Skip links and keyboard navigation

Treat coarse sediment

Coarse and medium sized sediments can be lost from agricultural production systems via surface water run-off. Sediments can increase turbidity, alter habitat and smother plants and animals including corals, wetlands and marine environments. Treatment systems to remove sediment from run-off use physical processes to settle out coarse and medium sized sediments (generally larger than 125μm, i.e. sand[3]). These treatment systems need to be designed to slow the water velocity sufficiently to trap the target sediment type. Fine sediments such as silts, clays and colloidal material (less than 125μm[3]) need to be removed through different processes, such as enhanced sedimentation, adsorption and filtration[4]. See fine sediments, nutrients and other toxicants for more information.

Vegetated buffers can minimise sediment loss Photo by Queensland Government

Quick facts

The trapping efficiency of dams,
such as the Burdekin Falls dam (1,860,000 ML), is about 60% for suspended sediments, and 95% for coarser sediment (>30 ųm)[2].
Which
treatment systems can be used?

Treatment systems for agriculture – Treat coarse sediment

Select from the tabs below

The soil type within the catchment will influence the type and size of sediment requiring removal and the treatment system will need to be designed and sized accordingly (Table 1). A coarse sand (1000μm) has a settling velocity of 0.1 metres per second (m/s) whereas a very fine sand (125μm) has a settling velocity of 0.011m/s[1]. Therefore, to remove a very fine sand requires slower water velocities and a longer detention time which typically requires a larger structure.

Usually a simple, open, pond-like structure (e.g. sediment basin) is adequate to reduce the velocity sufficiently to enable coarse and medium sediments to settle out, provided it is sized appropriately for the site conditions when considering catchment area, soil types, local rainfall and hydrology. Dense vegetation, such as grasses and reeds, can also act to slow water velocity and physically trap coarse sediments and other pollutants, such as leaf litter and rubbish (plastics etc.).

Table 1: Suitability and complexity of different treatment systems for treating coarse to medium sediments
Treatment system Coarse-medium sediment removal capacity

Relative complexity (design, construction and operation)

Vegetated buffers and swales Medium Low
Vegetated drain Medium Low
Sediment basin High Low
High efficiency sediment basin High Med
Recycle pit Medium Med
Treatment wetland High* High
Bioreactor Not designed for this purpose  
Algae treatment Not designed for this purpose  
Floating wetland Not designed for this purpose  

*NB: Assuming a sediment basin is part of the wetland design

Table 1 on the main treatment system page provides more details on main treatment processes, type of flow treated and land uses treatment systems have been primarily used in.

Additional information

Minnesota Pollution Control Agency—Processes for removing pollutants from stormwater runoff

Melbourne Water—Constructed wetlands

Wetland Management Handbook

Wetland Technical Design Guidelines


References

  1. ^ Pilgrim, D (2001), 'Australian Rainfall and Runoff: a guide to flood estimation', Institution of Engineers Australia Barton, vol. 1, Institution of Engineers Australia Barton, ACT.
  2. ^ Tomkins, K (2013), Estimated sediment infilling rates for dams in northern Australia based on a review of previous literature. A technical report to the Australian Government from the CSIRO Flinders and Gilbert Agricultural Resource Assessment, part of the North Queensland Irrigated Agriculture Strategy.. [online], CSIRO Water for a Healthy Country and Sustainable Agriculture flagships, Australia.. Available at: https://publications.csiro.au/rpr/download?pid=csiro:EP137367&dsid=DS5.
  3. ^ a b Wentworth (1922), 'A Scale of Grade and Class Terms for Clastic Sediments', The Journal of Geology, vol. 30, no. 5, pp. 377-392.
  4. ^ Wong, T, Fletcher, T, Duncan, H, Coleman, J & Jenkins, G (2002), 'A model for urban stormwater improvement conceptualization', Global Solutions for Urban Drainage, pp. 8-13.

Last updated: 10 June 2022

This page should be cited as:

Department of Environment and Science, Queensland (2022) Treatment systems for agriculture – Treat coarse sediment, WetlandInfo website, accessed 5 October 2022. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/treatment-systems/for-agriculture/treat-sed.html

Queensland Government
WetlandInfo   —   Department of Environment and Science