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Meandering rivers
- 2. Meandering Stream : • A stream consisting of successive meanders. – A meander in general is a bend in a sinous watercourse.
- 3. Formation : •A meander is formed when the moving water in a river changes its speed of water eroding sediments from the outside of a bend and depositing them on the inside. •Combination of the erosion and deposition helps expand the size of the meander. •The result is a ’movement of snake’ pattern as the stream meanders back and forth across its down- valley axis.
- 4. River flow movement Pool Riffle Deposition on inside Erosion on outside The meanders are found in the lower part of the course as all rivers flow down a slope towards the sea and will take the easiest route available. However, the geology of the land means a river will rarely flow in a straight path so this is why it will meander. The rates of deposition and lateral erosion are highest at this part of the river. Inside bend Outside bend
- 5. Flow In Meanders : Helical Flow ◦ It is the major flow in the meander bends. ◦ This flow causes an elevation of water level on the outside of meander. ◦ The water flows in a cork screw motion called helical flow.
- 6. Features : These includes; ◦ Channel Lag – below the common floor the coarsest material is sorted out & left behind on the stream bed. ◦ Point Bar - sediments accumulatation on the convex side of the meandering loop . ◦ Overbank Deposits – deposition of sediments by a river on a valley floor outside the stream channel resulting in five layer of sand deposition. ◦ Natural Levees - mounds of soil piled up along the rivers edge each time the river floods ◦ Crevasse-splays – spilling of large quantities of water & sediments at the time of flood from the river bank. ◦ OX Bow Lake - lake created when growing meanders intersect with each other & cut off a meander loop.
- 8. Formation of an Oxbow Lake : Oxbow lakes are created when growing meanders intersect each other and cut off a meander loop. This occurs when meanders grow literally through errosion & deposition. It includes four stages :- 1. When rivers flow over flatter land they develop large bends called meanders. 2. Inside of the bend there is much less water making the river deep & slow flowing.
- 9. 3. During flood, the river will cut right through the neck i.e the river will take new shorter loop. 4. With the fastest current in the centre of the river deposition occurs next to the banks.