River Landscapes in the UK Flashcards
Abrasion
Rocks carried along by the river wear down the river and banks. Most common form of erosion.F
Attrition
Rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
Cross Profile
The side to side cross-section of a river channel and/or valley.
Dam and Reservoir
A barrier (made of earth, concrete or stone) built across a valley to interrupt river flow and create a man-made lake (reservoir) which stores water and controls the discharge of the river.
Discharge
The quantity of water that passes a given point on a stream or river-bank within a given period of time.
Measured in cubic metres per second.
Hydrographs show this over time.
Embankments
Raised banks constructed along the river; they effectively make the river deeper so it can hold more water. They are expensive and do not look natural but they do protect the land around them.
Estuary
The tidal mouth of a river where it meets the sea; wide banks of deposited mud are exposed at low tide.
The river here is tidal, rising and falling each day.
Deposits are made when it floods carrying sand and silt which is deposited at its highest tidal point.
Creates mudflats which are exposed at low tide. E.g. is the River Severn.
Flood
Occurs when river discharge exceeds river channel capacity and water spills out of the channel onto the floodplain and other areas.
Flood Plain
The relatively flat area forming the valley floor on either side of a river channel, which is sometimes flooded.
When a river floods onto a pain it slows down and deposits eroded material. This builds up the flood plain.
Flood Plain Zoning
This attempts to organise the flood defences in such a way that land that is near the river and often floods is not built on. This could be used for pastoral farming, playing fields, etc. the areas that rarely get flooded would therefore be used for houses, transport and industry.
Flood Relief Channels
Building new artificial channels which are used when a river is close to maximum discharge. They take the pressure off the main channels when floods are likely, therefore reducing flood risk.
Flood Risk
The predicted frequency of floods in an area.
Flood Warning
Proving reliable advance information about possible flooding. Flood warning systems give people time to remove possessions and evacuate areas.
Fluvial Processes
Processes relating to erosion, transportation and deposition by a river.
Gorge
A narrow, steep sided valley, often formed where a waterfall retreats upstream.
Hard Engineering
Involves the building of entirely artificial structures using various materials such as rock, concrete and steel to reduce, disrupt or stop the impact of river processes.
Hydraulic Action
The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
Hydrograph
A graph which shows the discharge of a river, related to rainfall, over a period of time.
Interlocking Spurs
A series of ridges projecting out on alternate sides of a valley and around which a river winds its course.
Lateral Erosion
Sideways erosion by a river on the outside of a meander channel. It eventually leads to the widening of the valley and contributes to the formation of the flood plain. Dominant in middle and lower courses of a river.
Levees
Embankment of sediment along the bank of a river. It may be formed naturally by regular flooding or be built up by people to protect the area against flooding.
The heaviest material is deposited closest to the river channel and overtime this builds up.
Long Profile
The gradient of a river, from its source to its mouth.
Meander
A pronounced bend in a river.
Ox-bow Lake
An arc-shaped lake which has been cut off from a meandering river.
Precipitation
Moisture falling from the atmosphere as rain, hail, sleet or snow.
Saltation
Particles bouncing down the river bed.
Soft Engineering
Involves the use of the natural environment surrounding a river, using schemes that work with the river’s natural processes. Soft engineering is usually much cheaper and offers a more sustainable option as it does not interfere directly with the river’s flow.
Solution
Soluble particles are dissolved into the river.
(Channel) Straightening
Removing meanders from the river to make the river straighter. Straightening the river (also called channelizing) allows it to carry more water quickly downstream, so it doesn’t build up and is less likely to flood.
Suspension
Fine solid material held in the water while the water is moving.
Traction
The rolling of boulders and pebbles along the river bed.
Vertical Erosion
Downward erosion of a river bed. V shaped. More dominant in the upper course where the terrain is steeper.
Waterfall
Sudden descent of a river or stream over a vertical or very steep slope in its bed. It often forms where the river meets a band of softer rock after flowing over an area of more resistant material. The erosion of the soft material forms a step. Eventually the hard rock is undercut by erosion and collapses creating a deep plunge pool
Cross profile
Shows what the cross section of a river will look like.
Four processes of transportation
Traction (pushed along), saltation (pebble sized bounced along), suspension (small particles carried along) and solution (dissolve).
Why does a river slow down and deposit?
1) Volume of water falls.
2) Amount of material increases.
3) Shallower.
4) Reaches its mouth.
How are meanders formed?
Develops in middle and lower course of a river where there are shallow and deep sections.
The current on the outside is faster as it’s deeper with less friction. Erosion forms river cliffs.
The current on the inside is slower as it’s shallower with more friction. Deposition forms slip off slopes.
How are ox-bow lakes formed?
When meanders get larger, there is only a small bit of land between the bends (the neck) which eventually breaks through during a flood. The river flows along the shortest course and then deposition cuts off the meander.
What is the lag time of a river?
The delay between peak rainfall and peak discharge.
What are the rising and falling limbs on a hydrograph?
Rising limb is when the river discharge is increasing.
Falling limb is when the river discharge is decreasing.
What impacts flooding?
1) Prolonged rainfall - saturated soil increases runoff into rivers.
2) Heavy rainfall - Too much rainfall for inflltration
3) Geology - clay soils and some rocks are impermeable which increase runoff.
4) In steep sided valleys, water reaches channel much quicker.
Changing land use impacts flood risk - concrete buildings, roads, removing trees
