1.3-River landscapes Flashcards
What are 2 physical processes that shape a river?
weathering and mass movement
What are the 3 types of weathering?
mechanical
chemical
biological
What is biological weathering?
Roots growing and animals burrowing into cracks in rocks causing them to split apart.
What is chemical weathering?
slightly acidic rainwater dissolves rocks
What is mechanical weathering?
freeze thaw action
What is the process of freeze thaw action?
water fills a crack
water freezes and the crack widens
repeated action increases the size of the crack
loose blocks if rocks are called scree
What are 2 processes of mass movement?
sliding and slumping
What is sliding?
where rock or material moves down a slope under the influence of gravity
what is slumping?
Where the river erodes the bottom of the valley slope causing the rock to become saturated and slump/collapse, making the slope steeper.
What does slumping cause?
material to slide downwards particularly if it’s saturated with rainwater
What is hydraulic action?
where the force of the water of the bed and banks removes material
What is attrittion?
the load that is carried by the river bumps together and wears down into smoother pieces
what is solution?
some minerals dissolving in river water
What is abrasion?
material carried by the river rubs against the bed and banks
What are the 4 main types or river transportation?
traction
salatation
suspension
soloution
What is it when large boulders are rolled along the river bed?
traction
What is it when smaller pebbles are bounced along the river bed?
salatation
What is it when finer sand and silt particles are carried along in the flow?
suspension
What is it called when some minerals are dissolved in the water and carried along in the flow?
solution
What shows how a river changes from source to mouth?
The Bradshaw model
what are charectaristics of the upper course of rhe river?
steep gradient small discharge shallow depth narrow steep sides fast velocity
What are some charectaristics characteristics of the middle course?
shallower gradient large discharge deeper depth flatter channel shape fast velocity
What are some charectaristics of the lower course of a river?
shallow gradient
very large discharge
deep depth
fast velocity
What features are formed in the upper course?
waterfalls
interlocking spurs
What features are formed in the lower course?
meanders
floodplain
leeves
ox bow lakes
What features are formed in the middle course?
meanders
floodplains
What increases the frequency of storms?
more periods of heavy rain and overflowing rivers
What increases the risk of flooding?
frequency of storms
periods of hot dry weather
soil becoming inpermeable during cold conditions
how are waterfalls formed?
The soft rock erodes more quickly,undercuttingthe hard rock.
The hard rock is leftoverhangingand because it isn’t supported, it eventually collapses.
The fallen rocks crash into theplunge pool. They swirl around, causing more erosion.
Over time, this process isrepeatedand the waterfall moves upstream.
A steep-sidedgorgeis formed as the waterfall retreats.
how are gorges formed?
over time this undercutting process is repeated and the waterfall retreats
What is a floodplain?
the wide flat area of land either side of a river that experiences frequent floods.
how do levees develop?
the deposition process which takes place during flooding continues until embankments are created along the side of the river.
What is formed in the inside bend of a meander?
a point bar
how is an ox bow lake formed?
narrow neck gradually eroded water takes the quickest route deposition seals of old meander neck has been cut off completely free flowing lake left behind when meander is cut off
is the current stronger on the inside or outside of river bends?
outside
What 3 main human activitys change river land use?
urbanisation
agriculture
industry
how does urbanisation change river landscapes?
houses being build on flood plains changes the natural landscape
channelisation for urban developments means deposition and erosion can’t take place
growing towns means there are fewer permeable surfaces so flooding is increased
how does agriculture change river landscapes?
abstracting water for irrigation causes a reduced velocity so deposition occurs instead
ploughing fields increases the around amount of sediment in rivers
trees intercepting rainfall reduces surface run off so water reaches rivers more quickly
field drains destroy natural wetland landscapes
how does industry change river landscapes?
reducing water in rivers leads to less erosion
industry processes can pollute rivers and destroy plants and animals
What are 4 physical causes of flooding?
rainfall intensity
geology
snowmelt
drainage basin
how does rainfall intensity affect flooding?
a lot of rarainfall prevents soil infiltration which means it flows towards the river quicker and cause the bank level to rise
how does geology affect flooding?
rocks like granite are impermeable so water is unable to percolate from the thin soil above which means it flows
towards the river quicker and cause the bank level to rise
how does snowmelt affect flooding?
at spring time warmer temprature will will melt snow creating more water which means it flows towards the river quicker and cause the bank level to rise
how does the drainage basin affect flooding?
steep sides valleys mean the water enters the river system quicker which means it flows towards the river quicker and cause the bank level to rise
what are 2 methods of hard river engineering?
channelisation
dams and resevoirs
what are 2 types of soft river engineering?
floodplain zoning
washlands
what are the advantages and disadvantages of dams and resevoirs?
+store water until needed
+can be used to generate hydrielecteuc power
-expensive to build
-sediment can build up in reservoirs
what are the advantages and disadvantages of channelisation?
+allows water to flow more quickly away from areas of flood risk
- -visually unattractive
- -more water is taken downstream which increases flood risk elsewhere
what are the advantages and disadvantages of flood plains zoning?
+ reduces number of homes at risk
+allows infiltration so surface runoff is reduced
–restricts growth of settlements
what are the advantages and disadvantages of washlands?
+creates area for floodwater to go
+allows natural river processes
–might limit the use of land
