Rivers (Paper 1) Flashcards
(31 cards)
How many metres above sea level is the source of the River Dee?
460m
Where is the source of the River Dee?
Ddaullt in Snowdonia National Park
How many km long is the River Dee?
100km
Between 1972 and 1976, how many km of the River Dee underwent channelization?
8km
How many people got their water from the River Dee in 2016?
3 million
How many people died in the UK November 2012 floods?
9
How many homes flooded in the UK November 2012 floods?
8000
In what year did the Boscastle floods occur?
2004
How many homes and businesses were destroyed in the Boscastle floods?
100
How many cars were washed out to sea during the Boscastle floods?
75
How many homes were affected during the Tewkesbury 2007 floods?
48,000
How much money did the Tewkesbury 2007 floods cost the local council?
£140,000
In the Somerset 2014 floods, how many weeks did it take the flood waters to reduce?
12
How many hectares of farmland were left underwater in the Somerset floods?
1000
How are waterfalls and gorges formed?
-A band of more resistant rock lies over a band of soft rock
-The river erodes the soft rock which undercuts the resistant rock
-Eventually the more resistant rock collapses under its weight and gravity
-The force of the falling water erodes the riverbed through hydraulic action and abrasion from large boulders. This creates a plunge pool
-As the soft rock keeps eroding the hard rock collapses causing a gorge to form as the water fall retreats
-Gorges form from hard rocks where vertical erision by rivers is dominant
How are interlocking spurs formed?
-Rivers are small near the source and don’t have much power
-They flow around valley ridges (spurs) as they do not have the power to erode the usually more resistant rock
-Spurs are left interlocking with those from one side of the valley overlapping from the other
How are rivers cliffs formed?
-These are formed on the outside bend of a meander
-The thalweg (the deepest and fastest part of the current) is directed to the outside of the river bend as the water swings side to side
-Here there is maximum velocity and force causing lateral erosion through abrasion and hydraulic action
-The erosion undercuts the bank and a steep bank is formed
How are floodplains formed?
A floodplain is a wide flat area of land either side of a river and experiences flood when the river tops its banks
-When the river floods excess water spills over the surrounding area
-During flooding, the velocity of the river decreases, it loses energy and so deposits sediment flattening the floodplain
-The floodplain is also shaped by lateral erosion of meanders as they gradually migrate across the valley floor downstream
How are levees formed?
A levee is a natural embankment of sediment formed along the riverbank
-When flooding occurs, water and sediment come out of the channel as the river overflows
-As it overflows the river loses velocity and energy so deposists the larger and heavier sediment first on its banks
-As it repeats the banks get higher forming levees
How are point bars formed?
-On the inside of a meander the velocity and force of the water is less leading to deposition
-Larger and heavier sediment is deposited first, gently forming a sloping bank
How are meanders formed?
A meander is a bend in the river’s course commonly found on floodplains
-The flow of water swings from side to side causing the maximum velocity and force of the water to be on the outside of the bend
-A river cliff is formed
-On the inside bend the velocity is slower causing deposition
-Due to erosion and deposition the cross section of the meander is asymmetrical (steep on outside gentle on the inside)
How are oxbow lakes formed?
-As a meander bends and develops its neck becomes narrower
-Eventually the river may erode through the neck
-Water then flows through the straight channel as water follows the quickest route
-The old bend is abandonded by the river
-Depostion at the neck seals off the bend which dries up
-This leaves a horseshoe shaped lake behind this is an oxbow lake
What are the 4 types of hard engineering?
-Embankments (levees)
-Channelisation
-Flood relief channels
-Dams and Reservoirs
What are embankments (levees) and the pros and cons of it?
High banks built on or near riverbanks.
+Stops the water from spreading into other areas
-Can burst under pressure
