Vegetated buffers and swales

Vegetated buffers and swales — Construction and operation

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

Approvals

Buffers and swales can make use of existing vegetation and should not involve removing any native vegetation.

Approvals may be required for the construction of a treatment system. Contact your local government before any construction is undertaken to understand requirements.

For example:

• As the hydrology of the area may be altered (e.g. introduction of more flow through the vegetation or redirecting flows), the sensitivity of the existing vegetation to periodic or extended wetting should be considered as should the potential impacts on any downstream wetlands and waterways.
• Earthworks within the vicinity of an area mapped as a wetland protection area may trigger an approval process.

Construction

Buffers and swales should require only minimal earthworks, as they should be located where flows naturally enter the area as sheet flow. Buffers and swales will generally be constructed at the same time as the farm or block is being established. Construction will generally involve earthworks to create the swale (batters, flat base, channel etc.) and to create a contour drain along the upper edge of the buffer to disperse flows into the buffer. The earthworks should be kept to a minimum to avoid disturbing acid sulfate soils and shallow bedrock. Exposing bare soils should be minimised during construction to reduce the risk of sediment moving off site.

Establishment

Buffers and swales need to be well vegetated using a mix of native grasses, sedges and rushes. Plants with a spreading/rhizomatous habit are ideal to promote even water flow and help resist traffic impacts[1].

The most cost-effective approach is to seed the system with a mix of native species, or if suitable vegetation exists nearby on farm, allow the vegetation to recruit or colonise naturally. Natural recruitment runs the risk of erosion, increased weediness and increased maintenance and may need to be supplemented with seed. Cost savings can be gained by using existing vegetated areas as buffers and swales. Where this is not an option grass seed can be a cheaper alternative to seedlings.

Use local guidelines if they are available to assist with plant selection or contact your local Landcare or NRM group. Naturally vegetated systems such as waterways, wetlands and riparian zones are a good reference from which to create a species template. See plant guides.

The dry season is the best time to establish a buffer or swale to reduce the risk of run-off induced erosion and allow time for  plant establishment and root growth before heavy summer rainfall. Irrigation and weed management may be needed until the vegetation is fully established. A lack of vegetation cover in the buffer or swale can result inreduced treatment performance, erosion and weeds. Therefore, it is important that the vegetation in the buffer or swale is established successfully, as quickly as possible after earthworks.

A buffer or swale can be constructed and established within a few months or it can take two to three years to establish vegetation depending on site conditions[2]. A sterile grass such as rye or millet can be used as an interim measure while slower growing species establish.

Operation

Covered in maintenance (below).

Monitoring and maintenance

Ensuring adequate, dense (at least 80% groundcover) vegetation growth is the key maintenance objective for these systems[1]. Buffers and swales should be inspected every 6 months or after major rain events, to check vegetation cover is intact and ensure there is no erosion or sediment build-up. Regular maintenance will also minimise habitat for pests, such as rats. In addition, buffers can be actively managed to provide habitat for predators (e.g. plant trees and install nest boxes to attract owls)[3].

Typical maintenance will involve:

• Weed management to prevent undesirable species taking over the buffer or swale. Weeds should be controlled by slashing or selective herbicide, to avoid killing desirable species.
• Replanting/reseeding of desired species to achieve required vegetation density.
• Mowing/slashing of grass buffers and swales to maintain good cover and growth (avoid slashing if heavy rain is imminent, so that the grass clippings don’t wash into waterways).
• Irrigating vegetation, as required.
• Removing sediment if build-up is concentrated and impedes even flows through the buffer or swale. This should be done during the dry season to allow re-establishment of vegetation before the next wet season. Removed sediment should be disposed of in the farm blocks, away from any drainage lines.
• Filling any low points, boggy areas or eroded areas in the buffer or swale that will cause channeling of flows or bog holes.

If farm best management practices are not adopted in the catchment, large amounts of sediment may be exported, quickly smothering buffers and swales. This will require frequent sediment removal and reshaping of buffers and swales, therefore preventing soil loss through best management practices is a priority.

Lifespan/replacement time

Vegetated buffers and swales should last indefinitely if adequately maintained and farm best management practices adopted.

References

1. ^ a b Department of Employment, EDI (2011), Wetland Management Handbook: Farm Management Systems (FMS) guidelines for managing wetlands in intensive agriculture.. [online], Queensland Wetlands Program, Brisbane. Available at: https://wetlandinfo.des.qld.gov.au/resources/static/pdf/resources/reports/fms/fms_025_handbook_web.pdf.
2. ^ State of Queensland, Soil conservation waterways – construction and management. [online], vol. Science Notes Land series L270, Brisbane. Available at: https://www.publications.qld.gov.au/dataset/science-notes-soils/resource/5bfb8622-f091-4dd1-a712-d45b841cc72e.
3. ^ Sugar Research Australia (2013), Rat management in sugarcane, vol. B14023, Sugar Research Australia, Brisbane.

Last updated: 5 November 2022