SectionC: Physical Landscapes Of The UK-Rivers Flashcards
Relief
Difference in height from the surrounding terrain
Geology
the science which deals with the physical structure and substance of the earth, their history, and the processes which act on them.
Bed
Bottom of a river
Bank
Sides of a river
Load
Sédiment river carries
Channel
Fluid in river-water
Hydraulic action
Sheer force of the water wearing away bed and banks
Attrition
Stones carried by the river knock against one another making them smaller and smoother
Abrasion
Load carried by the river scraping across the bed and banks- sand paper effect
Solution
Some rocks are mildly soluble in mildly acidic river water and is therefore slowly dissolved
Vertical erosion
Mainly erodes downwards to reach base level, V-shaped areas in valleys near to the source. Makes valleys narrow and shallow
Lateral erosion
Eroding horizontally in the middle and lower course, makes it wider and deeper
Two directions of erosion
Vertical and lateral
Four types of erosion
Hydraulic action, abrasion, attrition, solution
Four types of transportation
Traction, saltation, solution, suspension
Traction
Big boulders rolling along the bed
Saltation
Small pebbles bouncing along the bed
Suspension
When alluvium is carried in the water
Solution
Particles are dissolved
Deposition
Leaving behind material
When does deposition occur
When the river loses energy
What will a river deposit first
Largest material as it is the heaviest to carry
Source
River behind steep and in the mountains
Watershed
High land around the basin
Confluence
Two or more rivers meeting
Drainage basin
Area of land drained by a river and it’s tributaries
Mouth
River meets sea
Long profile
Shape of the land from source to mouth
Cross profile
How the river chances from side to side
River depth and width at the source
Narrow and shallow
River width and depth in the middle course
Wider and deeper
River width and depth at the mouth
Widest and deepest
Size of load at the source
Large boulders
Size of load in the middle course
Medium pebbles/ silt
Size of load at mouth
Alluvium
Water velocity source
Slow but increasing
Water velocity middle course
Medium but increasing
Water velocity mouth
Fastest point but slow at the mouth itself
Direction/type of erosion source
Vertical, hydraulic, abrasion, attrition
Direction/type of erosion middle course
Lateral, hydraulic, abrasion, solution
Direction/type of erosion mouth
Lateral, abrasion
Transportation source
Traction, saltation
Transportation middle
Solution, suspension
Transportation mouth
Suspension, solution
Is there deposition at the source
No
Is there deposition in the middle course
Yes but only when the water levels drop
Is there deposition in the mouth
Yes when river loses energy
Interlocking Spurs
The vertical erosion in the upper course create a v-shaped valley which is steep sided and narrow. As the river erodes downwards, soil and loose rock on the valley sides are moved downhill by slope wash or soil creep. The river also winds its way around interlocking spurs of hard rock. There is no flat valley floor and the valley gradient is steep
Upper course featured in a river
V-shaped valleys, interlocking Spurs, waterfalls and gorges
Define waterfall
A stream or river flows over a steep drop, this is due to erosion and both hard and soft rock are present. Usually located in the upper course
Characteristics of high force
White water- fast flowing, hydraulic action
Hard rock- igneous, more résistant whin sill
Steep sided gorge
Steps
Plunge pool
Overhang
Soft rock-Carboniferous limestone, less resistant
Step by step formation of waterfall and gorge
A river meets a band of soft and hard rock on top of each other, underlying softer rock is eroded more quickly, processes of erosion such as abrasion cause undercutting, the rock causes abrasion of the river bed, hydraulic action also helps create a deep plunge pool, the more resistant hard rock is left unsupported and overhangs, eventually the more resistant rock is left unsupported and collapses onto the riverbed, this process is repeated and the waterfall retreats upstream, a steep sided river valley is created called a gorge
Meander definition
Bends in the river formed in lower courses of a river due to lateral erosion and deposition
What landforms are in the middle course
Meanders and oxbow lakes
Thalweg
Fastest flow of the river
How is a meander formed
A meander is a bend in the river, the outer bend has deep water, a steep river cliff and the thalweg. Due to the process of erosion called hydraulic action the fast flowing water erodes the bed so the water is deep. On thé inner bend the river loses energy so this is the slowest flow so the river deposits it’s load onto the slip off slope. As deposition occurs here the water is shallow
How are oxbow lakes formed
The meander has a neck, the outside of the neck has a faster flow therefore more hydraulic action which creates river cliffs. The current on the inside is slower and the channel is shallower so the erodes material is deposited forming slip-off slopes. The neck is getting smaller due to erosion. During a flood the water will pass over the neck and take the fastest flow in a straight line. The original part of the meander is cut off as deposition occurs. The feature left is an oxbow lake. This is horse shoe shaped and may dry up and grow vegetation
What is the flood plain
The flood plain is the wide, flat area of land either side of the river in its lower course. The flood plain is formed by both erosion and deposition
How is the flood plain formed
The wide valley floor on either side which occasionally gets flooded, when the river flood onto the flood plain, the water slows down and deposits the eroded material that its transporting. This makes the flood plain higher. Meanders migrate across the flood plain making it wider, the deposition that happens on the slip off slopes of meanders also builds up the flood plain
What are levees
Natural embankments of silt along the banks of a river. Levées formed along rivers that flow slowly, carry a large load and periodically flood
How are levees formed
The river during normal flow remains within the river banks, the valley either side of the channel is flat and wide. The load is carried in suspension. During a period of flood the river flows onto the flood plain. Coarse material is deposited on the edge of the banks as the river loses energy. Fine material will be deposited further out. During a dry period where the river is at flow. The speed will be slow therefore the load will be deposited on the bed. This will repeat many times and will leave raised banks either side of the channel. The flood plain will have layers of materials and will be very fertile
