HR: 17:45h
AN: H54A-07    [Abstracts]
TI: Sediment Budgets, Scale and the Fallacy of the Sediment-Delivery Problem
AU: * Wainwright, J
EM: J.Wainwright@sheffield.ac.uk
AF: Sheffield Centre for International Drylands Research, Department of Geography, University of Sheffield, Winter Street, Sheffield, S10 2TN United Kingdom
AU: Parsons, A J
EM: ajp16@le.ac.uk
AF: Department of Geography, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AU: Brazier, R E
EM: richard.brazier@sheffield.ac.uk
AF: Sheffield Centre for International Drylands Research, Department of Geography, University of Sheffield, Winter Street, Sheffield, S10 2TN United Kingdom
AU: Powell, D M
EM: dmp6@le.ac.uk
AF: Department of Geography, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AB: The calculation of watershed sediment budgets involves significant scale issues. What are essentially point measurements of erosion are extrapolated over several orders of magnitude (often temporally as well as spatially) to estimate what has been termed the gross erosion of a watershed. Since the 1950s it has been recognized that such estimates of the gross erosion are usually significantly greater than the sediment yield estimated at the catchment outlet. The sediment-delivery ratio was defined as a means of relating these estimates, and was recognized as being a generally inverse function of catchment area. The sediment-delivery problem was thus defined as a practical way of estimating the sediment-delivery ratio and thus the sediment stored within a catchment system. Notwithstanding several critiques based on the violation of fundamental geomorphological principles or mass balance over historical to geological timescales, the concept has persisted. We argue from first principles of sediment-transport processes that the concept of the sediment-delivery ratio is fundamentally flawed. It has arisen from a basic misunderstanding of how erosion scales spatially and the lack of a process basis in the extrapolation of gross erosion. Using the concept of travel distance to provide this basis overcomes these problems and the difficulties with the sediment-delivery ratio. This case is demonstrated using analytical and numerical modelling results. The sediment-delivery problem can thus be seen to be fallacious. One upshot of the approach to estimating gross erosion was the standardization of erosion-plot size. Consequently, there exists a large body of data that is unsuitable for testing ideas relating to erosion and scale. We present results from field monitoring in the US Southwest that uses a spatially explicit sampling strategy to support the case further. It is thus suggested from theoretical and empirical grounds that the sediment-delivery ratio is a flawed concept and that it should be avoided to prevent the misinterpretation of sediment budgets.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1826 Geomorphology: hillslope (1625)
DE: 1839 Hydrologic scaling
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005