P1 - Unit 1C - River Landscapes In The UK Flashcards
What’s a cross profile of a river?
The side to side cross-section of a river channel and or valley
What’s a long profile of a river?
The gradient of a river from its source to its mouth
-shows you how the gradient changes over the different courses
What’s vertical and lateral erosion?
Vertical-downward
Lateral-sideways erosion
What’s a river discharge?
The quantity of water that passes a certain point within a given period of time
What’re the three sections of a river in its long profile?
Upper course, middle course, lower course
What’s the Bradshaw model?
It’s a geographical model which describes how a river’s characteristics vary between the upper and lower course of a river.
What’re the characteristics in the upper course of a river?
- steep gradient
- channel is shallow and narrow
- vertical erosion
- v-shaped valley, steep sides
What’re the landforms found in the upper course of a river?
Interlocking spurs
Waterfalls
Gorges
What’re the characteristics in the middle course of a river?
- medium gradient
- channel is deeper and wider
- more lateral and some vertical erosion
- gently sloping valley sides
What’re the landforms found in the middle course of the river?
- meanders
- flood plains
- levées
What’re the characteristics in the lower course of a river?
- gentle gradient
- channel is deepest and widest
- lateral erosion but loads of deposition
- very wide almost flat valley
What’re the landforms in the lower course of a river?
- estuary
- meanders
- flood plain
- levées
- oxbow lakes
What’re the four processes of erosion?
Abrasion, attrition, hydraulic action, solution
Define abrasion/corrasion:
When smaller material, carried in suspension, rubs against the banks of the river(this cause a sand papering action)
Define attrition:
When boulder or other material, which are being transported along the bed of the river, collide and break up into smaller pieces(this leads to rocks becoming more rounded)
-the further a material travels the more rounded and small it becomes
Define hydraulic action:
When the sheer force of the river dislodges particles from the river bed and banks
Define solution/corrosion:
When acids in the river dissolves rocks
e.g. chalk and limestone
What’re the four types of transportation?
Traction
Saltation
Suspension
Solution
Define traction:
Large boulders and rocks are rolled along the river bed by the force of the water
Define saltation:
-small pebbles and stones are bounced along the river bed by the force of the water
Define suspension:
Fine, light material is carried along by the river
Define solution:
Minerals are dissolved in the water
-this is a chemical change
Why does deposition take place?
Deposition occurs when the velocity of a river decreases, it no longer has enough energy to transport its sediment so it is deposited
How is a waterfall formed?
- waterfalls are most commonly formed when a river flows over a resistant band of hard rock
- the less resistant rock beneath is eroded rapidly by hydraulic action and abrasion, undercutting the hard rock above
- When the river plunges over a waterfall it forms a deep plunge pool
- this creates a ledge of overhanging hard rock, eventually this rock collapses into the plunge pool
- the waterfall retreats upstream leaving a gorge behind
What’s a gorge?
A gorge is a narrow, steep-sided called, with bare, rocky walls. A gorge of recession is found immediately downstream of a waterfall.
Describe a case study for a waterfall in the U.K:
High Force Waterfall, River Tees, Teesdale
- has hard Whinsill cap rock, below this there’s softer rock such as limestone, sandstone and shale
- there’s a 700m gorge
- the waterfall is 21m high
What features are there at a meander?
Inside of the bend- slip off slope, deposition
Outside of the bend-fastest flow(thelweg),river cliff, lateral erosion(hydraulic action, abrasion), deeper channel
How do oxbow lakes form?
- due to erosion on the outside of the bend and deposition on the inside the shape of a meander will change over time
- erosion narrows the neck of land between the meander
- the neck is then eroded so that a new straighter channel is formed, the river will take this straighter route
- deposition will eventually cut off the old meander to leave an oxbow lake
What’re levées?
Naturally raised river banks found on either or both sides of river which is prone to flooding
How are levées formed?
- During a flood when a river bursts its banks it deposits sediment(heaviest load closest to the river deposited)
- with every flood these banks of deposited sediment are built a little bit higher but also the river bed builds up bedload deposits over time so this increases the rivers probability of flooding
How is a flood plain formed?
The width of a flood plain is due to meander migration where the outside bends erode laterally into the edges of the valley.