Evaporation
Process whereby liquid changes to a vapour
Transpiration
Evaporation through pores in vegetation
Condensation
Process where vapour changes to a liquid
Precipitation
Any form of water eg rain sleet and snow
Infiltration
Water being absorbed into the soil
Surface runoff
Movement of water over the land
Through flow
Water flowing through the soil layer
Ground water flow
Water that has sunk through the soil into the rocks below the surface
Permeable
Surfaces that allow infiltration eg grass
Impermeable
Surfaces that prevent infiltration eg concrete, roads, tarmac
What is a flood
When a river bursts it’s banks, where the river receives more water than the channel has room for
How does deforestation affect flooding
Less trees to intercept surface runoff, less transpiration, cut down trees to build cities
Physical factors that affect flooding
Heavy rainfall, saturated ground, steep relief, snow melting, impermeable rock
Human factors that affect flooding
Déforestation, urbanisation, imperméable rock
How does heavy rainfall affect flooding
Infiltration is slow which causes more surface runoff, ground gets saturated, rock may be impermeable
Saturated ground affects on flooding
Acts as impermeable surface, less infiltration and more surface run off, gets saturated as heavy rainfall
Steep relief affect on flooding
Water can’t infiltrate land as gradient too steep so water moves too fast, snow falls on mountains then it melts
Impermeable rock affect on flooding
Water can’t infiltrate, more surface run off, heavy rainfall with impermeable rock floods the ground
Urban areas affect on flooding
Built up areas makes impermeable surfaces so infiltration is reduced, cut down trees to build land
Snow melt affect flooding
Water flows quickly and more of it, more surface run off, snow falls on mountains and then melts and falls fast due to the steep gradient
Discharge
How much water passes through a certain point in the river per second
Rising limb
Rising flood water in the river
Peak rainfall
Maximum amount of rainfall
Falling limb
Decreasing flood water in the river
Lag time
Time difference between peak rainfall and peak discharge
Base flow
Normal discharge in the river
What is a flood hydrograph
A line graph and a bar chart that shows how the discharge of a river changes before, during and after a rainfall event
What processes from the hydrological cycle are occurring if the time taken for peak rainfall to reach peak discharge is long
Infiltration, where precipitation travels through either ground water flow or through flow
What processes from the hydrological cycle are occurring if the lag time is short
Surface run off from impermeable surfaces
What does it mean if the lag time is short
Flash flood
What happens if the lag time is long
No flood
What is hard engineering
Using man made structures to prevent flooding or natural process from taking place
What is soft engineering
Involves working with natural river processes to manage the flood risk
What is a dam
Control natural river flow and hold back flood water in large reservoirs
Hard engineering strategies
Dams, channel straightening, embankments, flood relief channels
Benefits of dams
Dammed water can provide hydroelectric power, dammed floodwater can be used for irrigation, reservoirs used for tourism and water supplies
Disadvantages of dams
Very expensive £500m, sediment can be trapped leading to erosion further downstream, settlements lost
What are Embankments
Raising the river bank so the channel can hold more water
Benefits of embankments
Allows the river channel to hold more water, mud from dredging can be used to make the river deeper, cheaper, natural
Disadvantages of embankments
Not high enough, concrete embankments are ugly, wildlife disrupted
What is channel straightening
River channel may be straightened so the water can travel faster along the course
Benefits of channel straightening
Speeds up the flow of water to reduce floods
Disadvantages of channel straightening
Flooding may happen downstream, more downstream erosion
What are flood relief channels
Man made river channel constructed to bypass an urban area
Benefits of flood relief channels
Makes the people who love close feel safe, can be used for water sports
Disadvantages of flood relief channels
Large amount of land, extremely expensive
Soft engineering strategies
Floodplain zoning, afforestation, river restoration, flood preparation
What is flood plain zoning
Low value land allowed to be flooded, houses are safer, less impermeable surfaces close to the flood plain
Disadvantages of flood plain zoning
Limits building on land close to the river where the land is flat, if a flood plain has already been developed on there isn’t anything you can do
What is afforestation
Trees are planted near to the river, greater interception of rainwater and lower river discharge and water absorbed by the tree roots
Benefits of afforestation
Relatively low cost option, enhances the environmental quality of the drainage basin, creates habitats
Disadvantages of afforestation
take 10-20 years for the trees to grow, lots of space is required for this to be fully effective
What is river restoration
Involves changing a tier that has undergone hard engineering back to its original course, this can involve un straightening a channel or removing artificial levees
Benefits of river restoration
Improve the damaged environment, reintroduce wildlife back into the area, land may no longer be valuable
River restoration disadvantages
Introduce flooding again, land surrounding the river could still be used and will get flooded
What is flood warning
Environmental agency makes maps identifying areas most at risk from flooding
Benefits of flood warning
People can prepare and protect
Disadvantages of flood warning
Insurance, reduce the value of homes in the area
Flood management scheme case study
Banbury
Where is Banbury
50km north of oxford, on the flood plain of the river Cherwell, 45,000 live here
What happened in Banbury in 1998
Railway closure, 150 homes affected, £12.5 million of damage
What’s been done to improve Banbury
4.5m embankment, flood storage area which holds 1200 Olympic swimming pools, natural flood plain, raised road, control structure which controls flow
Benefits of Banbury
Reduced anxiety, quality of life improved, business and houses protected, new biodiversity action plan created with ponds and trees
Disadvantages of Banbury scheme
£18.5 million, part of flood plain Will deliberately be able to flood, 100,000 tonnes of earth required for the embankment
