Rivers
Describe the change in depth, gradient, velocity, and discharge downstream
Velocity – (slowly) increases, gets faster downstream due to reduced friction due
to reduced wetted perimeter
Volume = volume increases downstream as the upper course is made of shallow
streams. Then faster moving water causes riverbed erosion, and the river starts
getting deeper and more tributaries join the river, so more water fills the river
Valley = the valley starts as a V shape profile caused by vertical erosion of the
river. As the river flows downstream, the river has more energy to erode
laterally as the valley is flatter and has gentler slopes – widening the valley.
Width = increases downstream as more water from the tributaries causes more
lateral erosion. This leads to more erosion on the wetted perimeter, widening the
channel.
Depth = increases with distance downstream as greater discharge has more
erosive power; therefore eroding a deeper channel
Discharge – Increases downstream due to increased input from tributaries,
urbanisation increasing the water entering the channel and more water entering
from surface run-off and direct precipitation. This greater energy in channel
provides more erosive power and thus greater width and capacity.
Gradient – decreases downstream/less steep due to geology. In upper course,
geology is harder therefore there is greater friction with bed, therefore vertical
erosion cuts into rock leading to steeper profile.
Formation of a waterfall
Waterfalls are formed in areas where hard rock overlies softer rock.
Soft rock is eroded as water cascades down due to hydraulic action (the impact
of water) and abrasion (where sediments are thrown against the softer rock).
This leads to an over-deepening of the bedrock forming a plunge pool. The
erosive action also cuts into the softer rock and over time an overhang of harder
rock is created. When the overhang becomes top heavy and unstable it breaks off
and collapses into the plunge pool, as a consequence of gravity. Repetition of this
process led to the migration of the waterfall upstream leading to a gorge
formation.
Formation of Meander
Channel flow is directed towards the outside of the meander bend and erosion
occurs forming river cliff due to hydraulic action and abrasion. It is also faster
flowing (Thalweg) as there is less friction because of depth. Slower flowing water
passes around the inside of the channel and deposition occurs forming a slip-off
slope. The meander then migrates in direction of outside bend.
Describe the change in depth, gradient, velocity, and discharge downstream
Velocity – (slowly) increases, gets faster downstream due to reduced friction due
to reduced wetted perimeter
Volume = volume increases downstream as the upper course is made of shallow
streams. Then faster moving water causes riverbed erosion, and the river starts
getting deeper and more tributaries join the river, so more water fills the river
Valley = the valley starts as a V shape profile caused by vertical erosion of the
river. As the river flows downstream, the river has more energy to erode
laterally as the valley is flatter and has gentler slopes – widening the valley.
Width = increases downstream as more water from the tributaries causes more
lateral erosion. This leads to more erosion on the wetted perimeter, widening the
channel.
Depth = increases with distance downstream as greater discharge has more
erosive power; therefore eroding a deeper channel
Discharge – Increases downstream due to increased input from tributaries,
urbanisation increasing the water entering the channel and more water entering
from surface run-off and direct precipitation. This greater energy in channel
provides more erosive power and thus greater width and capacity.
Gradient – decreases downstream/less steep due to geology. In upper course,
geology is harder therefore there is greater friction with bed, therefore vertical
erosion cuts into rock leading to steeper profile.
Formation of a waterfall
Waterfalls are formed in areas where hard rock overlies softer rock.
Soft rock is eroded as water cascades down due to hydraulic action (the impact
of water) and abrasion (where sediments are thrown against the softer rock).
This leads to an over-deepening of the bedrock forming a plunge pool. The
erosive action also cuts into the softer rock and over time an overhang of harder
rock is created. When the overhang becomes top heavy and unstable it breaks off
and collapses into the plunge pool, as a consequence of gravity. Repetition of this
process led to the migration of the waterfall upstream leading to a gorge
formation.
Formation of Meander
Channel flow is directed towards the outside of the meander bend and erosion
occurs forming river cliff due to hydraulic action and abrasion. It is also faster
flowing (Thalweg) as there is less friction because of depth. Slower flowing water
passes around the inside of the channel and deposition occurs forming a slip-off
slope. The meander then migrates in direction of outside bend.
