Please enable JavaScript.
Coggle requires JavaScript to display documents.
Rivers, image - Coggle Diagram
Rivers
1.7
-
b.
Bradshaw's model
load quantity
- how much the water is transporting
- increases as you go downstream
- with more water there is greater erosional potential (more erosion happens) and river has more energy (higher velocity) so can transport heavier rocks that wouldn't be transported upstresam
load particle size
- size of the particles the river is transporting
- decreases as you go downstream
- more attrition (has been happening for longer), so smaller, smoother rocks
velocity
- the speed that the water is travelling at
- increases as you go downstream
- with a larger, deeper channel, friction has less of an impact on the water (impact of friction reduces downstream). a rocky, narrow channel has lots of friction and because the channel is small the friction has a high impact
channel bed roughness
- how smooth the banks and bed of the river are
- decreases as you go downstream (rough to smooth)
- more abrasion downstream as there is a higher load quantity
occupied channel width and depth
- how much space the river channel occupies
- increases as you go downstream (becomes wider + deeper)
- more water downstream means there is much more erosion (lateral) of the banks and bed downstream
slope angle
- the gradient of the river
- decreases as you go downstream (gradient angle reduced)
- rivers flow from upland to lowland areas. upland areas are often steep, whereas when the river reaches sea level, the gradient is flat
discharge
- the amount of water passing a specific point at a particular time (quantity of water)
- increases as you go downstream
- water is added by tributaries and groundwater flow (water that flows through the ground
definitions:
- wetted perimeter - the part of the channel in contact with water
- cross-sectional area - area of water taken from a cross-section
- hydraulic radius - a measure of efficiency in a river channel. it is calculated by comparing the wetted perimeter with the cross-sectional area of the channel. the higher the hydraulic radius, the more efficient the river
- hydraulic radius = cross-sectional area/wetted perimeter
river Dee
middle course
- valley becomes wider and flatter as flood plains are created
- some deposition. sediments will be eroded again and become smaller, more rounded and then transported further downstream
- tributaries join the river, so its discharge increases
lower course
- average annual rainfall is now less than 750mm
- river flows through softer rocks, sandstones, towards Chester
- valley and channel widen even further
- velocity is at its greatest
- more tributaries increase discharge
- water becomes muddy as its sediment load is high and more deposition happens
- after 110km the river meets its mouth in the Irish sea between Wales and the Wirral Peninsula. this part of the river is called the estuary because it is affected by the tides
upper course
- source is on the slopes of Dduallt in Snowdonia national park, north Wales
- average annual rainfall exceeds 3000mm and there is high runoff from upland slopes
- geology is mainly resistant igneous rocks
- near the source the channel is narrow, shallow and full of angular rocks. a v-shaped valley has formed
- sliding and slumping happen here
river profile
middle course
- flatland
- lateral erosion - meanders
- floodplains
- wider channels
- transporting a high load - material
lower course
- braided channels - mouth
- deposition - deltas
- loses energy - deposition
- estuaries
- large floodplains
- ox bow lakes
- levees - banks getting higher
- as you get further away from the source, the height of the river decreases
upper course
- rocky - resistant rocks
- rapid
- white water (air in it) - turbulent flow
- gravity - vertical erosion
- waterfalls - gorge
- steep sided valleys - v-shaped
- small channel
- in the mountains - steep
definitions:
- source - the starting point of a river
- drainage basin - an area of land that is drained by a river and its tributaries
- confluence - the point at which two rivers meet
- watershed - the perimeter of a drainage basin, separating areas that are drained by different rivers
- mouth - the ending point of a river
c.
impact of climate
- quantity of rainfall
- in areas of high rainfall, rivers have higher discharge in the channels, leading to higher rates of erosion
- this leads to increased vertical erosion in the upper course, forming v-shaped valleys
- this also leads to increased lateral erosion in the lower course, forming flood plains
- transportation also increases with increased discharge as the capacity of the river to transport material increases
- areas with higher quantities of rainfall tend to experience greater chemical weathering as the rocks along the river become exposed to higher volumes of slightly acidic rain, this could make river valley steeper and prone to mass movements
- temperature
- when temperatures fall below 0 in the winter, there is greater freeze-thaw weathering
- this means lots of sediments that have been eroded fall into the river, influencing erosion and deposition
- as temperatures rise in the summer, chemical weathering becomes more prominent as the higher temperatures provide optimum conditions for chemical reactions to occur
- increased weathering makes mass movements more likely and results in steeper valleys
impact of weather
- storms
- storms bring significant quantities of rainfall to river landscapes
- the rainwater saturates the sediment of the valley making it vulnerable to mass movements through sliding and slumping actions
- as the ground surrounding the river is saturated, surface run-off becomes more rapid, resulting in increased volume and discharge of the river
- this means erosion and transportation of weathered material increases
- increased river flow and therefore erosion can lead to the formation of ox-bow lakes as the flow breaks through a meander neck
- levees can be formed when storms cause flooding in the lower course
- drought
- droughts can occur when there is a lack of precipitation, this results in less runoff and therefore a reduction in the river's discharge and volume
- erosion and transportation rates decrease as a result
- smaller streams may dry up
- mass movement is less likely in drought conditions as the sediment is not saturated with water. however, heavy following a period of drought can cause flash flooding as the ground can become hard and impermeable
1.8
b.
