The use of buffer zones to protect water quality: A review

It is popularly accepted that vegetated buffer zones are effective in removing water pollutants from surface runoff. However, there is a paucity of detailed information about establishing and maintaining buffer zones under different conditions, particularly in large catchments with diverse land uses. This paper reviews information on the application and effectiveness of vegetated buffer zones, and seeks to provide guidelines on their use for water quality control.Investigations into the use of buffer zones are grouped here into three major categories: studies of runoff plots or confined field areas; studies of operational forestry catchments; and studies of agricultural catchments. The degree of effectiveness of buffer zones for water pollution control in all these categories is generally attributed either to physical properties of the buffer zones (such as width, slope, vegetative cover, or soil type) or to the type of pollutant encountered. However, it is clear that although buffer zones have been shown to work well under small scale, experimental conditions, they lack success for water quality control on a broad catchment basis.In this respect, it is important that runoff must enter a buffer zone as shallow, overland flow in order to be slowed or detained, and that excessively channelised runoff will pass through a buffer zone unhindered. Buffer zones positioned close to sources of surface water pollution are therefore more likely to succeed in controlling water quality.It is suggested that although buffer zones are capable of removing pollutants from surface runoff, the proximity of buffer zones to sources of pollution is more important to their effectiveness than has been generally recognised. In view of this, the successful use of buffer zones for water quality control would require that they be comprehensively arranged along streams and around pollution sources in a catchment, and therefore that a large proportion of catchment area be set aside for this purpose. The real value of buffer zones in any situation would rest not only on their ability to control water quality, but on a number of other benefits and costs associated with maintaining large areas of natural vegetation.