Studied by 10 peopleWhat is a long river profile?
A line representing the river from its source (where it starts) to its mouth (where it meets the sea). It shows how the river changes over its course
Explain the key points on the upper course of a river
steep gradient
V-shaped valley, steep sides, narrow, shallow channel
Explain the key points on the middle course of a river
medium gradient
gently sloping valley sides, wider, deeper channel
Explain the key points on the lower course of a river
gentle gradient
very wide, almost flat valley, very wide, deep channel
What does the cross river profile show?
A cross profile shows a cross-section of a river's channel and valley at a certain point along the river's course.
What is the course?
The path of a river as it flows downhill
What is vertical erosion?
deepens valley, V-shaped
dominant in upper course
high turbulence causes intense downward erosion
What is lateral erosion?
widens valley + channel during meander formation
dominant in lower + middle course
How can a cross profile of a river change?
It can change through lateral or vertical erosion
What are the four processes of erosion in rivers?
Hydraulic action, Abrasion, Attrition and Solution
The faster the river is flowing...
the more erosion happening
What is hydraulic action?
The force of the water breaks rock particles away from the river channel
What is abrasion?
Eroded rocks picked up by the river scrape and rub against the channel, wearing it away.
What is attrition?
Eroded rocks picked up by river smash into each other and break into smaller fragments. Their edges also get rounded off as they rub together.
What is solution?
River water dissolves some types of rocks e.g. chalk + limestone
How can rivers transport eroded material?
traction, suspension, solution, saltation
What is traction?
Large particles like boulders are pushed along the river bed by the force of the water
What is suspension?
Small particles like silt and clay are carried along by the water
What is saltation?
Pebble sized particles are bounced along the river bed by the force of the water
What is solution? (transport)
Soluble materials (e.g. limestone) dissolve in the water and are carried along
What is deposition?
the process in which sediment moved by erosion is dropped and comes to rest
When does deposition occur?
When a river loses velocity and energy
Why could a river slow down and deposit material?
volume of water falls
eroded material increases
water is shallower (e.g. inside of bend)
river reaches its mouth
How material is transported depends on...
velocity of water
size of particles
Explain the formation of waterfalls and gorges
forms over an area of hard rock then soft rock below
softer rock erodes by H.A and abrasion more than the hard rock, creating a 'step' in the river
water flows over step eroding more of softer rock
steep drop is created, called the waterfall (e.g. High Force waterfall on the River Tees, County Durham)
hard rock undercut by erosion, unsupported + collapses
collapsed rock swirls around foot of waterfall where they erode softer rock by abrasion creating deep plunge pool
undercutting causes more collapses, waterfall retreats leaving a steep-sided gorge
What does fluvial mean?
river
What are interlocking spurs?
Hillsides that interlock with each other as the river winds around them
How are meanders formed?
faster current on outside bend as river channel is deeper
erosion takes place on outside bend, forming river cliffs
slower current on inside bend as river is shallower
deposited eroded material in inside bend, forming slip-off slopes
How are oxbow lakes formed?
erosion causes outside bends to get closer until narrow neck is created
flooding makes river breaks through neck
river flows along the shortest course, through neck
deposition cuts of meander forming ox-bow lake
e.g. River Calder, near Castleford, West Yorkshire
How do flood plains form?
during floods, water slows down + loses energy and deposits transported material building floodplain
meanders widen as they move across floodplains laterally
over time, meanders move downstream
What is a flood plain?
Area of low-lying ground adjacent to river
How do levees form?
during floods, eroded material deposited over flood plain
heaviest material deposited closest to the river channel as it gets dropped first when the river slows down and loses energy
gradually, deposited material builds up, creating levees along edges of channel
e.g. River Trent, Nottinghamshire
What are levees?
Natural embankments along the edges of a river channel
What are estuaries?
regions where fresh water and salt water mix
How do mudflats form?
water floods over river banks carrying silt + sand on valley floor
tide reaches highest point and waves moves slowly with little energy depositing sediment
mud builds up creating large mudflats
at low tide, wide + muddy banks are exposed
What are contour lines?
