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PRACTICAL ASPECTS OF BED FORMATION
- The bed of the channel in which water is flowing, may adopt various shapes depending upon the velocity of flow.
- At very low velocity of flow, bed of the channel does not move at all.
- When velocity is slowly increased a stage is reached when the sediment load is just at the point of motion.
- This stage is known as ‘‘threshold of motion”. If bed is
- made of fine sand, having particles of less than 2 mm diameter, saw tooth type ripples develop in the bed on slightly further increasing the velocity.
- This phenomenon can be easily seen in sand at beaches.
- At still larger velocity, dunes with ripples appear at the bed, which on the further increase on the velocity take the shape of rounded dunes.
- When velocity is still further increased, the dunes are eliminated and a flat surface becomes available.
- If velocity is increased still further, sand waves are formed in association with surface waves.
- When velocity is still further increased.
- Froude number V gD approaches almost unity and surface waves to become so steep.
- That they break and the whole wave system gradually moves upwards.
- The sand waves at this point of velocity are know anti-nodes.
- Antinodes can form only in open channel flows and not in wind blown sand.
- Because they require an interaction between the bed.
- The channel and the water surface for their formation.