Establishment and restoration of riparian buffers (2015)
Vegetated and unfertilized buffer zones alongside watercourses can significantly contribute to improve micro-climatic conditions, they act as a shield against overland flow from agricultural fields by reducing the run-off of sediments and pollutants reaching the watercourse and increasing groundwater recharge, and they contribute to reduce vulnerability to floods. A general, multi-purpose, riparian buffer design consists of a strip of grass, shrubs, and trees between the normal bank-full water level and cropland. Riparian Buffer Strips are linear bands of permanent vegetation adjacent to an aquatic ecosystem intended to maintain or improve water quality by trapping and removing various nonpoint source pollutants from both overland and shallow subsurface flow. Buffer strips also provide (additional) habitat for aquatic species and may result in increased recharge of groundwater.
Riparian areas with trees also provide direct shade for the water body, reducing the influx of solar radiation on it and thus avoiding the corresponding increase in water temperature. In the case of wide riparian wooded areas (i.e. over several tens of meters), these can also increase the relative air humidity, which also contributes to a reduced temperature. This measure is considered particularly relevant for headwaters, with influence on water temperature and related biological processes which extends to downstream regions. Riparian buffers may be constituted by any type of vegetation along riverbanks, lakeshores, or other adjacent land to other surface waters. Wooded riparian areas are, however, more widely advocated as an effective way to provide water protection.
Buffer strips are being widely supported as agri-environmental measures in European rural development programs. A typical value for buffer strips’ width is around 5 m. Wider buffer strips, which provide additional protection but used to be considered too costly, are finding additional support: a new option of the English Environmental Stewardship program supports 12 m wide buffer strips for watercourses on cultivated land. Based upon fish migration criteria the recommended width of a buffer is 10 m for upland streams and 100 m for lowland.
Vegetated buffer strips can also be considered as strategies to protect coastal dikes, thus contributing to cope with the impacts of sea level rise. Like dunes, also wooded salt marshes in front of dikes have the potential to lower the wave load on the embankment. These areas may fulfil this flood protection function only when they can fully benefit from the hydrodynamic processes that ensure the supply of sediment and vegetation is able to develop without disturbances. Salt marshes reach their greatest extent along low-energy coasts where wave action is limited and mud can accumulate.
- Stakeholder participation
- Success and Limiting Factors
- Costs and Benefits
- Legal Aspects
- Implementation Time
- Life Time
The implementation of riparian buffer strips require the involvement of various actors (river managers, farmers, etc.) who should be involved to make the adoption of the adaptation option feasible. The option is usually well accepted by the general public for the positive effects on the landscape.
Success and Limiting Factors
The success of vegetated buffer strips is strongly dependent on characteristics such as buffer zone width, slope of the adjacent fields, , soil type and variety, and density of vegetation. The measure can have temporary negative side-effects during the plantation of vegetation and related works along the water body, but medium to long term effects are in general positive if the option is carefully designed and planned.
Flood mitigation effects could be positive, null or negative, depending on local conditions and on the quality of the design and implementation. Anyway, there are a variety of social and economic factors that can curb the adoption of riparian buffers. These include: a lack of incentives programmes, poorly defined goals, lack of maintenance, and opposition from landowners.
Costs and Benefits
Wooded riparian buffers provide several environmental services but are mostly documented by their ability to increase water quality. A study performed by the Trust for Public Land and the American Water Works Association concluded that forest cover in a watershed reduces water treatment costs. According to these authors a 10 percent increase in forest cover, decreases treatment and chemical costs by circa 20 percent. In addition, a large number of studies found evidence of public willingness to pay for higher water quality.
Benefits go well beyond pollution control, including several ecosystem services, as green corridors with increased biodiversity and aesthetic value, increasing people’s enjoyment of the environment and providing green recreation spaces. Moreover they can reduce risk of flooding, as the vegetation in the buffer decreases flood water speed, trapping also sediments and other materials carried by floodwaters. As a climate change adaptation the main benefits are related to the cooling of water body, increased air humidity and temperature stabilisation, and water retention.
Buffer Strips are currently mandatory under the Common Agricultural Policy (cross compliance). However currently there is no common definition of a buffer strip and governments can apply their own rules. Yet under the Rural Development program payments are provided to extend such buffer zones. This can also include more wooden zone. Salt marshes are protected within the EU Habitats Directive. In addition, within the Water Framework Directive (WFD), salt marshes are considered as part of the quality element “angiosperms” which is one element to assess the ecological status of water bodies.
More than 25 years.