They are the orange lines over a map; they tell you:
height of land (in metres) by the numbers marked on them
steepness of the land by how close together they are (closer the lines= steeper slope)
How do maps contain evidence for upper course rivers?
waterfalls are marked on maps but the symbol for cliffs are black, blocky lines and the close contour lines are evidence for an upper course waterfall
the height gives it away
river crosses a lot of contour lines in a short distance showing it's steep
the river is narrow (thin blue line)
How do maps contain evidence for lower course rivers?
nearby land is low
river doesn't cross any contour lines so it's gently sloping
river meanders across a large flat area
rivers wide (thick blue line)
river has large meanders + ox-bow lake may have formed
What is the river discharge?
The volume of water that flows in a river per second
What are hydrographs?
They show how the discharge at a certain point in a river changes over time in relation to rainfall.
peak discharge: highest discharge in the period of time you're looking at
lag time: the delay between peak rainfall and peak discharge
rising limb: increase in river discharge as rainwater flows into the river
falling limb: decrease in river discharge as river returns to its normal speed
Why does lag time occur?
surface runoff (flows quickly overland)
infiltration (soaks into ground and runs underground)
What are the causes of flooding?
heavy rainfall
geology (rock type)
prolonged rainfall
relief (changes in land height)
land use
How does heavy rainfall cause flooding?
Heavy rainfall means water arrives too quickly to infiltrate, so there's a lot of surface runoff, increasing discharge
How does geology cause flooding?
impermeable rocks do not allow infiltration and increase surface runoff e.g. granite/shale
How does prolonged rainfall cause flooding?
Prolonged rainfall saturates soil and any further rainfall cannot infiltrate, increasing runoff into river channels
How does relief cause flooding?
steep-sided valley -> water reaches channel faster as it flows quicker on steeper slopes increasing discharge causing a flood
How does land use cause flooding?
buildings and roads are made from impermeable materials increasing surface runoff; man-made drains transport runoff to rivers increasing discharge
cutting down trees increases the volume of water that enters the river channel as trees intercept water on their leaves which evaporates
What are the hard engineering methods for reducing flooding + effects of flooding?
dams and reservoirs
channel straightening
embankments
flood relief channels
What are the soft engineering methods for reducing flooding + effects of flooding?
flood warnings + preparation
flood plain zoning
planting trees
river restoration
What are dams & reservoirs, its benefits and cons?
What are they?
dams are barriers built across the river, usually in the upper course + a reservoir is formed behind the dam
Benefits
stores water (e.g. after heavy rain) controlling water flow preventing flooding downstream
generates HEP
Cons
expensive to build
farmland downstream becomes less fertile as material is deposited in the dam
What is channel straightening, its benefits and cons?
What is it?
meanders are removed by building straighter + artificial channels
Benefits
water leaves area quicker rather than building up, lowers flood risk
Cons
flooding may happen downstream instead
faster-moving water may cause more erosion downstream
What are embankments, its benefits and cons?
What are they?
raised walls built along river banks
Benefits
river holds more water lowering flooding
Cons
expensive
risk of flooding if water flows above embankments
What are flood relief channels, its benefits and cons?
What are they?
channels built to divert water around built-up areas or to divert excess water if river level gets to high
Benefits
gates control water release
Cons
increased discharge where the relief channel rejoins the river which could cause flooding in that area
What are flood warnings + preparation, its benefits and cons?
What are they?
E.A issues flood warnings through various media/buildings are modified to minimise flood damage/residents can prepare sand bags and flood boards prior to floods
Benefits
give people time to move possessions upstairs
evacuation
Cons
warnings don't prevent floods
modifying buildings is expensive
What is flood plain zoning, its benefits and cons?
What is it?
restrictions prevent building on part of a flood plain that are likely to be affected by floods
Benefits
reduced flood risk, less impermeable surfaces
no buildings to damage
Cons
expansion of an urban area is difficult is there isn't any other suitable building sites
can't help in areas with existing buildings
What is tree planting, its benefits and cons?
What is it?
planting trees in river valleys increases interception of rainwater + lag time
Benefits
discharge and flood risk decrease
vegetation reduces soil erosion in valleys providing habitats for wildlife
Cons
less land available for farming
What is river restoration?, its benefits and cons?
What is it?
making the river more natural
Benefits
improves wildlife habitats
little maintenance
Cons
local flood risk can increase, especially if nothing is done to prevent major flooding
Note
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