i-CONN Seminar Series Hillslope Processes: a connectivity perspective
25th February 2021, (Online, via Zoom) 1 pm UTC, (2 pm CET, 3 pm EET) Professor Tony Parsons, University of Sheffield
Most hillslopes are valley-side slopes. As Young (1972, p.1) put it “At a given point on the ground surface it is normally possible to follow the line of maximum slope downwards until a drainage channel is reached”. Setting aside glacial and aeolian processes, from the perspective of connectivity, hillslopes may be regarded as conveyor belts transferring water (derived from the atmosphere) and sediment and nutrients (derived mainly from the weathering of their constituent materials) to other parts of the geomorphic system, of which rivers are probably the most important recipients. Ferguson (1981) used the expression “jerky conveyor belt” to characterise sediment transport in rivers. The expression is equally apt as a metaphor for the connectivity in the movement of water, sediment and nutrients on hillslopes, which may be summarised in the question ‘how far and how fast?’. In the long run, connectivity must equal 100%. All the water that arrives from the atmosphere must, in due course, leave the hillslope system. Likewise, all the eroded sediment must be transferred off the hillslope. The key issues here are ‘what constitutes the ‘long run’?’, and ‘what happens up to that point?’ In this seminar I will consider these questions from the standpoint of the transport of sediment by water (so-called fluid gravity processes) and gravity (so-called sediment-gravity processes).
There can be no doubt that in recent years there has been a growing recognition of the importance of connectivity in understanding the effects of hillslope processes. At best, however, that understanding remains patchy and incomplete. To conclude with another metaphor: we currently have some bits of the jigsaw, but do not necessarily know how these bits fit together, and nor do we know what the full picture looks like. Much remains to be done.
Young, A. (1972). Slopes. Edinburgh: Oliver & Boyd
Ferguson, R.I. (1981). Channel form and channel changes. In J. Lewin (ed.) British Rivers, 90– 125, Allen and Unwin, London.
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