[1] 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, gravelsurfaced 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.
This paper examines the patterns of sediment transport in rivers in terms of
the sources of sediment and its transport and deposition through the river
network. The analysis is in the context of dramatic human influences on river
sediment transport and how they might influence freshwater ecosystems. The
review of Australian work shows that erosion of hillslopes and stream banks
has greatly increased in historical times, supplying vast quantities of
sediment to rivers, much of which is still stored within the river system. The
stored sediment will continue to effect in-stream and estuarine ecosystems for
many decades. In most Australian catchments the dominant source of sediment is
streambank erosion. An analysis of historical channel widening suggests that a
conceptual framework of relative stream power can explain the diversity of
behaviour observed in the numerous case studies. Sediment delivery through
catchments is considered first in a generic whole network sense, which
emphasizes the crucial role played by riverine deposition in determining
catchment sediment budgets. A method is then presented for analysing the
diverse spatial patterns of sediment storage in any river network. Finally,
the paper considers the temporal changes to channel morphology in response to
a human-induced pulse of sediment.
Abstract. Sediment budgets typically require an estimate of the proportional yield from erosion sources to sediments in transport and storage. This becomes increasingly difficult as catchments become larger, and erosion, storage, and deposition processes become more complex. We demonstrate how fallout radionuclides can be used to estimate the proportional contributions to sediment load, from a tripartite classification of erosion sources in a large catchment (the mid-Murrumbidgee, 13,500 km2). The three major
IntroductionSediment budgets typically require estimates of (1) basinwide sediment yield, (2) erosion rates from upland, channel, and floodplain sources, and (3) changes to the volume and residence time of material in downslope storages [Trimble, 1983] tribution to sediments from various erosion sources, to be measured directly, rather than inferred by manipulation of erosion rate and sediment yield terms. The residence time of this material in channels can also potentially be estimated. In this paper we present a method for using fallout tracers to deconvolve the proportionate contributions to suspended sediment from various erosion sources in a large catchment (13,500 kn12). We also provide some constraints for the residence time of suspended fine-grained material within it, and combine this information with the known annual sediment yield and surface areas of the erosion sources, to estimate the changes in specific yield from these sources over a 10-year period.
Study AreaThe Murrumbidgee River drains one of Australia's largest
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.