Paper 1 - Section C, Uk River Landscapes Flashcards
What does fluvial mean
River related, for example fluvial flooding is flooding caused by a river
What does pluvial mean
Rainfall related, for example pluvial flooding is flooding cause by heavy or prolonged rainfall
What are the 3 actions performed by a river
- Transportation (movement of eroded materials from one location to another)
- Erosion (wearing away and removal of material by a moving force)
- Deposition (when material being transported by river is dropped due to river losing energy)
What are the 4 processes of transportation
- Traction - moving largest and heaviest material (boulders rolled along river bed)
- Saltation - moves smaller stones by bouncing them along river bed
- Suspension - carrying very fine material within water (floats in river)
- Solution - dissolved load (only occurs with certain type of rock eg chalk)
What are the 4 processes of erosion
- Abrasion - when the load river is carrying repeatedly hit against bank + bed causing material to break off
- Hydraulic action - sheer force of water hitting bed and banks
- Attrition - stones carried in river hit against each other over time causing bits to break off and reduce in size
- Solution - when river flows over certain stone (eg chalk) they are solvable and dissolve and become part of water
What is deposition
- occurs when river dumps or leaves behind any material it was carrying
- deposits heavy material first as requires more energy
- smaller load can be transported further downstream
Why does a river deposit its load
When there is a slowing in the speed of the flow due to a bend in the river (meander) or a change in the gradient of the slope
What landforms form in the upper course of a river
- waterfall
- gorge
- interlocking spurs
What landforms form in the middle course of a river
- meanders
- flood plain
What landforms form in the lower course of a river
- meanders
- floodplains
- ox bow lakes
What is the discharge of a river
The amount of water that passes a given point on a stream or riverbank in a given amount of time
How are waterfalls formed
- A layer of hard rock overlays a layer of softer rock
- as river passes over softer rock it is able to erode it at a faster rate forming a step in river bed
- River now flows vertically + force of falling water results in plunge pool
- Rocks trapped in plunge pool are swirled around causing abrasion of the sides of the pool
- With little support the hard rock over hangers collapses and collapsed rock adds more rocks to plunge pool
How are ox-bow lake formed
- Erosion happens on outside of a meander bend, because fastest flow of river so load is Theon at bank and causes lateral erosion through abrasion and hydraulic action
- Deposition occurs on inside bend as a result of slow flowing water and lower energy forming a slip off slope. Neck of meander will eventually narrow due to erosion forming a river cliff
- Eventually neck of meander keeps narrowing until it’s completely broken (usually due to flood).forms a new straighter channel cutting off the meander leaving an ox-bow lake
What is abrasion
Rocks carried along a river wear down the river bed and banks
What is alluvium
A sediment deposited by a river when it floods
What is attrition
Rocks being carried by the river smash together and break into smaller, smoother and rounder particles
What is a channel
The main water course
What is channel straightening
Removing meanders from a river to make it straighter
What is the confluence
Where a tributary joins a large river
What is solution (corrosion)
When the river flows over limestone or chalk, the rock is slowly dissolved
What is the cross profile
A cross section of a river channel or it’s valleys
What is a dam
A barrier built across a valley to interrupt river flow
What is deposition
Occurs when material being transported by the river is dropped due to the sea loosing energy
What is a drainage basin
An area of land drained by a river and its tributaries
What is embankment
Artificially raised river banks often using concrete walls
What is erosion
Wearing away and removal of material by a moving force
What is an estuary
Tidal mouth of a river where it meets the sea - wide banks of deposited mud are exposed at low tides
What is a flash flood
A very sudden flood event resulting from a torrential rainstorm
What is a flood
Where river discharge exceeds river channel capacity and water spills onto the floodplain
What is a flood relief channel
Artificial channels that are used when a river is close to maximum discharge; they take the pressure off the main channels when floods are likely
What are flood storage areas
Water is deliberately allowed to flood wetlands to reduce the risk of further flooding downstream
What is a floodplain
Relatively flat area forming the valley floor either side of a river channel that is sometimes flooded
What is a gorge
A narrow steep-sided valley often formed as a waterfall retreats upstream
What is hydraulic action
Power of the water erodes the bed and banks of rivers
What is a hydrograph
A graph which shows the discharge of a river, related to rainfall, over a period of time
What are interlocking spurs
Outcrops of land along the river course in a valley
What is a Knick point
A step or drop in a rivers bed which often cause waterfalls
What is lateral erosion
Erosion of river banks rather than the bed - helps to form floodplains
