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Fluvial Reservoirs |
Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK
The three-dimensional geometry of fluvial sandbodies may be very complicated. Factors influencing this complexity include the processes of fluvial scour and incision, both of which can promote local or widespread increases in sandbody thickness. Incision, as caused by downstream relative base-level fall, produces entrenched valleys that control the location of subsequent alluvial deposits. A simple model is presented that attempts to quantify the scale of this extrinsic incision and, in turn, highlights several sedimentary implications of base-level fall. In contrast, scour is an intrinsic process common to all fluvial systems, and is promoted by constriction, curvature or confluences within the major channels. Existing empirical relationships that predict fluvial sandbody width from thickness are oversimplistic, failing to consider the modification of sandbody dimensions by such intrinsic processes. At low aggradation rates sandbody thickness may exceed channel bankfull depth by 100%, due purely to the effects of scour.
It is proposed that future fluvial width: thickness databases should stem from the classification of deposits according to the aggradational regime during their deposition. This will encourage the specific recognition of scour and incision, particularly in coastal plain alluvial deposits, and lead to an improved understanding of the controls upon sandbody deposition.
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  S. E. Love and B. P. J. Williams Sedimentology, cyclicity and floodplain architecture in the Lower Old Red Sandstone of SW Wales Geological Society, London, Special Publications, 2000; 180: 371 - 388. [Abstract] [PDF]
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M. R. Leeder and M. D. Stewart Fluvial incision and sequence stratigraphy: alluvial responses to relative sea-level fall and their detection in the geological record Geological Society, London, Special Publications, 1996; 103: 25 - 39. [Abstract] [PDF]
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