Channel processes and features

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RIVER STUDIES

• Channel processes and features
• Valley slope processes and landforms

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Satellite view of river drainage, Middle East
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Microscale drainage basin
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Upper valley characteristics
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Upper valley characteristics
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Upper valley characteristics
Vshape valley, vertical erosion dominant
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Interlocking spurs
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Interlocking spurs
Slumping and landslides - very active
hillslopes
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Terracettes formed by soil creep
Interlocking spurs
Slumping and landslides - very active
hillslopes
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Terracettes formed by soil creep
Narrow, shallow channel, low velocity and
discharge
Interlocking spurs
Slumping and landslides - very active
hillslopes
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Upper valley characteristics
Vshape valley, vertical erosion dominant
Terracettes formed by soil creep
Narrow, shallow channel, low velocity and
discharge
Interlocking spurs
Slumping and landslides - very active
hillslopes
Large bedload derived from upstream and from
valley sides
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Interlocking spurs, Robinson, Lake District
A typical upper course valley with interlocking
spurs, steep valley sides and active slope
processes
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Choked runnel, N. Pennines
Ephemeral stream or runnel - water present only
during high rainfall events
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Choked runnel, N. Pennines
Ephemeral stream or runnel - water present only
during high rainfall events
Debris brought downslope towards channel -
dropped when water disappears after storm
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Choked runnel, N. Pennines
Vertical erosion creating steep, bare slopes
vulnerable to further erosion - an example of
positive feedback in a slope system
Ephemeral stream or runnel- water present only
during high rainfall events
Debris brought downslope towards channel -
dropped when water disappears after storm
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River load in upper course
Load is dumped in summer due to the low discharge
unable to carry the c________ and c__________ of
load at higher flow levels
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River load in upper course
Load is dumped in summer due to the low discharge
unable to carry the capacity and competence of
load at higher flow levels
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River load in upper course
Load is dumped in summer due to the low discharge
unable to carry the capacity and competence of
load at higher flow levels
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River load in upper course
Boulders are large and semi-rounded, due to
attrition within the load and abrasion with the
stream bed and banks
Load is dumped in summer due to the low discharge
unable to carry the capacity and competence of
load at higher flow levels
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Rapids in the Upper Tees Valley
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Rapids in the Upper Tees Valley
Rapids are mini-waterfalls
Protruding bands of more resistant strata create
steps over which rapids fall - the river bed is
ungraded
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Rapids in the Upper Tees Valley
Rapids are mini-waterfalls
Shallow, slow flowing river due to large amount
of friction.
Protruding bands of more resistant strata create
steps over which rapids fall - the river bed is
ungraded
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Rapids in the Upper Tees Valley
Rapids are mini-waterfalls
Shallow, slow flowing river due to large amount
of friction. Wetted perimeter is large compared
to cross sectional area of water - resulting in a
low ????????????
Protruding bands of more resistant strata create
steps over which rapids fall - the river bed is
ungraded
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Rapids in the Upper Tees Valley
Rapids are mini-waterfalls
Shallow, slow flowing river due to large amount
of friction. Wetted perimeter is large compared
to cross sectional area of water - resulting in a
low hydraulic radius (low efficiency)
Protruding bands of more resistant strata create
steps over which rapids fall - the river bed is
ungraded
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High Force waterfall, R. Tees
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High Force waterfall, R. Tees
Huge step in river bed due to igneous intrusion
of dolerite into the limestone.
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High Force waterfall, R. Tees
Huge step in river bed due to igneous intrusion
of dolerite into the limestone.
Plunge pool where the dolerite wall is undercut,
causing rockfalls and recession of the waterfall
upstream
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High Force waterfall, R. Tees
Huge step in river bed due to igneous intrusion
of dolerite into the limestone.
Waterfall creates gorge as it recedes upstream by
eroding the base and neck
Plunge pool where the dolerite wall is undercut,
causing rockfalls and recession of the waterfall
upstream
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High Force waterfall, R. Tees
The long profile will be graded over time
Huge step in river bed due to igneous intrusion
of dolerite into the limestone.
Waterfall creates gorge as it recedes upstream by
eroding the base and neck
Plunge pool where the dolerite wall is undercut,
causing rockfalls and recession of the waterfall
upstream
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Headward erosion, Offas Dyke
This is amazing!!
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Headward erosion, Offas Dyke
Spring erodes ground over which it flows and
lubricates base of cliff, causing slumping and
headward erosion
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Headward erosion, R. Colorado
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Headward erosion, R. Colorado
River seeps out from spring at base and
undermines steep cliff, causing rockfalls and
headwall recession
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Headward erosion, R. Colorado
Rivers erode in a headward direction, eating back
into plateau
River seeps out from spring at base and
undermines steep cliff, causing rockfalls and
headwall recession
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Potholes in R. Wharfe
Smooth sculpturing of rock by abrasion, showing
evidence of water levels during high discharge
events
Vertical erosion is dominant
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Close-up of potholes
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Close-up of potholes
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Close-up of potholes
Circular potholes due to eddying motion when
river energy is high
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Close-up of potholes
Circular potholes due to eddying motion when
river energy is high
Potholes will join together by abrasion, and
deepen by vertical erosion
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Close-up of potholes
Circular potholes due to eddying motion when
river energy is high
Potholes will join together by abrasion, and
deepen by vertical erosion
Load is picked up and used to scour or abrade
pothole. Load itself becomes rounded by attrition
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Potholes, human scale!!
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Middle course, R. Tees
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Middle course, R. Tees
Valley opens out, more gentle slopes, wider
valley bottom
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Middle course, R. Tees
Valley opens out, more gentle slopes, wider
valley bottom
First signs of meanders
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Middle course, R. Tees
Valley opens out, more gentle slopes, wider
valley bottom
First signs of meanders
Floodplain
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Middle course, R. Tees
Valley opens out, more gentle slopes, wider
valley bottom
First signs of meanders
Floodplain
River channel wider, deeper, greater velocity and
discharge
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Meander, R. Lavant, Chichester
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Meander, R. Lavant, Chichester
Floodplain
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Meander, R. Lavant, Chichester
Floodplain
Point bar deposits on the inner meander bend
where there is low energy
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Meander, R. Lavant, Chichester
Floodplain
Point bar deposits on the inner meander bend
where there is low energy
Steep bank known as the river bluff or cliff,
caused by concentrated erosion due to the
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Meander, R. Lavant, Chichester
Floodplain
Point bar deposits on the inner meander bend
where there is low energy
Steep bank known as the river bluff or cliff,
caused by concentrated erosion due to the thalweg
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Meander, R. Lavant, Chichester
Floodplain
Point bar deposits on the inner meander bend
where there is low energy
Steep bank known as the river bluff or cliff,
caused by concentrated erosion due to the thalweg
and
helicoidal flow
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Meander, R. Lavant, Chichester
Floodplain
Steep bank known as the river bluff or cliff,
caused by concentrated erosion due to the thalweg
and
Point bar deposits on the inner meander bend
where there is low energy
pool
riffle
pool
helicoidal flow
Pools develop at meander bends and riffles in the
stretches between bends
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Meander on the R. Colorado
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Meander on the R. Colorado
Meander incised into plateau due to rejuvenation
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Meander on the R. Colorado
Meander incised into plateau due to rejuvenation
Different strata show evidence of past climates
or hydrological events
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Meander on the R. Colorado
Meander incised into plateau due to rejuvenation
Different strata show evidence of past climates
or hydrological events. Stratum with large
boulders must have formed in wetter conditions
when higher river discharge carried a greater
competence of load
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Migrating meanders, R. Gongola, Nigeria
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Migrating meanders, R. Gongola, Nigeria
Former course marked by white sediments
Current channel is braided
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Lower Severn Valley
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Lower Severn Valley
Well developed meanders with bars in the channel
indicating high sediment load
Very wide floodplain Very gentle valley side
gradients
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River terraces, R. Agri, S. Italy
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River terraces, R. Agri, S. Italy
River has been rejuvenated causing renewed
vertical erosion - base level has dropped either
due to rising land or falling sealevel
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River terraces, R. Agri, S. Italy
Flat terraces represent former floodplains
River has been rejuvenated causing renewed
vertical erosion - base level has dropped either
due to rising land or falling sealevel
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Flooding in the Severn Valley
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Flooding in the Severn Valley
Floodplain can be mapped into risk zones high to
low
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Flooding in the Severn Valley
Floodplain can be mapped into risk zones high to
low
Floods can be beneficial - they renew soil
fertility by depositing sediment on floodplain
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Flooding in the Severn Valley
Floodplain can be mapped into risk zones high to
low
Floods can be beneficial - they renew soil
fertility by depositing sediment on floodplain
Floods result in large amounts of sediment
transported in the channel
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Padstow estuary
Estuaries are tidal, dominated by marine
sediments At low tide, mudflats are exposed
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Alluvial fan, Buttermere, Lake District
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Alluvial fan, Buttermere, Lake District
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Alluvial fan, Buttermere, Lake District
Lake Buttermere acts as a local baselevel for the
stream, leading to deposition of load in a
triangular shape - an alluvial fan
This is the same process that forms major deltas
at the coast e.g. R. Nile
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Braided river, Swiss Alps
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Braided river, Swiss Alps
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Braided river, Swiss Alps
Daytime snowmelt in summer produces flashy regime
Vast amounts of sediment supplied from
frost-shattered valley sides
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Braided river, Swiss Alps
Daytime snowmelt in summer produces flashy regime
Vast amounts of sediment supplied from
frost-shattered valley sides
Channel course can change daily due to changes in
discharge and loose sediments
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Summary of channel characteristics(1) Processes
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Summary of channel characteristics(1) Processes
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Summary of channel characteristics(1) Processes
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Summary of channel characteristics(1) Processes
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Summary of channel characteristics(2) Landforms
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Summary of channel characteristics(2) Landforms

