Fluvial scour and incision: models for their influence on the development of realistic reservoir geometries

Abstract

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.

Sources of low-arsenic groundwater in the Bengal Basin: investigating the influence of the last glacial maximum palaeosol using a 115-km traverse across Bangladesh

“…At both traverse ends, this central PI sequence is bounded by grey sands of As-polluted PC aquifers which occupy 40 km of the traverse. The post-LGM channels have not much truncated the PI sequence because their depth of incision has been mostly too shallow to do so, being imposed by decreased base-level gradients (Salter 1993) as sea level rose after 18 ka.…”

Scaling and Hierarchy in Braided Rivers and their Deposits: Examples and Implications for Reservoir Modelling

“…10) this problem is reduced with the thickness more likely to correspond to the channel depth, recognizing that 'channel depth as routinely measured and inferred from sedimentary features (i.e. point bars) will be less than total scour depth' (Salter, 1993). It should also be noted that maximum scour and aggradation will tend to produce sandbodies that are thicker than channel depth (Fielding & Crane, 1987;Salter, 1993).…”

“…point bars) will be less than total scour depth' (Salter, 1993). It should also be noted that maximum scour and aggradation will tend to produce sandbodies that are thicker than channel depth (Fielding & Crane, 1987;Salter, 1993). Despite these caveats, it is suggested that reliable depth estimates from stratasets or storeys can be used to estimate palaeochannel depth, and this estimate can then be used in estimating bar size and distribution from the empirical relationships derived for modern braided rivers.…”

A model for simulating the deposition of water-lain sediments in dryland environments

“…The flashiness of flood hydrographs and the susceptibility of surface sediments to entrainment mean that dryland flows act as non-uniform, non-steady, discontinuous agents of mass sediment transfer. A dryland storm can be thought of as giving rise to a non-synchronised, autogenic scour and fill event, controlled more by local flow conditions than by trends in allogenic stresses (Salter, 1993).…”