Vegetated buffers and swales

Vegetated buffers and swales — Key Considerations

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• Overview
• Key Considerations
• Planning and design
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• Links and references

What makes an effective buffer or swale for treating run-off?

• Sized to ensure an adequate detention time for the target pollutant to be removed.
• Low to moderate slope to ensure low water velocities that enable infiltration, filtration and sedimentation and prevent erosion.
• Designed so that flow into and through the buffer or swale is Eevenly dispersed and, shallow.
• Relatively small catchment area.
• Dense vegetation, with at least 80% ground cover to promote uniform water flows and facilitate sedimentation[2] (Figure 1)
• The adoption of farm best management practices and appropriate siting of vegetated buffers and swales within the drainage system of the farm to protect the buffer or swale from scour and high levels of sedimentation will improve the overall water quality leaving the farm.

Note: Other factors will need to be considered if the function of the buffer or swale is for erosion prevention, bank stabilisation or habitat.

Treatment processes

Suitability and limitations

Vegetated buffers and swales are suitable in all agricultural production systems and climates and are used throughout Queensland. Buffers may have many different purposes, other than water quality improvement including habitat, flood mitigation, spray drift management and bank stabilisation. The purpose of the buffer will depend on the values of, and threats to, the receiving environment. This will in turn influence the design and management of the buffer.

Vegetated buffers and swales can be used as part of an overall farm drainage strategy to improve run-off water quality, provided best practice farm management is implemented and design considerations are addressed.

The effectiveness of vegetated buffers and swales as a treatment system is limited by their capacity to achieve sufficiently slow flows for effective pollutant removal when there are large volumes of water (high rainfall, steep slopes) and a risk of channelisation, scour, exfiltration (loss of nutrients or pesticides via groundwater) and sediment build-up with subsequent resuspension[1][2]. The capacity of buffers and swales to remove pollutants from surface run-off is also reduced when the soil is saturated thereby preventing infiltration[3].

The cost-effectiveness of vegetated buffers and swales in removing the target pollutant/s needs to be considered relative to other treatment structures. Refer to cost considerations for more information.

References

1. ^ McKergow, LA, Prosser, IP, Grayson, RB & Heiner, D (2004), 'Performance of grass and rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water quality.', Australian Journal of Soil Research, vol. 42, no. 4, pp. 485-498.
2. ^ a b Reichenberger, S, Bach, M, Skitschak, A & Frede, H (2007), 'Mitigation strategies to reduce pesticide inputs into ground- and surface water and their effectiveness; a review.', Science of the Total Environment, vol. 384, pp. 1-35.
3. ^ USDA (2000), Conservation buffers to reduce pesticide losses.. [online], USDA Natural Resources Conservation Service. Available at: https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_023819.pdf.

Last updated: 5 November 2022