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WATER RESOURCES RESEARCH, VOL. 39, NO. 3, 1056, doi:10.1029/2001WR000794, 2003

Determining the sources of suspended sediment in a forested catchment in southeastern Australia

J. A. Motha

Cooperative Research Centre for Catchment Hydrology, CSIRO Land and Water, Canberra, ACT, Australia
Department of Civil and Environmental Engineering, University of Melbourne, Victoria, Australia


P. J. Wallbrink

Cooperative Research Centre for Catchment Hydrology, CSIRO Land and Water, Canberra, ACT, Australia


P. B. Hairsine

Cooperative Research Centre for Catchment Hydrology, CSIRO Land and Water, Canberra, ACT, Australia


R. B. Grayson

Department of Civil and Environmental Engineering and the Cooperative Research Centre for Catchment Hydrology, University of Melbourne, Melbourne, Victoria, Australia


Abstract

Knowledge is scarce regarding the relative contributions from harvested areas and unsealed roads to sediments in forested catchments. We investigate the source composition of suspended sediment using sediment tracers and an improved multivariate mixing model. Sediment samples were collected during six rainfall events. Geochemical and radiometric tracer properties were corrected for particle size and organic content as well as conservativeness during erosion and sediment delivery. The mixing model incorporates variability of the tracer properties, using a Monte Carlo simulation technique. Mean sediment contribution from the undisturbed forest was 50–70%; harvested areas, gravel-surfaced roads, and ungravelled roads contributed 5–15%, 6–14%, and 12–25%, respectively. The unsealed roads contribute 20 to 60 times more sediment than the undisturbed forest and about 10 times more sediment than the harvested areas on a per unit area basis. Harvested areas contribute 1 to 5 times greater sediment than the undisturbed forest. These results support other studies that identify unsealed roads as important sediment sources in forested catchments.

Published 14 March 2003.

Index Terms: 1815 Hydrology: Erosion and sedimentation.

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Citation: Motha, J. A., P. J. Wallbrink, P. B. Hairsine, and R. B. Grayson (2003), Determining the sources of suspended sediment in a forested catchment in southeastern Australia, Water Resour. Res., 39(3), 1056, doi:10.1029/2001WR000794.