levees
- natural embankments of sediment formed along banks of rivers that carry a large load and occasionally flood
- when the river floods, water and sediment come out of the channel
- when the water overflows, it loses velocity and deposits larger and heavier sediment
- this repeats
- the river banks get higher forming levees
point bars
- also known as slip off slopes
- on the inside of a meander, the velocity and force is less (less energy)
- this leads to deposition
- this forms a point bar
- which are characteristically curved in shape
flood plains
- the flat area of land either side of the river in its lower course, which flood
- lateral erosion on the outside bends of meanders mean that they migrate across the valley floor, so it becomes wide and flat
- during floods, water spreads out across the valley floor
- during flooding, deposition of sediment (alluvium) means the land is extremely fertile
deltas
- depositional landforms
- in the river's lower course
- where the river meets the sea/other large body of water (river mouth)
- loses energy, deposition
- material accumulates - delta forms
- braiding/braided channels - when rivers suddenly lose energy, deposition causes channels to separate and braid
- distributary - a smaller river channel that separates and flows away from the main channel
- the accumulation of sediments (alluvium) means that deltas are extremely fertile land. vegetation is rich with huge agricultural potential. they are however prone to flooding
- types of delta - arcuate, cuspate, bird's foot
c.
meanders
- bends in a river's course - commonly found on flood plains
- flow of water swings from side to side, directing the line of fastest flow (Thalweg line) and the force of the water towards the outside of the bend
- results in lateral erosion by undercutting
- an outer, steep bank called a river cliff forms
- on the inside of the bend the velocity and force is les, leading to deposition and the formation of a gently sloping bank, known as a slip-off slope/point bar
- characteristically curved in shape
- due to erosion and deposition, the cross section of a meander is asymmetrical - steep on the outside of the bend, gentle on the inside
- meander migrates - becomes a more exaggerated bend - due to erosion and deposition
ox-bow lakes
- as a meander develops, its neck becomes narrower (migration of meander)
- during a flood/period of high discharge the river erodes through the neck
- a new channel forms
- the river flows through the straight channel (faster) and leaves behind the bend
- bend is eventually sealed up by deposition
- leaving a horse-shoe shaped ox-bow lake
a.
waterfalls
- upper course, discordant geology
- vertical erosion, gravity, created rapids as soft rock erodes faster than hard rock, differential erosion
- river step forms
- continued erosion of river step - plunge pool
- plunge pool expands
- under cutting takes place, forming a hard rock overhang
- overhang collapses
gorges
- the process of the overhang collapsing for waterfalls continues
- the waterfall retreats
- this forms a gorge
- a gorge is a steep sided, narrow valley carved out by a retreating waterfall
interlocking spurs
- valley formed by river - upper course
- vertical erosion
- channel deepens, banks become exposed and are weathered
- weathered material is transported away
- v shapes valley moves side to side in mountainous areas so that it can flow around hard rock outcrops
- erosion happens where the river flows
- over time, this erosion leads to interlocking spurs which the river flows between
river cliffs
- in a meander, the Thalweg line (line of fastest flow) swings from side to side as the river bends
- the line of fastest flow is always on the outside of the bend
- this results in lateral erosion (as the water has lots of energy) and an outer, steep bank is formed
- this is called a river cliff
1.9
a.
causes of flooding
physical
- intense and prolonged rainfall
- impermeable geology - prevents geology - increases surface runoff
- snow melt - seasonal melting - sudden increase in river discharge
- relief - steep valleys transport water to channel very quickly
human
- urbanisation - impermeable surfaces - increased surface runoff - increased chance of flooding
- deforestation - dense vegetation intercepts rainfall, roots take in water - no vegetation, water reaches river channel very quickly
impacts of flooding
environmental
- crops and wildlife destroyed
- saturated ground, immediate runoff
- materials/waste/rubble/cars washed into rivers
economic
- ruins crops (expensive)
- businesses destroyed
- tourist and other industries affected
- costs council money
- impact on economy
social
- death of people + injuries
- homes flooded
- floods schools
- roads, railways destroyed
- damage to personal property
- trauma
-
1.10
river Dee
change
- human factors
- growing demand for water in the summer led to reservoirs being built. these help control the flow and can reduce its discharge
- near Bangor-on-Dee (mid-course) earth embankments are used
- 8km of the river underwent channelisation between Chester Weir and its estuary. this increases velocity and discharge
- physical factors
- UK's climate is variable and there can be periods of drought, resulting in low river flows and heavy rainfall results is high river flows and more erosion and deposition
- climate change could lead to even more variable weather and an increased flood risk across the entire Dee catchment
flood risk
- why the flood risk is increasing
- increasing population (more people in areas at risk)
- urban development and other changes in land use (more surface runoff)
- climate change (20% increase in flows and 1m sea level rise)
-
-
-
