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the long profile of a river (upper course landforms (waterfalls (form when…
the long profile of a river
factors that increase or decrease
things that increase as the river progresses
width of channel
more water enters from tributaries and such
depth of channel
more water enters
amount of load
tributaries bring in more sediment
roundness and smoothness of load
Attrition and abrasion chip off the edges of the rocks.
velocity
the river becomes more efficient due to less friction from the smoother and deeper channel
human activity
fertile soil, near the sea for pots, wider and deeper for transport
things that decrease as the river progresses
load particle size
attrition and abrasion break down the particle size
gradient of valley sides
lateral erosion eats in to and flattens valley sides.
channel bed roughness
abrasion helps to smoothen the channel bed
bradshaw model
upper course landforms
v shaped valley
the steep gradient will make the river cut down through vertical erosion
the valley sides start to break down through weathering processes such as freeze thaw
the combination of gravity, highly weathered rock and rainfall cause the sides of the valley to fall in
this produces a v shaped valley, the fallen rock continues to help the river erode downwards
interlocking spurs
the river flows along natural lines of weakness, bending around areas of more resistant rock. this creates interlocking spurs comparable to a zip
rapids
less resistant rock erodes away faster than more resistant rock (differential erosion)
this creates an uneven river bed
this makes the river more turbulent and breaks up the natural flow of the river, resulting in white water rapids
potholes
the river flow is broken by an object in the river, usually a rock
a void is created on the downstream side of the rock. once over the rock the current fills the rock
this causes erosion in the void gradually creating a pothole
rocks get trapped in the pothole, helping it to further erode downwards through abrasion
waterfalls
form when there is a band of harder, more resistant rock over softer, less resistant rock
the softer, less resistant rock erodes more quickly, through processes of erosion such as hydraulic action and abrasion
this begins to form a deep plunge pool and undercuts the harder rock, forming an overhang
the overhang increases until it eventually collapses into the plunge pool because of gravity.
the rock from the overhang helps to continually erode the plunge pool further
this process causes the waterfall to retreat over time, leaving behind a steep sided gorge
main process in the upper course: erosion
middle course landforms
main process - transportation
meanders
a bend in the river's course
components
slip off slope - on the inside of the bend, where the velocity is at its lowest, so the material is deposited
river cliff - the river velocity is high on the outside of the bend, so there is more erosion. this forms a steep river cliff. the river is also deeper at this point
lateral erosion where the river cliff is
oxbow lakes
a former meander that has been cut off from the rest of the river
how it is formed
the river flows fastest on the outside bend of a meander, causing lateral erosion
the channel migrates in the direction of the outer bend of the meander, narrowing the neck between the meanders
during a high discharge event such as a flood the river breaks through the neck to form a straighter and more efficient channel
deposition of material will result in a complete cut off from the river forming an oxbow lake
the oxbow lake forms a new water habitat, however it will eventually dry up, forming an oxbow scar
lower course
deposition is the main process
flood plains
low lying, flat ground on either side of a river which gets covered with water during a flood event
leeves
a high discharge event causes the water to burst its banks. the river loses energy very quickly, and deposits it's heaviest material first
smaller sediment is carried further away from the river, making the ground fertile and good for farming
this causes large embankments called leeves to form
river delta
when a river reaches the mouth of the sea, the tide slows down the velocity of the water, causing the river to deposit its sediment
the process of flocculation binds the particles of sediment together
(happens only when the conditions are right, calm and shallow seas)
sediment builds up in layers called beds, and overtime these will build up to form islands
vegetation grows on the delta, stabilising it
the river splits into distributaries around the delta
