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Suspended sediment monitoring in alluvial gullies: a laboratory and field evaluation of available measurement techniques
  • +2
  • Nicholas Doriean,
  • Andrew Brooks,
  • Peter Teasdale,
  • David Welsh,
  • William Bennett
Nicholas Doriean
Griffith University
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Andrew Brooks
Griffith University - Gold Coast Campus
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Peter Teasdale
University of South Australia School of Natural and Built Environments
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David Welsh
Griffith University
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William Bennett
Griffith University
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Peer review status:ACCEPTED

29 Jan 2020Submitted to Hydrological Processes
18 Feb 2020Submission Checks Completed
18 Feb 2020Assigned to Editor
18 Feb 2020Reviewer(s) Assigned
15 Mar 2020Review(s) Completed, Editorial Evaluation Pending
16 Mar 2020Editorial Decision: Revise Major
15 Apr 20201st Revision Received
16 Apr 2020Submission Checks Completed
16 Apr 2020Assigned to Editor
16 Apr 2020Reviewer(s) Assigned
10 May 2020Review(s) Completed, Editorial Evaluation Pending
10 May 2020Editorial Decision: Revise Minor
15 May 20202nd Revision Received
15 May 2020Assigned to Editor
15 May 2020Submission Checks Completed
15 May 2020Reviewer(s) Assigned
16 May 2020Review(s) Completed, Editorial Evaluation Pending
16 May 2020Editorial Decision: Accept

Abstract

Gully erosion is a significant source of fine suspended sediment (<63µm) and associated nutrient pollution to freshwater and marine waterways. Researchers, government agencies, and monitoring groups are currently using monitoring methods designed for streams and rivers (e.g., autosamplers, rising stage samplers, and turbidity loggers) to evaluate suspended sediment in gullies. This is potentially problematic because gullies have unique hydrological and operational challenges that differ to those of streams and rivers. Here we present a laboratory and field-based assessment of the performance of common suspended sediment monitoring techniques applied to gullies. We also evaluate a recently-described method; the pumped active suspended sediment (PASS) sampler, which has been modified for monitoring suspended sediment in gully systems. Discrete autosampling provided data at high temporal resolution, but had considerable uncertainty associated with the poor collection efficiency (25 ± 10%) of heavier sediment particles (i.e., sand). Rising stage sampling, while robust and cost-effective, suffered from large amounts of condensation under field conditions (25-35% of sampler volume), thereby diluting sample concentrations and introducing additional measurement uncertainty. The turbidity logger exhibited low uncertainty (< 10%) when calibrated with suspended sediment concentration data from physically collected samples, however, this calibration approach needs to be performed on a site-specific basis to overcome the error associated with the impact of different particle size distributions on the turbidity measurement. The modified PASS sampler proved to be a reliable and representative measurement method for gully sediment water quality, however, the time-integrated nature of the method limits its temporal resolution compared to the other monitoring methods. We recommend monitoring suspended sediment in alluvial gully systems using a combination of complementary techniques (e.g., PASS and RS samplers) to account for the limitations associated with individual methods.