Tracer pebble entrainment and deposition loci: influence of flow character and implications for riffle-pool maintenance
D. J. Milan, G. L. Heritage, A. R. G. Large, 2002. "Tracer pebble entrainment and deposition loci: influence of flow character and implications for riffle-pool maintenance", Sediment Flux to Basins: Causes, Controls and Consequences, S.J. Jones, L.E. Frostick
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This paper considers the influence of flow character upon scour and deposition loci of tracer clasts in a gravel-bed river, and discusses implications for riffle–pool maintenance. Overall, bars were found to be the dominant depositional zones where over 54% of the tracer clasts accumulated during a 13-month period, followed by riffles (31%) and, finally, pools (<15%). Variability in the location of scour and deposition zones were apparent and could be broadly linked to four flow categories: (i) low-magnitude, high-frequency flows below 29% bankfull appeared responsible for intra-unit re-distribution of sediment particles; (ii) medium-magnitude and -frequency flows (up to 70% bankfull) appeared capable of inter-unit transfer, with pool scour and immediate deposition on riffle heads downstream, and some movement from riffles to bar edges and heads; (iii) high-magnitude, low-frequency flows (70–90% bankfull) appeared capable of riffle–riffle transport, with routing around bar edges; and (iv) very high-magnitude, very low-frequency flows (bankfull and over) capable of bar to bar transport and clast transport distances exceeding the length of a single riffle–pool unit. Tracers originating from riffles do not appear to be fed into pools on the outside of meander bends, instead they appear to be routed over shallower bar surfaces. High competence and low sediment supply explains the coarse nature of the pools (D50 =110 mm) in comparison to the riffles (D50 = 85 mm). An improved understanding of the sediment transport mechanisms operating during different flood types is needed to better predict morphological response to changes in hydrological regime and sediment
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There is an increasing trend in the Earth sciences towards the integration of many subdisciplines. The sedimendatry basin, is a fundamental focal point of many studies, which as a consequence often neglects the complimentary drainage basin or catchment. Sedimentary basins provide a record of Earth history, reflecting the geographical, lithological, oceanographic and ecological development through the rock record. Drainage basins in comparison record ephemeral landscape evolution, where topography is eroded and provides the flux of sediment to the basin. The basin fill reflects the sediment flux from the hinterland and provides evidence of the dynamic geomorphic processes. In context the drainage system and sedimentary basin can be regarded as a ‘production line’ with sedimentary record giving valuable insight into long-term landscape evolution and geomorphological processes illuminating the evolution of sedimentary basins.
This volume assesses the current position of understanding sediment supply to basins with the integration of the many sub-disciplines in the Earth sciences. It documents a mix of hinterland and sedimentary basin studies with a gradation from orogenic belts to the deep marine. The authors represent a wide spectrum of Earth scientist, with leaders in the science providing review papers and new-directive papers in their field of specialization.