As well as providing valuable wetland habitat benefiting a range of wildlife, drainage channels can be important corridors which allow species to move through the countryside.
The wildlife value of drainage channels is sensitive to many factors which can be influenced by the 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 and drainage channels benefit different species depending on their type and where they are in the country.
Drainage channels which have water in them all year around tend to have the highest wildlife value.
In the uplands, small ditches which 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.
The slow-flowing waters of many lowland drainage channels can support a great variety of wetland plants, providing food and cover for a wealth of invertebrates and other wildlife, some of which can be very rare. Larger drainage channels provide habitats for many species of bird, fish, amphibian and mammal such as the otter and water vole.
Benefits to the land
A grass strip of four to six metres established either side of drainage channels can increase the farm’s wildlife value, as well as offering additional benefits.
- Take out land which 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 which are suited to the soils to colonise.
How to manage edges and banks
The edges and banks of drainage channels are of great importance to their suitability for wildlife.
You should 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.
Managing drainage channels
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 which grow up from the bottom, such as rushes and reeds. These spread to choke the ditch and accelerate silting, preventing the channel from maintaining good drainage of the surrounding land and reducing 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 ever before.
- 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.
- On larger drainage channels, leave a third of the width unexcavated, to maintain a fringe of aquatic plants. Next time around, reverse 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.
- If this is not possible, clear sections bit-by-bit throughout the rotation period rather than all at once. The length of time that drainage channels can be left can vary greatly between different sites.
- Extend this length of time to the longest period which 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.