Define flood plain:
A large area of land wither side of a river that is prone to flooding
Define river estuary:
The tidal part of a river where the channel broadens out as it reaches the sea
How’s an estuary formed?
- a large river entered the sea at a narrow mouth before the last ice age
- after the last ice age, the ice melted causing a rise in sea level, do either sides of the river became flooded, forming a estuary
How are estuary mud flats formed?
Mudflats are formed in sheltered areas where tidal water flows slowly.
As a river transports alluvium(mineral rich soil) to the sea, and incoming tide transports sand and marine silt up the estuary, where the waters meet velocity is reduced so deposition is increased
Define drainage basin:
A river drainage basin(or catchment area) is an area of land drained by a river and its tributaries
Define watershed:
The boundary between two drainage basins marked by a ridge of high land
Define percolation:
Water seeping deeper below the surface into the rock
Define transpiration:
Water lost through pores in vegetation
Define interception:
Water being prevented from reaching the surface by trees and vegetation
Define throughflow:
Water flowing through the soil layer parallel to the surface
Define infiltration:
Water sinking into the soil from the ground surface
Define groundwater flow:
Water flowing through the rock layer parallel tot the surface
Define water table:
The upper level of saturated rock/soil where no more water can be absorbed
What increases flood risk?
Bands of depression(rain)
Sudden bursts of heavy rain(flash floods)
Prolonged light rainfall
Sudden snow melt
What physical features can increase the risk of flooding?
Geology(type of rock), determines how long the rainfall takes to get to the river
Relief(height and slop of the land), how much surface runoff there is depends on the rate by which water flows over the land
What’re human causes of flooding?
Urbanisation-infrastructure(more impermeable surfaces on the land), new houses(more houses built on greenfield sites), disappearing gardens(people will get rid of their garden to have a parking space which increase the amount of impermeable surfaces) Deforestation-reduces interception, roots no longer take water from the soil Agriculture-hedges have been ripped out, leaving soil bare in winter
What’s a hydrograph?
A hydrograph shows how a rivers discharge changes in response to a precipitation event.
What are the two main ways to manage flooding?
Hard engineering-using man made structures to prevent or control natural processes from taking place
Soft engineering-a strategy that involves adapting to a river and learning to live with it
What’re examples of hard engineering schemes to manage flooding?
- building dams and reservoirs
- channel straightening
- building embankments(artificially raised river bank)
- making a flood relief channel
What’re examples of soft engineering schemes to manage flooding?
- flood plain zoning(where you plan out areas due to how high above the river they are)
- flood warnings and preparation work
- planting trees
- river restoration
What are the advantages and disadvantages of dams and reservoirs?
Advantages -boosts tourism -provides HEP Disadvantages -costs a lot to build -the reservoir can destroy areas of vegetation
What’re the advantages and disadvantages of channel straightening?
Advantages
-water will flow through that area quicker because of less friction with banks
-home owners gain confidence that they won’t flood
Disadvantages
-expensive and dredging is also expensive
-can endanger animals and destroy habitats
What’re the advantages and disadvantages of flood-relief channel?
Advantages
-recreation can happen on the new channel(walking, canoeing)
-the value of property in the area increases
Disadvantages
-expensive
-habitats are disturbed int eh construction of the channel
What’re the advantages and disadvantages of river restoration?
Advantages -creates new wetland habitats and increases biodiversity -aesthetically pleasing Disadvantages -loss of agricultural land -can be expensive, initially
What’re the advantages and disadvantages of planting trees?
Advantages -reduces water flowing downstream as more water is used -encourages new habitats Disadvantages -loss of potential grazing land -costs to plant trees
What’re the advantages and disadvantages of flood plain zoning?
Advantages
-low cost
-by preserving the flood plain it provides more green space in towns
Disadvantages
-approach has limited impact
-housing shortage in the U.K, restricting building makes the problem worse
How is flooding managed in Cockermouth after the flooding at the confluence between the river Derwent and the river Cocker in November 2009?
- self raising barriers
- flood warning services(81% of people signed up)
- gravel removal from the river Derwent
- embankments, walls and gates to lessen the risk
When does the velocity of a river decrease?
- when the volume of water in the river falls
- amount of eroded material being transported increases
- water is shallower
- river reaches its mouth