Right Measure

The interactions of place/risk-context with buffer design, and consideration of ongoing maintenance are vital components of buffer efficacy and ensuring Good Agricultural and Environmental Condition (GAEC). The linear versus spatially targeted buffers bring options of incorporating features (tree planting, changing riparian topography) in the locally-wider areas. The natural extension of this is the possibility of incorporation of ‘wet buffer’ features including mini-wetland areas for subsurface drain interception, natural flood management (NFM) approaches (‘leaky’ bunds/barriers), or harvestable materials (wood biomass, or even fruits). A common discussion concerns the most appropriate vegetation in RBZ. Some studies indicate that trees favoured N and P uptake, whereas the dense grass cover favoured sediment trapping, but combining grass and trees reduced sediment trapping. Often vegetation management is prescribed. Close cut/grazed vegetation increases density and runoff trapping. Vegetation also presents a rare potential removal process for P. Whereas nitrogen and most pesticides undergo biogeochemical transformations (denitrification, degradation and decomposition) that reduce the quantities present over time, this does not occur for P. Therefore, P accumulation in the buffer may occur such that the soil and vegetation can no longer store additional P, leading to the buffer becoming a source of soluble P close to the stream. The solution for this is management of grasses by cutting and removal, or by periodic grazing, although this should be managed with regard to ground nesting birds, risk of impacts of FIO contamination or bank erosion and practical issues of vegetation harvest. The prescriptions for design and management of buffers are intimately linked to considerations of ‘right place’, the priorities given for different pollution, habitat, other (e.g. flood management) and on-farm activities. These considerations are key to realising effective buffers in the landscape.

November 16th, 2021

Grass Buffer Strips at Watercourse

There is a wealth of evidence on functioning for sediment, total P and to a lesser extent N and pesticides that shows the general effectiveness of grass buffers from relatively narrow widths. This is associated with roughness and infiltration that traps particles. Dissolved N and P functioning is worse and more complex to predict at a site.

November 17th, 2021

Wildflower Buffers

Wildflower buffers can benefit vegetation diversity to benefit invertebrates. But they are unlikely to promote increased numbers of rare plant species. Fencing out livestock from buffers can increase diversity of vegetation but has been found to reduce number of plant species and favour competitive weeds.

November 18th, 2021

Wooded buffer strips at watercourse (one or both banks, continuous or scattered)

Need time to establish, with some benefits such as inputs of deadwood being slow to be realised. If placed in a livestock field, these features need to be fenced. Reduces size of productive field and can impact crop yield due to shading, depending on aspect.

November 19th, 2021

Magic Margins

A practical ‘magic margins’ solution to soil erosion was devised by the James Hutton Institute’s Farm, Field & Glasshouse team. These ‘magic margins’ consist of a system of barriers created across the bottom of a sloping field with a potato drill plough and tied ridging machine.

November 20th, 2021

Raised Buffer (Temporary Ponding of Field Runoff Water and Sediments)

A bund (usually constructed of soil, but can be timber or stone) placed across an overland flow pathway disconnects the pathway and temporarily stores surface run-off. Feature has a designed spillway (in case of overtopping) and usually a pipe is placed through the bund to aid with draining.

November 21st, 2021

Raised buffers and depressions (temporary ponding of channel water during overbank events)

These are simple low earthen banks (usually max. 1m high) constructed on floodplains to temporarily store floodwater during flood events. These storage areas then drain back out into the watercourses after the main flood peak has passed downstream.

November 22nd, 2021

Sediment Traps

For areas where sediment and sediment transported contaminants degrade water quality a sediment trap is a useful point-based measure placed in an existing buffer zone uplsope of the watercourse banks. A closely related type of sediment trap that can be placed within an agricultural ditch is here described seperately.

November 23rd, 2021

Buffer wetlands receiving surface and groundwater inputs, either natural or enhancing existing wet areas

Wetlands are inundated with surface or ground water for periods leading to a dominance of vegetation adapted to saturated conditions (including swamps, marshes, bogs and fens). Wetlands have very diverse habitats for plants, insects, birds, mammals, amphibians and filter runoff water by slowing water, depositing particles and prmoting microbial degradation of pollutants in high organic matter environments.

November 24th, 2021

Tile drainage fed to a surface water constructed wetland or small semi-natural wetland area

A point-based measure that intercepts water from a main drainage line being suitable to receive subsurface artificial drainage or surface runoff. In the example of being routed to a small constructed wetland the draining water passes one or more deeper basins seperated by berms/raised areas planted with emerging (rooted underwater) vegetation.

November 25th, 2021

Integrated buffer zones

This comprises a zoned buffer approach with integrated elements for higher pollution pressure locations. The erosion slope is interrupted by a ditch into which field drains are broken back from the stream. The ditch increases the residence time of nutrient-rich waters.

November 26th, 2021

Denitrifying bioreactor

Bioreactors reduce nitrate in subsurface waters in agricultural land in order to improve water quality. The bioreactor comprises a treatment bed containing a carbon source to promote dentrification. The drainage water is routed horzontally or vertically through a treatment bed with an enriched carbon supply.

November 27th, 2021

Controlled Drainage

Field drain direct discharges to watercourses are managed and the soil is used to promote denitrification of drain waters. Controlled drainage utilises a control valve in the riparian zone to wet the upslope field area during periods of minimum required access. Control opened manually in spring before trafficking on field.

November 28th, 2021

Surface irrigation onto a saturated buffer zone after interruption of tile drainage

An edge of field measure that removes nitrate from subsurface tile drainage water before entering surface water drainage. A water control structure intercepts the tile drainage upslope of the outlet to the stream (fig (a)).

November 29th, 2021

Edge of field sediment filter fences (temporary)

Some sites with erosion risk (e.g. sloping, sandy textured soils, compacted soils) may be subject to cultivation practices that greatly enhance soil loss potential (e.g. potato cultivations). Where such activities are part of a crop rotation the risks may be large but only present in e.g. autumn each 4-5 years, then a temporary mitigation measure that can be set-up and moved may effectively follow a crop round a rotation.

November 30th, 2021

In Ditch: Two-Stage Channels

Drainage is important for agricultural productivity but issues arise from conventional ditches that are oversize for small flows and have no floodplains (flushing out stored sediment) during high flows. Two stage ditchjes include the modification of the banks by addition of mini floodplain benches to mimic small natural floodplains but in engineered channels.

December 1st, 2021

In Ditch: Sediment traps or filters

In channel sediment traps include settlement bains widened into an existing channel, usually done on artificial open drainage ditches, to allow suspended sediment to settle out and collect. Another less common type that introduces filtration materials through which the water passes (e.g. stone, woodchip) are more specialised...