Sediment Transport and Hydraulics
Published:January 01, 1987
The development of three separate devices at Birkbeck College, London, and their deployment in a gravel-bed stream allows us to pinpoint entrainment thresholds, to measure bedload continuously and to quantify the ingress of matrix fines. This provides a comprehensive picture of processes and gives clear indication of the reasons why gravel beds appear to react unpredictably to flood flows and why a universal bedload equation has yet to be developed. We show that ubiquitous bed microforms (e.g., pebble clusters) delay initial motion so that stream power is 5 times greater than it is when bedload transport ceases. We also show that low-flow ingress of matrix fines increases the difference to 16 times by increasing shear strength of the stream bed. Our continuous monitoring devices indicate a regular pulsation of bedload transport (mean wave period 1.7 hrs) that cannot be attributed to deficiencies in the samplers because it is corroborated by distinctly different and independent instruments; the pulses are not explained by changes in hydraulic parameters. We suggest that they are kinematic waves of mobile bed particles, the first dynamic manifestation of this phenomenon in a natural stream. Our data give a clear indication of those facets of water-sediment interaction that must be investigated in order to arrive at a general bedload transport equation for gravel-bed streams, and the data highlight the naive assumptions currently made in paleohydraulics when using clast size as an indicator of paleo-flow conditions.
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Recent Developments in Fluvial Sedimentology
This volume brings together 36 of the manuscripts that were presented at the Third International Fluvial Sedimentology Conference hosted by Colorado State University in August, 1985. Fluvial systems and sedimentary rock sequences discussed range in age from Holocene to Precambrian and include many diverse areas. The principal objective of the volume was to document the recent developments in the application of facies analysis to the reconstruction of the architecture of fluvial systems. Reconstruction of architecture is an integral part of the overall process of basin analysis.