Vegetated buffers and swales
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Vegetated buffers and swales, filter strips, riparian buffers
Vegetated buffers and swales for agricultural water quality improvement are vegetated areas that separate an agricultural production area from a waterway or wetland. Buffers are usually located perpendicular to water flows whereas swales are located parallel to the flow and convey water in a drainage line (as shown in the diagrams). Vegetated buffers and swales are primarily used as a best management practice in agricultural production systems to prevent erosion, but they can have a secondary benefit as a treatment system, although their effectiveness in treating agricultural run-off varies depending on site conditions. Vegetated buffers and swales help protect wetlands and waterways from the impact of adjacent land uses and can also protect agricultural land from flooding and bank erosion. They can be vegetated with grass, trees or both and the type of vegetation influences the services that buffers can provide.
A grass buffer located immediately adjacent to the crop has been shown to be more effective than trees for treating run-off while deep rooted trees in the riparian area are more effective for bank stabilisation. A buffer with grass closest to the agricultural production area and trees adjoining the receiving environment could therefore help achieve multiple water quality, bank stabilisation and habitat benefits (Figure 1).
When used as part of a treatment system, vegetated buffers and swales work by increasing the roughness of the ground surface and therefore increasing friction, which slows the water velocity and causes settling of coarse to medium sediments and some particulate nutrients and pesticides. By slowing the flow velocity, water is given more opportunity to infiltrate into the soil, rather than run off. Infiltration of water into the soil is the most efficient way for vegetation structures to assist in removal of finer sediments (e.g. less than 40μm (microns) in diameter), nutrients and pesticides. In some cases, pollutants can also be removed through adsorption to the plant or soil material or uptake by vegetation.
Vegetated buffers and swales are best positioned as one of the first systems in a treatment train to prevent erosion and enable trapping of coarse to medium sediments prior to run-off entering other treatment systems. They provide an important pre-treatment function for other elements in a treatment train.
For more information on the different buffer designs and principles refer to the Queensland Wetland Buffer Planning Guideline on WetlandInfo.
In addition to the standard disclaimer located at the bottom of the page, please note the content presented is based on published knowledge of treatment systems. Many of the treatment systems described have not been trialled in different regions or land uses in Queensland. The information will be updated as new trials are conducted and monitored. If you have any additional information on treatment systems or suggestions for additional technologies please contact us using the feedback link at the bottom of this page.
Last updated: 5 October 2018
This page should be cited as:
Vegetated buffers and swales, WetlandInfo 2018, Department of Environment and Science, Queensland, viewed 14 December 2018, .