Channel processes and features Valley slope processes and landforms

Channel processes and features Valley slope processes and landforms
RIVER STUDIES Channel processes and features Valley slope processes and landforms

Satellite view of river drainage, Middle East

Microscale drainage basin

Upper valley characteristics

“V”shape valley, vertical erosion dominant

“V”shape valley, vertical erosion dominant Interlocking spurs

“V”shape valley, vertical erosion dominant Interlocking spurs Slumping and landslides - very active hillslopes

“V”shape valley, vertical erosion dominant Terracettes formed by soil creep Interlocking spurs Slumping and landslides - very active hillslopes

“V”shape valley, vertical erosion dominant Terracettes formed by soil creep Narrow, shallow channel, low velocity and discharge Interlocking spurs Slumping and landslides - very active hillslopes

“V”shape 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

Interlocking spurs, Robinson, Lake District
A typical upper course valley with interlocking spurs, steep valley sides and active slope processes

Choked runnel, N. Pennines
Ephemeral stream or runnel - water present only during high rainfall events

Ephemeral stream or runnel - water present only during high rainfall events Debris brought downslope towards channel - dropped when water disappears after storm

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

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

Load is dumped in summer due to the low discharge unable to carry the capacity and competence of load at higher flow levels

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

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

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

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

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

High Force waterfall, R. Tees

Huge step in river bed due to igneous intrusion of dolerite into the limestone.

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

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

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

Headward erosion, Offa’s Dyke
This is amazing!!

Headward erosion, Offa’s Dyke
Spring erodes ground over which it flows and lubricates base of cliff, causing slumping and headward erosion

Headward erosion, R. Colorado

River seeps out from spring at base and undermines steep cliff, causing rockfalls and headwall recession

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

Potholes in R. Wharfe Smooth sculpturing of rock by abrasion, showing evidence of water levels during high discharge events Vertical erosion is dominant

Close-up of potholes

Close-up of potholes Circular potholes due to eddying motion when river energy is high

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

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

Potholes, human scale!!

Middle course, R. Tees

Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom

Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders

Middle course, R. Tees Valley opens out, more gentle slopes, wider valley bottom First signs of meanders Floodplain

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

Meander, R. Lavant, Chichester

Floodplain

Floodplain Point bar deposits on the inner meander bend where there is low energy

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

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

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

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 pool riffle pool helicoidal flow Pools develop at meander bends and riffles in the stretches between bends

Meander on the R. Colorado

Meander incised into plateau due to rejuvenation

Meander incised into plateau due to rejuvenation Different strata show evidence of past climates or hydrological events

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

Migrating meanders, R. Gongola, Nigeria

Migrating meanders, R. Gongola, Nigeria
Former course marked by white sediments Current channel is braided

Lower Severn Valley

Lower Severn Valley Well developed meanders with bars in the channel indicating high sediment load Very wide floodplain Very gentle valley side gradients

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

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

Flooding in the Severn Valley

Floodplain can be mapped into risk zones high to low

Floodplain can be mapped into risk zones high to low Floods can be beneficial - they renew soil fertility by depositing sediment on floodplain

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

Padstow estuary Estuaries are tidal, dominated by marine sediments
At low tide, mudflats are exposed

Alluvial fan, Buttermere, Lake District

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

Braided river, Swiss Alps

Daytime snowmelt in summer produces flashy regime Vast amounts of sediment supplied from frost-shattered valley sides

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

Summary of channel characteristics (1) Processes

Summary of channel characteristics (2) Landforms

Rapids Waterfall Pothole

Rapids Waterfall Pothole Meander Bluff/cliff Point bar Pool Riffle

Rapids Waterfall Pothole Meander Bluff/cliff Point bar Pool Riffle Knick point Braids Alluvial fan Delta

Summary of channel characteristics (3) Concepts and technical terms

Discharge Regime - flashy - regular Capacity Competence

Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter

Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter Long profile Graded profile Rejuvenation Base level

Discharge Regime - flashy - regular Capacity Competence Hydraulic radius - cross sectional area - wetted perimeter Long profile Graded profile Rejuvenation Base level Thalweg Helicoidal flow Meander migration

Summary of valley characteristics

Channel processes and features Valley slope processes and landforms

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Channel processes and features Valley slope processes and landforms

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