of the water
saltation
small pebbles are bounced along the river bed
traction
large boulders and rocks are rolled along the river bed (bed load)
deposition
materials in a river are dropped due to a decrease in velocity
why do rivers deposit sediment
due to a decrease in velocity
where does deposition occur
river enters a shallow area (when it floods and touches the floodplain)
at the base of a waterfall
on the inside bend of a meander
towards the mouth of a river where it meets the sea
source
the area in which a river begins
mouth
where a river ends its journey flowing into a lake or sea
tributary
a smaller river that joins a larger river
confluence
the point at which two rivers join
watershed
the boundary between two drainage basins marked by a ridge of high land
drainage basin
the area which is drained by a river and its tributaries
drainage density
the total length of all the streams in the basin divided by the total area of the basin
long profile
shows the gradient of the river from the source to where it enters the sea
upper course
vertical erosion
weathering
steep gradient
v shaped valley
small discharge
middle course
lateral erosion
transportation
discharge is higher due to tributaries
meanders
river cliffs
lower course
discharge at its highest
transportation
deposition
levees ox bow lakes
cross profile
shows the shape of the valley not the river
upper valley
v shaped valley
erosion
load size is large
vertical erosion
middle valley
deeper and wider
lateral erosion
load size is smaller
bradshaw model
model showing the changes of a river from the upper course to the lower course
load quantity
how much material being carried
load particle size
material size
formation of a v shaped valley
vertical erosion lowers the river bed
sides of the valley are subjected to weathering which weakens the sides of the valley, moves down slope (mass movement)
the gradient decreases of the valley sides
interlocking spurs
formation of interlocking spurs
river doesnt have a lot of energy and the rock is hard to weather so the valley is v shaped
freeze thaw weathering widens the valley leaving more material to erode with
the river cant erode harder rock so it winds and bends around the rock forming interlocking spurs
formation of a waterfall
a river meets a band of softer rock
the underlying, softer rock is eroded away more quickly
processes of erosion such as abrasion cause undercutting
the more resistant rock is left overhanging and unsupported
eventually the harder rock collapses onto the riverbed
the rock causes abrasion of the river bed
hydraulic action also helps to form a deep plunge pool with eddy currents
this process is repeated as the waterfall retreats
a gorge is created
gorge
a steep sided river valley
formation of a meander
in the middle course the river flows over flatter land, lateral erosion dominates as the river swings in large bends called meanders which are constantly changing shape
formation of an ox bow lake
during high flow conditions the meander neck is broken through the river now flows by the old meanders as it is shortest
the meander neck narrows due to lateral erosion on the opposite sites of meander bend
deposition occurs at the edge of the new straight section cutting off the meander leaving an ox bow lake which will silt up over time and form marshland
what is a levee
natural embankments deposited on either sides of the river channel
formation of levees
during a flood the water flows over into the floodplain and an increase in friction causes large sediment to be deposited instantly on each side, deposition makes the levees higher and higher
what is a floodplain
the area either side of a river in its lower course which is prone to flooding
formation of a floodplain
when a river floods, material is carried from the river to the floodplain, the finer silt are deposited further than the larger material, layers of material will build up over time continuing to build up the floodplain
bluff
area of higher ground which mark a floodplain
alluvium
fine silt
what is an estuary
a wide sheltered body of water found at a river’s mouth
formation of an estuary
a large river entered the sea at a narrow mouth and after the ice age melting ice caused a rise in sea level ,this caused the sides of river to become flooded. The original channel of the river is now on the estuary floor where it provides a deep channel for shipping
characteristics of an estuary
high tidal range
may be very wide
mudflats visible at low tide
how are estuary mudflats formed
they are formed in sheltered areas, as the water transports material down the sea an incoming tide transports the material up the estuary, deposition occurs downstream as fresh and saltwater mix (velocity drop). This builds up layer of mud called mudflats
how are salt marshes formed
mudflats will become colonised by vegetation forming slat marshes
the river severn
longest river in britain
source in the cambrian mountains
600m area
2650 mm of rainfall
lag time
the difference between peak rainfall and peak discharge
discharge
the amount of water flowing in a river
hydrograph
a graph to show river discharge and rainfall over time
what is discharge measured in
cumecs
cubic meters per second
how can hydrographs be used
to predict flooding
physical factors affecting storm hydrographs
size of drainage basins
steep sided basins
high drainage density
saturation
rock type
vegetation
precipitation
size of drainage basin
large catch more precipitation so have a higher peak discharge
small have a shorter lag time as rain doesnt have to travel as far
steep sides
