River Processes and Landforms, Knowledge Organiser

Key Terms

• Hydraulic action: Water pressure shattering rock
• Abrasion: Load scraping bed/banks
• Attrition: Load particles wearing each other
• Corrosion: Acid dissolving soluble rock
• Traction: Boulders rolling along bed
• Saltation: Pebbles bouncing along bed
• Suspension: Fine silt carried in water
• Meander: S-shaped river bend
• Ox-bow lake: Isolated former meander loop
• Floodplain: Flat valley floor of alluvium
• Levée: Natural embankment beside channel
• Alluvium: Fertile silt deposited by floods
• Discharge: Volume of water per second (m³/s)
• Competence: Max particle size river can carry

Key Processes

• Upper course: Vertical erosion → V-valley + waterfalls
• Waterfall formation: Hard rock over soft → differential erosion → undercutting → collapse → retreat → gorge
• Meander formation: Deflection → faster outside → lateral erosion → river cliff; helical flow → deposition inside → point bar; positive feedback amplifies bend
• Ox-bow lake: Meander neck narrows → flood cuts through → deposition seals old loop
• Floodplain: Lateral meander migration + repeated alluvium deposition during floods
• Levée: Coarse material deposited beside channel during floods → builds embankment
• Bradshaw Model: Discharge, velocity, width, depth all increase downstream; sediment size decreases

Named UK Example

• River Tees — 137km, Cross Fell (893m) to Teesmouth
• High Force: 21m waterfall, Whin Sill dolerite over limestone/shale, gorge 700m long
• Low Force: 7m waterfall, 1.5km downstream — younger stage of same process
• Whin Sill: Hard dolerite — most resistant rock in North Pennines
• Teesside floodplain: Wide alluvial plain, historic steel/chemical industry on flat land
• River Great Ouse, Cambridgeshire: Ox-bow lakes and meander scars visible in aerial photography
• River Severn: Source at Plynlimon (752m), mouth at Gloucester — textbook upper to lower course transition

Must-Know Facts

• Lower course rivers are typically faster than upper course — lower friction despite lower gradient
• Velocity drop = deposition (Hjulström Curve principle)
• Meander: outside = erosion (river cliff); inside = deposition (point bar); helical flow links them
• Mnemonic: RSVP (Rolling, Skipping, Very fine suspension, Pure solution)
• Mnemonic: MOAT (Material smashing, Opening cracks, Abrasion, Taking dissolved rock)
• Hjulström Curve: larger particles need more energy to move (transport) than to keep moving; very fine clay also needs high velocity (cohesion) — deposition occurs in a band between these thresholds
• Ox-bow lake → meander scar → marsh → dry land over time
• High Force = largest waterfall in England by volume
• Discharge increases downstream (tributaries add water)
• Sediment gets smaller and rounder downstream (attrition)

Common Mistakes

• Confusing erosion processes: Hydraulic action uses water pressure; abrasion uses load as a tool; attrition is load particles wearing each other — attrition does NOT erode the riverbed
• Saying upper course rivers are fastest: Lower course rivers are typically faster despite lower gradient — reduced friction from a larger cross-section means greater velocity
• Describing meanders without helical flow: A full explanation of meander formation requires helical (corkscrew) flow — erosion on the outside creates the river cliff; deposition on the inside creates the point bar
• Not naming a UK example: Always use a named river with specific evidence — High Force waterfall on the River Tees (21 m, Whin Sill dolerite over limestone) is the standard AQA example

Memory Aid

RSVP: The Four Transportation Methods (in order, largest to finest) Rolling (traction — boulders rolling along the bed) Skipping (saltation — pebbles bouncing along the bed) Very fine suspension (silt and clay floating within the flow) Pure solution (dissolved minerals, invisible) Think of it as a party invitation: the river is RSVP-ing its load from source to sea — from the largest boulders it rolls along the floor to the dissolved minerals it carries invisibly to the ocean. MOAT: The Four Erosion Processes Material smashing together (attrition — load particles colliding and breaking apart) Opening cracks by force (hydraulic action — water pressure shattering rock) Abrasion — load scraping the bed and banks like sandpaper Taking dissolved rock (corrosion/solution — chemical dissolution of soluble rock) A river cuts its valley through the landscape like digging a MOAT — using all four erosion processes working simultaneously. The Meander Memory Rule: ODES Outside = fast flow = Erosion (river cliff) Inside = slow flow = Deposition (point bar) Spiral (helical) flow transfers material from outside to inside ODES — Outside Deposits? Erase that! Deposition and Erosion are the other way round! The outside is where the fast water goes → erosion. The inside is where slow water goes → deposition. Bradshaw Model: The "DVWS" Rule As you go Downstream from source to mouth: Discharge and velocity increase Width and depth increase Sediment size decreases (smaller, rounder particles) Slope (gradient) decreases