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Durham University

Department of Earth Sciences

Postgraduate Students

Publication details for Professor Fred Worrall

Worrall, F., Burt, T.P., Howden, N.J.K. & Hancock, G.R. (2014). Variation in suspended sediment yield across the UK – A failure of the concept and interpretation of the sediment delivery ratio. Journal of Hydrology 519(Part B): 1985-1996.

Author(s) from Durham

Abstract

The sediment delivery ratio (SDR) has been a common approach developed to understand change in sediment yield and flux through a catchment. In this study we propose that the underlying concept of the sediment delivery ratio is flawed for a number of reasons: its linear extrapolation is physically meaningless; there is no evidence of the magnitude of storage required by the SDR approach on annual to decadal timescales; and the SDR approach assumes suspended sediment transport is conservative yet it is known to undergo both loss and production in-channel.

This study considers the sediment yield from 192 UK catchments from 1974 to 2010 for catchment areas between 4 and 9948 km2 and shows that linear extrapolation of the SDR approach overpredicts source terms and underpredicts fluxes for large catchments. The SDR approach hides a range of behaviours of suspended sediment flux within catchments with patterns of net deposition, net increase or no change all apparent in UK catchments. The approach proved to be self-correlated which meant that it can result in spurious correlations when compared to catchment area. The change in yield with catchment area can be just as well understood as a change in sediment supply from channels rather than as a change in delivery from hillslope sources. We propose that suspended sediment flux change with catchment area be modelled as a more physically-meaningful Gompertz function (step function) rather than using the traditional SDR approach.