As well as providing valuable wetland habitat that benefits a variety of wildlife, drainage channels can be important corridors that allow species to move through the countryside.
Their wildlife value is sensitive to many factors, several of which can be influenced by our management of the channels and surrounding land.
Drainage channels (dykes, drains, ditches, lanes, rheens, rhines or rhynes) come in a variety of types and are common features on farmland. This page deals with the standard farmland drainage channels. Where more specialised drainage channel habitats are involved, you should seek more detailed advice.
- High water quality is essential to the wildlife value of drainage channels.
- Clean drainage channels on a little and often basis.
- Maintain a variety of habitats on drainage channel banks.
Benefits to wildlife
Water is a huge attraction to wildlife.
Drainage channels benefit different species depending on their type and where they are in the country. In the uplands, small ditches that are only occasionally wet provide a niche for certain plants and invertebrates.
These can, in turn, be important foods for many birds, including wading birds (such as lapwings, redshanks, curlews and snipe) and their chicks in fields where they breed. Drainage channels that have water in them all year tend to have the highest wildlife value.
The slow-flowing waters of many lowland drainage channels can support a great variety of wetland plants that, in turn, provide food and cover for a wealth of invertebrates and other wildlife, some of which can be very rare. Larger drainage channels can provide habitat for many species of bird, fish, amphibian and mammal such as the otter and water vole.
The edges and banks of drainage channels are of great importance to their suitability for wildlife.
Avoid shading out drainage channels by planting new hedges too close to them, particularly on the southern side. Allowing isolated trees or patches of scrub to develop can, however, add to the variety of habitat.
In arable situations, maintain a variety of bank habitats around the farm by cutting banks on a rotation of 2–5 years. Regular cutting prevents a few species becoming dominant, while less frequently cut bank sides are favoured by small mammals. Cutting should be avoided between March and the end of August.
A grass strip of 4-6 m established either side of drainage channels can increase the farm’s wildlife value, as well as offering additional benefits.
- take out land that cannot be sprayed by certain chemicals due to aquatic buffer zone requirements and potentially increase overall gross margin per hectare
- stabilise banks
- offer more flexible timing for maintenance
- filter water run-off to reduce sediment leaving the field
- reduce the spread of annual weeds into cropped areas by encouraging a thick sward of perennial plants: regular topping in the first couple of years after establishment can achieve this.
- Such strips can be established through agri-environment schemes or by locating set-aside strips next to ditches. Natural regeneration of such margins allows species that are suited to the soils to colonise.
A 'little and often' approach is important. Over time, drainage channels have a natural succession of changes, each phase having its characteristic species.
Aquatic plants such as pondweeds are shaded out by plants that grow up from the bottom, such as rushes and reeds, which spread to choke the ditch and accelerate silting. This prevents the channel from maintaining good drainage of the surrounding land and reduces its overall wildlife value.
The most diverse drainage channel systems for wildlife have all phases of the succession represented, from recently cleared sections to silted and well-vegetated ones. This requires a careful programme of rotational management around the farm. Modern machinery enables vegetation to be cleared more efficiently and far larger sections to be cleared at once than was ever possible in the past.
If large sections are completely cleared in one go, re-colonisation will be slow and will result in drainage channels of low wildlife value. It is therefore vital to leave some areas uncleared and take a ‘little and often’ approach to cleaning on slow-flowing lowland channels.
Weed cutting buckets are less severe than hard-edged buckets and can be used more regularly to allow the time between using hard-edged buckets to be extended.
On larger drainage channels, leave a third of the width unexcavated, to maintain a fringe of aquatic plants. Next time around, clear this and leave a third on the other side. If this will seriously affect land drainage, consider widening small sections, perhaps at channel intersections, so that some silted and vegetated areas can remain.
Where this is not possible, only clear sections of the farm’s drainage channels in any year, so they are cleared over the usual rotation length rather than in one go. The length of time that drainage channels can be left before returning to the same section can vary greatly between different sites.
Extend this length of time to the longest period that drainage efficiency will allow. If drainage channels need clearing every six years, consider doing a sixth of the total ditch length every year, or a third every two years if this is more practical. Ideally, maintenance should be done in the six months after the end of August.
Last updated: 28 November 2008