Meanders:
● Meander = a bend in a river → formed by a combination of fluvial erosion and deposition
→ Characteristics:
● Inside bank:
○ Curved, beach-like features
○ Gentle, convex slope
○ Sediment consists of sand/gravel/pebbles
○ Vegetation grows furthest from water
● Outside bank:
○ Steep drop down into river
○ Several metres high
○ Composed mostly of bare earth
○ Unconsolidated material at base
→ Formation:
1. Water flows slowly over shallow areas (riffles) in
riverbed, faster through deeper sections (pools )
○ Sets in motion a helicoidal flow = water
corkscrews across from one bank to
another
■ Thalweg = line of fastest flow → causes erosion
■ Slack water = line of slowest flow → causes deposition
2. Thalweg on outside bank causes lateral erosion through abrasion/hydraulic action
○ Undercuts bank
○ Forms a river cliff
○ Corkscrews from the outside of one bend across to the outside of the next bend
3. Slack water corkscrews down to inside bend → deposits its load as friction slows the flow
○ Fast flow causes vertical erosion → deepens river bed resulting in an asymmetrical cross-profile
4. Sand/pebbles deposited on inside bank → forms slip-off slope
Oxbow lakes:
● Oxbow lakes = a small, horseshoe-shaped lake
→ Characteristics:
● Gentle slip-off slope into lake
● Marsh plants colonise the edges
● Still water
○ Rainfall adds water
○ Evaporation reduces water
● Deepest water in outside bank
→ Formation:
● Stage 1
○ Meander loop becomes very large
○ Only a narrow strip of land separates river channel
○ Continued lateral erosion
● Stage 2
○ River floods , so main flow cuts straight through neck
○ “Shortcut” begins to break down banks and create a new channel
Stage 3
○ Flood recedes and river reverts to normal channel
○ Process is repeated every flood event
○ New channel becomes established by continued erosion → becomes main channel
● Stage 4
○ Loop of old river becomes increasingly detached → no longer receiving water
○ Flooding causes deposition on new river banks → aids detachment of old loop
○ Marsh plants colonise area → further widens gap