Measurements in a braided river chute and lobe: 1. Flow pattern, sediment transport and channel change

R.I. Ferguson, P.E. Ashmore, Philip Ashworth, C. Paola, K.L. Prestegaard

Research output: Contribution to journalArticle

Abstract

This paper and its companion (Ashworth et al., this issue) discuss measurements of channel change and associated flow and sediment transport processes in a representative chute-and-bar reach within a proglacial gravel-bed river, the Sunwapta River in the Canadian Rockies. During a week in which water discharge through the reach increased then decreased, a sediment wave passed into and partly along the reach. At first the chute aggraded, then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries. Measurements of velocity, shear stress, and gravel transport rate revealed day-to-day changes in the divergent pattern of flow and sediment transport. The off-center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport, but as the lobe grew, the flow and transport gradually switched away to the other distributary. Width-averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill; the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations. By the end of the study the new lobe had almost accreted onto the original bar head, supporting the idea that most braid bars are of compound origin. Temporal and spatial patterns in grain size distributions of the bed, bed load, and deposited sediment are discussed in the companion paper.
Original languageEnglish
Pages (from-to)1877-1886
Number of pages10
JournalWater Resources Research
Volume28
Issue number7
Publication statusPublished - 1 Jan 1992

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channel change
braided river
flow pattern
sediment transport
bedload
gravel
sediment wave
river bed
scour
transport process
sediment
shear stress
asymmetry
fill
grain size
sampling
river
rate

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Ferguson, R. I., Ashmore, P. E., Ashworth, P., Paola, C., & Prestegaard, K. L. (1992). Measurements in a braided river chute and lobe: 1. Flow pattern, sediment transport and channel change. Water Resources Research, 28(7), 1877-1886.
Ferguson, R.I. ; Ashmore, P.E. ; Ashworth, Philip ; Paola, C. ; Prestegaard, K.L. / Measurements in a braided river chute and lobe: 1. Flow pattern, sediment transport and channel change. In: Water Resources Research. 1992 ; Vol. 28, No. 7. pp. 1877-1886.
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Ferguson, RI, Ashmore, PE, Ashworth, P, Paola, C & Prestegaard, KL 1992, 'Measurements in a braided river chute and lobe: 1. Flow pattern, sediment transport and channel change', Water Resources Research, vol. 28, no. 7, pp. 1877-1886.

Measurements in a braided river chute and lobe: 1. Flow pattern, sediment transport and channel change. / Ferguson, R.I.; Ashmore, P.E.; Ashworth, Philip; Paola, C.; Prestegaard, K.L.

In: Water Resources Research, Vol. 28, No. 7, 01.01.1992, p. 1877-1886.

Research output: Contribution to journalArticle

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AB - This paper and its companion (Ashworth et al., this issue) discuss measurements of channel change and associated flow and sediment transport processes in a representative chute-and-bar reach within a proglacial gravel-bed river, the Sunwapta River in the Canadian Rockies. During a week in which water discharge through the reach increased then decreased, a sediment wave passed into and partly along the reach. At first the chute aggraded, then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries. Measurements of velocity, shear stress, and gravel transport rate revealed day-to-day changes in the divergent pattern of flow and sediment transport. The off-center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport, but as the lobe grew, the flow and transport gradually switched away to the other distributary. Width-averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill; the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations. By the end of the study the new lobe had almost accreted onto the original bar head, supporting the idea that most braid bars are of compound origin. Temporal and spatial patterns in grain size distributions of the bed, bed load, and deposited sediment are discussed in the companion paper.

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