• Rapids
• Waterfall
• Pothole

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Summary of channel characteristics(2) Landforms

• Rapids
• Waterfall
• Pothole

• Meander
• Bluff/cliff
• Point bar
• Pool
• Riffle

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Summary of channel characteristics(2) Landforms

• Rapids
• Waterfall
• Pothole

• Meander
• Bluff/cliff
• Point bar
• Pool
• Riffle

• Knick point
• Braids
• Alluvial fan
• Delta

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Summary of channel characteristics(3) Concepts
and technical terms
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Summary of channel characteristics(3) Concepts
and technical terms

• Discharge
• Regime
• - flashy
• - regular
• Capacity
• Competence

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Summary of channel characteristics(3) Concepts
and technical terms

• Discharge
• Regime
• - flashy
• - regular
• Capacity
• Competence

• Hydraulic radius
• - cross sectional
• area
• - wetted
• perimeter

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Summary of channel characteristics(3) Concepts
and technical terms

• Discharge
• Regime
• - flashy
• - regular
• Capacity
• Competence

• Hydraulic radius
• - cross sectional
• area
• - wetted
• perimeter

• Long profile
• Graded profile
• Rejuvenation
• Base level

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Summary of channel characteristics(3) Concepts
and technical terms
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Summary of valley characteristics
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Summary of valley characteristics
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Summary of valley characteristics
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Summary of valley characteristics