Bed load

Bed load sediment in the thalweg of Campbell creek in Alaska.

The term Bed load describes particles in a flowing fluid (usually a river) that are transported along the bed. This is in opposition to suspended load and wash load which are carried entirely in suspension.

Bedload moves by a variety of methods, including rolling, sliding, traction, and saltation.

Generally, bed load downstream will be smaller and more rounded than bed load upstream (a process known as downstream fining). This is due in part to attrition and abrasion which cause the stones to bump against each other and against the river channel, thus removing its rough texture and making it smaller. However, selective transport of sediments also plays a role in relation to downstream fining: larger-than average particles are more easily entrained than small-than average particles, since larger particles are protruding from the bed whereas small particles are shielded/ hidden by larger particles thus requiring a higher lift and drag force to entrain.

References

• Waugh, D. "The New Wider World", Cheltenham: Nelson Thorns Ltd, 2003.
• Ashworth, P.J and Ferguson, R.I (1989) Size-selective entrainment of Bed Load in Gravel Bed Streams, 'Water Resources Research, Vol 25 (4): 627-634

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