shorter lag times as water flows more quickly on the steep slopes
high drainage density
basin that have more streams drain quicker so they have a shorter lag time
saturation
if the basin is already saturated this increases surface runoff , shortening the lag time
rock type
if rock is an impermeable surface, surface runoff will increase and lag time will be shortened
vegetation
the more vegetation the more interception and slow the rain will enter the river this increases lag time
precipitation
heavy storms result in more water entering the drainage basin which results is a higher discharge
if there is snow the lag time will increase but the peak discharge will increase when there is rapid melting of snow
human factors affecting storm hydrographs
deforestation
draining wetlands
digging artificial drains
downhill ploughing
compaction by animals or machinary
deforestation
less trees means less interception increasing SRO and discharge and a shorter lag time
draining wetlands
lag time will shorten, discharge increases as more water enter the river due to the wetland being drained as before it acted like a sink ,this means that water will flow directly into the river
digging artificial drains
peak discharge will increase and lag time decrease as artificial drains carry water straight to the river
downhill ploughing
peak discharge will increase and lag time decrease as the land is ploughed towards the river causing the water to flow easily into the river carrying sediment decreasing the river capacity
compaction by animals or machinary
soil is compacted by animal hooves or machinery which means there is more SRO, higher discharge and shorter lag time
what is hard engineering river management
involves the construction of structures built to control the flow of water
what is channel straightening
removing meanders to straighten a river channel
benefits and costs of channel straightening
benefits
water moves quickly away from urban areas
navigation improved
reduces flood risk in prone areas
reduces insurance costs
costs
expensive
ugly
increases flood risk downstream
aquatic habitats affected
what is a dam and reservoir
a dam is a structure across a river to control the flow of water and a reservoir is where water is stored
benefits and costs of
benefits
large storage capacity
generate electricity
controlled release of water
source of drinking water
costs
expensive
people displaced
large area of land flooded
sediment is trapped behind the dam
what is an embankment
building up the banks of a river creating levees or creating walls
benefits and costs of embankments
benefits
increases river capacity
new habitats created
provides walkways
reduces flood risk
cost
ugly
expensive
ongoing maintenance
if embankments fails flooding is more serious
what is a flood relief channel
an artificial channel to divert water
benefits and costs of flood relief channel
benefits
flood risk reduced near urban areas
new habitats created
recreational activities (fishing etc)
reduces insurance cost
costs
expensive
habitats disturbed
ongoing maintenance
ugly is concrete is used
what is soft engineering river management
adapting to a river and learning to live with it
what is afforestation
trees being planted to increase interception
benefits and costs of afforestation
benefits
interception reduces surface run-off
increases carbon storage
creates new habitats and increases biodiversity
relatively inexpensive
costs
loss of potential grazing land
changing the appearance of the countryside
can increase soil acidity
what is flood warning and prep
an alert system to the risk of flooding
benefits and costs of flood warning and prep
benefits
cheap and dependent on communication
if warned in advance people can protect valuables
ensures safety without the cost of hard engineering
costs
only effective if people listen and take action
not everyone has access to digital communications
floods continue to occue
what is flood plain zoning
land in a river valley is used in a way to minimise flooding
benefits and costs of flood plain zoning
benefits
impermeable surfaces are not increased
low cost as it only involves administration
traditional water meadows protected
creates welcome green space
costs
limited impact as most floodplains are developed
house prices inflated due to lack of housing stock
other greenfield sites affected
what is river restoration
returning an engineered river to its natural state
benefits and costs of river restoration
benefits
creates new wetland habitats and increases biodiversity
increased water storage in areas affected by flooding
reduces risk of flooding downstream
costs
possible loss of agricultural land
can be very expensive
warm, moist air blowing from the sw meets the cumbrian mountains
it cools, condenses, producing cloud and relief rain (314mm in 24hrs)
the ground was saturated so
water could not infiltrate the ground, increasing surface runoff
the drainage density in the cumbrian mountains around the river cocker and derwent is high so
more water is entering the river from the drainage basin causing flooding
deforestation has occurred in the cumbrian mountains over the past few decades resulting in
less interception, increasing surface runoff and a higher discharge
cockermouth is at the confluence of the rivers derwent and cocker resulting in
more water joining together increasing the discharge which causes flooding
the derwent and cocker river were already swollen with previous rainfall so
meaning you didnt need much more water to fill the river which causes flooding
Note
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