What is a levee
Raised bank found on either side of a river, formed naturally by regular flooding or built up by people to protect the area against flooding
What is the long profile
The gradient of a river from its source to its mouth
What are mudflats
Areas of fine sediment deposits which over time can develop in saltmarshes
What is an ox-bow lake
An arc shaped lake on a floodplain formed by a cut off meander
What is a plunge pool
A deep and turbulent area of water where the river plunges over a waterfall
What is a resovoir
A large natural or artificial lake used as a source of water supply
What is river restoration
Modifying the course of a river to return it to its natural state
What is saltation
Hopping movement of pebbles along a river or sea bed
What is suspension
Small particles carried in river flow or sea water eg sand and clays
What is the thalweg
The course of the fastest flow (velocity) within a river
What is time lag
The time in hours between the highest rainfall and the highest discharge
What is traction
Where material is rolled along a river bed or by waves
What is transportation
The movement of eroded material
What is a tributary
A small stream that joins a large river
What is vertical erosion
Downward erosion of the river bed
What is a waterfall
A step in the long profile of a river usually formed when a river crosses over a hard band of rock
What is the watershed
The edge of the river basin
Explain the change in a rivers long profile from upstream to downstream
Near the source, the long profile is steep and as it makes its way downstream, it reduces quickly in height as the slope of the river valley reduces, the river loses height with increasing distance towards the sea
What does the long profile of a river show you
Long profile is a way of displaying the channel slope (gradient) of a river along its entire length
How does the cross profile of a river change downstream
It changes with distance downstream from a steep-sided, narrow valley near the source to a wider, deeper valley towards the mouth
How do interlocking spurs form
Because there is more vertical erosion in the upper course, if there are areas of hard rock which are harder to arose the river will bend around it creating an interlocking spur
How are gorges formed
- river flows over band of hard rock that lies over softer, less resistant rock
- river erodes softer rock through hydraulic action and abrasion
- erosion leads to undercutting of rocks
- overhang forms and eventually collapses
- waterfall retreats upstream leaving steep and narrow gorge
How are levees formed
- formed by repeating flooding of a river
- when river floods, the water and the load it is carrying leaves the channel
- due to drop in energy caused by friction, the biggest most course material gets dumped close to river banks
- repeated flooding builds the levee up
How are floodplains formed
Erosion of the outer bends of a meander will gradually wear down and flatten the land either side of a channel
When the river overflows its banks during a flood, the river will leave the channel and due to increased friction between water and the floodplain, river looses energy and deposits its sediment load
How are estuaries formed
The seas rose and it drowned river valleys and glacial troughs forming estuaries and become traps for sediment and tidal flats begin to grow along the shore as the sediment grows
What is the River Tees source and mouth
Source: Pennine Hills near Cross Fell
Mouth: North Sea at Middlesbrough
What is the name of the waterfall on the River Tees
High force
How was the High Force waterfall formed
- formed due to resistant band of indigenous rock which cuts across river valley
- unable to erode the rock, the river has formed a step in the long profile of river and this has developed over hundreds of years to form High Force waterfall
How will the gorge form at the High Force Waterfall
- the underlying weaker, darker rock (Carboniferous Limestone) will get undercut forming an overhang, this will eventually collapse and the waterfall will retreat upstream to form a gorge
What physical factors affect flood risk
- Precipitation - torrential rainstorms = flash floods and rivers cannot contain sheer volume of water
- Geology - impermeable rocks (water cannot pass through them) encourage water to flow overland and into river channels, speeding up water flow + more chance of flooding
- Steep slopes - in mountains, steep slopes encourage rapid transfer of water towards river channels, increased risk of flooding
What human factors affect flood risk
- Urbanisation - building on floodplains creates impermeable surfaces (eg tarmac), water is transferred quickly to drains and sewers and then into river channels = higher chance of flooding
- Deforestation- most water that falls on trees is evaporated or stored temporarily in leaf or used for growth so without trees, much more water is able to be transferred into river channels, increasing flood risk
- Agriculture - in arable farming, soil left unused and exposed to elements and this can lead to more surface runoff off
What is hard-engineering
Man-made structures to prevent or control natural processes from taking place
What are the costs and benefits of hard-engineering
Costs: very expensive, any negative impacts on environment and on peoples lives
Benefits: financial savings made by preventing flooding along with any environmental improvements
