The Sediment-delivery Fallacy
Abstract
The expression `sediment-delivery rate' was used by Glymph (1954) to denote the percentage relationship between annual sediment yield of a catchment and the annual gross erosion of the catchment. In subsequent literature, `sediment-delivery ratio' has been used. The latter is preferable. These ratios are typically less, often much less, than one. Both Boyce (1975) and Graf (1988) recognised that such ratios are problematic. They contravene Playfair's Law and mean that catchments must progressively fill with undelivered sedim ent. Both catchment sediment yield and gross erosion are measured in units of weight/area. These units are inappropriate for the data on which the ratios are based. Sediment yield is obtained either by measuring sedimentation in reservoirs or by sampling the sediment load carried in streamflow. These data are fluxes. There is no basis for assuming that the sediment flux at a point along a stream is proportional to the catchment area. Likewise, for hillslope erosion, it cannot be assumed that the flux of sediment measured at the outlet of an erosion plot has been derived from and is, therefore, proportional to the area of the plot. For both streams and hillslopes, data on travel distances of particles indicate that much of the sediment flux may be locally derived. The relationship of sediment flux to contributing area is both complex and dependent on the erosion processes. The sediment-delivery ratio is a fallacy born out of use of incorrect units of measurement.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27...28P